Access to this full-text is provided by Frontiers.
Content available from Frontiers in Cell and Developmental Biology
This content is subject to copyright.
REVIEW
published: 21 May 2015
doi: 10.3389/fcell.2015.00030
Frontiers in Cell and Developmental Biology | www.frontiersin.org 1May 2015 | Volume 3 | Article 30
Edited by:
Bulent Mutus,
University of Windsor, Canada
Reviewed by:
Ruchi Chaube,
Case Western
Reserve University, USA
Daniel Sexton,
Dyax Corp., USA
*Correspondence:
Julie D. Atkin,
Department of Biomedical Sciences,
Faculty of Medicine and Health
Sciences, Macquarie University, 2
Technology Place, Sydney,
NSW 2109, Australia
julie.atkin@mq.edu.au;
website:www.medicine.mq.edu.au
Specialty section:
This article was submitted to
Cellular Biochemistry,
a section of the journal
Frontiers in Cell and Developmental
Biology
Received: 30 January 2015
Accepted: 28 April 2015
Published: 21 May 2015
Citation:
Parakh S and Atkin JD (2015) Novel
roles for protein disulphide isomerase
in disease states: a double edged
sword? Front. Cell Dev. Biol. 3:30.
doi: 10.3389/fcell.2015.00030
Novel roles for protein disulphide
isomerase in disease states: a
double edged sword?
Sonam Parakh 1and Julie D. Atkin 1, 2*
1Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW,
Australia, 2Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Bundoora, VIC,
Australia
Protein disulphide isomerase (PDI) is a multifunctional redox chaperone of the
endoplasmic reticulum (ER). Since it was first discovered 40 years ago the functions
ascribed to PDI have evolved significantly and recent studies have recognized its distinct
functions, with adverse as well as protective effects in disease. Furthermore, post
translational modifications of PDI abrogate its normal functional roles in specific disease
states. This review focusses on recent studies that have identified novel functions for PDI
relevant to specific diseases.
Keywords: protein disulfide isomerase family, neurodegnerative diseases, protein chaperones, post-translational
modifications, cancer, amyotrophic lateral sclerosis
Introduction
Protein disulphide isomerase (PDI) was the first folding catalyst isolated from rat liver (Goldberger
et al., 1963) and it is found abundantly in many tissues, accounting for 0.8% of total cellular
protein (Freedman et al., 1994). PDI is induced during endoplasmic reticulum (ER) stress
(Wilkinson and Gilbert, 2004) and it serves as a vital cellular defense against general protein
misfolding via its chaperone activity. It is also responsible for the isomerization, formation, and
rearrangement of protein disulphide bonds, thereby providing another mechanism by which
native protein conformation is maintained. Disulphide bonds play an important role in the
folding and stability of proteins and they are present in more than 30% of all human proteins
that traverse the secretory pathway (Fewell et al., 2001). Since most cellular compartments are
reducing environments, protein disulphide bonds are usually unstable in the cytosol, although
there are exceptions (Frand et al., 2000). PDI assists in redox protein folding, involving oxidation,
multiple intramolecular thiol-disulphide exchanges, and isomerization (reduction) activities and it
is highly specific in its interaction with different substrates. Whilst PDI is considered to be resident
primarily within the ER, nonetheless it has been detected in many other diverse cellular locations,
including the cell surface, cytosol, mitochondria, and extracellular matrix (Turano et al., 2002).
However, the mechanism by which PDI escapes from the ER is still unclear. PDI is also present
in the extracellular medium where it facilitates protein folding and reduces protein aggregation
(Delom et al., 2001). Furthermore, specific functions of cell surface PDI have been identified in
hepatocytes, platelets, and endothelial cells (Turano et al., 2002). This review focusses on recent
advances recognizing the versatile roles of PDI in normal cellular function and also in disease
states. These studies highlight novel therapeutic possibilities based on the functional properties
of PDI.
Parakh and Atkin Novel roles for PDI in health and disease
Structure and Superfamily of PDI
PDI is a soluble 55-kDa protein that is the prototype of the
PDI family of proteins which all contain the thioredoxin-like
βαβαβαββα domain (Kemmink et al., 1997). Thioredoxins are a
class of oxidoreductase enzymes containing a dithiol-disulphide
active site that are involved in redox signaling (Moran et al.,
2001). Besides PDI, 21 more family members have been described
(Kozlov et al., 2010). However, the enzymatic properties of
these proteins differ in their redox potential and hence substrate
specificity (Jessop et al., 2009), the sequence of their active site
and the pKa of the active site cysteine residues (Ellgaard and
Ruddock, 2005). They are primarily localized in the ER where
they maintain an oxidative environment and thereby contribute
to ER homeostasis (Anelli et al., 2002).
Full length PDI contains 508 amino acids and consists of four
domains namely a, b, b’, a’ (Figure 1). The homologous aand a’
domains share 47% similarity and contain the active site, CGHC
(Kemmink et al., 1996). The active site cysteine residues interact
with the thiol group of a newly synthesized substrate, thus
mediating the formation and isomerization of protein disulphide
bonds (Gilbert, 1998). The intermediate band b’ domains are
28% identical and they assist in the binding of protein substrates
but they lack the catalytically active cysteine residues (Gruber
et al., 2006). PDI also contains a xlinker region and an acidic C
terminus containing a KDEL-ER retrieval sequence (Darby et al.,
1996). Whilst the three dimensional structure of human PDI is
still under investigation, the structures of each single thioredoxin
domain (Nguyen et al., 2008) and the domain combinations bb’c
(Denisov et al., 2009) and bb’cxac (Wang et al., 2012a) have been
determined. However, the structure of yeast PDI has been solved
(Tian et al., 2006) revealing that it adopts a U shape structure,
with the catalytic aand a’ domains facing each other. NMR and x-
ray crystallography has further demonstrated that the b’ domain
contains the chaperone activity responsible for binding ligands
and protein substrates in its hydrophobic pocket (Denisov et al.,
2009).
The CGHC motif modulates the overall reduction potential
of PDI and thus it regulates the catalytic ability of the active
site cysteines to actively oxidize or reduce disulphide bonds
(Chivers et al., 1997). The reduction potential of PDI is −180 mV,
higher than other PDI family members, thus making it a strong
oxidizing agent. The individual aand a’ domains have similar
oxidizing ability but conversely they have low isomerase activity
FIGURE 1 | Domain structure of PDI. The thioredoxin-like domains are
shown in green, representing the catalytically active domains aand a’. The
catalytically inactive bdomain and b’ domains are illustrated in orange and red
respectively. The linker region x (shown in white) is responsible for the U shape
structure of PDI. The C terminus is illustrated in yellow, followed by an ER
retrieval signal, KDEL.
(Darby et al., 1998). The b’ domain is the main site for binding
misfolded protein substrates but the other domains also assist
in this process (Klappa et al., 1998). The catalytic domains can
only catalyze basic disulphide exchange and all the domains are
required to isomerize a protein substrate that has undergone
conformational changes (Darby et al., 1996). Deletion of the C-
terminal residues of PDI results in deactivation of its chaperone-
like activity and its peptide binding ability, but this does not affect
its catalytic activity in disulphide bond formation (Dai and Wang,
1997).
Although it is implied that all PDI family members possess
the ability to rearrange disulphide bonds, only a few members
have actually been demonstrated to perform these activities and
the rest are linked to the family through evolution rather than
function (Galligan and Petersen, 2012). The most commonly
studied members of the PDI family after PDI are ERp57, ERp72,
ERp29, ERp44, and PDIA2 (Appenzeller-Herzog and Ellgaard,
2008). There appears to be an interplay of functions amongst the
PDI family and some family members are able to recompense
for each other. For example, ERp72 is known to compensate for
ERp57 deficiency, where it can assist in folding specific proteins
(Solda et al., 2006). Certain protein substrates also appear to
interact simultaneously with PDI and its family members. ERp57
and PDI engage simultaneously in forming mixed disulphides
with thyroglobulin during the production and isomerization of
new disulphide bonds. In addition both ERp57 and PDI are
released from thyroglobulin when it dissociates from the ER
(Di Jeso et al., 2005). Transferrin also requires both PDI and
ERp57 for optimal folding. Furthermore, depletion of both PDI
and ERp57 leads to generalized protein misfolding, impaired
export from the ER, and degradation in human hepatoma
cells, implying that these proteins function together (Rutkevich
et al., 2010). Functional analysis in yeast revealed that ERp46
substitutes for PDI-mediated disulphide bond formation in vivo
(Knoblach et al., 2003). However, PDI itself plays a key role
in oxidative protein folding and no other family member can
entirely compensate for its loss (Rutkevich et al., 2010).
There is also evidence that PDI family members dimerise
and that this property is involved in its function. PDI was
recently shown to form disulphide-independent dimers in vivo
suggesting that dimerization may control efficient protein folding
in the ER (Bastos-Aristizabal et al., 2014). This may be achieved
by generating a reserve of inactive protein that allows the
ER to respond competently to an abrupt increase in substrate
availability (Bastos-Aristizabal et al., 2014). PDI family member
ERp29 also dimerises, and it acts as an escort protein in the
binding of thyroglobulin in the ER (Rainey-Barger et al., 2007).
