Hermansky–Pudlak syndrome: a disease of protein
trafficking and organelle function
Maria L. Wei
Department of Dermatology, Veterans Affairs Medical Center 190,
University of California, 4150 Clement St., San Francisco, CA, USA
Address correspondence to Maria L. Wei,
The Hermansky–Pudlak syndrome (HPS) is a collec-
tion of related autosomal recessive disorders which
are genetically heterogeneous.
human HPS subtypes, characterized by oculocutane-
ous albinism and platelet storage disease; pro-
longed bleeding, congenital neutropenia, pulmonary
fibrosis, and granulomatous colitis can also occur.
HPS is caused primarily by defects in intracellular
protein trafficking that result in the dysfunction of
intracellular organelles known as lysosome-related
organelles. HPS gene products are all ubiquitously
expressed and all associate in various multi-protein
complexes, yet HPS has cell type-specific disease
cells such as melanocytes, platelets, lung alveolar
type II epithelial cells and cytotoxic T cells are
observed in HPS. This review summarizes recent
molecular, biochemical and cell biological analyses
together with clinical studies that have led to the
correlation of molecular pathology with clinical
manifestations and led to insights into such diverse
disease processes such as albinism, fibrosis, hemor-
rhage, and congenital neutropenia.
Key words: Hermansky-Pudlak/melanosome/melanocyte/
pigment disorder/oculocutaneous albinism
Received 26 June 2005, revised and accepted for publi-
cation 26 November 2005
In 1959, the Czechoslovakian physicians Hermansky and
Pudlak described two patients with oculocutaneous
albinism, prolonged bleeding and pigmented macrophag-
es in the bone marrow; one patient also had interstitial
pulmonary fibrosis and died at 34 yr of age (Hermansky
and Pudlak, 1959). Since that time, the Hermansky–
Pudlak syndrome (HPS), has been recognized as a gen-
etically heterogeneous set of related autosomal reces-
sive conditions due to mutations in genes that mostly
function in membrane and protein trafficking. Defects in
proteins encoded by these genes can affect the biogen-
esis and/or function of intracellular organelles found in
specialized secretory cells such as pigment cells (i.e.
melanocytes and pigment epithelial cells), platelets,
T cells, neutrophils, and lung type II epithelial cells. The
organelles affected by HPS genes belong to the family
of organelles known as lysosome-related organelles
(LROs), which share in common with lysosomes at
least one integral membrane protein and intralumenal
acidic pH (Cutler, 2002; Dell’Angelica et al., 2000b).
Although HPS disease phenotype appears to be con-
fined to only certain specialized cell types, expression of
HPS genes has been detected in all tissues tested, and
HPS genes are thought to be ubiquitously expressed.
There are eight known human HPS genes, each of
which can lead to a particular clinical HPS subtype. There
are 15 murine HPS genes, which have been cloned
and sequenced; eight of the mouse genes are ortholo-
gous to the eight human HPS genes (Table 1), and many
HPS genes have orthologues in the Drosophila melano-
gaster genome as well (Dell’Angelica, 2004). It is likely
that additional human HPS subtypes will be described,
corresponding to the known mouse strains.
Of the 15 identified HPS genes, only five have known
functions (AP3B1, AP3D1, VPS33A, RABGGTA, and
Slc7a11), and four of these have roles in regulating mem-
brane/vesicle and protein trafficking. The AP3B1 gene
encodes the b subunit and AP3D1 encodes the d subunit
of the adaptor protein AP-3, which plays a role in enrich-
ing cargo proteins in vesicles for transport through the
intracellular endosomal/lysosomal pathway. The VPS33A
gene encodes a protein that is part of the class C Vps
complex (C-Vps complex) which plays an integral role in
vesicular trafficking to the yeast vacuole, an organelle
functionally homologous to the mammalian lysosome
(Suzuki et al., 2003), by binding a syntaxin homolog to
mediate transport vesicle docking and fusion with a target
membrane such as the vacuolar membrane (Sato et al.,
2000; Suzuki et al., 2003). The C-Vps complex is also a
component of the larger HOPS complex which is essen-
tial for vacuole to vacuole fusion and vacuole protein sort-
ing (Seals et al., 2000). The RABGGTA gene product Rab
geranylgeranyl transferase-a is a subunit of a heterodimer
that attaches prenyl moieties to Rab molecules, which
Copyright ª 2006 The Author
Journal compilation ª 2006 Blackwell Munksgaard
Pigment Cell Res. 19; 19–42
are small GTP-binding proteins in the Ras-like GTPase su-
perfamily which regulate vesicular trafficking and organ-
elle motility (Detter et al., 2000).
Two other HPS gene products are known to bind to
previously described proteins. The dystrobrevin binding
protein-1 (DTNBP1) gene product is dysbindin, that
binds to a- and b-dystrobrevins, components of the dys-
2001), which is found at the synapses in brain and mus-
cle cells (Sillitoe et al., 2003); dysbindin has been sug-
gested to play a role in the exocytosis of glutamate in
neuronal cells (Numakawa et al., 2004). The Pldn gene
product, pallidin, binds to syntaxin 13 in yeast two
hybrid studies (Huang et al., 1999). Syntaxin 13 is a
member of the SNARE family of molecules that mediate
membrane docking and fusion (Advani et al., 1998); the
interaction of syntaxin 13 with pallidin suggests a role
for pallidin in membrane trafficking.
The only HPS gene of known function that does not
have an identified role in protein or membrane traffick-
ing, Slc7a11, is defective in the subtle gray mouse
strain, which has been classified as a model for mild
HPS because of mild depression of platelet dense gran-
ule numbersby electron
(Swank et al., 1996). Slc7a11 encodes the cystine/guta-
mate exchanger xCT (Chintala et al., 2005). This protein
appears to regulate the ratio of pheomelanin and mel-
anin synthesized in melanocytes, and affects cells’ abil-
ity to respond to oxidative stress.
Strikingly, many of the HPS proteins have one or two
predicted regions of coiled coil motif, which have been
et al., 2001; Dell’Angelica, 2004). Furthermore, all of the
HPS proteins are associated in multi-protein complexes,
the majority involving multiple HPS proteins (Table 2).
complex (Bensonet al.,
Thus, biogenesis of lysosome-related organelle com-
plex-1 (BLOC-1) includes as subunits the HPS proteins
pallidin, cappuccino, muted, reduced pigmentation (rp)
and dysbindin (Ciciotte et al., 2003; Falcon-Perez et al.,
2002; Gwynn et al., 2004; Starcevic and Dell’Angelica,
2004); BLOC-2 has as subunits the HPS3, HPS5, and
HPS6 proteins (Di Pietro et al., 2004; Gautam et al.,
2004; Zhang et al., 2003); BLOC-3 contains HPS1 and
HPS4 proteins (Chiang et al., 2003; Martina et al., 2003;
Nazarian et al., 2003). The adapter protein complex AP-3
Table 1. Hermansky–Pudlak syndrome subtypes and corresponding mouse strains
Cargo selection and vesicle trafficking to the lysosome
Binds a- and b-dystrobrevin, myospryn
Binds syntaxin 13
Vesicle trafficking to yeast vacuole
Adds lipophilic prenyl groups to carboxyl terminus of rab proteins
Cargo selection & vesicle trafficking to the lysosome
Cystine/glutamate exchanger xCT
AP3B1, adaptor protein complex-3 b3A subunit; DTNBP1, dystrophin binding protein-1, also known as dysbindin; Pldn, pallidin; RABGGTA, Rab
geranylgeranyl transferase a subunit; AP3D1, adaptor protein complex-3 d-subunit, ? denotes unknown.
Table 2. Hermansky–Pudlak syndrome protein complexes
Vps33a, Vps11, Vps16, Vps18
Rab geranylgeranyl transferase
Pigment Cell Res. 19; 19–42
(Dell’Angelica et al., 1999) and the d-subunit, defective
in the murine HPS mocha strain (Kantheti et al., 1998).
Two other proteins, VPS33A and RGGTA, are defective
in murine HPS, and are also known to form multiprotein
complexes (Detter et al., 2000; Rieder and Emr, 1997;
Seals et al., 2000) but no human diseases have yet
been found to be caused by defects in these proteins.
Clinically, HPS is defined by pigment dilution (affect-
ing skin, hair, and eyes) – resulting in oculocutaneous
albinism – and platelet storage pool deficiency (causing
prolonged bleeding), but different HPS subtypes have
additional distinguishing features, discussed in subse-
quent sections. Some subtypes, notably HPS-1 and
HPS-4, can be debilitating and can lead to premature
mortality; there is no known cure or effective therapy
for HPS. A diagnosis of HPS can be made by (1) an oph-
thalmologic examination showing iris transillumination,
fundus hypopigmentation, the presence of nystagmus
and decreased visual acuity; and (2) a wet mount elec-
tron microscopic examination of platelets showing
absent or greatly decreased numbers of platelet dense
granules (organelles that store ATP, ADP, calcium, sero-
tonin for release upon platelet aggregation) (Huizing and
Gahl, 2002). Accumulation of an autofluorescent ceroid-
like material can be detected in the reticuloendothelial
system (Nakatani et al., 2000; White et al., 1973; Wit-
kop et al., 1989). Confirmation of the diagnosis and sub-
typing is done by molecular analysis demonstrating
mutation of an HPS gene.
Even in cases in which mutations in HPS genes are
identified, ascertaining and attributing gene effects can
sometimes be tentative due to low numbers of patients
(in some HPS subtypes only one to three patients have
been identified) and background gene effects (i.e. muta-
tions or polymorphisms in other genes) can be difficult
to control for. Studying the mouse models of HPS can
be illuminating, as most of the HPS subtypes occurred
spontaneously in or were bred subsequently onto a
common inbred genetic background (C57BL/6), and
gene effects can be more reliably identified. However,
the mouse strains do not harbor the same mutations as
seen in human patients, so phenotypes occurring in
humans may not be represented in the mouse strains.
The study of both HPS affected patients and mice has
yielded complementary information that has recently
allowed a better understanding of the pathogenesis and
cellular basis of HPS, and has spurred interest in HPS in
diverse fields such as dermatology, ophthalmology, pul-
monology, hematology, genetics and cell biology.
b3A subunit, defectiveinHPS-2
Gene and protein structure
The human HPS1 gene spans 30.5 kb on chromosome
segment 10q23.1–q23.3 and has 9730 base pairs enco-
ding 20 exons, the first two of which are noncoding
(Bailin et al., 1997); a major 3.0 kb and minor 3.9 kb
mRNA (attributed to the use of proximal and distal
polyadenylation sites) have been demonstrated (Oh
et al., 1996; Wildenberg et al., 1998). Alternative splicing
of exon 9 occurs, with up to 50% of mRNA noted to
lack exon 9 (Gonzalez-Conejero et al., 2003; Oh et al.,
1996). A pseudogene has been detected on chromo-
some 22q12.2–12.3 which has high sequence similarity
to HPS1 exons 2–5 and 100% sequence homology to
HPS1 exon 6 (Huizing et al., 2000).
The 700 amino acid polypeptide has a predicted MW of
79.3 kDa, is not N-glycosylated in melanoma cells (Oh
et al., 2000), and is predicted to have a coiled-coil region
(Dell’Angelica, 2004). A minor 75.9 kDa protein results
from the alternative splicing of exon 9 (Oh et al., 2000).
noted in HPS1, 3 of which cause amino acid changes:
G283W, P491R, and R603Q (Bailin et al., 1997).
Twenty-three disease causing mutations have been
reported in HPS1 (Figure 1). The most common HPS1
mutation is found in Puerto Ricans (over 400 hundred
patients have been identified) and is caused by a 16-bp
frameshift duplication in exon 15 (Oh et al., 1996).
HPS-1 is the most frequently presenting HPS subtype,
the most common genetic disease among Puerto
Ricans, occurring with a frequency of one in 1800 in
northwest Puerto Rico (Witkop et al., 1990), and
accounts for ?50% of non-Puerto Rican cases (Oh
et al., 1998). Mutations have been found in European,
Japanese, Turkish and Pakistani cohorts.
The homozygous 16-bp duplication in the HPS1 gene
is found exclusively in those of Puerto Rican heritage,
and is associated with a severe phenotype: restrictive
lung disease was found to occur in 68% of affected
individuals, hemorrhage in 17%, and granulomatous coli-
tis in 15% (Witkop et al., 1990). Recent advances in
genetic testing have led to several studies detailing the
specifics of the clinical phenotype resulting from the 16-
Forty-nine percent of patients have been noted to
have abnormal chest radiographs and 82% have abnor-
mal high resolution chest computed tomography (CT)
scans, but all patients maintain normal oxygen satura-
tion at rest (Brantly et al., 2000). Lung tissue showed
cystic/honeycomb changes (Nakatani et al., 2000), sim-
ilar to findings seen in HPS mouse lungs (McGarry
et al., 1999), and patchy fibrosis. Cells were filled with
phospholipids droplets; enlarged lamellar bodies (organ-
elles that store surfactant protein and phospholipids
prior to secretion) were increased in number, suggest-
ing a defect in their secretion (Nakatani et al., 2000).
Onset and rate of progression of pulmonary disease
can be followed with pulmonary function tests and high
resolution CT (Avila et al., 2002; Brantly et al., 2000).
The anti-fibrotic agent pirfenidone appears to slow the
Pigment Cell Res. 19; 19–42
progression of lung disease in HPS1 patients with a
residual forced vital capacity (FVC) > 50% (Gahl et al.,
2002). The restrictive lung disease has an average age
of symptomatic onset at 35 yr, leading to an average
age of death at 37 yr, but there is a wide individual vari-
ability in pulmonary function, suggesting the influence
of environmental triggers/exacerbators and/or modifying
genes. Health maintenance measures, e.g. avoidance of
primary and secondary cigarette smoke/lung toxins,
prompt treatment of respiratory infections, administra-
tion of the influenza and pneumovax vaccines, were
recommended (Brantly et al., 2000).
Prolonged bleeding is usually noted with the onset of
walking, but can vary from easy bruisability to frequent
(more than twice a month) or prolonged (>1 h) bleeding
episodes to major bleeding episodes lasting >12 h
requiring transfusions, hospitalization, or treatment such
as cautery (Gahl et al., 1998; Hermos et al., 2002). One
study, in which patients were genotyped, concluded
that platelet transfusion remains the treatment of choice
for HPS-1 patients (Cordova et al., 2004). All patients
had absence of platelet dense granules by electron
microscopic examinations (Gahl et al., 1998). Avoidance
of aspirin was recommended.
The best corrected vision in HPS-1 patients ranges
from 20⁄250 to 20⁄80. Iris, choroid and retinal pig-
mentation, while variably decreased, does not correlate
with skin pigmentation. Horizontal nystagmus is present
in the primary position with a rotary component often
also noted. On slit lamp examination, iris transillumina-
tion is present to variable degrees, and fundus hypopig-
mentation and foveal hypoplasia are noted (Gahl et al.,
Inflammatory bowel disease is generally diagnosed
between the ages of 11 and 25 yr, and only involved
the large intestine, with most patients requiring surgical
resection and colostomy placement (Gahl et al., 1998).
