*Corresponding author. Hee Gu Lee, Ph.D. or Jong-Wan Kim, M.D.,
Ph.D. Tel: 82-42-860-4182, 82-41-550-6662; Fax: 82-42-860-4593,
82-41-555-7155; E-mail: firstname.lastname@example.org or email@example.com
#These authors contributed equally to this work.
Received 4 July 2008, Accepted 7 July 2008
Keywords: Akt, Mac-2 BP , NGF, PI3K
Induction of Mac-2BP by nerve growth factor is regulated by the
PI3K/Akt/NF-κB-dependent pathway in the HEK293 cell line
Yuk Pheel Park1, Seung-Chul Choi1, Bo-Yeon Kim1, Jong-Tae Kim1, Eun Young Song1, Seong Ho Kang2, Do-Young Yoon3,
Sang-Gi Paik4, Kwang Dong Kim5, Jong Wan Kim6,*,# & Hee Gu Lee1,*,#
1Stem Cell Research Center, KRIBB, Daejeon, 2Department of Chemistry and Basic Science Research Institute, Chonbuk National
University, Jeonju, 3Department of Bioscience and Biotechnology, Konkuk University, Seoul, 4Department of Biology, Chungnam National
University, Daejeon, 5Division of Applied Life Science, Gyeongsang National University, Jinju, 6Department of Laboratory Medicine,
Dankook University College of Medicine, Cheonan, Korea
Mac-2BP is a ligand of the galectin family that has been suggested
to affect tumor proliferation and metastasis formation. We as-
sessed Mac-2BP expression at the transcriptional and transla-
tional levels to evaluate nerve growth factor (NGF)-induced
Mac-2BP expression. A time kinetic analysis using reverse tran-
scription-polymerase chain reaction showed that NGF-induced
Mac-2BP transcript levels were 4-5 times higher than in controls.
Mac-2BP enzyme-linked immunosorbent assay and immuno-
fluorescence staining showed a 2-3-fold increase in intracellular
and secreted Mac-2BP as a result of NGF stimulation. This in-
crease was regulated by Akt activation and NF-κ κB binding. p65
and p50-NF-κ κB are major transcriptional factors in the Mac-2BP
promoter region, and were shown to be regulated in accordance
with the Akt activation states. Collectively, these results suggest
that NGF induces Mac-2BP expression via the PI3K/Akt/NF-κ κB
pathway. [BMB reports 2008; 41(11): 784-789]
Mac-2BP is a large oligomeric glycoprotein that has been identi-
fied in the fluid from human breast cancer cells (1,2). Supranor-
mal serum levels of Mac-2BP have been found in patients with
breast, lung, pancreatic, and gastric tumors, Non-Hodgkin's
lymphoma, asthma, and human immunodeficiency virus in-
fection (2-9). The reported evidence implicates Mac-2BP as a di-
agnostic and/or prognostic marker of poor outcome in several
tumor types. Mac-2BP, like other members of its family, is in-
volved in the host response to tumors and infections (10).
Moreover, several reports have shown that the protein may
function in cell adhesion processes. In particular, it has been
demonstrated that Mac-2BP, as a ligand of galectin-1, -3, and -7,
may promote homotypic cell-to-cell contacts (11,12), or may
regulate cell adhesion by binding to cellular matrix proteins in-
cluding β1-integrin, collagens, and fibronectins (13). Therefore,
Mac-2BP may favor the establishment of new tumor colonies
via enhancement of adhesive interactions between tumor cells
and the extracellular matrix (14,15).
Neurotrophins are a family of structurally related secretory
proteins that are involved in the survival, development, and
death of specific populations of neuronal and non-neuronal
cells (16). Nerve growth factor (NGF) is the best-characterized
member of this family. NGF interacts with two classes of mem-
brane receptors: the TrkA proto-oncogene product p140TrkA,
which exhibits intrinsic tyrosine kinase activity, and a secon-
dary receptor, p75NTR, which is a member of the tumor ne-
crosis factor (TNF) receptor family (17).
In the current study, we have determined that NGF induces
Mac-2BP expression at the transcriptional level, and is depend-
ent on an Akt/NF-κB-dependent pathway.
Nerve growth factor induces Mac-2BP expression
To evaluate the role of NGF in Mac-2BP expression, we uti-
lized reverse transcription-polymerase chain reaction (RT-PCR).
NGF was applied to serum-starved HEK293 cells; Mac-2BP
transcripts peaked within 6 h and then slowly diminished over
time. Mac-2BP transcripts were increased steadily as the result
of NGF treatment (Fig. 1A). Mac-2BP ELISA showed a 2-3-fold
increase in the secreted Mac-2BP in culture supernatants of
HEK293 or SNU-638 cell line treated with NGF (Fig. 1B). An
increase of Mac-2BP was verified via immunofluorescence
staining with an anti-Mac-2BP monoclonal antibody. The in-
crease in Mac-2BP was verified by immunofluorescence stain-
ing with an anti-Mac-2BP monoclonal antibody. We inhibited
glycosylation by pretreatment with 10 μg/ml tunicamycin for
30 min prior to NGF treatment, and staining of Mac-2BP. As
Mac-2BP secretion was prohibited by the inhibition of glyco-
sylation, intracellular Mac-2BP was more readily detectable in
Regulation of Mac-2BP expression
Yuk Pheel Park, et al.