It has been suggested that the formation of a dimer of PDIA2,
which is mediated through glycosylation (Walker et al., 2013),
is increased under conditions of oxidative stress, and this dimer
has increased chaperone activity compared to the monomeric
form (Fu and Zhu, 2009). Several excellent recent reviews have
discussed the structural aspects of the PDI family in more detail
and the reader is directed to these for further information
(Hatahet and Ruddock, 2009; Kozlov et al., 2010; Galligan and
Petersen, 2012). This review will focus on recent advances made
into the functional roles of PDI.
Frontiers in Cell and Developmental Biology | www.frontiersin.org 2May 2015 | Volume 3 | Article 30
Parakh and Atkin Novel roles for PDI in health and disease
Functions of PDI
PDI is found in all eukaryotic organisms, whereas in prokaryotes
a related homolog, Dsb, performs similar functions in facilitating
protein folding (Inaba, 2009). The importance of PDI in cellular
function was first realized in yeast, where PDI was found to be
essential for cellular viability (LaMantia et al., 1991). To date, no
viable PDI knockout strain has been reported in rodents, further
emphasizing the importance of PDI in normal cellular physiology
(Hatahet and Ruddock, 2009). The disulphide interchange and
chaperone functions of PDI are well documented and will be
summarized briefly below. Emerging evidence describing novel
functions for PDI will then be described.
PDI is a Chaperone Present in the ER
PDI has the ability to distinguish between partially folded,
unfolded, and properly folded protein substrates, and it has a
higher affinity to bind to misfolded proteins rather than native
proteins through hydrophobic interactions (Klappa et al., 1997).
These properties, together with its conformational flexibility,
make PDI a highly effective chaperone (Irvine et al., 2014). PDI
binds to a large number of protein substrates in the ER, although
it is difficult to isolate and identify the individual substrates in
vivo. Several methods are used to measure the chaperone activity
of PDI in vitro. The rate of protein aggregation is assessed using
protein substrates that do not possess cysteine residues, including
GAPDH (Cai et al., 1994), rhodanese (Song and Wang, 1995),
citrate synthase, alcohol dehydrogenase (Primm et al., 1996), or
GFP, which on interaction with PDI causes increased fluorescent
intensity as it folds into its native conformation (Mares et al.,
2011).
A major function of PDI is a chaperone upregulated during
ER stress. Accumulation of misfolded proteins within the
ER activates the unfolded protein response (UPR). The UPR
aims to reduce the load of unfolded proteins by increasing
the curvature of ER, reducing protein synthesis, and by the
induction of PDI and other chaperones to further increase the
protein folding capacity (Hetz and Mollereau, 2014). This is
achieved by activation of sensor ER proteins inositol requiring
enzyme-1(IRE-1), protein kinase RNA like ER kinase (PERK),
and activating transcription factor kinase 6 (ATF6), which
subsequently activate UPR signaling pathways [detailed in
(Sovolyova et al., 2014)]. While initially protective, prolonged
UPR causes apoptosis (Schroder and Kaufman, 2005).
PDI facilitates the degradation of misfolded proteins via
ER association degradation (ERAD) by translocation of these
proteins from the ER to the cytoplasm, for subsequent
degradation by the ubiquitin protease system. (Molinari et al.,
2002; Lee et al., 2010b). It also helps in protein quality control
by retaining unassembled procollagen until the correct native
structure is achieved (Bottomley et al., 2001).
Other specific functions involving the chaperone activity
of PDI have been described, including maintenance of the
active conformation of the βsubunit of collagen prolyl 4-
hydroxylase (Vuori et al., 1992) and stabilization of the
major histocompatibility complex’s (MHC) class 1 peptide
loading complex (PLC) that mediates MHC class 1 folding.
Interestingly, PDI exhibits both chaperone and anti-chaperone
activity depending upon its initial concentration. When PDI’s
chaperone activity is dominant, virtually all of the substrate
protein is correctly folded. However, at low concentrations, PD1
promotes intermolecular disulphide crosslinking of substrates
into large inactive aggregates via anti-chaperone activity (Puig
and Gilbert, 1994).
Redox Regulation of PDI
Multiple studies have suggested that the disulphide interchange
enzymatic activity of PDI is more important for its function
than its chaperone activity. When its catalytic cysteines are
reduced, PDI is able to react with non-native disulphides of
substrate proteins to form a mixed disulphide complex. PDI then
catalyzes the rearrangement of incorrectly formed disulphide
bonds via isomerization reactions. This takes place with cycles
of reduction (breaking of non-native disulphide bonds) and
oxidation (to introduce correct pairing of cysteines) to eventually
form the native disulphide bonds (Schwaller et al., 2003). The
tripeptide glutathione constitutes the cellular redox buffer that
maintains the redox environment of the ER (Hwang et al.,
1992). After PDI has oxidized substrate proteins, it then has
to be oxidized itself to complete the catalytic cycle. This
function is carried out by a number of proteins including
FAD binding oxidases, Ero1α, oxidized glutathione, glutathione
peroxidase 7, glutathione peroxidase 8 or quiescin sulfhydryl
oxidase (Wilkinson and Gilbert, 2004)(Figure 2). Interestingly,
the chaperone activity of PDI is regulated by the redox state of
its oxidized and reduced forms (Wang et al., 2013), suggesting a
link between the two separate functions of PDI. Redox regulation
of PDI can be examined experimentally in vitro using scrambled
RNAse, ribonuclease and bovine pancreatic trypsin inhibitor
(Darby et al., 1998; Xiao et al., 2001).
The in vivo redox state of PDI is complex and determined by
numerous factors including the reduction potential of PDI, the
glutathione redox state in the ER, and the potential reductase
activity of the substrate and its availability. However, redox
conditions can have a major impact on the functions of PDI.
For example, PDI regulates the organization of the cytoskeleton
by forming a disulphide bond to Cys 374 of β-actin via a redox
dependent mechanism (Sobierajska et al., 2014).
PDI in Disease States
Recent studies provide compelling evidence for a role for PDI
in both the physiology and pathophysiology of disease states
including diabetes (Grek and Townsend, 2014), cardiovascular
diseases (Khan and Mutus, 2014), cancer (Xu et al., 2014),
neurodegenerative conditions (Andreu et al., 2012) and the entry
of pathogens in infectious diseases (Benham, 2012). However,
precise roles for PDI in these diseases have not yet been
elucidated. PDI is upregulated in various tissues during disease
and surprisingly, both protective and detrimental effects have
been described. These effects relate to either a loss of its normal
protective function in some situations, or gain of toxic function
in others. While the association between the PDI family and
human disease states still requires further validation, current
Frontiers in Cell and Developmental Biology | www.frontiersin.org 3May 2015 | Volume 3 | Article 30
Parakh and Atkin Novel roles for PDI in health and disease
FIGURE 2 | Diagram representing disulphide bond formation in the eukaryotic ER and redox reactions involving PDI. Oxidative folding of PDI leads to
disulphide bond formation in native protein substrates. Reduced PDI facilitates isomerization of non-native bonds in protein substrates.
improvements in our understanding of the functional roles of
PDI provide new insights into the physiological contribution of
PDI in vivo.
PDI in Cancer
PDI is highly expressed and up-regulated in numerous cancer
cell types, including kidney, lung, brain, ovarian, melanoma,
prostrate, and male germ cell tumors (Xu et al., 2014). Also,
lower levels of PDI are associated with a higher survival rate
in patients with breast cancer and glioblastoma (Thongwatchara
et al., 2011), suggesting that PDI promotes the survival of cancer
cells. Consistent with this notion, knockdown of PDI induces
cytotoxicity in human breast cancer and neuroblastoma cell lines
due to caspase activation (Hashida et al., 2011). Suppression of
apoptosis by PDI has been proposed as mechanism for tumor
growth and metastasis. Over-expression of PDI may therefore
serve as a diagnostic marker for cancer, as suggested for glial
cell cancer (Goplen et al., 2006), colorectal cancer (Ataman-Onal
et al., 2013), and breast cancer (Thongwatchara et al., 2011).
Cell surface PDI is also associated with cancer progression and
administering of anti-PDI monoclonal antibodies inhibits the
invasion of glioma cells (Goplen et al., 2006).
As increasing evidence suggests that PDI supports the survival
and progression of various cancers, inhibitors of PDI may
therefore have a therapeutic role against cancer progression (Xu
et al., 2014). A synthesized series of PACMA (propynoic acid
carbamoyl methyl amides) compounds demonstrated anticancer
activity in human ovarian cancer in vitro and in vivo by
a mechanism involving inhibition of PDI (Xu et al., 2012).
Bacitracin, a pharmacological inhibitor of PDI, reduced the
in vitro migration and invasion of human brain glial cells (Goplen
et al., 2006). However, the specificity of bacitracin as an inhibitor
of PDI has recently been questioned (Karala and Ruddock, 2010).