On skin examination, there is a broad variability in hair
and skin pigmentation (Gahl et al., 1998), but interest-
ingly, as is reported for pale ear mouse coat color (the
mouse model for HPS-1), the hair and skin of individuals
affected with HPS-1 darkens as patients age (Lane and
Green, 1967; Toro et al., 1999). Patients have melanocy-
tic nevi, 29% have acanthosis nigricans-like epidermal
changes on the neck and axilla without signs or symp-
toms of endogenous or iatrogenic insulin resistance,
and 70% have trichomegaly of the arms, legs, and eye-
lashes (Toro et al., 1999).
Figure 1. Mutations found in HPS-1 and pale ear.
Pigment Cell Res. 19; 19–42
A study of renal function in HPS-1 patients carrying
the homozygous 16-bp duplication revealed no signifi-
cant dysfunction in glomerular or renal tubular functions,
although creatinine clearance was decreased in one-
third of the HPS-1 patients with the 16-bp duplication
compared with one-tenth of the HPS-1 patients without
(Gahl et al., 1998).
The clinical findings in HPS-1 patients not bearing the
16-bp duplication can range from mild to severe. For
example, the homozygous mutation P324ins found in
Swiss patients was not associated with intracellular cer-
oid accumulation, pulmonary fibrosis or inflammatory
bowel disease and was generally noted to result in a
mild HPS phenotype (Frenk and Lattion, 1982; Oh et al.,
1996; Schallreuter et al., 1993). In contrast, HPS-1
caused by the homozygous mutation IVS17-2C>T resul-
ted in death secondary to lung fibrosis and pulmonary
insufficiency (Brantly et al., 2000), and the double homo-
zygous mutation at amino acids S459 and S463 caused
colitis with small bowel involvement in a patient at the
age of 17 yr old (Hermos et al., 2002).
While HPS-1 heterozygotes are clinically asympto-
matic, abnormalities can be detected on the cellular
level. Individuals heterozygous for the mutation P324ins
had decreased numbers of platelet dense granules
detected by electron microscopy and decreased platelet
aggregation in response to stimulation with various
agonists (Gonzalez-Conejero et al., 2003).
Cell biology and biochemistry
HPS1 protein is reported to be ubiquitous and primarily
localized to the cytosol, with a small proportion being
membrane associated (Dell’Angelica et al., 2000a; Oh
et al., 1996). Immunostaining for the HPS1 protein in
normal fibroblasts was reported to yield a relatively
homogeneous cytoplasmic pattern (Oh et al., 2000),
while in normal melanocytes HPS1 demonstrated a peri-
nuclear reticular pattern, and a more granular appear-
ance (Oh et al., 2000; Richmond et al., 2005). In FME
melanoma cells, endogenous HPS1 colocalized perinu-
clearly with both tyrosinase and tyrosinase related pro-
melanogenic enzymes normally transported to the mel-
anosome. No colocalization was noted with TGN46, a
trans-Golgi marker, or lysosomal associated membrane
protein-1 (LAMP-1), a marker of late endosomes and
lysosomes (Oh et al., 2000). Ultrastructurally, HPS1 was
found in melanoma cells on tubulovesicular structures
near the Golgi apparatus, on uncoated vesicles and early
melanosomes (Oh et al., 2000).
Subcellular fractionation studies demonstrated that in
melanotic and non-melanotic cells, HPS1 protein was
associated with the HPS4 protein in the ?200 kDa cyto-
solic BLOC-3 complex, with a minor proportion of
BLOC-3 alsofound to
(Dell’Angelica et al., 2000a; Martina et al., 2003; Nazari-
an et al., 2003; Oh et al., 2000). In melanoma cells,
be membrane associated
HPS1 is also associated with large vesicle/organelle
membranes consistent with melanosomes in a 500 kDa
complex together with the HPS4 protein. The 500 kDa
complex is also detected in nonmelanotic cells such as
fibroblasts in low amounts associated with endosomal/
vesicular cell fractions (Chiang et al., 2003; Oh et al.,
2000). Interestingly, although the HPS1 and HPS4 pro-
teins copurified by immunoprecipitation, gel filtration
and sedimentation velocity analysis, no direct binding of
HPS1 to HPS4 was detected by yeast two-hybrid analy-
sis, suggesting that at least one other subunit is a com-
ponent of BLOC-3 (Chiang et al., 2003; Martina et al.,
2003; Nazarian et al., 2003; Oh et al., 2000).
Lack of endogenous HPS1 may affect membrane traf-
ficking differently in fibroblasts compared with in mel-
anocytes.One group noted
fibroblasts from pale ear mice (the mouse model for
HPS-1), LAMP-1 appeared more dispersed and less peri-
nuclear in distribution compared with in control cells,
and suggested that the HPS1 protein is required for
clustering of endosome and lysosomes in the perinu-
clear region and that movement of those organelles is
impaired in BLOC-3 deficient fibroblasts (Falcon-Perez
et al., 2005; Nazarian et al., 2003). It was noted that
LAMP-2 in HPS-1 fibroblasts also exhibited an abnormal
dispersed distribution when compared with control cells,
but the distribution of CD63/LAMP-3 was the same as
in control fibroblasts (Dell’Angelica et al., 2000a). In con-
trast, in melanocytes from HPS-1 patients, CD63/LAMP-
3 and LAMP-1 were found in large vesicular structures,
compared with the more granular pattern seen in con-
trol melanocytes, but LAMP-2 distribution was normal
(Richmond et al., 2005).
HPS1 appears to play a role in regulating protein
traffic targeted to the melanosome. In melanocytes
derivedfrom HPS-1 patients,
tyrosinase, Tyrp1 and TRP2/DCT produced a pattern
with large vesicular structures in the cell body and
dendrites (Boissy et al., 1998; Richmond et al., 2005),
similar to that seen when HPS-1 melanocytes are
stained for LAMP-1 and LAMP-3, instead of a small
granular pattern seen throughout the control cells. The
melanin production (Boissy et al., 1998). On electron
microscopic examination, cultured human HPS-1 mel-
anocytes are observed to contain enlarged membrane
bound compartments up to 2 lm in length containing
50 nm vesicles, melanosomes and other membranous
structures (Boissyet al.,
2005); these compartments were also identified occa-
sionally in 10% of melanocytes in skin biopsies from
HPS patients and in melanoma cells in which HPS1
expression was abrogated by the introduction of anti-
sense HPS1 cDNA (Sarangarajan et al., 2001). How-
ever, in another study, skin biopsies from 40 patients
bearing the 16-bp duplication mutation did not detect
any enlarged structures (Toro et al., 1999).
1998; Richmondet al.,
Pigment Cell Res. 19; 19–42
Recent data indicates that defects in HPS1 (and
HPS4) also cause more global effects. Cultured cells
defective in HPS1 and HPS4 have aggregated and dis-
tended Golgi apparati, longer dendrites and flatter cell
bodies, suggestinga possible
(Chiang et al., 2005).
In mice, two allelic strains of pale ear (ep) have been se-
quenced at the Hps1 locus (Feng et al., 1997; Gardner
et al., 1997) (Figure 1). The mouse Hps1 protein is pre-
dicted to be 703 amino acids and to have a molecular
mass of 79.7 kDa. On the amino acid level, the mouse
sequence is 81% identical to human HPS1 and 89%
similar (Feng et al., 1997; Gardner et al., 1997). Mouse
HPS1 and human HPS4 were co-purified together from
mouse immortalized melanocytes expressing human
HPS1, demonstrating the conservation of protein–pro-
tein interaction domains across species (Chiang et al.,
2003). In platelets from pale ear mice, decreased dense
granule contents serotonin, ATP and ADP were noted,
observed by electron microscopy (Novak et al., 1984;
Swank et al., 1998).
Enlarged pigmented structures termed macromelano-
somes were observed in the choroid of the eyes of pale
ear mice and melanocytes cultured from the mice were
also noted to have the macromelanosomes (Gardner
et al., 1997). However, in vivo examination of dorsal
back follicular melanocytes did not find similar enlarged
structures (Nguyen et al., 2002).
While other HPS strains are relatively homogenously
hypopigmented, the pale ear mouse and the model for
HPS-4 (light ear mouse), are unique in having a coat
color similar to the parental black-colored C57BL/6
strain, but in also having markedly hypopigmented ears,
tails, and paws. Studies show that there is a decreased
number of dermal melanocytes at these sites, suggest-
ing that defects in HPS-1 (and HPS-4) may affect mel-
anocyte migration to those areas during development or
alternatively may affect melanocyte survival and/or pro-
liferation (T. Nguyen and M.L. Wei, personal communi-
cation), consistent with the observations of altered
cytoskeletal elements in HPS1 and HPS4 cells observed
by others (Chiang et al., 2005).
Gene and protein structure
HPS-2 is caused by mutations in the AP3B1 gene enco-
ding the b3A subunit of the heterotetrameric adapter
protein complex AP-3. AP-3 plays a role in mediating
cargo protein selection into transport vesicles and traf-
ficking those membrane proteins to the lysosome
(Bonifacino and Dell’Angelica, 1999). The AP-3 molecule
consists of b3A-, d-, l3-, and r3-subunits (Figure 2).
Electron microscopic studies of a related molecule, the
AP-2 adaptor, suggest that the b3A and d-subunits of
AP-3 have three domains: the head or core region,
which mediates protein–protein interactions with the
other subunits, the hydrophilic hinge region and the ear
or appendage region (Heuser and Keen, 1988). The
gene encoding b3A consists of 3968 bp comprising 27
exons (Huizing et al., 2002).
Four patients have been reported in the literature with
HPS-2 (Clark et al., 2003; Huizing et al., 2002) which is
Figure 2. Mutations found in HPS-2 and pearl.
Pigment Cell Res. 19; 19–42
distinguished from the other forms of HPS by the pres-
ence of neutropenia and susceptibility to recurrent res-
piratory illnesses. An initial diagnosis of Chediak–Higashi
Syndrome (CHS), a related disorder characterized by pig-
ment dilution, recurrent infections and large intracellular
granules, may initially be considered (Huizing et al.,
2002); however, the large intracellular granules seen in
CHS are not present in HPS-2.
Two brothers who were compound heterozygous
with a 63 bp deletion at amino acid K389 and a single
nucleotide substitution at L580R both had neutropenia,
recurrent upper respiratory infections and otitis media,
congenital hip dislocations secondary to dysplastic ace-
tabulae and neurological abnormalities including poor
balance. They also had dermatologic findings similar to
those found in HPS-1 patients: acanthosis nigricans and
hypertrichosis. Both also had slightly depressed results
on pulmonary function testing and granulocyte hypopla-
sia on bone marrow biopsy (Shotelersuk et al., 2000).
On the cellular level, these patients had detectable pres-
ence of the b3A protein, albeit in diminished amounts
(Dell’Angelica et al., 1999).
A patient with two nonsense mutations at R509X and
E659X had a very serious phenotype, which correlated
with the lack of detectable b3A mRNA and protein in
his cells. No l3 protein was detected either, suggesting
that in the absence of binding to b3A, the l3 subunit
was degraded. The patient had severe respiratory infec-
tions, leading to the need for continual oxygen supple-
mentation, neutropenia requiring G-CSF administration,
mild conductive hearing loss, hemorrhage requiring
platelet transfusions and failure to thrive (Huizing et al.,
A fourth patient reported with HPS-2 had the classic
defects, and had immunodeficiency necessitating treat-
ment with immunoglobulin and prophylactic antibiotics.
On the cellular level, this patient had no detectable b3A,
d, or l3A protein by immunoblot analysis, but did have
residual r3A protein (Clark et al., 2003).
Cell biology and biochemistry
AP-3 has been shown to mediate protein trafficking to
the lysosome and lysosome-related compartments via
binding to amino acid-encoded sorting signals in the
cytoplasmic tails of lysosomally targeted molecules (Bo-
nifacino and Traub, 2003; Ihrke et al., 2004; Sugita
et al., 2002). Specifically, the amino acids tyrosine and
leucine form the basis of two different sorting signals
that have been demonstrated to bind to AP-3. In cells
derived from HPS-2 patients deficient in AP-3, mole-
cules normally targeted to lysosomes (e.g. CD63/LAMP-
3, LAMP-1, LAMP-2, and CD1b), have an increased cell
surface expression due to impaired trafficking to the
lysosome, while the trafficking of the nonlysosomally
targeted transferrin receptor (TfR) and cation-dependent
mannose 6-phosphate receptor remained unchanged
(Clark et al., 2003; Dell’Angelica et al., 1999; Sugita
et al., 2002).
The misrouting of the lysosomally targeted molecules
such as LAMP-1 does not appear to play a central role
in HPS disease pathogenesis, however, since only
those HPS mouse models that harbor mutations in the
AP-3 molecule subunits (i.e. pearl and mocha mouse
strains) have detectable increased cell surface expres-
sion of LAMP-1, whereas the other mouse models of
HPS have normal cell surface levels (Dell’Angelica et al.,
2000a). It is more likely that the LAMP-1 molecule
serves as a marker for dysregulated membrane traffick-
ing and the disease phenotype is a result of disrupted
trafficking to LROs such as the melanosome, platelet
dense granule, lytic granule, and lung lamellar body. For
example, in cultured melanocytes derived from an HPS-
2 patient, the tyrosinase protein (a melanogenic enzyme
necessary for pigment synthesis) is mislocalized to a
perinuclear compartment, compared with a perinuclear
and dendritic distribution in control melanocytes (Huizing
et al., 2001b). The steady state distribution of another
melanosomal protein, Tyrp1, appeared unchanged by
defects in AP-3 (Huizing et al., 2001b), suggesting that
Tyrp1 primarily utilizes an AP-3 independent pathway to
melanosomes, or that Tyrp1 normally uses an AP-3
pathway, but in the absence of AP-3 can access a sec-
ond, AP-3-independent, pathway.
Recent evidence is consistent with AP-3 mediating a
significant trafficking pathway from endosomes to lyso-
somes and LROs. In HepG2 cells, AP-3 is localized to
endosomal structures that contained transferrin, TfR,
asialoglyoprotein receptor, and the lysosome-associated
membrane proteins LAMP-1 and 2 (Peden et al., 2004).
In AP-3 deficient cells, molecules normally targeted to
lysosomes appear to accumulate in endosomes and on
the cell surface, and endosomes appear to increase in
size. In HPS-2 lymphoblastoid cell lines, the CD1b mole-
instead with TfR, a marker for early endosomes, as well
as being increased on the cell surface (Sugita et al.,
2002). In melanocytes from HPS-2 patients, abundant
multivesicular structures resembling endosomes are
seen, containing intralumenal tyrosinase enzyme activ-
ity, whereas similar structures were only occasionally
seen in control melanocytes (Huizing et al., 2001b). In
CTL from HPS-2 patients, an increased size of the entire
endosomal network was observed (Clark et al., 2003).
Together, these data suggest that molecules targeted
to lysosomes or LROs first traverse from the TGN to an
endosomal compartment where AP-3 mediates sorting
and subsequent trafficking to the lysosome or LRO. In
the absence of AP-3, molecules accumulate in the endo-
somal compartment, causing increased endosomal size,
and are recycled to the cell surface by a default mech-
Investigations into the cellular basis for the immuno-
deficiency seen in HPS-2 patients demonstrated an
Pigment Cell Res. 19; 19–42
impairment in the presentation of lipid antigen to T cells
by CD1b molecules transduced into B-lymphoblastoid
cells derived from an HPS-2 patient, whereas trans-
duced CD1c molecules presented antigen at the same
level as wild type cells (Sugita et al., 2002). HPS-2 CTL
had a decreased ability to kill targets and to secrete the
lysosomal hydrolase hexosaminidase with T-cell recep-
tor linking. Incubation of HPS-2 CTL with target cells
failed to induce polarization of lytic granules to the
immunological synapse, suggesting that AP-3 function
is required for microtubule-mediated movement of lytic
granules (Clark et al., 2003).