Small-molecule inhibitors of PDI which bind to the CGHC
active site may also have potential for improving the efficacy
of chemotherapy in melanoma, as inhibition of PDI function
proliferates apoptosis (Lovat et al., 2008). However, the effect of
PDI in supporting tumor survival is based on the specific type of
cancer and may be cell type dependent. Hence it is important to
recognize the specific type of cancer cell for future applications in
cancer therapy.
PDI in Neurodegenerative Disorders
Neurodegenerative diseases are also known as protein misfolding
disorders due to their characteristic property of accumulating
insoluble ubiquitinated aggregated proteins within affected
tissues. Protein misfolding within the ER triggers ER stress,
and hence up-regulation of PDI, and ER stress is increasingly
implicated in these diseases (Hetz and Mollereau, 2014). Most
studies suggest that the induction of PDI during ER stress
in neurodegenerative diseases reduces the load of misfolded
proteins, and is therefore protective thus restoring proteostasis
and increasing neuronal viability.
PDI is upregulated in dopaminergic neurons and Lewy
bodies of patients with Parkinson’s disease. Similarly PDI
reduces aggregation of the Parkinson’s disease-associated protein
synphilin-1 in neuroblastoma cells, an activity which relies on
the presence of the CGHC active site motif (Uehara et al., 2006).
Similarly, PDI also prevents aggregation of another Parkinson’s
associated protein, α-synuclein, in cell-free in vitro systems
(Cheng et al., 2010). PDI also co-localizes with neurofibrillary
tangles in Alzheimer’s disease patient brain tissue, and is
upregulated in brains of Alzheimer’s rodent models (Lee et al.,
2010a) implying a role in refolding misfolded proteins in these
conditions. Consistent with this notion, ERp57 is present in CSF,
where it binds and reduces aggregation of β-amyloid peptides
Frontiers in Cell and Developmental Biology | www.frontiersin.org 4May 2015 | Volume 3 | Article 30
Parakh and Atkin Novel roles for PDI in health and disease
(Erickson et al., 2005). Furthermore, PDI is upregulated in
response to hypoxia in the brain and PDI prevents neuronal and
cardiomyocyte apoptosis, triggered by hypoxia-ischaemia in cell
culture and in rodent models, by decreasing protein misfolding
(Tanaka et al., 2000). In prion disorders, Wang and group
suggested a pleiotropic role of PDI in the cellular management
of misfolded prion protein (Wang et al., 2012b) because PDI and
ERp57 are protective against prion induced toxicity in vitro (Hetz
et al., 2005) and inhibition of PDI increases the production of
misfolded prion proteins (Watts et al., 2009).
An important role for PDI has been implicated in
amyotrophic lateral sclerosis (ALS). PDI is up-regulated
and recruited to misfolded protein aggregates in sporadic human
ALS (Atkin et al., 2008). PDI is also up-regulated in lumbar
spinal cords from transgenic SOD1G93A mice, the most widely
used animal disease model (Atkin et al., 2006). Furthermore,
over-expression of PDI is protective against the formation of
mutant SOD1 inclusions and ER stress, whereas knockdown
of PDI using siRNA increases mutant SOD1 aggregation and
inclusion formation (Walker et al., 2010). Similarly, a small
molecule mimic of PDI reduces mutant SOD1 aggregation in
vitro (Walker et al., 2010). Endogenous PDI co-localizes with
mutant superoxide dismutase 1 (SOD1) (Atkin et al., 2006), TAR
DNA-binding protein-43 (TDP-43) (Honjo et al., 2011), vesicle
associated protein B (VAPB) (Tsuda et al., 2008), and Fused in
Sarcoma (FUS) (Farg et al., 2012) in neuronal cells. PDI and
ERp57 were identified as potential biomarkers for ALS using
peripheral blood mononuclear cells (Nardo et al., 2011) and
mutations in intronic variants of PDI are predicted to be a risk
factor in ALS (Kwok et al., 2013).
There is also evidence that the cellular location of PDI is
linked to disease outcomes in ALS. PDI is redistributed away
from the ER via a reticulon-dependent process in transgenic
SOD1G93A mice (Yang et al., 2009). The reticulon family of
proteins function in maintaining the curvature of ER and
several members of this family modulate the re-distribution of
PDI away from the ER when overexpressed (Bernardoni et al.,
2013). Furthermore, deletion of reticulon 4a,b enhances disease
progression in SOD1G93A mice (Yang et al., 2009), highlighting
the importance of a non-ER location of PDI in ALS.
Roles of PDI in Cardiovascular Disease
Both beneficial and harmful roles for PDI in cardiovascular
disease have been proposed. PDI prevents protein misfolding
in the myocardium during ischemic myocardial injury (Toldo
et al., 2011). PDI is also up-regulated in hypoxia induced in
myocardial capillary endothelial cells (Tian et al., 2009) and this
is linked to significant decreases in the rate of cardiomyocyte
apoptosis in murine models (Severino et al., 2007). Similarly,
PDI is also involved in endothelial cell endurance (Severino
et al., 2007) and it is required for platelet derived growth
factor (PDGF)-induced vascular smooth muscle cell migration
(Primm and Gilbert, 2001) which is an important therapeutic
target in atherosclerosis (Pescatore et al., 2012). Furthermore,
increased expression of PDI is protective against endothelial
cellular migration, adhesion, and tubular formation in mice
suggesting an important role for PDI in angiogenesis (Tian et al.,
2009). Hence these studies raise the possibility that upregulating
PDI has possible future pharmacological applications in treating
ischemic cardiomyopathy (Severino et al., 2007).
Diabetes is associated with coronary artery disease and an
increased risk of heart failure, and PDI function is impaired in
mouse models of diabetes. This may be due to alterations in its
oxidoreductive state (Toldo et al., 2011). Reduced PDI has been
detected in the diabetic heart after ischemia, which could explain
why PDI is not protective in diabetes (Toldo et al., 2011).
However, in contrast to these protective functions, PDI has
also been implicated in detrimental activities in cardiovascular
diseases. Over-expression of PDI in myocytes attenuates
the levels of misfolded pro-insulin while decreasing glucose
stimulated insulin secretion, thereby inducing ER stress and
apoptosis (Zhang et al., 2009). PDI on the surface of platelets
plays an important role in thrombus formation and it is vital for
the aggregation of platelets (Kim et al., 2013). Similarly, PDI is
also present on at the surface of human B-lymphocytes where
it has a putative role in regulating leukocyte adhesion (Bennett
et al., 2000). PDI has also been implicated in platelet integrin
function, tissue-factor activation, and in mice, it accumulates
during fibrin and thrombus formation at sites of vascular
injury (Jurk et al., 2011). PDI inhibition prevents both platelet
accumulation and fibrin generation during thrombus formation
(Jasuja et al., 2012). Therefore, inhibition of PDI could prevent
thrombosis in coronary artery disease, suggesting that PDI
inhibitors have potential as antithrombotic agents (Jasuja et al.,
2012).
PDI Mediates Pathogen Entry in Infectious
Diseases
PDI is also implicated in mediating the entry of pathogens during
infectious disease. Over-expression of PDI increases the fusion of
viral membranes, leading to internalization of HIV-1 (Auwerx
et al., 2009). Similarly, cell surface PDI facilitates infection of
HeLa cells by mouse polyoma virus (Gilbert et al., 2006), and it
also mediates the entry of cholera toxin (Stolf et al., 2011). The
chaperone activity of PDI is important for folding cholera toxin
subunit A1 and reducing its aggregation (Taylor et al., 2011).
However, cholera intoxication is a redox dependent process. The
oxidized form of PDI mediates translocation of cholera toxin into
the host cell cytoplasm (Tsai et al., 2001) whereas the reduced
form of PDI leads to its unfolding.
Post Translational Modification of PDI
Redox-dependent post translational modifications of PDI are
also linked to disease states. Due to cellular conditions, high
levels of reactive nitrogen species (RNS), hydrogen peroxide and
reactive oxygen species (ROS) can accumulate in cells, inducing
nitrosative or oxidative stress. Nitrosative stress can lead to post
translation modification of PDI by the addition of NO to active
site cysteine residues, resulting in S-nitrosylation. S-nitrosylation
of proteins under pathological conditions is an abnormal,
irreversible process that is linked to protein misfolding, ER stress
and apoptosis. Furthermore, proteins resident in the ER are
particularly vulnerable to post translation modification due to
Frontiers in Cell and Developmental Biology | www.frontiersin.org 5May 2015 | Volume 3 | Article 30
Parakh and Atkin Novel roles for PDI in health and disease
the presence of critical redox regulated cysteines. Since PDI is the
major enzyme responsible for modification of protein disulphide
bonds, the loss of function of PDI could increase cellular protein
misfolding and thus increase ER stress. S-nitrosylation of PDI
inhibits its normal enzymatic activity and hence the beneficial
effects of PDI, and S-nitrosylated PDI has been detected in several
neurodegenerative diseases (Nakamura and Lipton, 2011; Chen
et al., 2012). S-nitrosylation reduces both its chaperone and
isomerase activity (Uehara et al., 2006).
S-nitrosylation of PDI has been detected in postmortem
brain tissues of patients with Alzheimer’s disease, Parkinson’s
disease (Uehara et al., 2006) and in lumbar spinal cord tissues
of ALS patients and transgenic SOD1G93A mice (Walker et al.,
2010). S-nitrosylation has also been reported in prion disease
models using brain tissues of scrapie-263K-infected hamsters
(Wang et al., 2012b). Exposure of cultured neurons to N-
methyl-D-aspartate receptor (NMDA), leading to calcium influx
and nitric oxide production, also resulted in the S-nitrosylation
of PDI (Forrester et al., 2006). S-nitrosylated PDI (SNO-
PDI) increases the levels of polyubiquitinated proteins and
triggers cell death, and it is also associated with hyper-
activation of NMDA (Forrester et al., 2006) and inhibition of
mitochondria, leading to the generation of ROS and nitric oxide
(Halloran et al., 2013). SNO-PDI accentuates the misfolding
of synphilin in Parkinson disease (Forrester et al., 2006) and
S-nitrosylation also increases mutant SOD1 aggregation via
incorrect disulphide cross-linking of the immature, misfolded
mutant SOD1, leading to neuronal cell death (Jeon et al.,
2014).
As well as S-nitrosylation, other aberrant post-translational
modifications of PDI have been described, including
carbonylation and S-glutathionylation. Oxidized low density
lipoproteins induce carbonylation, which disrupts the catalytic
activity of PDI, inducing ER stress and apoptosis in vascular cells
(Muller et al., 2013). Furthermore, carbonylated PDI detected
in the lipid rich atherosclerotic region of human endothelial
cells activates CHOP and XBP1 and induces apoptosis (Muller
et al., 2013). S-glutathionylation is induced by reactive oxygen
or nitrogen species and it results in formation of a disulphide
bond between GSH and a cysteine residue of another protein
(Xiong et al., 2011). S-glutathionylation, leading to increased
protein misfolding and enhancement of the UPR (Townsend
et al., 2009), has been detected primarily in relation to cancer.
S-glutathionylation of PDI obliterates estrogen receptor α
stability in breast cancer cells, which prevents binding of PDI
to the receptor. This subsequently leads to dysregulation in
ERαsignaling (Xiong et al., 2012), and cell death via UPR
induction (Xiong et al., 2012). S-glutathionylation also reduces
the isomerase activity of PDI in ovarian cancer cells and
human leukemia cells and it also decreases chaperone activity.
In cultured astrocytes after cerebral ischemic reperfusion,
SNO-PDI increases the levels of ubiquitinated aggregates that
co-localize with SOD1 (Chen et al., 2012). These modifications
can further attenuate UPR and cause neuronal cell death.
Hence, aberrant modifications of PDI lead directly to harmful
effects as well as loss of the normally protective properties
of PDI.
PDI Causes Oxidative Stress
Recent evidence implicates PDI in increasing the levels of ROS,
thus directly inducing oxidative stress and apoptosis via its
chaperone activity rather than the disulphide interchange activity
(Fernandes et al., 2009). Similarly, only oxidized PDI triggers the
production of ROS, whereas reduced PDI inhibits the production
of ROS (Paes et al., 2011). PDI associates with the NAPDH
peroxidase complex (Nox), a major source of ROS, where it
stabilizes and associates with the oxidase subunit of Nox in
vascular smooth muscle cells (Janiszewski et al., 2005). Similar
effects are observed in macrophages and murine microglial cells,
where PDI interacts with Nox and increases the levels of ROS
(Fernandes et al., 2009). PDI also activates the transcription
factors NF-kB and AP-1, thus promoting their binding to DNA
(Clive and Greene, 1996). PDI is also a major catalyst of trans-
nitrosation reactions, mediating nitric oxide internalization from
extracellular S-nitrosothiols (Zai et al., 1999), thus further
promoting the production of SNO proteins (Ramachandran
et al., 2001).
PDI Causes Apoptosis
Whilst SNO-PDI is implicated in triggering apoptosis, recent
studies have revealed a direct role for unmodified PDI in
apoptosis. In rat models of Huntington and Alzheimer’s disease,
PDI accumulation at the ER-mitochondrial junction triggers
apoptosis via mitochondrial outer membrane permeabilisation
(Hoffstrom et al., 2010). This effect is specific for the
accumulation of misfolded proteins, but not other triggers
of apoptosis, suggesting a specific role for pro-apoptotic PDI
in neurodegenerative disease. Inhibitors of PDI including
hypotaurine, thiomuscimol, and shRNA that inhibited the
activity of PDI, were found to suppress the toxicity associated
with misfolded Huntingtin and β-amyloid proteins.
Summary
PDI is an important cellular protein given its abundance, multiple
biological functions, versatile redox behavior, interaction with
other proteins and its implied role in various diseases.
However, many issues remain unresolved that warrant further
investigation, in particular the role of PDI in non-ER sub-cellular
locations, and substrate specificity of the PDI family members.
In future studies it will be important to replicate the precise
functions of PDI in the ER and other cellular locations, separately
from roles ascribed in vitro, before its normal cellular roles are
fully understood.
PDI performs an impressive array of cellular functions and
the up-regulation of PDI is a cellular defensive mechanism to
restore proteostasis. However, despite this up-regulation, the
functional properties of PDI can become abrogated due to
aberrant post translational modifications. This is of particular
relevance in neurodegenerative diseases where disruption to
redox regulation is implicated (Parakh et al., 2013). Furthermore,
neurons are particularly susceptible to ROS/RNS damage due
to their high oxygen demand and a lower availability of
antioxidants. Recent evidence implicates PDI as a trigger for
apoptosis specifically in relation to the accumulation of misfolded
Frontiers in Cell and Developmental Biology | www.frontiersin.org 6May 2015 | Volume 3 | Article 30
Parakh and Atkin Novel roles for PDI in health and disease
FIGURE 3 | Schematic diagram outlining the dual nature of
PDI, focusing on neurodegenerative disorders as an example.
Under normal conditions, PDI reduces the load of misfolded
proteins either by its chaperone activity or by isomerization of
non-native bonds. However, during disease states, loss of the
normal protective function of PDI as well as the gain of
additional, toxic functions, leads to PDI becoming apoptotic, thus
contributing to pathology.
FIGURE 4 | Schematic diagram illustrating possible therapeutic applications to modulate PDI function.
proteins. PDI may therefore act as a regulatory switch, in
which PDI is initially is protective against protein misfolding
and aggregation. However, in response to an unknown trigger
PDI subsequently becomes apoptotic when proteostasis cannot
otherwise be resolved (Figure 3). Therefore aberrant post
translational modifications together with the pro-apoptotic
function of PDI could further accentuate the adverse effects
of PDI.
In conclusion, PDI is an efficient catalyst and protein
chaperone. It has the ability to restore proteostasis by catalyzing
the efficient folding of newly synthesized proteins, and it plays
an important role in protein quality control and ERAD by
Frontiers in Cell and Developmental Biology | www.frontiersin.org 7May 2015 | Volume 3 | Article 30
Parakh and Atkin Novel roles for PDI in health and disease
reducing the burden of misfolded proteins, thus inhibiting
abnormal protein aggregation. The protective or harmful
functions of PDI may be modulated by the subcellular location
of PDI, levels of ER stress and the redox environment. While
further investigations are clearly needed in this area, PDI
has the potential to be exploited therapeutically in a variety
of diseases. However, specific approaches depending on the
disease in question will be required. In neurodegenerative
conditions, elevation of the levels of total PDI, with the aim
of restoring PDI function to reduce protein misfolding, could
be an effective therapeutic approach. However, in contrast,
reduction of the levels of PDI might be an appropriate
strategy in cancer or cardiovascular diseases (Figure 4). Similarly,
reducing the levels of aberrantly modified PDI might also be
necessary in neurodegeneration in order to defend against the
pro-apoptotic properties of PDI. At the cellular level there are
important unanswered questions that need addressing, before
the therapeutic applications of PDI can become realized in the
future.
Acknowledgments
This work was supported by the National Health and Medical
Research Council of Australia (NHMRC) Project grants (1006141
and 1030513), Bethlehem Griffiths Research Foundation, and
Motor Neurone Disease Research Institute of Australia Angie
Cunningham Laugh to Cure MND Grant, Zo-ee Research Grant
and Grants in Aid. SP is supported by a Macquarie University
Postgraduate Research Scholarship, and previously by a La Trobe
Post Graduate Research Scholarship.