The pigment dilution and neutropenia characterizing
HPS-2 are similar to findings in a disease affecting dogs,
canine cyclic neutropenia (also called gray collie syn-
drome), a stem-cell disease in which the number of
neutrophils oscillates in weekly phases; the defective
gene in canine cyclic neutropenia is also AP3B1 (Benson
et al., 2003). In neutrophils, AP-3 was associated with
the serine protease neutrophil elastase (NE) via a tyro-
sine based signal in the cytoplasmic tail of NE. AP-3
mediated trafficking of NE to lysosome-like granules
(Benson et al., 2003), likely azurophilic granules (Bain-
ton, 1999). In the absence of intact AP-3, NE accumu-
lated at the plasma membrane. Furthermore, mutations
in the NE molecule which disrupted the tyrosine based
AP-3 recognition signal caused plasma membrane local-
ization of NE and were associated with the human gen-
etic disease severe congenital neutropenia (Horwitz
et al., 2004). Thus, disruption of AP-3 mediated NE tar-
geting to an LRO appears to underlie the neutropenia
observed in HPS-2 and gray collie syndrome. The down-
stream events that lead to clinical neutropenia remain
Two syndromes similar to HPS-2 in affecting CTL
granule mobility/function result in clinical signs of he-
mophagocytic lymphohistiocytosis (HLH). The Griscelli
syndrome (caused by mutations in the RAB27A gene)
and the Chediak–Higashi syndrome (caused by muta-
tions in the LYST gene) are syndromes that also
cause pigment dilution, platelet dysfunction and CTL
granule defects; both also lead to HLH (Menasche
et al., 2000; Nagle et al., 1996; Rubin et al., 1985).
HLH without pigment dilution can also be caused by
mutations in the perforin 1, syntaxin 11 or MUNC13-4
genes (Feldmann et al., 2003; zur Stadt et al., 2005;
Stepp et al., 1999). An earlier study attributed the
accumulation of ceroid material in HPS reticuloendot-
helial cells as secondary to hemophagocytosis or cellu-
lar ingestion of erythrocytes (White et al., 1973). It is
not clear if perhaps the HPS-2 patients, aged 5, 20,
and 25 yr at the time of reporting, may experience
later onset of clinical HLH compared with in the other
syndromes, or perhaps T-cell type-specific defects
account for the clinical differences (i.e. distinct sub-
sets of T cells or NK cells are affected by granule
defects in the different syndromes).
The mouse model for HPS-2 is the pearl strain (pe),
which exhibits pigment dilution, prolonged bleeding and
impaired kidney and platelet lysosomal enzyme secre-
tion (Swank et al., 1998). This strain also exhibits
reduced sensitivity in the dark-adapted state and is sug-
gested to also be a model for human congenital station-
ary night blindness (Balkema et al., 1983). Constitutive
secretion of lysosomal enzymes from the kidney prox-
imal tubules is decreased to one-third of normal (Novak
and Swank, 1979) and thrombin mediated secretion of
lysosomal enzymes from platelets is 50% of normal
(Novak et al., 1984). Enlarged multilamellar structures
resembling lysosomes are observed in kidney proximal
tubule cells from pearl mice and cultured pearl melano-
cytes have distinctive organelles with multilamellar con-
lysosomes (Zhen et al., 1999). The prolonged bleeding
in pearl mice can be corrected by bone marrow trans-
plantation, indicating that the AP-3 defect affects hema-
topoietic progenitor cells (McGarry et al., 1986), in
agreement with the observations in the gray collie syn-
drome and congenital neutropenia.
Three mutant alleles of pearl have been described:
pe, pe8Jand pe9J(Feng et al., 1999, 2000). In the cases
of pe and pe8J, residual decreased amounts of mRNA
are detected (Feng et al., 1999; Yang et al., 2000; Zhen
et al., 1999). Low levels of b3A protein are expressed in
pe, and small amounts of AP-3 heterotetramers are
detected by immunoprecipitation from extracts of pe
spleen cells, formed by the association of the truncated
b3A subunit with the remaining d-, l- and r-subunits
(Peden et al., 2002). Transgenic mice in which the
Ap3b1 gene has been disrupted to produce a null phe-
notype have a greater degree of coat color pigment dilu-
tion compared with pe mice and cell extracts from the
transgenic mice have a decreased of detection of d, l,
and r due to degradation of the unassembled subunits
(Yang et al., 2000). Thus pe mice are phenotypic hypo-
Immunofluorescence analysis of fibroblasts from pearl
and Ap3b1 null mice demonstrate increased cell surface
expression of LAMP-1 and LAMP-2, in agreement with
studies on cells from HPS-2 patients, and steady-state
tyrosinase was mislocalized in Ap3b1-null melanocytes
(Dell’Angelica et al., 2000a; Yang et al., 2000).
A related mouse strain is the mocha mouse (mh), in
which a different subunit of AP-3 is defective, the d-sub-
unit; no corresponding patients have been identified.
There are two allelic strains of mocha, mh and mh2J,
the first of which is a functional null and the second of
which is a hypomorph (Kantheti et al., 1998, 2003).
While the mocha strains have variable degrees of pig-
ment dilution and platelet dysfunction, the most striking
defects are neurological (Kantheti et al., 1998, 2003). In
contrast, the pearl mice and HPS-2 patients (with
defects in AP-3 subunit b3A) do not exhibit neurological
Pigment Cell Res. 19; 19–42
deficits because a neuronal tissue-specific isoform of b
exists, called b3B (Newman et al., 1995; Simpson et al.,
1997). This neuronal isoform is intact in pearl mice
(Zhen et al., 1999) and continues to mediate normal
neuronal AP-3 functions such as synaptic vesicle forma-
tion from endosomes (Faundez et al., 1998; Seong
et al., 2005), despite defects in the non-neuronal iso-
In contrast, no tissue-specific forms of the d-subunit
have been detected. In mh mice a large out-of-frame
deletion causes the absence of any detectable d-protein
in all tissue and cells tested, including brain; loss of d
also caused the loss of detection of the other 3 AP-3
subunits, due to instability of the unassembled units
(Kantheti et al., 1998). The neurological defects in
mocha mice were associated with a loss of immunore-
activity for the zinc transporter protein ZnT-3 and with a
dramatic of reduction of vesicular zinc staining in the
central nervous system, but with normal number and
appearance of the normally zinc containing presynaptic
vesicles (Kantheti et al., 1998). The ZnT-3 molecule has
both tyrosine- and dileucine-based sequences (Kantheti
et al., 1998), consistent with a role for AP-3 in linking
the ZnT-3 cargo molecule via its cytoplasmic targeting
signals with vesicular coat proteins, such as clathrin, for
trafficking to target organelles.
Gene and protein structure
The HPS3 gene is found on chromosome 3q24, has 17
exons with a 3015 open reading frame encoding a pro-
tein of 1004 amino acids predicted to have a molecular
mass of 113.7 kDa (Anikster et al., 2001), but with an
apparent molecular mass of 130 kDa by sodium dodecyl
sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)
analysis (Nazarian et al., 2003). A clathrin binding site is
predicted from codons 172–176 (Figure 3). The mRNA
transcript is 4.4 kb and appears to be ubiquitous,
expressed in heart, brain, placenta, lung, liver, skeletal
muscle, kidney, and pancreas (Anikster et al., 2001).
Twenty-one patients with HPS3 have been reported
in the literature, with eight mutations described (Anik-
ster et al., 2001; Huizing et al., 2001a). The most com-
mon mutation is found among families from central
Puerto Rico due to a founder effect; all of these patients
are homozygous for a large 3904-bp deletion encompas-
sing all of exon 1, >2 kb of upstream sequence and
673 bp of intron 1 (Figure 3). One mutation is associ-
ated with patients of Ashkenazi Jewish descent: the
IVS5 + 1G>A splice site mutation occurred in five Ash-
kenazi Jews, and not in any of the three patients not of
Ashkenazi Jewish descent (Huizing et al., 2001a).
HPS-3 is clinically mild compared with HPS-1 (Anikster
et al., 2001; Huizing et al., 2001a; Tsilou et al., 2004). In
some patients, extra-ocular symptoms were so mild,
they carried an initial diagnosis of ocular albinism for
decades. On average, the best corrected is 20⁄125
(range 20/50–20/320) compared with 20⁄160 in HPS-1,
and the iris transillumination in HPS-3 on average is less
than in HPS-1. All reported HPS-3 patients exhibited
excessive bruising and epistaxis, but only an occasional
patient required transfusion. Pulmonary testing revealed
minimal reduction in FVC (75–96% of normal).
Figure 3. Mutations found in HPS-3 and cocoa.
Pigment Cell Res. 19; 19–42
Cell biology and biochemistry
Studies of HeLa cells demonstrated that the HPS3 pro-
tein associated with the HPS5 and HPS6 proteins in a
multimeric protein complex, BLOC-2, which had an esti-
mated molecular mass of 340 kDa (Di Pietro et al., 2004).
Immunofluorescent imaging of melanocytes derived
from HPS-3 patients demonstrated that molecules nor-
mally targeted to later stage melanosomes (e.g. the
melanogenic enzymes tyrosinase and Tyrp1) were mis-
localized (Boissy et al., 2005; Richmond et al., 2005);
mislocalization of tyrosinase correlated with decreased
levels of melanin in melanocytes (Boissy et al., 2005). In
contrast, the steady-state distribution of molecules tar-
geted to stage I melanosomes (e.g. silver/Pmel17/
unchanged from that in control cells. Transmission elec-
tron microscopic analysis of HPS-3 melanocytes detec-
ted 50-nm vesicles, containing melanogenic enzymatic
activity as measured by DOPA staining, more numer-
ously and in a more dispersed distribution than found in
control melanocytes. The DOPA staining also detected
melanogenic enzymatic activity in melanosomes, sug-
gesting that melanogenic enzymes can access melano-
somes via an HPS3-independent pathway, and that the
lack of detected melanin in later stage melanosomes in
HPS-3 cells is due to the limiting quantity of another
shown that the activity of tyrosinase increases with
phosphorylation and upon association with Tyrp1 (Wu
and Park, 2003; Park et al., 1993, 1999), and that tyros-
inase phosphorylation may be RACK1 mediated (Park
et al., 2004); thus molecular events other than delivery
of melanogenic enzymes to melanosomes influence
melanin production. The LAMP-1 and LAMP-3 mole-
cules had a similar pattern of mislocalization in HPS-3
melanocytes as did tyrosinase: in HPS-3 cells, the distri-
bution was more diffuse than in control cells (Boissy
et al., 2005).
HPS3 has a clathrin binding motif (Anikster et al.,
2001). Clathrin was co-immunopreciptated with HPS3,
clathrin and HPS3 were observed to partially colocalize
and live cell imaging demonstrated fusion of HPS3 labe-
led vesicles with clathrin labelled vesicles. Furthermore,
mutation of the clathrin binding motif in HPS3 abrogated
the association of HPS3 with small vesicles and resulted
in a primarily cytoplasmic localization for HPS3, suggest-
ing a functional role for clathrin in localizing HPS3 to
vesicular membranes (Helip-Wooley et al., 2005).
The cocoa mouse strain (coa) is the model for HPS-3
(Novak et al., 1988; Suzuki et al., 2001). The mouse
Hps3 gene contains 17 exons, coding for a protein with
1002 amino acids and a predicted molecular mass
113.1 kDa, which appears to be ubiquitously expressed
(Suzuki et al., 2001). Four allelic strains of cocoa have
mutations in the Hps3 gene (Figure 3).
Cocoa is distinguished from most of the other HPS
mouse models by normal secretion of kidney lysosomal
enzymes (Novak et al., 1988; Swank et al., 1998) and
skin fibroblasts from cocoa mice do not have a defect in
basal levels of secretion of lysosomal enzymes (Di Pie-
tro et al., 2004).
Immortalized cultured melanocytes from cocoa mice
show little visible pigment and melanin production was
decreased to approxmately 25% of that found in control
cells (Suzuki et al., 2001). Ultrastructural studies of
cocoa eye tissue found decreased numbers of melano-
somes in the retinal pigment epithelium and choroid; in
addition, multilamellar bodies and abnormal melano-
somes were observed in the choroid (Suzuki et al.,
2001). Examination of the dorsal back follicular melano-
cytes by transmission electron microscopy showed a
preponderance of immature melanosomes, with an
apparent block in melanosome biogenesis occurring
before the formation of stage II melanosomes (Nguyen
et al., 2002).
The association of Hps3, Hps5, and Hps6 in the
BLOC-2 complex was demonstrated by coimmunopre-
cipitation, but yeast two-hybrid analysis did not detect
direct binding of Hsp3 to Hps5 or Hps6, suggesting the
possible existence of another small subunit (Gautam
et al., 2004; Zhang et al., 2003).
Gene and protein structure
The HPS4 gene is found on chromosome 22q11.2-q12.2
and has a distant homology with the yeast CCZ1 protein
(Anderson et al., 2003; Hoffman-Sommer et al., 2005)
which is implicated in trafficking and fusion of vesicles
from the yeast prevaculoar compartment (functionally
equivalent to the mammalian late endosome) to the
vacuole (equivalent to the mammalian lysosome). HPS4
consists of 14 exons that covers approximately 32 kb of
genomic DNA (Anderson et al., 2003). A major transcript
consisting of 14 exons with a 2127-bp open reading
frame, coding for a 708-amino acid protein (predicted
molecular mass of 76.9 kD, apparent molecular mass of
100 kDa by SDS-PAGE (Martina et al., 2003; Nazarian
et al., 2003)), is expressed in all tissue types tested. A
second alternatively spliced isoform has 12 exons with
a 2112-bp open reading frame, coding for a 703-amino
acid protein, is limited in expression to brain, thymus,
lymph node, fetal liver, bone marrow and melanocytes
and no homologs have been identified in other mamma-
lian species for this minor protein. These two transcripts
differ in 5’ exon usage, but are identical after codon 15
in the major isoform (codon 10 of the minor isoform).
Three other transcript variants of uncertain biological
importance have also been reported (Anderson et al.,
To date, 15 patients worldwide have been reported
with HPS-4 and 10 mutations in the HPS4 gene have
Pigment Cell Res. 19; 19–42
been identified (Figure 4). The functional importance of
the far carboxyl terminus of HPS4 is demonstrated by
patients, one patient carrying a deletion at codon 685,
resulting in a loss of 24 normally coded amino acids
from the carboxyl terminus and another carrying an
insertion of five nucleotides at codon 698, causing a
loss of 10 normally coded amino acids. The first patient
had severe, progressive pulmonary fibrosis notable for
hypoxemic respiratory failure requiring supplemental
oxygen (Bachli et al., 2004). The second patient, in
which HPS4 RNA was detected in fibroblasts, suffered
from severe pulmonary fibrosis resulting in death at
61 yr of age (Anderson et al., 2003).
Eight polymorphisms of HPS4 have been detected,
four of which cause amino acid substitutions: E229G,
V552M, H606Y, and Q625H (Anderson et al., 2003).