References
Andreu, C. I., Woehlbier, U., Torres, M., and Hetz, C. (2012). Protein disulfide
isomerases in neurodegeneration: from disease mechanisms to biomedical
applications. FEBS Lett. 586: 2826–2834. doi: 10.1016/j.febslet.2012.07.023
Anelli, T., Alessio, M., Mezghrani, A., Simmen, T., Talamo, F., Bachi, A.,
et al. (2002). ERp44, a novel endoplasmic reticulum folding assistant of the
thioredoxin family. EMBO J. 21, 835–844. doi: 10.1093/emboj/21.4.835
Appenzeller-Herzog, C., and Ellgaard, L. (2008). The human PDI family:
versatility packed into a single fold. Biochim. Biophys. Acta 1783, 535–548. doi:
10.1016/j.bbamcr.2007.11.010
Ataman-Onal, Y., Beaulieu, C., Busseret, S., Charrier, J.-P., Choquet-Kastylevsky,
G., Rolland, D., et al. (2013). Protein disulfide isomerase assay method for the
in vitro diagnosis of colorectal cancer. Patents 1–30.
Atkin, J. D., Farg, M. A., Turner, B. J., Tomas, D., Lysaght, J. A., Cheema, S. S., et al.
(2006). Induction of the unfolded protein response in familial amyotrophic
lateral sclerosis and association of protein-disulfide isomerase with superoxide
dismutase 1. J. Biol. Chem. 281, 30152–30165. doi: 10.1074/jbc.M603393200
Atkin, J. D., Farg, M. A., Walker, A. K., McLean, C., Tomas, D., and Horne, M.
K. (2008). Endoplasmic reticulum stress and induction of the unfolded protein
response in human sporadic amyotrophic lateral sclerosis. Neurobiol. Dis. 30,
400–407. doi: 10.1016/j.nbd.2008.02.009
Auwerx, J., Isacsson, O., Söderlund, J., Balzarini, J., Johansson, M., and Lundberg,
M. (2009). Human glutaredoxin-1 catalyzes the reduction of HIV-1 gp120 and
CD4 disulfides and its inhibition reduces HIV-1 replication. Int. J. Biochem. Cell
Biol. 41, 1269–1275. doi: 10.1016/j.biocel.2008.10.031
Bastos−Aristizabal, S., Kozlov, G., and Gehring, K. (2014). Structural insight
into the dimerization of human protein disulfide isomerase. Protein Sci. 23,
618–626. doi: 10.1002/pro.2444
Benham, A. M. (2012). The protein disulfide isomerase family: key players in health
and disease. Antioxid. Redox Signal. 16, 781–789. doi: 10.1089/ars.2011.4439
Bennett, T. A., Edwards, B. S., Sklar, L. A., and Rogelj, S. (2000). Sulfhydryl
regulation of L-selectin shedding: phenylarsine oxide promotes activation-
independent L-selectin shedding from leukocytes. J. Immunol. 164, 4120–4129.
doi: 10.4049/jimmunol.164.8.4120
Bernardoni, P., Fazi, B., Costanzi, A., Nardacci, R., Montagna, C., Filomeni, G.,
et al. (2013). Reticulon1-C modulates protein disulphide isomerase function.
Cell Death Dis. 4:e581. doi: 10.1038/cddis.2013.113
Bottomley, M. J., Batten, M. R., Lumb, R. A., and Bulleid, N. J. (2001).
Quality control in the endoplasmic reticulum: PDI mediates the ER retention
of unassembled procollagen C-propeptides. Curr. Biol. 11, 1114–1118. doi:
10.1016/S0960-9822(01)00317-7
Cai, H., Wang, C.-C., and Tsou, C.-L. (1994). Chaperone-like activity of protein
disulfide isomerase in the refolding of a protein with no disulfide bonds. J. Biol.
Chem. 269, 24550–24552.
Chen, X., Guan, T., Li, C., Shang, H., Cui, L., Lui, X.-M., et al. (2012).
SOD1 aggregation in astrocytes following ischemia/reperfusion injury: a
role of NO-mediated S-nitrosylation of protein disulfide isomerase (PDI).
J. Neuroinflammation 9:237. doi: 10.1186/1742-2094-9-237
Cheng, H., Wang, L., and Wang, C.-C. (2010). Domain a’of protein disulfide
isomerase plays key role in inhibiting α-synuclein fibril formation. Cell Stress
Chaperones. 15, 415–421. doi: 10.1007/s12192-009-0157-2
Chivers, P. T., Prehoda, K. E., and Raines, R. T. (1997). The CXXC motif: a rheostat
in the active site. Biochemistry 36, 4061–4066. doi: 10.1021/bi9628580
Clive, D. R., and Greene, J. J. (1996). Cooperation of protein disulfide isomerase
and redox environment in the regulation of NF−κB and AP1 binding to DNA.
Cell Biochem. Funct. 14, 49–55. doi: 10.1002/cbf.638
Dai, Y., and Wang, C.-C. (1997). A mutant truncated protein disulfide
isomerase with no chaperone activity. J. Biol. Chem. 272, 27572–27576. doi:
10.1074/jbc.272.44.27572
Darby, N. J., Kemmink, J., and Creighton, T. E. (1996). Identifying and
characterizing a structural domain of protein disulfide isomerase. Biochemistry
35, 10517–10528.
Darby, N. J., Penka, E., and Vincentelli, R. (1998). The multi-domain structure of
protein disulfide isomerase is essential for high catalytic efficiency. J. Mol. Biol.
276, 239–247. doi: 10.1006/jmbi.1997.1504
Delom, F., Mallet, B., Carayon, P., and Lejeune, P.-J. (2001). Role of extracellular
molecular chaperones in the folding of oxidized proteins refolding of colloidal
thyroglobulin by protein disulfide isomerase and immunoglobulin heavy chain-
binding protein. J. Biol. Chem. 276, 21337–21342. doi: 10.1074/jbc.M101086200
Denisov, A. Y., Määttänen, P., Dabrowski, C., Kozlov, G., Thomas, D. Y.,
Gehring, K., et al. (2009). Solution structure of the bb’ domains of human
protein disulfide isomerase. FEBS J. 276, 1440–1449. doi: 10.1111/j.1742-
4658.2009.06884.x
Di Jeso, B., Park, Y.-N., Ulianich, L., Treglia, A. S., Urbanas, M. L., High, S.,
et al. (2005). Mixed-disulfide folding intermediates between thyroglobulin and
endoplasmic reticulum resident oxidoreductases ERp57 and protein disulfide
isomerase. Mol. Cell. Biol. 25, 9793–9805. doi: 10.1128/MCB.25.22.9793-
9805.2005
Ellgaard, L., and Ruddock, L. W. (2005). The human protein disulphide isomerase
family: substrate interactions and functional properties. EMBO Rep. 6, 28–32.
doi: 10.1038/sj.embor.7400311
Erickson, R. R., Dunning, L. M., Olson, D. A., Cohen, S. J., Davis, A. T., and
Holtzman, J. L., et al. (2005). In cerebrospinal fluid ER chaperones ERp57 and
calreticulin bind β-amyloid. Biochem. Biophys. Res. Commun. 332, 50–57. doi:
10.1016/j.bbrc.2005.04.090
Farg, M. A., Soo, K. Y., Walker, A. K., Pham, H., Orian, J. and Atkin,
J. D., et al. (2012). Mutant FUS induces endoplasmic reticulum stress
in amyotrophic lateral sclerosis and interacts with protein disulfide-
isomerase. Neurobiol. Aging 33, 2855–2868. doi: 10.1016/j.neurobiolaging.
2012.02.009
Fernandes, D. C., Manoel, A. H. O., Wosniak, J. Jr., and Laurindo, F. R. (2009).
Protein disulfide isomerase overexpression in vascular smooth muscle cells
induces spontaneous preemptive NADPH oxidase activation and Nox1 mRNA
Frontiers in Cell and Developmental Biology | www.frontiersin.org 8May 2015 | Volume 3 | Article 30
Parakh and Atkin Novel roles for PDI in health and disease
expression: effects of nitrosothiol exposure. Arch. Biochem. Biophys. 484,
197–204. doi: 10.1016/j.abb.2009.01.022
Fewell, S. W., Travers, K. J., Weissman, J. S., and Brodsky, J. L. (2001). The action
of molecular chaperones in the early secretory pathway. Annu. Rev. Genet. 35,
149–191. doi: 10.1146/annurev.genet.35.102401.090313
Forrester, M. T., Benhar, M., and Stamler, J. S. (2006). Nitrosative stress in the ER:
a new role for S-nitrosylation in neurodegenerative diseases. ACS Chem. Biol.
1, 355–358. doi: 10.1021/cb600244c
Frand, A. R., Cuozzo, J. W., and Kaiser, C. A. (2000). Pathways for protein
disulphide bond formation. Trends Cell Biol. 10, 203–210. doi: 10.1016/S0962-
8924(00)01745-1
Freedman, R. B., Hirst, T. R., and Tuite, M. F. (1994). Protein disulphide isomerase:
building bridges in protein folding. Trends Biochem. Sci. 19, 331–336. doi:
10.1016/0968-0004(94)90072-8
Fu, X.-M., and Zhu, B. T. (2009). Human pancreas-specific protein disulfide
isomerase homolog (PDIp) is an intracellular estrogen-binding protein that
modulates estrogen levels and actions in target cells. J. Steroid Biochem. Mol.
Biol. 115, 20–29. doi: 10.1016/j.jsbmb.2009.02.008
Galligan, J. J., and Petersen, D. R. (2012). The human protein disulfide isomerase
gene family. Hum. Genomics 6, 1–15. doi: 10.1186/1479-7364-6-6
Gilbert, H. F. (1998). Protein disulfide isomerases. Meth. Enzymol. 290, 26–50. doi:
10.1016/S0076-6879(98)90005-2
Gilbert, J., Ou, W., Silver, J., and Benjamin, T. (2006). Downregulation of protein
disulfide isomerase inhibits infection by the mouse polyomavirus. J. Virol. 80,
10868–10870. doi: 10.1128/JVI.01117-06
Goldberger, R. F., Epstein, C. J., and Anfinsen, C. B. (1963). Acceleration of
reactivation of reduced bovine pancreatic ribonuclease by a microsomal system
from rat liver. J. Biol. Chem. 238, 628–635.
Goplen, D., Wang, J., Enger, P. Ø., Tysnes, B. B., Terzis, A., and Bjerkvig, R.,
et al. (2006). Protein disulfide isomerase expression is related to the invasive
properties of malignant glioma. Cancer Res. 66, 9895–9902. doi: 10.1158/0008-
5472.CAN-05-4589
Grek, C., and Townsend, D. (2014). Protein disulfide isomerase superfamily in
disease and the regulation of apoptosis. Endoplasmic Reticulum Stress Dis. 1,
4–17. doi: 10.2478/ersc-2013-0001
Gruber, C. W., ˇ
Cemažar, M., Heras, B., Martin, J. L., and Craik, D. J. (2006). Protein
disulfide isomerase: the structure of oxidative folding. Trends Biochem. Sci. 31,
455–464. doi: 10.1016/j.tibs.2006.06.001
Halloran, M., Parakh, S., and Atkin, J. (2013). The role of S-nitrosylation and
S-glutathionylation of protein disulphide isomerase in protein misfolding
and neurodegeneration. Int. J. Cell Biol. 2013:797914. doi: 10.1155/2013/
797914
Hashida, T., Kotake, Y., and Ohta, S. (2011). Protein disulfide isomerase
knockdown-induced cell death is cell-line-dependent and involves apoptosis
in MCF-7 cells. J. Toxicol. Sci. 36, 1–7. doi: 10.2131/jts.36.1
Hatahet, F., and Ruddock, L. W. (2009). Protein disulfide isomerase: a critical
evaluation of its function in disulfide bond formation. Antioxid. Redox Signal.
11, 2807–2850. doi: 10.1089/ars.2009.2466
Hetz, C., and Mollereau, B. (2014). Disturbance of endoplasmic reticulum
proteostasis in neurodegenerative diseases. Nat. Rev. Neurosci. 15, 233–249. doi:
10.1038/nrn3689
Hetz, C., Russelakis-Carneiro, M., Wälchli, S., Carboni, S., Vial-Knecht,
E., Maundrell, K., et al. (2005). The disulfide isomerase Grp58 is a
protective factor against prion neurotoxicity. J. Neurosci. 25, 2793–2802. doi:
10.1523/JNEUROSCI.4090-04.2005
Hoffstrom, B. G., Kaplan, A., Letso, R., Schmid, R. S., Turmel, G. J. and
Stockwell, B. R., et al. (2010). Inhibitors of protein disulfide isomerase suppress
apoptosis induced by misfolded proteins. Nat. Chem. Biol. 6, 900–906. doi:
10.1038/nchembio.467
Honjo, Y., Kaneko, S., Ito, H., Horibe, T., Nagashima, M., Nakamura, M., et al.
(2011). Protein disulfide isomerase-immunopositive inclusions in patients
with amyotrophic lateral sclerosis. Amyotroph. Lateral Scler. 12, 444–450. doi:
10.3109/17482968.2011.594055
Hwang, C., Sinskey, A. J., and Lodish, H. F. (1992). Oxidized redox state
of glutathione in the endoplasmic reticulum. Science 257, 1496–1502. doi:
10.1126/science.1523409
Inaba, K. (2009). Disulfide bond formation system in Escherichia coli.J. Biochem.
146, 591–597. doi: 10.1093/jb/mvp102
Irvine, A. G., Wallis, A. K., Sanghera, N., Rowe, M. L., Ruddock, L. W., Freedman,
R. B., et al. (2014). Protein disulfide-isomerase interacts with a substrate
protein at all stages along its folding pathway. PLoS ONE 9:e82511. doi:
10.1371/journal.pone.0082511
Janiszewski, M., Lopes, L. R., Carmo, A. O., Pedro, M. A., Brandes, R. P.,
Laurindo, F. R., et al. (2005). Regulation of NAD (P) H oxidase by associated
protein disulfide isomerase in vascular smooth muscle cells. J. Biol. Chem. 280,
40813–40819. doi: 10.1074/jbc.M509255200
Jasuja, R., Passam, F. H., Kennedy, D. R., Kim, S. H., van Hessem, L., Furie, B.,
et al. (2012). Protein disulfide isomerase inhibitors constitute a new class of
antithrombotic agents. J. Clin. Invest. 122, 2104–2113. doi: 10.1172/JCI61228
Jeon, G. S., Nakamura, T., Lee, W.-J., Choi, S.-W., Ahn, K.-W., Lipton, S. A.,
et al. and (2014). Potential effect of S-nitrosylated protein disulfide isomerase
on mutant SOD1 aggregation and neuronal cell death in amyotrophic lateral
sclerosis. Mol. Neurobiol. 49, 796–807. doi: 10.1007/s12035-013-8562-z
Jessop, C. E., Watkins, R. H., Simmons, J. J., Tasab, M., and Bulleid, N. J.
(2009). Protein disulphide isomerase family members show distinct substrate
specificity: P5 is targeted to BiP client proteins. J. Cell Sci. 122, 4287. doi:
10.1242/jcs.059154
Jurk, K., Lahav, J., Van Aken, H., Brodde, M., Nofer, J. R., and Kehrel, B.
(2011). Extracellular protein disulfide isomerase regulates feedback activation
of platelet thrombin generation via modulation of coagulation factor
binding. J. Thromb. Haemost. 9, 2278–2290. doi: 10.1111/j.1538-7836.2011.
04509.x
Karala, A. R., and Ruddock, L. W. (2010). Bacitracin is not a specific inhibitor
of protein disulfide isomerase. FEBS J. 277, 2454–2462. doi: 10.1111/j.1742-
4658.2010.07660.x
Kemmink, J., Darby, N. J., Dijkstra, K., Nilges, M., and Creighton, T. E. (1996).
Structure determination of the N-terminal thioredoxin-like domain of protein
disulfide isomerase using multidimensional heteronuclear 13C/15N NMR
spectroscopy. Biochemistry 35, 7684–7691. doi: 10.1021/bi960335m
Kemmink, J., Darby, N. J., Dijkstra, K., Nilges, M., and Creighton, T. E. (1997).
The folding catalyst protein disulfide isomerase is constructed of active and
inactive thioredoxin modules. Curr. Biol. 7, 239–245. doi: 10.1016/S0960-
9822(06)00119-9
Khan, H. A., and Mutus, B. (2014). Protein disulfide isomerase a multifunctional
protein with multiple physiological roles. Front. Chem. 2:70. doi:
10.3389/fchem.2014.00070
Kim, K., Hahm, E., Li, J., Holbrook, L.-M., Sasikumar, P., Cho, J., et al. (2013).
Platelet protein disulfide isomerase is required for thrombus formation but
not for hemostasis in mice. Blood 122, 1052–1061. doi: 10.1182/blood-2013-
03-492504
Klappa, P., Hawkins, H. C., and Freedman, R. B. (1997). Interactions between
protein disulphide isomerase and peptides. Eur. J. Biochem. 248, 37–42. doi:
10.1111/j.1432-1033.1997.t01-1-00037.x
Klappa, P., Ruddock, L. W., Darby, N. J., and Freedman, R. B. (1998). The b domain
provides the principal peptide-binding site of protein disulfide isomerase
but all domains contribute to binding of misfolded proteins. EMBO J. 17,
927–935.
Knoblach, B., Keller, B. O., Groenendyk, J., Aldred, S., Zheng, J., Michalak, M.,
et al. (2003). ERp19 and ERp46, new members of the thioredoxin family
of endoplasmic reticulum proteins. Mol. Cell. Proteomics 2, 1104–1119. doi:
10.1074/mcp.M300053-MCP200
Kozlov, G., Määttänen, P., Thomas, D. Y., and Gehring, K. (2010). A structural
overview of the PDI family of proteins. FEBS J. 277, 3924–3936. doi:
10.1111/j.1742-4658.2010.07793.x
Kwok, C. T., Morris, A. G., Frampton, J., Smith, B., Shaw, C. E., de Belleroche,
J., et al. (2013). Association studies indicate that protein disulfide isomerase is
a risk factor in amyotrophic lateral sclerosis. Free Radic. Biol. Med. 58, 81–86.
doi: 10.1016/j.freeradbiomed.2013.01.001
LaMantia, M., Miura, T., Tachikawa, H., Kaplan, H. A., Lennarz, W. J., Mizunaga,
T., et al. (1991). Glycosylation site binding protein and protein disulfide
isomerase are identical and essential for cell viability in yeast. Proc. Natl. Acad.