As in other subtypes of HPS, HPS-4 patients have great
variability in the degree of hypopigmentation. Many, but
not all, have clinical signs and symptoms of platelet
dysfunction, marked by epistaxis, bruising and in the
case of female patients, menorrhagia. Best corrected
visual acuity varies from 10⁄30 to 20⁄200 (Anderson
et al., 2003). HPS-4 patients can have a severe clinical
phenotype, with features similar to those observed in
HPS-1 patients. In one study, one of seven patients
with HPS-4 was diagnosed with granulomatous colitis,
and three of seven had restrictive pulmonary fibrosis
(Anderson et al., 2003). In another detailed clinical study
of the patient carrying the homozygous P685del muta-
tion who suffered from severe pulmonary fibrosis, skin
biopsy was reported to show normal numbers of mel-
anocytes and decreased melanin content by Masson–
Fontana staining and perivascular macrophages contain-
ing ceroid pigment; lung biopsy revealed an increased
number of type II pneumocytes with foamy cytoplasm,
and macrophages contained ceroid pigment (Bachli
et al., 2004).
Platelets from an HPS-4 patient were found to have
altered localization of the ATP-dependent pump MRP4
(also known as ABCC4), a transport pump for cyclic nu-
cleotides and nucleotide analogs (Jedlitschky et al.,
2004). In control platelets, MRP4 is found in intracellular
granules, as well as on the plasma membrane, whereas
in HPS-4 platelets, intracellular staining was greatly
decreased, with staining predominantly seen on the cell
The corresponding mouse model for HPS-4 is the light
ear (le) strain (Suzuki et al., 2002). The mouse light ear
protein is predicted to have 671 amino acids and have a
molecular mass of 72.7 kD. Two isoforms of RNA tran-
scripts are detectable in light ear tissue, 3.6 and 3.1 kb
in size. Ultrastructural analysis of melanosomes in the
eyes of light ear mice showed abnormalities in the ret-
inal pigment epithelium, in which melanosomes were
decreased in number, and in the choroid, which had
markedly enlarged melanosomes. Cultured melanocytes
from light ear skin had small, abnormally shaped imma-
ture melanosomes (Suzuki et al., 2002), consistent with
observations in vivo on epidermal melanocytes from
light ear tail skin (T. Nguyen and M.L. Wei, personal
Figure 4. Mutations found in HPS-4 and light ear.
Pigment Cell Res. 19; 19–42
In a cell line established from light ear mouse skin,
cellular activity of lysosomal hydrolases were elevated
compared with in control cells, while secreted lysosom-
al hydrolase activities were 10% of control cell levels
(Delprato et al., 2000). This result was consistent with
the earlier findings of increased kidney lysosomal hydrol-
ase activity in light ear and pale ear mice and concomit-
ant decreased levels of activity found secreted into
urine (Meisler, 1978; Novak and Swank, 1979), suggest-
ing impaired secretion.
Gene and protein structure
The HPS5 gene is found on chromosome 11p14, has 23
exons and encodes a protein 1129 amino acids in length
with a calculated molecular mass of 127 kDa (Huizing
et al., 2004; Zhang et al., 2003) and an apparent molecu-
lar mass of 170 kDa (Di Pietro et al., 2004). The 4.8 kb
transcript was found to be expressed in all tissues tes-
ted, but was very highly expressed in lung and testis
(Huizing et al., 2004). Two alternatively spliced isoforms
were detected, both predicted to result in proteins with
114 fewer amino acids at the amino terminus, because
of an alternative start sites in exon 5 (Huizing et al.,
2004; Zhang et al., 2003). Both of these latter isoforms
were also expressed in all tissues surveyed, but one
(719 bp) was expressed at high levels in placenta, kid-
ney, testis, and ovary, while the other (588 bp) was
found to be expressed at high levels in placenta, lung,
and thymus (Huizing et al., 2004).
Seven disease causing mutations in HPS5 have been
detected (Huizing et al., 2004; Zhang et al., 2003) (Fig-
ure 5). A pair of siblings had two missense mutations
(L624R and T1098I) that both occurred together in the
homozygous state, so whether both mutations are dis-
ease causing or only one is, with the other change
being a polymorphism, could not be determined (Huizing
et al., 2004).
The clinical features of five individuals with HPS-5, ages
3–51 yr, have been reported (Huizing et al., 2004; Zhang
et al., 2003). Most patients were of northern European
descent; one was Turkish. All had nystagmus or visual
symptoms (such as poor tracking) that led to an early
diagnosis of albinism. Visual acuity ranged from 20⁄100
to 20⁄200. All had bruising; one patient had menorrhagia
and metrorrhagia requiring blood or platelet transfusions.
All had absent platelet dense bodies, leading to a diag-
nosis of HPS. None had a diagnosis of inflammatory
bowel disease and none had shortness of breath.
Minimal to no impairment was detected by pulmonary
function testing (average FVC was 96% of normal,
range was 80–111%). Four of five patients had mildly to
minimally elevated creatinine clearance, testing for the
fifth patient was not noted. All patients had elevated
cholesterol levels, and a few had mildly elevated triglyc-
erides as well. The significance of these elevated lipid
levels, and whether they are a result of the underlying
membrane trafficking defect, is not known.
Cell biology and biochemistry
As noted previously, HPS3, HPS5, and HPS6 associate
together in a complex designated BLOC-2 (Di Pietro
et al., 2004). Studies on fibroblasts from HPS-5 patients
noted that the distribution of LAMP-3 (CD63) was
confined to granules in a perinuclear region, unlike in
Figure 5. Mutations found in HPS-5 and ruby eye-2.
Pigment Cell Res. 19; 19–42
normal fibroblasts, in which LAMP-3 was also found in
granules distributed in the dendritic processes (Huizing
et al., 2004). The HPS5 molecule was reported to bind
to the cytoplasmic domain of the a3A integrin molecule
(Wixler et al., 1999), but another group was unable to
duplicate the finding (Zhang et al., 2003).
The ruby eye-2 (ru2) mouse strain is the model for HPS-
5 (Zhang et al., 2003). The mouse Hps5 gene is on chro-
mosome 7 and has a 3381-bp open reading frame with
23 exons, encoding a 1126 amino acid protein, 81%
homologous to the human sequence, and with predic-
ted molecular mass 126.3 kDa. By Northern blot analy-
sis, all tissues examined contained the 4.8 kb transcript.
Alternate transcripts were also detected in kidney tis-
sue, one that results in truncation of 165 amino acids
from the amino terminus, and another that truncates
600 amino acids from the carboxyl terminus. The signifi-
cance and general tissue distribution of these transcripts
is not known.
abnormal in eye and skin. In retinal pigment epithe-
lium, melanosomes are decreased in number and ab-
errantlyshaped. In the
bodies are observed, a finding unique to ruby eye-2
and ruby (Zhang et al., 2003). In dorsal skin follicular
melanocytes, the steady state distribution of melano-
somes was shifted to more immature stages; most
remained spherical, without progression to the ellipti-
cal shape characteristicof
(Nguyen et al., 2002), suggesting that the ru2 protein
functions in melanosome maturation from stage I to
In COS7 cells expressing introduced Hps5 and Hps6,
the two molecules coimmunoprecipitated, demonstra-
in ruby eye-2is
ting that, similar to the human counterparts, these pro-
teins associated together in a complex. Yeast two-
hybrid analysis demonstrated
between Hps5 and Hps6 (Zhang et al., 2003).
a direct interaction
Gene and protein structure
The HPS6 gene, on chromosome 10q24.32, consists of
a single exon (Zhang et al., 2003). The predicted HPS6
protein length is 775 amino acids (Figure 6).
Three patients have been reported in the literature with
HPS-6 (Zhang et al., 2003). One 39-yr-old woman had
no pulmonary or gastrointestinal symptoms, but did
have epistaxis and bleeding after dental extractions and
surgeries. Two other patients were both under 27 yr of
age and had typical oculocutaneous albinism but no pul-
monary fibrosis or colitis.
The mouse model for HPS-6 is the ruby eye (ru) strain
(Zhang et al., 2003). The Hps6 gene is on chromosome
19 and encodes a 2418-bp open reading frame, and is
similar to the human gene, containing a single exon.
The encoded 805 amino acid protein has a predicted
molecular mass of 88.8 kDa and has 80% identity with
the human HPS6 protein; the mouse and rat proteins
have an extension of 31 amino acids.
There are four allelic ruby eye strains (Zhang et al.,
2003). Two strains, ru and ru4J, have in-frame dele-
tions in Hps6, a three amino acid deletion encompas-
sing amino acids H187 to P189 and a 22 amino acid
deletion encompassing amino acids L65–W86, respect-
ively (Figure 6). The loss of the three amino acids in
the ru strain suggested that the interaction of Hps6
Figure 6. Mutations found in HPS-6 and ruby eye.
Pigment Cell Res. 19; 19–42
with Hsp5 might depend on these three residues (his/
cys/pro). This was confirmed using yeast two hybrid
analysis which found that Hps6rudoes not bind to
Hps5wt(Gautam et al., 2004). When each residue in
this binding sequence was singly mutated to an alan-
ine, binding between Hps5 and Hps6 remained intact,
suggesting that the sequence only indirectly mediates
the protein–protein interaction, perhaps by influencing
secondary structural features.
In ruby eye and ruby eye-2 mice, as with the
majority of HPS mouse strains (Swank et al., 1998),
there is a decreased rate of kidney lysosomal enzyme
secretion after testosterone treatment, compared with
in control cells (Novak et al., 1980). However, ruby
eye skin fibroblasts demonstrate no defect in basal
secretion of lysosomal enzymes (Di Pietro et al.,
2004) suggesting that perhaps in the kidney, an LRO
(vs. the lysosome) is affected by mutations in HPS
genes. In mast cells collected from ruby eye mice, an
approximately threefold increase in the number and
duration of transient fusion events with the plasma
membrane was recorded (Oberhauser and Fernandez,
1996), suggesting that the Hps6 protein may have a
role in mediating the exocytosis of mast cell granules.
However, this function in exocytosis could not be
assigned unambiguously to Hps6, as cells derived
from control mice with the same genetic background
as the ruby eye mice could not be assayed.
Gene and protein structure
The DTNBP1 gene is defective in HPS-7, encodes the
dysbindin protein on chromosome 6p22.3 and has 10
exons (Li et al., 2003; Straub et al., 2002). Six non-dis-
ease causing polymorphisms have been detected, and a
single mutation has been reported (Figure 7).
The single patient reported with HPS-7, a 48-yr-old Por-
tuguese woman, was homozygous for the Q103X muta-
tion (Li et al., 2003). She had oculocutaneous albinism,
easy bruisability, a bleeding tendency, mild shortness of
breath with exertion, decreased lung compliance, but
otherwise normal pulmonary function tests and high-
resolution chest CT. No muscle weakness, ataxia or
symptoms of schizophrenia were noted (Li et al., 2003,
Cell biology and biochemistry
In addition to a role in causing HPS-7, dysbindin is
implicated in the molecular pathology of Duchenne mus-
cular dystrophy (DMD) because of its binding to
members of the dystrophin-associated protein complex,
a- and b-dystrobrevin; the DMD gene encodes dystrophin
(Benson et al., 2001). Yeast two-hybrid analysis also
detected binding to a novel binding partner, myospryn,
Figure 7. (A) Mutations found in HPS-7 and sandy; (B) mutations found in HPS-8 and reduced pigmentation.
Pigment Cell Res. 19; 19–42
which associated with dysbindin via the coiled coil
domain of dysbindin (Benson et al., 2004). The tissue
expression of myospryn is limited to skeletal muscle and
heart, and provides an example of a tissue-specific bind-
ing partner for the ubiquitously expressed dysbindin.
Genetic susceptibility to schizophrenia
mapped to the DTNBP1 gene locus (Straub et al., 2002)
and dysbindin appears to play a role in the exocytosis of
glutamate containing synaptic vesicles in neurons. Over-
expression of dysbindin in cultured primary cortical neu-
rons induced the expression of SNAP25, a soluble
protein that regulates membrane fusion events, and also
upregulated synapsin I, a cytoskeletal protein associated
with synaptic vesicles. Depression of intracellular levels
of dysbindin mediated by siRNA resulted in decreased
detection of SNAP25 and synapsin I by immunoblotting
and reduced glutamate release by siRNA treated cells
(Numakawa et al., 2004).
The mouse model for HPS-7 is the sandy (sdy) strain (Li
et al., 2003; Swank et al., 1991). The defective gene,
Dtnbp1, encodes a 51 kDa, 352 amino acid protein (Li
et al., 2003) predicted to have a coiled-coil region
between amino acids 88 and 177 (Benson et al., 2001).
In sandy mice, an inframe deletion from genomic nu-
cleotides 3701–12 377 caused deletion of 52 residues
(amino acids 119–172) comprising exons 6 and 7 and
including the majority of the predicted coiled coil region
(Figure 7). While in wild-type mice, a 1.65-bp transcript
is expressed in brain, kidney, and heart (suggesting ubi-
quitous expression), in sandy mice a smaller 1.5-kb tran-
script is detected, and no protein product is detected by
immunoblotting (Li et al., 2003).
In yeast two-hybrid analysis, dysbindin was found to
bind b-dystrobrevin, in agreement with previous studies,
and also to two other proteins, muted and pallidin,
named for the HPS mouse strains in which they are
defective, muted and pallid (Benson et al., 2001; Li
et al., 2003). Muted and pallidin were previously shown
to associate together in the multiprotein BLOC-1 com-
plex, which included two other HPS proteins, rp and
cappuccino (Ciciotte et al., 2003; Falcon-Perez et al.,
2002; Gwynn et al., 2004).
Dysbindin was confirmed to be a component of
BLOC-1 by coimmunoprecipitation (Li et al., 2003); size
exclusion chromatography and sedimentation velocity
analysis further confirmed that endogenous dysbindin
and pallidin associated together in a 230 kDa complex
(Falcon-Perez et al., 2002). The bulk of b-dystrobrevin
did not appear to co-purify with BLOC-1 components,
although a small amount may be associated with murine
BLOC-1 (Li et al., 2003); no a- or b-dystrobrevin was iso-
lated in bovine BLOC-1 (Starcevic and Dell’Angelica,
2004). Thus it is not clear if the a- and b-dystrobrevin
proteins are involved in vesicle trafficking, or if dysbindin
is a component of two separate multiprotein complexes
which mediate distinct functions (Li et al., 2003). The b-
dystrobrevin containing dystrophin-associated protein
complex has been reported to interact with actin, as
has pallidin (Blake et al., 2002; Falcon-Perez et al.,
2002), but the functional significance of these interac-
tions is unclear.
Evidence suggests that BLOC-1 has a role in mem-
brane trafficking. Pallidin binds syntaxin 13, a member
of the SNARE family of proteins that have a role in vesi-
cle targeting, docking and fusion with target membranes
(Advani et al., 1998). Syntaxin 13 has been localized to
early and recycling endosomes, and also to endosomal
vacuoles, where it is often found in clathrin-coated
membrane areas (Prekeris et al., 1998). An additional
member of the BLOC-1 complex is snapin, a protein
previously implicated in the regulation of membrane
fusion events (Ilardi et al., 1999; Buxton et al., 2003)
Together with snapin, dysbindin, pallidin, muted, rp and
cappuccino, two novel proteins, BLOS-1 and BLOS-2,
are also componentsof
Dell’Angelica, 2004). While all of the BLOC-1 subunits
except for rp contain predicted coiled coil regions (impli-
cated in mediating protein–protein interactions), non-
coiled coil regions also appear capable of mediating pro-
tein–protein interactions, as deletion of the BLOS-1
coiled coil region is not required for BLOS-1 binding to
pallidin (Starcevic and Dell’Angelica, 2004).
Melanosomes in sandy mice are markedly abnormal.
In the eye, the retinal pigment epithelial melanosomes
are decreased in number and the choroidal melano-
somes are also decreased in number and smaller and
irregularly shaped (Li et al., 2003). In the dorsal back
skin follicular melanocytes, melanosome biogenesis
was blocked at or before stage I and numerous aberrant
vacuolar forms were noted (Nguyen and Wei, 2004).
BLOC-1 (Starcevic and
Gene and protein structure
HPS-8 has been identified as due to a defect in the
BLOC1S3 gene and is orthologous to the mouse rp
gene. A large consanguineous family with HPS was
identified to have a homozygous germline frameshift
mutation (Morgan et al., 2006) (Figure 7).
Patients had incomplete oculocutaneous albinism and
mild platelet dysfunction with easy bruising, hematomas
after venesection, frequent epistaxis and prolonged
bleeding after surgery or childbearing, sometimes requi-
ring blood transfusion (Morgan et al., 2006).
The reduced pigmentation mouse was observed to have
pigment dilution, increased kidney lysosomal glycosidase
activities, increased bleeding times, decreased platelet
dense bodies, predominantly immature melanosomes,
Pigment Cell Res. 19; 19–42
decreased melanin levels and an abnormal intracellular ty-
rosinase distribution, findings consistent with being a
model for an HPS subtype (Gibb et al., 1981; Gwynn
et al., 2004; Nguyen et al., 2002; Swank et al., 1998).
The mouse gene is found on chromosome 7, consists
of a 1867 bp ORF containing two exons encoding an
195 aa protein with an apparent molecular mass of
?32 kDa (Gwynn et al., 2004; Starcevic and Dell’Angel-
ica, 2004). Co-immunopreciptation studies, sedimenta-
tion analyses,yeast two-hybrid
exclusion chromatography analyzed by immunoblotting
established the protein defective in rp mice (BLOS3/rp),
as a component of BLOC-1 when in the phosphorylated
form (Gwynn et al., 2004; Starcevic and Dell’Angelica,
2004). However, unlike defects in other BLOC-1 compo-
nents, the defect in the rp protein does not cause disrup-
tion of the BLOC-1 complex, and thus the phenotype is
that of a hypomorph (Starcevic and Dell’Angelica, 2004).
Hermansky–Pudlak syndrome is an example of a gen-
etically heterogeneous syndrome that is the result of
defects in protein trafficking along the endocytic/lyso-
somal pathway. HPS gene products can be divided into
two types. Group A (AP3B1, AP3D1, RABGGTA, and
VPS33A), are those that have homologues in yeast,
which regulate trafficking to the yeast vacuole and in
higher eukaryotes function as major regulators of traf-
ficking to the lysosome. In contrast, the remaining HPS
group B gene products (HPS1, HPS3, HPS4, HPS5,
HPS6, DTNBP1, HPS8, Pldn, cno, and mu), are only
found in metazoans (Li et al., 2004), and although con-
taining regions with some homology to yeast proteins
(Hoffman-Sommer et al., 2005), they have apparently
developed as specialized cell types evolved with the
need to form specialized organelles. This evolutionary
development, together with the preponderance of data
accumulating on the cellular effects of defects in HPS
proteins, suggests that the HPS group B proteins func-
tion primarily to regulate membrane and protein traffick-
ing to the ‘newer’ specialized organelles, the LROs, but
may also contribute to lysosomal trafficking.
Mechanisms for cell type-specific disease
One intriguing aspect of HPS has been that the disease
expression seems to be limited to a certain few special-
ized cell types despite ubiquitous tissue expression of
HPS proteins. One explanation could lie in the way that
different cell types developed pathways of biogenesis for
their specialized organelles. In some specialized cell
types, such as the cytotoxic T cells (CTL), the specialized
organelle (in this case the lytic granule), is a secretory
lysosome; i.e. there are no separate lysosomes distinct
from the lytic granule (Stinchcombe and Griffiths, 1999).
In contrast, in another specialized cell type, the melano-
cyte, studies suggested that the specialized organelle
(the melanosome) coexists in the cell with lysosomes
(Raposo et al., 2001). This may have implications regard-
ing the impact of defects in HPS group A vs. group B pro-
teins. Group B proteins might not affect cells with
secretory lysosomes but rather primarily affect cells
which had specialized LRO organelles that were distinct
from lysosomes. Consistent with this prediction is the
finding that the function of CTLs deficient in BLOC-1, -2,
and -3 was found to be normal (Bossi et al., 2005).
Another potential mechanism for cell type specificity is
illustrated in the case of the protein affected in HPS-7,
dysbindin, which is observed to have a tissue specific
protein binding partner, myospryn. So while the HPS pro-
teins are ubiquitous, it is likely that HPS proteins function
via binding to cell-type specific effectors (e.g. myospryn)
and/or tissue-specific cargo such as tyrosinase (found
only in pigment cells). Similarly, in the case of AP-3, the
defective complex in HPS-2, tissue specific neuronal sub-
units provide a mechanism for mediating brain specific
functions such as synaptic vesicle biogenesis. An addi-
tional mechanism contributing to cell-type specificity may
come from regulating differential expression levels of
HPS proteins in different cells types. For example, a par-
ticular antibody was able to detect endogenous HPS1
protein in human melanoma cells by immunoblotting and
immunoprecititation, but was unable to detect endog-
enous HPS1 protein in HeLa cells by the same methods
(Dell’Angelica et al., 2000a; Sarangarajan et al., 2001),
suggesting the possibility that pigment cells may express
higher levels of HPS1 compared with non-pigment cells.
Further tissue specific regulation may derive from cell
type-specific use of alternative transcripts; for example,
alternatively spliced isoforms of HPS5 and HPS4 are
expressed at different levels in different tissues (Ander-
son et al., 2003; Huizing et al., 2004).
Molecular pathology and HPS clinical subtypes
While all HPS patients suffer from oculocutaneous albin-
ism (OCA) and prolonged bleeding, different subtypes,
some with distinguishing features, are now recognized.
Recent genetic and biochemical characterizations of
HPS subtypes have enabled the classification of the
subtypes into groups (Table 3); the heterogeneous clin-
ical phenotypes of HPS can now be understood in the
context of the molecular pathology. HPS-1 and HPS-4
subtypes are similar in causing the most serious morbid-
ity and premature mortality, with affected individuals at
high risk for developing restrictive pulmonary disease
and inflammatory bowel disease. These clinical similarit-
ies reflect the molecular association of HPS1 and HPS4
to form the intracellular BLOC-3 complex; this complex
regulates the biogenesis and/or function of the lung
lamellar body as well as the platelet dense body and
the melanosome. HPS-2 is unique in causing immuno-
deficiency. The HPS-3, HPS-5, and HPS-6 subtypes are
clinically similar; the respective proteins associate to
Pigment Cell Res. 19; 19–42
form the BLOC-2 complex, and defects in these pro-
teins result in relatively mild symptoms of platelet dys-
function, without pulmonary involvement. Patients with
HPS-7 and HPS-8, due to defects in BLOC-1 subunits,
had moderate signs and symptoms of HPS: OCA, a
bleeding tendency and mild pulmonary symptoms (in
the case of HPS-7). The relatively mild systemic symp-
toms of HPS-7 and HPSS-8 contrast with the markedly
severe pigmentary phenotype observed in the mouse
strains deficient in BLOC-1 genes; however, the moder-
ate phenotype of the few reported patients affected by
defects in BLOC-1 may not be representative of BLOC-
1 patients in general.
The pigment dilution in HPS appears to result from
mistrafficking of melanogenic enzymes such as tyrosin-
ase, which leads to decreased melanin production. The
trafficking of additional other melanocyte factors may
also be affected, as melanosome biogenesis appears to
be blocked at immature stages. The bleeding diatheses
appear to be secondary to mistrafficking of the MRP4/
ABCC4 transporter in platelets with a consequent lack
of intralumenal vesicular loading of nucleotides, leading
to decreased secretion of these nucleotides with plate-
let aggregation and impaired clotting. Pulmonary fibrosis
appears to result from impaired secretion of surfactant
and phospholipids from abnormal appearing lung lamel-
lar bodies. Moreover, congenital neutropenia results
from mistrafficking of NE. Thus, defects in protein traf-
ficking pathways and organelle function account for
much of the pathophysiology seen in HPS (Table 4).
HPS and melanocyte protein trafficking
Studies of HPS have also added to the understanding of
critical aspects of melanocytes function. In humans and
mice, the two major forms of pigment synthesized by
melanocytes are eumelanin, or black/brown melanin,
stored in eumelanogenic melanosomes, and pheomela-
nin, or yellow/red melanin, stored in pheomelanogenic
melanosomes. Past study of the biogenesis of melano-
somes was facilitated by the observation of four mor-
melanosome development (Marks and Seabra, 2001;
Seiji et al., 1963). Recent morphological studies were
done which analyzed where melanosome biogenesis
was blocked in melanocytes derived from HPS mice
(Nguyen and Wei, 2004; Nguyen et al., 2002) and sug-
gested an ordering for HPS protein function along the
pathway of melanosome biogenesis (Figure 8).
A model depicting trafficking pathways in the melano-
cyte, incorporating the data from HPS cells, together
with recent studies on melanosome biogenesis and pro-
tein trafficking to the melanosome, is shown in Figure 9.
At the trans-Golgi network (TGN), newly synthesized
molecules destined ultimately for the lysosome or the
melanosome are likely to undergo a first round of sort-
ing. Molecules such as Pmel17 (a melanocyte-specific
protein targeted to melanosomes and an integral compo-
nent of the intra-lumenal fibrils) and MART-1/melan-a (a
melanocyte-specific protein of unknown function) appear
to be transported to the stage I melanosome, possibly
via an AP1 mediated mechanism (De Maziere et al.,
2002; Raposo et al., 2001). The syntaxin 13 molecule is
localized to stage I melanosomes/coated endosomes
(De Maziere et al., 2002; Prekeris et al., 1998), and the
Table 3. Clinical manifestations of HPS subtypes
BLOC-3 Variable pigment dilution
Decreased visual acuity
Restrictive lung disease (68%)
Granulomatous colitis (15%)
Variable pigment dilution
Decreased visual acuity
Neutropenia, recurrent respiratory
Conductive hearing loss
Decreased visual acuity
Mild extra-ocular symptoms
Bruising and epistaxis
Mild reduction of forced vital
Variable pigment dilution
Decreased visual acuity
Easy bruisability, bleeding tendency
Shortness of breath (HPS-7)
Table 4. HPS: disease of protein
trafficking to lysosome related organelles
OrganelleCell type Mistrafficked protein(s)HPS subtype
Tyrp1, DCT/TRP2, CD63
Cytotoxic T cell
Lung type II epithelial cell
aMelanocytes and retinal pigment epithelial cells.
Pigment Cell Res. 19; 19–42
BLOC-1 subunit pallidin binds syntaxin 13 in yeast two-
hybrid studies (Huang et al., 1999), suggesting a role for
BLOC-1 at the level of the stage I melanosome, perhaps
in mediating fusion events, as syntaxin 13 plays a role in
endosomal fusion (Prekeris et al., 1998). Moreover, sup-
porting a function for BLOC-1 at this early step in mel-
anosome biogenesis are melanosome morphologies in
the majority of BLOC-1 defective mice (pallid, cappuc-
cino, muted, and sandy) that exhibited a block in melano-
some maturation at the level of the stage I melanosome
(Nguyen and Wei, 2004; Nguyen et al., 2002).
Other molecules such as Tyrp1 and tyrosinase are likely
targeted to later stage II or III melanosomes (Kushimoto
et al., 2001; Raposo et al., 2001), but may arrive via dis-
tinct routes. Steady state distribution of tyrosinase was
disrupted in AP-3-deficient melanocytes (Huizing et al.,
2001b), but Tyrp1 was unaffected, suggesting that traf-
ficking of tyrosinase is AP3-dependent and that of Tyrp1
is not. Tyrosinase appears to be targeted to melano-
somes via an endosomal route, and seems to follow an
initial pathway similar to that taken by the LAMP-1 and -3
molecules. In AP-3 deficient melanocytes, tyrosinase
accumulated in multivesicular structures with tubular
extensions resembling early endosomes (Huizing et al.,
2001b) and in AP-3 deficient CTL, LAMP-3/CD63 also
appeared to accumulate in endosomal structures, colocal-
izing with the early endosomal marker EEA1 (Clark et al.,
2003). Studies on mouse fibroblasts deficient in AP-3 and
AP-1 molecules have suggested that AP-1 mediates traf-
ficking from Golgi to endosome and that AP-3 mediates
trafficking from endosomes to lysosomes (Reusch et al.,
2002). The data for melanocytes seems to be consistent
with the findings in fibroblasts, with the extension that
AP-3 mediates trafficking to melanosomes as well, as ty-
rosinase is mis-localized in the absence of AP-3 (Huizing
et al., 2001b).
Figure 8. HPS protein complexes function along the pathway of melanosome biogenesis. Mutations in genes encoding BLOC-1 components
cause accumulation of stage I melanosomes and numerous aberrant vesicular structures lacking intralumenal striations, whereas defects in
BLOC-2 components cause accumulation of stage I melanosomes and a novel melanosome intermediate, stage Ia, which is similar to stage I
melanosomes in being vacuolar and not elliptical, but which contains intraluminal striations. BLOC-3 appears to function early in melanosome
biogenesis as well, causing accumulation of stage I melanosomes. In mouse dorsal back follicular melanocytes, defects in BLOC-3
components introduce a mild rate limiting step and accumulation of stage I melanosomes (Nguyen et al., 2002), but in tail epidermal
melanocytes, a more pronounced block in melanosome biogenesis is observed, so that mature melanosomes were relatively decreased in
number (M.L. Wei and T. Nguyen, personal communication), suggesting that HPS proteins may differentially regulate melanocytes located in
separate anatomic niches. Defects in the d-subunit of AP-3 affect melanosome maturation between stage III and IV. Mutation of the Rabggta
subunit of Rab geranylgeranyl transferase prevents the association of melanosomes with cortical actin filaments and impedes secretion of
melanin particles into the extracellular space. BLOS3 is also known as HPS8/reduced pigmentation.
Pigment Cell Res. 19; 19–42
Genetic and morphological data in mice indicated that
BLOC-1 mediated events likely precede BLOC-3 medi-
ated events, and that BLOC-1 and BLOC-3 may work
sequentially along the same pathway, as doubly homo-
zygous pa/pa, ep/ep mice had the same pigmentary
phenotype as BLOC-1 pallid mice (Nazarian et al., 2003).
Immunoelectron microscopy studies co-localized Tyrp1
and AP-1 in the vicinity of the TGN and suggested that
Tyrp1 may exit the TGN via an AP-1-mediated route and
traffic directly to stage II melanosomes, persisting in
stage III and IV melanosomes (Raposo et al., 2001). In
cultured melanocytes derived from HPS-1 patients,
defective in BLOC-3, Tyrp1 is found in large vesicles as
well as in granular structures, compared with in control
cells in which only the granular structures are noted
(Richmond et al., 2005). Together, the data are consis-
tent with Tyrp1 trafficking to early melanosomes from
the TGN via an AP-1 and BLOC-3-dependent pathway.