Sci.U.S.A. 88, 4453–4457. doi: 10.1073/pnas.88.10.4453
Lee, J. H., Won, S. M., Suh, J., Son, S. J., Moon, G. J., Park, U.-J., et al.
(2010a). Induction of the unfolded protein response and cell death pathway in
Alzheimer’s disease, but not in aged Tg2576 mice. Exp. Mol. Med. 42, 386–394.
doi: 10.3858/emm.2010.42.5.040
Frontiers in Cell and Developmental Biology | www.frontiersin.org 9May 2015 | Volume 3 | Article 30
Parakh and Atkin Novel roles for PDI in health and disease
Lee, S. O., Cho, K., Cho, S., Kim, I., Oh, C., and Ahn, K. (2010b). Protein
disulphide isomerase is required for signal peptide peptidase−mediated protein
degradation. EMBO J. 29, 363–375. doi: 10.1038/emboj.2009.359
Lovat, P. E., Corazzari, M., Armstrong, J. L., Martin, S., Pagliarini, V., Redfern,
C. P., et al. (2008). Increasing melanoma cell death using inhibitors of
protein disulfide isomerases to abrogate survival responses to endoplasmic
reticulum stress. Cancer Res. 68, 5363–5369. doi: 10.1158/0008-5472.CAN-
08-0035
Mares, R. E., Meléndez-López, S. G., and Ramos, M. A. (2011). Acid-denatured
Green Fluorescent Protein (GFP) as model substrate to study the chaperone
activity of protein disulfide isomerase. Int. J. Mol. Sci. 12, 4625–4636. doi:
10.3390/ijms12074625
Molinari, M., Galli, C., Piccaluga, V., Pieren, M., and Paganetti, P. (2002).
Sequential assistance of molecular chaperones and transient formation of
covalent complexes during protein degradation from the ER. J. Cell Biol. 158,
247–257. doi: 10.1083/jcb.200204122
Moran, L. K., Gutteridge, J., and Quinlan, G. J. (2001). Thiols in cellular
redox signalling and control. Curr. Med. Chem. 8, 763–772. doi:
10.2174/0929867013372904
Muller, C., Bandemer, J., Vindis, C., Camaré, C., Mucher, E., Guéraud, F., et al.
(2013). Protein disulfide isomerase modification and inhibition contribute to
ER stress and apoptosis induced by oxidized low density lipoproteins. Antioxid.
Redox Signal. 18, 731–742.
Nakamura, T., and Lipton, S. A. (2011). S-nitrosylation of critical protein
thiols mediates protein misfolding and mitochondrial dysfunction in
neurodegenerative diseases. Antioxid. Redox Signal. 14, 1479–1492. doi:
10.1089/ars.2010.3570
Nardo, G., Pozzi, S., Pignataro, M., Lauranzano, E., Spano, G., Garbelli,
S., et al. (2011). Amyotrophic lateral sclerosis multiprotein biomarkers
in peripheral blood mononuclear cells. PLoS ONE 6:e25545. doi:
10.1371/journal.pone.0025545
Nguyen, V. D., Wallis, K., Howard, M. J., Haapalainen, A. M., Salo, K. E., Ruddock,
L. W., et al. (2008). Alternative conformations of the x region of human protein
disulphide-isomerase modulate exposure of the substrate binding b’domain.
J. Mol. Biol. 383, 1144–1155. doi: 10.1016/j.jmb.2008.08.085
Paes, A. M. D. A., Veríssimo-Filho, S., Guimarães, L. L., Silva, A. C. B., Takiuti,
J. T. Lopes, L. R., et al. (2011). Protein disulfide isomerase redox-dependent
association with p47phox: evidence for an organizer role in leukocyte NADPH
oxidase activation. J. Leukoc. Biol. 90, 799–810. doi: 10.1189/jlb.0610324
Parakh, S., Spencer, D. M., Halloran, M. A., Soo, K. Y., and Atkin, J. D. (2013).
Redox regulation in amyotrophic lateral sclerosis. Oxid. Med. Cell. Longev.
2013:408681. doi: 10.1155/2013/408681
Pescatore, L. A., Bonatto, D., Forti, F. L., Sadok, A., Kovacic, H., Laurindo, F. R.,
et al. (2012). Protein disulfide isomerase is required for platelet-derived growth
factor-induced vascular smooth muscle cell migration, Nox1 NADPH oxidase
expression, and RhoGTPase activation. J. Biol. Chem. 287, 29290–29300. doi:
10.1074/jbc.M112.394551
Primm, T. P., and Gilbert, H. F. (2001). Hormone binding by protein disulfide
isomerase, a high capacity hormone reservoir of the endoplasmic reticulum.
J. Biol. Chem. 276, 281–286. doi: 10.1074/jbc.M007670200
Primm, T. P., Walker, K. W., and Gilbert, H. F. (1996). Facilitated protein
aggregation effects of calcium on the chaperone and anti-chaperone activity
of protein disulfide-isomerase. J. Biol. Chem. 271, 33664–33669. doi:
10.1074/jbc.271.52.33664
Puig, A., and Gilbert, H. F. (1994). Protein disulfide isomerase exhibits chaperone
and anti-chaperone activity in the oxidative refolding of lysozyme. J. Biol.
Chem. 269, 7764–7771.
Rainey-Barger, E. K., Mkrtchian, S., and Tsai, B. (2007). Dimerization of ERp29,
a PDI-like protein, is essential for its diverse functions. Mol. Biol. Cell. 18,
1253–1260. doi: 10.1091/mbc.E06-11-1004
Ramachandran, N., Root, P., Jiang, X.-M., Hogg, P. J., and Mutus, B. (2001).
Mechanism of transfer of NO from extracellular S-nitrosothiols into the cytosol
by cell-surface protein disulfide isomerase. Proc. Natl. Acad. Sci. U.S.A. 98,
9539–9544. doi: 10.1073/pnas.171180998
Rutkevich, L. A., Cohen-Doyle, M. F., Brockmeier, U., and Williams, D. B. (2010).
Functional relationship between protein disulfide isomerase family members
during the oxidative folding of human secretory proteins. Mol. Biol. Cell. 21,
3093–3105. doi: 10.1091/mbc.E10-04-0356
Schroder, M., and Kaufman, R. J. (2005). ER stress and the unfolded
protein response. mutation research/fundamental and molecular mechanisms
of mutagenesis. Mutat. Res. 569, 29–63. doi: 10.1016/j.mrfmmm.2004.
06.056
Schwaller, M., Wilkinson, B., and Gilbert, H. F. (2003). Reduction-reoxidation
cycles contribute to catalysis of disulfide isomerization by protein-disulfide
isomerase. J. Biol. Chem. 278, 7154–7159. doi: 10.1074/jbc.M211036200
Severino, A., Campioni, M., Straino, S., Salloum, F. N., Schmidt, N., and Bussani,
R., et al. (2007). Identification of protein disulfide isomerase as a cardiomyocyte
survival factor in ischemic cardiomyopathy. J. Am. Coll. Cardiol. 50, 1029–1037.
doi: 10.1016/j.jacc.2007.06.006
Sobierajska, K., Skurzynski, S., Stasiak, M., Kryczka, J., Cierniewski, C. S.,
Swiatkowska, M., et al. (2014). Protein disulfide isomerase directly interacts
with β-Actin Cys374 and regulates cytoskeleton reorganization. J. Biol. Chem.
289, 5758–5773. doi: 10.1074/jbc.M113.479477
Solda, T., Garbi, N., Hämmerling, G. J., and Molinari, M. (2006). Consequences
of ERp57 deletion on oxidative folding of obligate and facultative clients of the
calnexin cycle. J. Biol. Chem. 281, 6219–6226. doi: 10.1074/jbc.M513595200
Song, J. L., and Wang, C. C. (1995). Chaperone−like activity of protein
disulfide−isomerase in the refolding of rhodanese. Eur. J. Biochem. 231,
312–316. doi: 10.1111/j.1432-1033.1995.tb20702.x
Sovolyova, N., Healy, S., Samali, A., and Logue, S. E. (2014). Stressed to death–
mechanisms of ER stress-induced cell death. Biol. Chem. 395, 1–13. doi:
10.1515/hsz-2013-0174
Stolf, B. S., Smyrnias, I., Lopes, L. R., Vendramin, A., Goto, H., Santos, C.
X., et al. (2011). Protein disulfide isomerase and host-pathogen interaction.