In the absence of HPS1, Tyrp1 may be arrested in the
TGN or mislocalized to endosomal/lysosomal structures.
The localization of HPS1 near the Golgi and on uncoated
vesicles and on early melanosomes (Oh et al., 2000)
suggests that HPS1 may play a role in the transport of
vesicles destined for the melanosome. Ultrastructural
analysis of melanosome morphology in mice defective
in BLOC-3 is consistent with a role for BLOC-3 in mel-
anosome biogenesis before the stage II melanosome,
but after the delivery of Pmel17 to premelanosomes
Figure 9. Model of trafficking pathways in melanocytes mediated by HPS proteins. Melanosomal proteins such as MART-1 and Pmel17 exit
the TGN and traffic to the stage I melanosome/coated endosome via AP-1. Targeting and fusion of transport vesicles is possibly mediated by
BLOC-1 binding to syntaxin 13. LAMP-1 and tyrosinase are transported to an early endosome via AP-1, then tyrosinase proceeds to later
stage melanosomes via AP-3 and BLOC-3, whereas LAMP-1 continues on to late endosomes and lysosomes. BLOC-2 may mediate transport
vesicle targeting, docking or fusion to later stage melanosomes and lysosomes. Tyrp1 is transported directly from the TGN to later stage
melanosomes via BLOC-3 function. Alternatively, both tyrosinase and Tyrp1 could traffic to the late endosome via AP-3 and AP-1,
respectively, and then traffic via BLOC-3 to the melanosome. After secretion of melanin, via fusion of the melanosomal limiting membrane
with the plasma membrane, integral membrane molecules spanning the melanosome limiting membrane would remain on the cell surface,
and are predicted to be internalized into endosomes and subsequently trafficked to lysosomes for degradation. Consistent with this are data
which demonstrated MART-1, Pmel17 and Tyrp1 on the cell surface and also colocalizing with the lysosomal marker LAMP-1 (De Maziere
et al., 2002; Levy et al., 2005; Raposo and Marks, 2002; Sprong et al., 2001). TGN, trans-Golgi network; MVB, multivesicular body.
Pigment Cell Res. 19; 19–42
(Nguyen et al., 2002). In cells from HPS-1 patients, ty-
rosinase is also found in large vesicles, similarly to the
effect on Tyrp1 (Richmond et al., 2005), again consis-
tent with BLOC-3 having a role in vesicular transport to
In mice, the BLOC-2 subunit Hps6 is suggested to
mediate fusion of transport vesicles to the plasma
membrane (Oberhauser and Fernandez, 1996), and may
likewise mediate fusion events at the level of the mel-
anosome (and lysosome). In the absence of the BLOC-2
subunit HPS3, melanocytes from patients exhibited a
more diffuse cytoplasmic distribution of tyrosinase,
Tyrp1, LAMP-1, and LAMP-3, compared with a granular
distribution in control cells (Richmond et al., 2005) and
ultrastructural studies demonstrated an increased abun-
dance of 50 nm vesicles containing pigment in the pres-
ence of dihydroxy-phenylalanine (DOPA), suggesting the
intraluminal presence of either tyrosinase or Tyrp1 enzy-
matic activity (Boissy et al., 2005). The steady state dis-
tribution of Pmel17 and MART-1 were normal (Boissy
et al., 2005). Thus BLOC-2 may mediate the fusion of
transport vesicles containing tyrosinase or Tyrp1 with
stage II or III melanosomes and vesicles containing
LAMP-1 and LAMP-3 with melanosomes and/or lyso-
HPS effects on LROs
How have HPS defects affected other LROs, such as
platelet dense bodies, lytic granules, and lung lamellar
bodies? A common theme appears to be defects in
secretion of many of these organelles. Skin cells from
light ear mice (defective in HPS4) have decreased basal
secretion of lysosomal hydrolases (Delprato et al., 2000).
Platelets have abnormal thrombin stimulated secretion of
dense granule contents (Novak et al., 1984). Lamellar
bodies in lung alveolar type II epithelial cells in pale ear/
pearl double homozygous mice (defective in HPS1 and
AP-3 proteins) have decreased basal and ATP-stimulated
secretory capacity for surfactant protein and phospholi-
pids (Guttentag et al., 2005). A possible mechanism for
the loss in secretory activity is suggested in HPS-1 and
HPS-2, in which defective microtubule-meditated organ-
elle motility is demonstrated for lysosomes in fibroblasts
(Nazarian et al., 2003) and lytic granules in T cells (Clark
et al., 2003), respectively. It could be that one or more
motility factors, mediating attachment to or movement
along microtubules, are missing or decreased in amount
from the affected organelles in HPS, due to mis-targeting.
Alternatively, selected HPS proteins may bind to these
factors, which may be degraded in the absence of the
HPS binding partner. Another possibility for lamellar bod-
ies is that the process of exocytosis rather than motility is
defective, and factors mediating events such as vesicle
docking, targeting or fusion at the plasma membrane
may be missing.
In the case of melanosomes, defects in Rabggta
caused a marked block in secretion of melanin and an
et al., 2002). However, in other HPS mouse strains an
accumulation of melanosomes within melanocytes was
not observed, and immature melanosomes were noted
within neighboring keratinocytes, indicating that aberrant
melanosomes were secreted to some extent (Nguyen
and Wei, 2004).
In conclusion, the Hermanky–Pudlak syndrome is
made up of a complex set of related autosomal reces-
sive disorders caused by underlying defects in protein
trafficking. Recent molecular, biochemical and cell bio-
logic analyses together with clinical studies have provi-
ded insights into links between molecular and cellular
pathology and clinical disease expression. Studies on
HPS have led to a deeper understanding of basic cell
processes, in particular mechanisms of cell-type specific
specialized processes,led to the development of
molecular tools to identify increasing numbers of HPS
patients, and will likely help lead to targeted therapies
for this currently untreatable and often fatal disease.
of intracellular melanosomes (Nguyen
Many thanks to Drs Richard Swank and Edward Novak for critical
reading of this manuscript and to Jerelyn Magnusson and Edgardo
Caballero for excellent technical help.
Advani, R.J., Bae, H.R., Bock, J.B., Chao, D.S., Doung, Y.C., Preke-
ris, R., Yoo, J.S., and Scheller, R.H. (1998). Seven novel mamma-
compartments. J. Biol. Chem. 273, 10317–10324.
Anderson, P.D., Huizing, M., Claassen, D.A., White, J., and Gahl,
W.A. (2003). Hermansky–Pudlak syndrome type 4 (HPS-4): clin-
ical and molecular characteristics. Hum. Genet. 113, 10–17.
Anikster, Y., Huizing, M., White, J., Shevchenko, Y.O., Fitzpatrick,
D.L. et al. (2001). Mutation of a new gene causes a unique form
of Hermansky–Pudlak syndrome in a genetic isolate of central
Puerto Rico. Nat. Genet. 28, 376–380.
Avila, N.A., Brantly, M., Premkumar, A., Huizing, M., Dwyer, A.,
and Gahl, W.A. (2002). Hermansky–Pudlak syndrome: radiogra-
phy and CT of the chest compared with pulmonary function tests
and genetic studies. AJR Am. J. Roentgenol. 179, 887–892.
Bachli, E.B., Brack, T., Eppler, E., Stallmach, T., Trueb, R.M., Huiz-
ing, M., and Gahl, W.A. (2004). Hermansky–Pudlak syndrome
type 4 in a patient from Sri Lanka with pulmonary fibrosis. Am.
J. Med. Genet. A. 127, 201–207.
Bailin, T., Oh, J., Feng, G.H., Fukai, K., and Spritz, R.A. (1997).
Organization and nucleotide sequence of the human Hermansky–
Pudlak syndrome (HPS) gene. J. Invest. Dermatol. 108, 923–
Bainton, D.F. (1999). Distinct granule populations in human neu-
trophils and lysosomal organelles identified by immuno-electron
microscopy. J. Immunol. Meth. 232, 153–168.
Balkema, G.W., Mangini, N.J., and Pinto, L.H. (1983). Discrete vis-
ual defects in pearl mutant mice. Science 219, 1085–1087.
Benson, M.A., Newey, S.E., Martin-Rendon, E., Hawkes, R., and
Blake, D.J. (2001). Dysbindin, a novel coiled-coil-containing pro-
tein that interacts with the dystrobrevins in muscle and brain. J.
Biol. Chem. 276, 24232–24241.
Pigment Cell Res. 19; 19–42
Benson, K.F., Li, F.Q., Person, R.E., Albani, D., Duan, Z. et al.
(2003). Mutations associated with neutropenia in dogs and
humans disrupt intracellular transport of neutrophil elastase. Nat.
Genet. 35, 90–96.
Benson, M.A., Tinsley, C.L., and Blake, D.J. (2004). Myospryn is a
novel binding partner for dysbindin in muscle. J. Biol. Chem.
Blake, D.J., Weir, A., Newey, S.E., and Davies, K.E. (2002). Func-
tion and genetics of dystrophin and dystrophin-related proteins in
muscle. Physiol. Rev. 82, 291–329.
Boissy, R.E., Zhao, Y., and Gahl, W.A. (1998). Altered protein local-
ization in melanocytes from Hermansky–Pudlak syndrome: sup-
port for the role of the HPS gene product in intracellular
trafficking. Lab. Invest. 78, 1037–1048.
Boissy, R.E., Richmond, B., Huizing, M., Helip-Wooley, A., Zhao,
Y., Koshoffer, A., and Gahl, W.A. (2005). Melanocyte-specific
proteins are aberrantly trafficked in melanocytes of Hermansky–
Pudlak syndrome-type 3. Am. J. Pathol. 166, 231–240.
Bonifacino, J.S., and Dell’Angelica, E.C. (1999). Molecular bases for
the recognition of tyrosine-based sorting signals. J. Cell. Biol.
Bonifacino, J.S., and Traub, L.M. (2003). Signals for sorting of
transmembrane proteins to endosomes and lysosomes. Annu.
Rev. Biochem. 72, 395–447.
Bossi, G., Booth, S., Clark, R., Davis, E.G., Liesner, R. et al. (2005).
Normal lytic granule secretion by cytotoxic T lymphocytes defici-
ent in BLOC-1, -2 and -3 and myosins Va, VIIa and XV. Traffic 6,
Brantly, M., Avila, N.A., Shotelersuk, V., Lucero, C., Huizing, M.,
and Gahl, W.A. (2000). Pulmonary function and high-resolution
CT findings in patients with an inherited form of pulmonary fibro-
sis, Hermansky–Pudlak syndrome, due to mutations in HPS-1.
Chest 117, 129–136.
Burkhard, P., Stetefeld, J., and Strelkov, S.V. (2001). Coiled coils:
a highly versatile protein folding motif. Trends Cell Biol. 11,
Buxton, P., Zhang, X.M., Walsh, B., Sriratana, A., Schenberg, I.,
Manickam, E., and Rowe, T. (2003). Identification and characteri-
zation of Snapin as a ubiquitously expressed SNARE-binding pro-
tein that interacts with SNAP23 in non-neuronal cells. Biochem.
J. 375, 433–440.
Chiang, P.W., Oiso, N., Gautam, R., Suzuki, T., Swank, R.T., and
Spritz, R.A. (2003). The Hermansky–Pudlak syndrome 1 (HPS1)
and HPS4 proteins are components of two complexes, BLOC-3
and BLOC-4, involved in the biogenesis of lysosome-related or-
ganelles. J. Biol. Chem. 278, 20332–20337.
Chiang, P.W., Bennett, D.C., and Spritz, R.A. (2005). BLOC3 affects
the cytoskeleton of the secretory pathway. Pigment Cell Res.
18(Suppl. 1), Abstract OP16.
Chintala, S., Li, W., Lamoreux, M.L., Ito, S., Wakamatsu, K. et al.
(2005). Slc7a11 gene controls production of pheomelanin pig-
ment and proliferation of cultured cells. Proc. Natl. Acad. Sci. U.
S. A. 102, 10964–10969.
Ciciotte, S.L., Gwynn, B., Moriyama, K., Huizing, M., Gahl, W.A.,
Bonifacino, J.S., and Peters, L.L. (2003). Cappuccino, a mouse
model of Hermansky–Pudlak syndrome, encodes a novel protein
that is part of the pallidin-muted complex (BLOC-1). Blood 101,
Clark, R.H., Stinchcombe, J.C., Day, A., Blott, E., Booth, S., Bossi,
G., Hamblin, T., Davies, E.G., and Griffiths, G.M. (2003). Adaptor
protein 3-dependent microtubule-mediated movement of lytic
granules to the immunological synapse. Nat. Immunol. 4, 1111–
Cordova, A., Barrios, N.J., Ortiz, I., Rivera, E., Cadilla, C., and Santi-
ago-Borrero, P.J. (2004). Poor response to desmopressin acetate
(DDAVP) in children with Hermansky–Pudlak syndrome. Pediatr.
Blood Cancer 43, 1–4.
Cutler, D.F.(2002). Introduction:
Semin. Cell Dev. Biol. 13, 261–262.
De Maziere, A.M., Muehlethaler, K., van Donselaar, E., Salvi, S.,
Davoust, J., Cerottini, J.C., Levy, F., Slot, J.W., and Rimoldi, D.
(2002). The melanocytic protein Melan-A/MART-1 has a subcellu-
lar localization distinct from typical melanosomal proteins. Traffic
Dell’Angelica, E.C. (2004). The building BLOC(k)s of lysosomes and
related organelles. Curr. Opin. Cell Biol. 16, 458–464.
Dell’Angelica, E.C., Shotelersuk, V., Aguilar, R.C., Gahl, W.A., and
Bonifacino, J.S. (1999). Altered trafficking of lysosomal proteins
in Hermansky–Pudlak syndrome due to mutations in the beta 3A
subunit of the AP-3 adaptor. Mol. Cell. 3, 11–21.
Dell’Angelica, E.C., Aguilar, R.C., Wolins, N., Hazelwood, S., Gahl,
W.A., and Bonifacino, J.S. (2000a). Molecular characterization of
the protein encoded by the Hermansky–Pudlak syndrome type 1
gene. J. Biol. Chem. 275, 1300–1306.
Dell’Angelica, E.C., Mullins, C., Caplan, S., and Bonifacino, J.S.
(2000b). Lysosome-related organelles. Faseb J. 14, 1265–1278.
Delprato, A., Raghavan, S., and Lyerla, T.A. (2000). An established
light ear mutant (C57BL/6J-Pdeb(rd1) le) mouse cell line exhibits
a block to secretion of lysosomal enzymes. Exp. Cell. Res. 256,
Detter, J.C., Zhang, Q., Mules, E.H., Novak, E.K., Mishra, V.S. et al.
(2000). Rab geranylgeranyl transferase alpha mutation in the gun-
metal mouse reduces Rab prenylation and platelet synthesis. Proc.
Natl. Acad. Sci. U. S. A. 97, 4144–4149.
Di Pietro, S.M., Falcon-Perez, J.M., and Dell’Angelica, E.C. (2004).
Characterization of BLOC-2, a complex containing the Herman-
sky–Pudlak syndrome proteins HPS3, HPS5 and HPS6. Traffic 5,
Falcon-Perez, J.M., Starcevic, M., Gautam, R., and Dell’Angelica,
E.C. (2002). BLOC-1, a novel complex containing the pallidin
and muted proteins involved in the biogenesis of melano-
somesand platelet-dense granules.
Falcon-Perez, J.M., Nazarian, R., Sabatti, C., and Dell’angelica, E.C.
(2005). Distribution and dynamics of Lamp1-containing endocytic
organelles in fibroblasts deficient in BLOC-3. J. Cell. Sci. 118,
Faundez, V., Horng, J.T., and Kelly, R.B. (1998). A function for the
AP3 coat complex in synaptic vesicle formation from endo-
somes. Cell. 93, 423–432.
Feldmann, J., Callebaut, I., Raposo, G., Certain, S., Bacq, D. et al.
(2003). Munc13-4 is essential for cytolytic granules fusion and is
mutated in a form of familial hemophagocytic lymphohistiocyto-
sis (FHL3). Cell 115, 461–473.
Feng, G.H., Bailin, T., Oh, J., and Spritz, R.A. (1997). Mouse pale ear
(ep) is homologous to human Hermansky–Pudlak syndrome and
contains a rare ‘AT-AC’ intron. Hum. Mol. Genet. 6, 793–797.
Feng, L., Seymour, A.B., Jiang, S., To, A., Peden, A.A. et al.
(1999). The beta3A subunit gene (Ap3b1) of the AP-3 adaptor
complex is altered in the mouse hypopigmentation mutant pearl,
a model for Hermansky- Pudlak syndrome and night blindness.
Hum. Mol. Genet. 8, 323–330.
Feng, L., Rigatti, B.W., Novak, E.K., Gorin, M.B., and Swank, R.T.
(2000). Genomic structure of the mouse Ap3b1 gene in normal
and pearl mice. Genomics 69, 370–379.
Frenk, E., and Lattion, F. (1982). The melanin pigmentary disorder
in a family with Hermansky–Pudlak syndrome. J. Invest. Derma-
tol. 78, 141–143.
Gahl, W.A., Brantly, M., Kaiser-Kupfer, M.I., Iwata, F., Hazelwood,
S. et al. (1998). Genetic defects and clinical characteristics of
Pigment Cell Res. 19; 19–42
patients with a form of oculocutaneous albinism (Hermansky–
Pudlak syndrome). N. Engl. J. Med. 338, 1258–1264.
Gahl, W.A., Brantly, M., Troendle, J., Avila, N.A., Padua, A., Mont-
alvo, C., Cardona, H., Calis, K.A., and Gochuico, B. (2002). Effect
of pirfenidone on the pulmonary fibrosis of Hermansky–Pudlak
syndrome. Mol. Genet. Metab. 76, 234–242.
Gardner, J.M., Wildenberg, S.C., Keiper, N.M., Novak, E.K., Rusin-
iak, M.E. et al. (1997). The mouse pale ear (ep) mutation is the
homologue of human Hermansky–Pudlak syndrome. Proc. Natl.
Acad. Sci. U. S. A. 94, 9238–9243.
Gautam, R., Chintala, S., Li, W., Zhang, Q., Tan, J., Novak, E.K., Di
Pietro, S.M., Dell’Angelica, E.C., and Swank, R.T. (2004). The
Hermansky–Pudlak syndrome 3 (cocoa) protein is a component
of the biogenesis of lysosome-related organelles complex-2
(BLOC-2). J. Biol. Chem. 279, 12935–12942.
Gibb, S., Hakansson, E.M., Lundin, L.G., and Shire, J.G. (1981).
Reduced pigmentation (rp), a new coat colour gene with effects
on kidney lysosomal glycosidases in the mouse. Genet. Res. 37,
Gonzalez-Conejero, R., Rivera, J., Escolar, G., Zuazu-Jausoro, I., Vi-
cente, V., and Corral, J. (2003). Molecular, ultrastructural and
functional characterization of a Spanish family with Hermansky–
Pudlak syndrome: role of insC974 in platelet function and clinical
relevance. Br. J. Haematol. 123, 132–138.
Guttentag, S.H., Akhtar, A., Tao, J.Q., Atochina, E., Rusiniak, M.E.,
Swank, R.T., and Bates, S.R. (2005). Defective surfactant secre-
tion in a mouse model of Hermansky–Pudlak syndrome. Am. J.
Respir. Cell Mol. Biol. 33, 14–21.
Gwynn, B., Martina, J.A., Bonifacino, J.S., Sviderskaya, E.V., Lamo-
reux, M.L. et al. (2004). Reduced pigmentation (rp), a mouse
model of Hermansky–Pudlak syndrome, encodes a novel compo-
nent of the BLOC-1 complex. Blood 104, 3181–3189.
Helip-Wooley, A., Westbroek, W., Dorward, H., Mommaas, M., Bo-
issy, R.E., Gahl, W.A., and Huizing, M. (2005). Association of the
Hermansky–Pudlak syndrome type-3 protein with clathrin. BMC
Cell Biol. 6, 33.
Hermansky, F., and Pudlak, P. (1959). Albinism associated with
hemorrhagic diathesis and unusual pigmented reticular cells in
the bone marrow: report of two cases with histochemical stud-
ies. Blood 14, 162–169.
Hermos, C.R., Huizing, M., Kaiser-Kupfer, M.I., and Gahl, W.A.
(2002). Hermansky–Pudlak syndrome type 1: gene organization,
novel mutations, and clinical-molecular review of non-Puerto
Rican cases. Hum. Mutat. Mutation in Brief no. 568, online.
Hess, R.A., Claassen, D.A., White, J., Gahl, W.A., and Huizing, M.
(2003). Hermansky-Pudlak syndrome type 5 and type 6: Four
new patients. Am. J. Hum. Genet. 73 (suppl), 456. (Abstract)
Heuser, J.E., and Keen, J. (1988). Deep-etch visualization of pro-
teins involved in clathrin assembly. J. Cell Biol. 107, 877–886.
Hoffman-Sommer, M., Grynberg, M., Kucharczyk, R., and Rytka, J.
(2005). The CHiPS Domain–ancient traces for the Hermansky–
Pudlak syndrome. Traffic 6, 534–538.
Horikawa, T., Araki, K., Fukai, K., Ueda, M., Ueda, T., Ito, S., and
Ichihashi, M. (2000) Heterozygous HPS1 mutations in a case of
Hermansky-Pudlak syndrome with giant melanosomes. Br. J.
Dermatol. 143, 635–640.
Horwitz, M., Benson, K.F., Duan, Z., Li, F.Q., and Person, R.E.
(2004). Hereditary neutropenia: dogs explain human neutrophil
elastase mutations. Trends Mol. Med. 10, 163–170.
Huang, L., Kuo, Y.M., and Gitschier, J. (1999). The pallid gene
encodes a novel, syntaxin 13-interacting protein involved in plate-
let storage pool deficiency. Nat. Genet. 23, 329–332.
Huizing, M., and Gahl, W.A. (2002). Disorders of vesicles of lyso-
somal lineage: the Hermansky–Pudlak syndromes. Curr. Mol.
Med. 2, 451–467.
Huizing, M., Anikster, Y., and Gahl, W.A. (2000). Characterization of
a partial pseudogene homologous to the Hermansky–Pudlak syn-
drome gene HPS-1; relevance for mutation detection. Hum.
Genet. 106, 370–373.
Huizing, M., Anikster, Y., Fitzpatrick, D.L., Jeong, A.B., D’Souza,
M. et al. (2001a). Hermansky–Pudlak syndrome type 3 in Ashke-
nazi Jews and other non-Puerto Rican patients with hypopigmen-
tation and platelet storage-pool deficiency. Am. J. Hum. Genet.
Huizing, M., Sarangarajan, R., Strovel, E., Zhao, Y., Gahl, W.A., and
Boissy, R.E. (2001b). AP-3 mediates tyrosinase but not TRP-1
trafficking in human melanocytes. Mol. Biol. Cell 12, 2075–2085.
Huizing, M., Scher, C.D., Strovel, E., Fitzpatrick, D.L., Hartnell,
L.M., Anikster, Y., and Gahl, W.A. (2002). Nonsense mutations in
ADTB3A cause complete deficiency of the beta3A subunit of
adaptor complex-3 and severe Hermansky–Pudlak syndrome type
2. Pediatr. Res. 51, 150–158.
Huizing, M., Hess, R., Dorward, H., Claassen, D.A., Helip-Wooley,
A., Kleta, R., Kaiser-Kupfer, M.I., White, J.G., and Gahl, W.A.
(2004). Cellular, molecular and clinical characterization of patients
with Hermansky–Pudlak syndrome type 5. Traffic 5, 711–722.
Ihrke, G., Kyttala, A., Russell, M.R., Rous, B.A., and Luzio, J.P.
(2004). Differential use of two AP-3-mediated pathways by lyso-
somal membrane proteins. Traffic 5, 946–962.
Ilardi, J.M., Mochida, S., and Sheng, Z.H. (1999). Snapin: a SNARE-
associated protein implicated in synaptic transmission. Nat. Neu-
rosci. 2, 119–124.
Ito, S., Suzuki, T., Inagaki, K., Suzuki, N., Takamori, K., Yamada, T.,
Nakazawa, M., Hatano, M., Takiwaki, H., Kakuta, Y., Spritz, R.A.,
and Tomita, Y. (2005). High frequency of Hermansky-Pudlak syn-
drome type 1 (HPS1) among Japanese albinism patients and
functional analysis of HPS1 mutant protein. J. Invest. Dermatol.
Jedlitschky, G., Tirschmann, K., Lubenow, L.E., Nieuwenhuis, H.K.,
Akkerman, J.W., Greinacher, A., and Kroemer, H.K. (2004). The
nucleotide transporter MRP4 (ABCC4) is highly expressed in
human platelets and present in dense granules, indicating a role
in mediator storage. Blood 104, 3603–3610.
Kantheti, P., Qiao, X., Diaz, M.E., Peden, A.A., Meyer, G.E. et al.
(1998). Mutation in AP-3 delta in the mocha mouse links endo-
somal transport to storage deficiency in platelets, melanosomes,
and synaptic vesicles. Neuron 21, 111–122.
Kantheti, P., Diaz, M.E., Peden, A.E., Seong, E.E., Dolan, D.F., Robin-
son, M.S., Noebels, J.L., and Burmeister, M.L. (2003). Genetic
and phenotypic analysis of the mouse mutant mh2J, an Ap3d allele
caused by IAP element insertion. Mamm. Genome 14, 157–167.
Kushimoto, T., Basrur, V., Valencia, J., Matsunaga, J., Vieira, W.D.,
Ferrans, V.J., Muller, J., Appella, E., and Hearing, V.J. (2001). A
model for melanosome biogenesis based on the purification and
analysis of early melanosomes. Proc. Natl. Acad. Sci. U. S. A.
Lane, P.W., and Green, E.L. (1967). Pale ear and light ear in the
house mouse. Mimic mutations in linkage groups XII and XVII.
J. Hered. 58, 17–20.
Levy, F., Muehlethaler, K., Salvi, S., Peitrequin, A.L., Lindholm,
C.K., Cerottini, J.C., and Rimoldi, D. (2005). Ubiquitylation of a
melanosomal protein by HECT-E3 ligases serves as sorting signal
for lysosomal degradation. Mol. Biol. Cell 16, 1777–1787.
Li, W, Zhang, Q, Oiso, N, Novak, EK, Gautam, R et al. (2003) Her-
mansky–Pudlak syndrome type 7 (HPS-7) results from mutant
dysbindin, a member of the biogenesis of lysosome-related or-
ganelles complex 1 (BLOC-1). Nat. Genet. 35, 84–89.
Li, W., Rusiniak, M.E., Chintala, S., Gautam, R., Novak, E.K., and
Swank, R.T. (2004). Murine Hermansky–Pudlak syndrome genes:
regulators of lysosome-related organelles. Bioessays 26, 616–628.
Pigment Cell Res. 19; 19–42
Marks, M.S., and Seabra, M.C. (2001). The melanosome: membrane
dynamics in black and white. Nat. Rev. Mol. Cell Biol. 2, 738–748.
Martina, J.A., Moriyama, K., and Bonifacino, J.S. (2003). BLOC-3, a
protein complex containing the Hermansky–Pudlak syndrome
gene products HPS1 and HPS4. J. Biol. Chem. 278, 29376–29384.
McGarry, M.P., Novak, E.K., and Swank, R.T. (1986). Progenitor cell
defect correctable by bone marrow transplantation in five inde-
pendent mouse models of platelet storage pool deficiency. Exp.
Hematol. 14, 261–265.
McGarry, M.P., Reddington, M., Novak, E.K., and Swank, R.T.
(1999). Survival and lung pathology of mouse models of Herman-
sky–Pudlak syndrome and Chediak–Higashi syndrome. Proc. Soc.
Exp. Biol. Med. 220, 162–168.
Meisler, M.H. (1978). Synthesis and secretion of kidney beta-galac-
tosidase in mutant le/le mice. J. Biol. Chem. 253, 3129–3134.
Menasche, G., Pastural, E., Feldmann, J., Certain, S., Ersoy, F.
et al. (2000). Mutations in RAB27A cause Griscelli syndrome asso-
ciated with haemophagocytic syndrome. Nat. Genet. 25, 173–176.
Morgan, N.V., Pasha, S., Johnson, C.A., Ainsworth, J.R., Eady,
R.A.J., et al. (2006). A germline mutation in BLOC1S3/reduced
pigmentation causes a novel variant of Hermansky Pudlak syn-
drome (HPS8). Am. J. Hum. Genet. 78, 160–166.
Nagle, D.L., Karim, M.A., Woolf, E.A., Holmgren, L., Bork, P. et al.
(1996). Identification and mutation analysis of the complete gene
for Chediak-Higashi syndrome. Nat. Genet. 14, 307–311.
Nakatani, Y., Nakamura, N., Sano, J., Inayama, Y., Kawano, N.
et al. (2000). Interstitial pneumonia in Hermansky–Pudlak syn-
drome: significance of florid foamy swelling/degeneration (giant
lamellar body degeneration) of type-2 pneumocytes. Virchows
Arch. 437, 304–313.
Natsuga, K., Akiyama, M., Shimizu, T., Suzuki, T., Ito, S., Tomita,
Y., Tanaka, J., and Shimizu, H. (2005). Ultrastructural features of
trafficking defects are pronounced in melanocytic nevus in
Hermansky-Pudlak syndrome type 1. J. Invest. Dermatol. 125,
Nazarian, R., Falcon-Perez, J.M., and Dell’Angelica, E.C. (2003). Bio-
genesis of lysosome-related organelles complex 3 (BLOC-3): a
complex containing the Hermansky–Pudlak syndrome (HPS) pro-
teins HPS1 and HPS4. Proc. Natl. Acad. Sci. U. S. A. 100, 8770–
Newman, L.S., McKeever, M.O., Okano, H.J., and Darnell, R.B.
(1995). Beta-NAP, a cerebellar degeneration antigen, is a neuron-
specific vesicle coat protein. Cell 82, 773–783.
Nguyen, T., and Wei, M.L. (2004). Characterization of melanosome
in murine Hermansky–Pudlak syndrome: mechanisms of hypopig-
mentation. J. Invest. Dermatol. 122, 452–460.