ScientificWorldJournal 11, 1749–1761. doi: 10.1100/2011/289182
Tanaka, S., Uehara, T., and Nomura, Y. (2000). Up-regulation of protein-
disulfide isomerase in response to hypoxia/brain ischemia and its protective
effect against apoptotic cell death. J. Biol. Chem. 275, 10388–10393. doi:
10.1074/jbc.275.14.10388
Taylor, M., Banerjee, T., Ray, S., Tatulian, S. A., and Teter, K. (2011). Protein-
disulfide isomerase displaces the cholera toxin A1 subunit from the holotoxin
without unfolding the A1 subunit. J. Biol. Chem. 286, 22090–22100. doi:
10.1074/jbc.M111.237966
Thongwatchara, P., Promwikorn, W., Srisomsap, C., Chokchaichamnankit,
D., Boonyaphiphat, P., Thongsuksai, P., et al. (2011). Differential protein
expression in primary breast cancer and matched axillary node metastasis.
Oncol. Rep. 26, 185–191. doi: 10.3892/or.2011.1266
Tian, F., Zhou, X., Wikström, J., Karlsson, H., Sjöland, L.-M., Gan, J.,et al. (2009).
Protein disulfide isomerase increases in myocardial endothelial cells in mice
exposed to chronic hypoxia: a stimulatory role in angiogenesis. Am. J. Physiol.
297, H1078–H1086. doi: 10.1152/ajpheart.00937.2008
Tian, G., Xiang, S., Noiva, R., Lennarz, W., and Schindelin, H. (2006). The crystal
structure of yeast protein disulfide isomerase suggests cooperativity between its
active sites. Cell 124, 61–73. doi: 10.1016/j.cell.2005.10.044
Toldo, S., Boccellino, M., Rinaldi, B., Seropian, I. M., Mezzaroma, E., Paolisso,
G., et al. (2011). Altered oxido-reductive state in the diabetic heart: loss of
cardioprotection due to protein disulfide isomerase. Mol. Med. 17, 1012. doi:
10.2119/molmed.2011.00100
Townsend, D. M., Manevich, Y., He, L., Xiong, Y., Bowers, R., Tew, K. D.,
et al. (2009). Nitrosative stress–induced S-glutathionylation of protein disulfide
isomerase leads to activation of the unfolded protein response. Cancer Res. 69,
7626–7634. doi: 10.1158/0008-5472.CAN-09-0493
Tsai, B., Rodighiero, C., Lencer, W. I., and Rapoport, T. A. (2001). Protein disulfide
isomerase acts as a redox-dependent chaperone to unfold cholera toxin. Cell
104, 937–948. doi: 10.1016/S0092-8674(01)00289-6
Tsuda, H., Han, S. M., Yang, Y., Tong, C., Lin, Y. Q., Kwan, J., et al. (2008). The
amyotrophic lateral sclerosis 8 protein VAPB is cleaved, secreted, and acts as a
ligand for Eph receptors. Cell 133, 963–977. doi: 10.1016/j.cell.2008.04.039
Turano, C., Coppari, S., Altieri, F., and Ferraro, A. (2002). Proteins of the PDI
family: unpredicted non−ER locations and functions. J. Cell. Physiol. 193,
154–163. doi: 10.1002/jcp.10172
Uehara, T., Nakamura, T., Yao, D., Shi, Z.-Q., Gu, Z., Lipton, S. A., et al.
(2006). S-nitrosylated protein-disulphide isomerase links protein misfolding to
neurodegeneration. Nature 441, 513–517. doi: 10.1038/nature04782
Vuori, K., Pihlajaniemi, T., Marttila, M., and Kivirikko, K. I. (1992).
Characterization of the human prolyl 4-hydroxylase tetramer and its
Frontiers in Cell and Developmental Biology | www.frontiersin.org 10 May 2015 | Volume 3 | Article 30
Parakh and Atkin Novel roles for PDI in health and disease
multifunctional protein disulfide-isomerase subunit synthesized in a
baculovirus expression system. Proc. Natl. Acad. Sci. U.S.A. 89, 7467.
Walker, A. K., Farg, M. A., Bye, C. R., McLean, C. A., Horne, M. K., Atkin, J. D.,
et al. (2010). Protein disulphide isomerase protects against protein aggregation
and is S-nitrosylated in amyotrophic lateral sclerosis. Brain 133, 105–116. doi:
10.1093/brain/awp267
Walker, A. K., Soo, K. Y., Levina, V., Talbo, G. H., and Atkin, J., D. (2013). N–linked
glycosylation modulates dimerization of protein disulfide isomerase family A
member 2 (PDIA2). FEBS J. 280, 233–243. doi: 10.1111/febs.12063
Wang, C., Li, W., Ren, J., Fang, J., Ke, H., Gong, W., et al. (2013). Structural insights
into the redox-regulated dynamic conformations of human protein disulfide
isomerase. Antioxid. Redox Signal. 19, 36–45. doi: 10.1089/ars.2012.4630
Wang, C., Yu, J., Huo, L., Wang, L., Feng, W., Wang, C.-C., et al.
(2012a). Human protein-disulfide isomerase is a redox-regulated chaperone
activated by oxidation of domain a’. J. Biol. Chem. 287, 1139–1149. doi:
10.1074/jbc.M111.303149
Wang, S.-B., Shi, Q., Xu, Y., Xie, W.-L., Zhang, J., Chen, C., et al (2012b). Protein
disulfide isomerase regulates endoplasmic reticulum stress and the apoptotic
process during prion infection and PrP mutant-induced cytotoxicity. PLoS
ONE 7:e38221. doi: 10.1371/journal.pone.0038221
Watts, J. C., Huo, H., Bai, Y., Ehsani, S., Won, A. H., Xu, L., et al. (2009).
Interactome Analyses identify ties of PrPC and its mammalian paralogs to
oligomannosidic N-Glycans and endoplasmic reticulum-derived chaperones.
PLoS Pathog. 5:e1000608. doi: 10.1371/journal.ppat.1000608
Wilkinson, B., and Gilbert, H. F. (2004). Protein disulfide isomerase. Biochim.
Biophys. Acta 1699, 35–44. doi: 10.1016/j.bbapap.2004.02.017
Xiao, R., Solovyov, A., Gilbert, H. F., Holmgren, A., and Lundström-Ljung, J.
(2001). Combinations of protein-disulfide isomerase domains show that there
is little correlation between isomerase activity and wild-type growth. J. Biol.
Chem. 276, 27975–27980. doi: 10.1074/jbc.M104203200
Xiong, Y., Manevich, Y., Tew, K. D., and Townsend, D. M. (2012). S-
glutathionylation of protein disulfide isomerase regulates estrogen receptor
stability and function. Int. J. Cell Biol. 2012:273549. doi: 10.1155/2012/273549
Xiong, Y., Uys, J. D., Tew, K. D., and Townsend, D. M. (2011). S-glutathionylation:
from molecular mechanisms to health outcomes. Antioxid. Redox Signal. 15,
233–270. doi: 10.1089/ars.2010.3540/
Xu, S., Butkevich, A. N., Yamada, R., Zhou, Y., Debnath, B., Neamati, N., et al
(2012). Discovery of an orally active small-molecule irreversible inhibitor of
protein disulfide isomerase for ovarian cancer treatment. Proc. Natl. Acad. Sci.
U.S.A. 109, 16348–16353. doi: 10.1073/pnas.1205226109
Xu, S., Sankar, S., and Neamati, N. (2014). Protein disulfide isomerase: a
promising target for cancer therapy. Drug Discov. Today 19, 222–240. doi:
10.1016/j.drudis.2013.10.017
Yang, Y. S., Harel, N. Y., and Strittmatter, S. M. (2009). Reticulon-4A (Nogo-
A) redistributes protein disulfide isomerase to protect mice from SOD1-
dependent amyotrophic lateral sclerosis. J. Neurosci. 29, 13850–13859. doi:
10.1523/JNEUROSCI.2312-09.2009
Zai, A., Rudd, M. A., Scribner, A. W., and Loscalzo, J. (1999). Cell-
surface protein disulfide isomerase catalyzes transnitrosation and regulates
intracellular transfer of nitric oxide. J. Clin. Invest. 103, 393–399. doi: 10.1172/
JCI4890
Zhang, L., Lai, E., Teodoro, T., and Volchuk, A. (2009). GRP78, but not protein-
disulfide isomerase, partially reverses hyperglycemia-induced inhibition of
insulin synthesis and secretion in pancreatic β-cells. J. Biol. Chem. 284,
5289–5298. doi: 10.1074/jbc.M805477200
Conflict of Interest Statement: The authors declare that the research was
conducted in the absence of any commercial or financial relationships that could
be construed as a potential conflict of interest.
Copyright © 2015 Parakh and Atkin. This is an open-access article distributed
under the terms of the Creative Commons Attribution License (CC BY). The use,
distribution or reproduction in other forums is permitted, provided the original
author(s) or licensor are credited and that the original publication in this journal
is cited, in accordance with accepted academic practice. No use, distribution or
reproduction is permitted which does not comply with these terms.
Frontiers in Cell and Developmental Biology | www.frontiersin.org 11 May 2015 | Volume 3 | Article 30
Available via license: CC BY 4.0
Content may be subject to copyright.