Nguyen, T., Novak, E.K., Kermani, M., Fluhr, J., Peters, L.L.,
Swank, R.T., and Wei, M.L. (2002). Melanosome morphologies
in murinemodels of Hermansky–Pudlak
blocks in organelle development. J. Invest. Dermatol. 119,
Novak, E.K., and Swank, R.T. (1979). Lysosomal dysfunctions asso-
ciated with mutations at mouse pigment genes. Genetics 92,
Novak, E.K., Wieland, F., Jahreis, G.P., and Swank, R.T. (1980).
Altered secretion of kidney lysosomal enzymes in the mouse pig-
ment mutants ruby-eye, ruby-eye-2-J, and maroon. Biochem.
Genet. 18, 549–561.
Novak, E.K., Hui, S.W., and Swank, R.T. (1984). Platelet storage
pool deficiency in mouse pigment mutations associated with
seven distinct genetic loci. Blood 63, 536–544.
Novak, E.K., Sweet, H.O., Prochazka, M., Parentis, M., Soble, R.,
Reddington, M., Cairo, A., and Swank, R.T. (1988). Cocoa: a new
mouse model for platelet storage pool deficiency. Br. J. Haema-
tol. 69, 371–378.
Numakawa, T., Yagasaki, Y., Ishimoto, T., Okada, T., Suzuki, T. et al.
(2004). Evidence of novel neuronal functions of dysbindin, a sus-
ceptibility gene for schizophrenia. Hum. Mol. Genet. 13, 2699–
Oberhauser, A.F., and Fernandez, J.M. (1996). A fusion pore phe-
notype in mast cells of the ruby-eye mouse. Proc. Natl. Acad.
Sci. U. S. A. 93, 14349–14354.
Oetting, W.S., and King, R.A. (1999). Molecular basis of albinism:
mutations and polymorphisms of pigmentation genes associated
with albinism. Hum. Mutat. 13, 99–115.
Oh, J., Bailin, T., Fukai, K., Feng, G.H., Ho, L., Mao, J.I., Frenk, E.,
Tamura, N., and Spritz, R.A. (1996). Positional cloning of a gene
for Hermansky–Pudlak syndrome, a disorder of cytoplasmic
organelles. Nat. Genet. 14, 300–306.
Oh, J., Ho, L., Ala-Mello, S., Amato, D., Armstrong, L. et al. (1998).
Mutation analysis of patients with Hermansky–Pudlak syndrome:
a frameshift hot spot in the HPS gene and apparent locus hetero-
geneity. Am. J. Hum. Genet. 62, 593–598.
Oh, J., Liu, Z.X., Feng, G.H., Raposo, G., and Spritz, R.A. (2000).
The Hermansky–Pudlak syndrome (HPS) protein is part of a high
molecular weight complex involved in biogenesis of early mel-
anosomes. Hum. Mol. Genet. 9, 375–385.
Park, H.Y., Russakovsky, V., Ohno, S., and Gilchrest, B.A. (1993).
The beta isoform of protein kinase C stimulates human melano-
genesis by activating tyrosinase in pigment cells. J. Biol. Chem.
Park, H.Y., Perez, J.M., Laursen, R., Hara, M., and Gilchrest, B.A.
(1999). Protein kinase C-beta activates tyrosinase by phosphory-
lating serine residues in its cytoplasmic domain. J. Biol. Chem.
Park, H.Y., Wu, H., Killoran, C.E., and Gilchrest, B.A. (2004). The
receptor for activated C-kinase-I (RACK-I) anchors activated PKC-
beta on melanosomes. J. Cell. Sci. 117, 3659–3668.
Peden, A.A., Rudge, R.E., Lui, W.W., and Robinson, M.S. (2002).
Assembly and function of AP-3 complexes in cells expressing
mutant subunits. J. Cell. Biol. 156, 327–336.
Peden, A.A., Oorschot, V., Hesser, B.A., Austin, C.D., Scheller,
R.H., and Klumperman, J. (2004). Localization of the AP-3 adap-
tor complex defines a novel endosomal exit site for lysosomal
membrane proteins. J. Cell. Biol. 164, 1065–1076.
Prekeris, R., Klumperman, J., Chen, Y.A., and Scheller, R.H. (1998).
Syntaxin 13 mediates cycling of plasma membrane proteins via
tubulovesicular recycling endosomes. J. Cell Biol. 143, 957–971.
Raposo, G., and Marks, M.S. (2002). The dark side of lysosome-
related organelles: specialization of the endocytic pathway for
melanosome biogenesis. Traffic 3, 237–248.
Raposo, G., Tenza, D., Murphy, D.M., Berson, J.F., and Marks,
M.S. (2001). Distinct protein sorting and localization to premelan-
osomes, melanosomes, and lysosomes in pigmented melanocy-
tic cells. J. Cell Biol. 152, 809–824.
Reusch, U., Bernhard, O., Koszinowski, U., and Schu, P. (2002). AP-
1A and AP-3A lysosomal sorting functions. Traffic 3, 752–761.
Richmond, B., Huizing, M., Knapp, J., Koshoffer, A., Zhao, Y., Gahl,
W.A., and Boissy, R.E. (2005). Melanocytes derived from patients
with Hermansky–Pudlak Syndrome types 1, 2, and 3 have distinct
defects in cargo trafficking. J. Invest. Dermatol. 124, 420–427.
Rieder, S.E., and Emr, S.D. (1997). A novel RING finger protein
complex essential for a late step in protein transport to the yeast
vacuole. Mol. Biol. Cell. 8, 2307–2327.
Rubin, C.M., Burke, B.A., McKenna, R.W., McClain, K.L., White,
J.G., Nesbit, M.E., Jr., and Filipovich, A.H. (1985). The accelerated
phase of Chediak-Higashi syndrome. An expression of the virus-
associated hemophagocytic syndrome? Cancer 56, 524–530.
Sarangarajan, R., Budev, A., Zhao, Y., Gahl, W.A., and Boissy, R.E.
(2001). Abnormal translocation of tyrosinase and tyrosinase-rela-
Pigment Cell Res. 19; 19–42
ted protein 1 in cutaneous melanocytes of Hermansky–Pudlak Download full-text
Syndrome and in melanoma cells transfected with anti-sense
HPS1 cDNA. J. Invest. Dermatol. 117, 641–646.
Sato, T.K., Rehling, P., Peterson, M.R., and Emr, S.D. (2000). Class
C Vps protein complex regulates vacuolar SNARE pairing and is
required for vesicle docking/fusion. Mol. Cell. 6, 661–671.
Schallreuter, K.U., Frenk, E., Wolfe, L.S., Witkop, C.J., and Wood,
J.M. (1993). Hermansky–Pudlak syndrome in a Swiss population.
Dermatology 187, 248–256.
Seals, D.F., Eitzen, G., Margolis, N., Wickner, W.T., and Price, A.
(2000). A Ypt/Rab effector complex containing the Sec1 homolog
Vps33p is required for homotypic vacuole fusion. Proc. Natl.
Acad. Sci. U. S. A. 97, 9402–9407.
Seiji, M., Fitzpatrick, T.B., Simpson, R.T., and Birbeck, M.S. (1963).
Chemical composition and terminology of specialized organelles
(melanosomes and melanin granules) in mammalian melano-
cytes. Nature 197, 1082–1084.
Seong, E., Wainer, B.H., Hughes, E.D., Saunders, T.L., Burmeister,
M., and Faundez, V. (2005). Genetic analysis of the neuronal and
ubiquitous AP-3 adaptor complexes reveals divergent functions
in brain. Mol Biol Cell 16, 128–140.
Shotelersuk, V., Hazelwood, S., Larson, D., Iwata, F., Kaiser-Kupfer,
M.I., Kuehl, E., Bernardini, I., and Gahl, W.A. (1998). Three new
mutations in a gene causing Hermansky-Pudlak syndrome: clini-
cal correlations. Mol. Genet. Metab. 64, 99–107.
Shotelersuk, V., Dell’Angelica, E.C., Hartnell, L., Bonifacino, J.S.,
and Gahl, W.A. (2000). A new variant of Hermansky–Pudlak syn-
drome due to mutations in a gene responsible for vesicle forma-
tion. Am. J. Med. 108, 423–427.
Sillitoe, R.V., Benson, M.A., Blake, D.J., and Hawkes, R. (2003).
Abnormal dysbindin expression in cerebellar mossy fiber synap-
ses in the mdx mouse model of Duchenne muscular dystrophy.
J. Neurosci. 23, 6576–6585.
Simpson, F., Peden, A.A., Christopoulou, L., and Robinson, M.S.
(1997). Characterization of the adaptor-related protein complex,
AP-3. J. Cell Biol. 137, 835–845.
Spritz, R.A., and Oh, J. (1999). HPS gene mutations in Hermansky-
Pudlak syndrome. Am. J. Hum. Genet. 64, 658.
Sprong, H., Degroote, S., Claessens, T., van Drunen, J., Oorschot, V.
et al. (2001). Glycosphingolipids are required for sorting melano-
somal proteins in the Golgi complex. J. Cell Biol. 155, 369–380.
zur Stadt, U., Schmidt, S., Kasper, B., Beutel, K., Diler, A.S. et al.
(2005). Linkage of familial hemophagocytic lymphohistiocytosis
(FHL) type-4 to chromosome 6q24 and identification of mutations
in syntaxin 11. Hum. Mol. Genet. 14, 827–834.
Starcevic, M., and Dell’Angelica, E.C. (2004). Identification of snapin
and three novel proteins (BLOS1, BLOS2, and BLOS3/reduced pig-
mentation) as subunits of biogenesis of lysosome-related organ-
elles complex-1 (BLOC-1). J. Biol. Chem. 279, 28393–28401.
Stepp, S.E., Dufourcq-Lagelouse, R., Le Deist, F., Bhawan, S., Cer-
tain, S. et al. (1999). Perforin gene defects in familial hemophag-
ocytic lymphohistiocytosis. Science 286, 1957–1959.
Stinchcombe, J.C., and Griffiths, G.M. (1999). Regulated secretion
from hemopoietic cells. J. Cell Biol. 147, 1–6.
Straub, R.E., Jiang, Y., MacLean, C.J., Ma, Y., Webb, B.T. et al.
(2002). Genetic variation in the 6p22.3 gene DTNBP1, the human
ortholog of the mouse dysbindin gene, is associated with schizo-
phrenia. Am. J. Hum. Genet. 71, 337–348.
Sugita, M., Cao, X., Watts, G.F., Rogers, R.A., Bonifacino, J.S., and
Brenner, M.B. (2002). Failure of trafficking and antigen presenta-
tion by CD1 in AP-3-deficient cells. Immunity 16, 697–706.
Suzuki, T., Li, W., Zhang, Q., Novak, E.K., Sviderskaya, E.V. et al.
(2001). The gene mutated in cocoa mice, carrying a defect of
organelle biogenesis, is a homologue of the human Hermansky–
Pudlak syndrome-3 gene. Genomics 78, 30–37.
Suzuki, T., Li, W., Zhang, Q., Karim, A., Novak, E.K. et al. (2002).
Hermansky–Pudlak syndrome is caused by mutations in HPS4,
the human homolog of the mouse light-ear gene. Nat. Genet. 30,
Suzuki, T., Oiso, N., Gautam, R., Novak, E.K., Panthier, J.J., Sup-
rabha, P.G., Vida, T., Swank, R.T., and Spritz, R.A. (2003). The
mouse organellar biogenesis mutant buff results from a mutation
in Vps33a, a homologue of yeast vps33 and Drosophila carnation.
Proc. Natl. Acad. Sci. U. S. A. 100, 1146–1150.
Swank, R.T., Sweet, H.O., Davisson, M.T., Reddington, M., and
Novak, E.K. (1991). Sandy: a new mouse model for platelet stor-
age pool deficiency. Genet. Res. 58, 51–62.
Swank, R.T., Reddington, M., and Novak, E.K. (1996). Inherited pro-
longed bleeding time and platelet storage pool deficiency in the
subtle gray (sut) mouse. Lab. Anim. Sci. 46, 56–60.
Swank, R.T., Novak, E.K., McGarry, M.P., Rusiniak, M.E., and
Feng, L. (1998). Mouse models of Hermansky Pudlak syndrome:
a review. Pigment Cell Res. 11, 60–80.
Toro, J., Turner, M., and Gahl, W.A. (1999). Dermatologic manifes-
tations of Hermansky–Pudlak syndrome in patients with and
without a 16-base pair duplication in the HPS1 gene. Arch. Der-
matol. 135, 774–780.
Tsilou, E.T., Rubin, B.I., Reed, G.F., McCain, L., Huizing, M.,
White, J., Kaiser-Kupfer, M.I., and Gahl, W. (2004). Milder
ocular findings in Hermansky–Pudlak syndrome type 3 com-
pared with Hermansky–Pudlak syndrome type 1. Ophthalmo-
logy 111, 1599–1603.
White, J.G., Witkop Jr C.J., and Gerritsen, S.M. (1973). The Her-
mansky–Pudlak syndrome: ultrastructure of bone marrow macr-
ophages. Am. J. Pathol. 70, 329–343.
Wildenberg, S.C., Fryer, J.P., Gardner, J.M., Oetting, W.S., Brilliant,
M.H., and King, R.A. (1998). Identification of a novel transcript pro-
duced by the gene responsible for the Hermansky–Pudlak syn-
drome in Puerto Rico. J. Invest. Dermatol. 110, 777–781.
Witkop, C.J., Townsend, D., Bitterman, P.B., and Harmon, K.
(1989). The role of ceroid in lung and gastrointestinal disease in
Hermansky–Pudlak syndrome. Adv. Exp. Med. Biol. 266, 283–
296; discussion 297.
Witkop, C.J., Nunez Babcock, M., Rao, G.H., Gaudier, F., Sum-
mers, C.G. et al. (1990). Albinism and Hermansky–Pudlak syn-
drome in Puerto Rico. Bol. Assoc. Med. P. R. 82, 333–339.
Wixler, V., Laplantine, E., Geerts, D., Sonnenberg, A., Petersohn,
D., Eckes, B., Paulsson, M., and Aumailley, M. (1999). Identifica-
tion of novel interaction partners for the conserved membrane
proximal region of alpha-integrin cytoplasmic domains. FEBS
Lett. 445, 351–355.
Wu, H., and Park, H.Y. (2003). Protein kinase C-beta-mediated com-
plex formation between tyrosinase and TRP-1. Biochem. Bio-
phys. Res. Commun. 311, 948–953.
Yang, W., Li, C., Ward, D.M., Kaplan, J., and Mansour, S.L. (2000).
Defective organellar membrane protein trafficking in Ap3b1-defi-
cient cells. J. Cell Sci. 113 (Pt 22), 4077–4086.
Zhang, Q., Zhao, B., Li, W., Oiso, N., Novak, E.K. et al. (2003). Ru2
and Ru encode mouse orthologs of the genes mutated in human
Hermansky–Pudlak syndrome types 5 and 6. Nat. Genet. 33,
Zhen, L., Jiang, S., Feng, L., Bright, N.A., Peden, A.A. et al. (1999).
Abnormal expression and subcellular distribution of subunit pro-
teins of the AP-3 adaptor complex lead to platelet storage pool
deficiency in the pearl mouse. Blood 94, 146–155.
Pigment Cell Res. 19; 19–42