Fig. 1. Mac-2BP expression induced by NGF. (A) After the cells
were incubated with NGF for 6-24 h, cell morphology was assessed
under a microscope (left panel). Total RNAs were prepared from the
stimulated cells, and RT-PCR was conducted with Mac-2BP or
GAPDH primers. (B) The cells treated for 24 h with NGF were
lysed, and Mac-2BP ELISA was conducted with the protein extracts
that had been prepared. (C) HEK293 cells were serum-starved for
18 h followed by 24 h of NGF and/or tunicamycin treatment. For
immunofluorescence analysis, the cells were fixed and stained with
Mac-2BP monoclonal antibody and cellular localization and ex-
pression of Mac-2BP were observed with a confocal microscope.
Fig. 2. Regulation of Mac-2BP expression by NGF at the transcrip-
tional level. (A) Cells were pre-treated with 2 μg/ml of CHX for 40
min prior to NGF treatment. After an additional 24 h of incubation,
the cells were lysed and Mac-2BP ELISA was conducted using cyto-
solic soluble proteins. (B) The -2377 bp of the human Mac-2BP pro-
moter region was constructed and transfected into HEK293 cells using
Lipofectamine reagent, and then subjected to NGF treatment for 24
h. The cells were lysed, and the relative luciferase activities expressed
as the ratio of the pGL3 reporter activity to that of the pRL control
plasmid. Values are expressed as means ± SD of three independent
measurements. (C) Nuclear extracts were prepared from the HEK293
cells stimulated with 50 ng/ml of NGF for 24 hr, and the DNA binding
activity of NF-κB was determined with a consensus dsDNA oligomer
probe via an EMSA assay. The arrow indicates NF-κB complex.
these cells than in the NGF-treated cells (Fig. 1C).
NGF-induced Mac-2BP expression is regulated at the
To determine whether the increase in Mac-2BP was derived from
novel protein synthesis, we induced the inhibition of protein syn-
thesis by a 40 min pre-incubation with cycloheximide prior to the
NGF treatment. NGF-induced upregulation of Mac-2BP was de-
creased to the levels seen in the untreated control cells (Fig. 2A).
Moreover, in an effort to assess the regulation steps of Mac-2BP
expression, we cloned -2377 bp of the Mac-2BP promoter flank-
ing regions within the pGL3 basic luciferase reporter vector sys-
tem (pGL3-Mac Pro-2377), and transiently introduced it into
HEK293 cells. The relative luciferase activities of the Mac-2BP
promoter were clearly increased by NGF (Fig. 2B)
To test whether NF-κB might be involved in the expression
of Mac-2BP, serum-starved HEK293 was treated for 24 h with
NGF, and the nuclear extracts were prepared. The DNA bind-
ing activity of NF-κB was clearly enhanced to a greater degree
than was observed with the control extracts. This indicates that
NGF increases the expression of Mac-2BP at the transcriptional
level via NF-κB activation (Fig. 2C).
NGF-induced Mac-2BP expression is dependent on the
PI3K/Akt/NF-κ κB pathway
To evaluate the signal transduction of Mac-2BP expression by
NGF, we assessed the activation of MAP kinase or Akt. As
shown in Fig. 3A, phosphorylated-p140TrkA tyrosine kinase re-
ceptor was detected within 1 h, and the results of time kinetic
analysis showed that phospho-p44/42 MAP kinase (Thr202/
Tyr204) and phospho-Akt (Ser 473) were detected between 3 h
and 6 h of incubation with NGF (Fig. 3B). To evaluate the rela-
tionships between Akt, NF-κB, and Mac-2BP expression, we
pre-incubated HEK293 cells with PI3 kinase inhibitors prior to
NGF treatment. Mac-2BP expression was analyzed at the tran-
scriptional and translational levels using RT-PCR and Mac-2BP
enzyme-linked immunosorbent assay (ELISA) (Figs. 3C-E) in-
dicating that the inhibition of PI3 kinase induced a reduction
in the Mac-2BP transcripts and its protein via the inhibition of
Akt, although this did not completely suppress the expression.
These results indicate that the expression of Mac-2BP as a con-
sequence of NGF signaling is dependent on Akt activation.
DNA binding activity of NF-κ κB is crucial for Mac-2BP
There are two putative binding sites of NF-κB on the promoter
region of Mac-2BP (NCBI number; U91729). To characterize
the Mac-2BP promoter region, we conducted a competition as-
say using cold probes and a supershift analysis with anti-p50 or
p65 antibodies. The results of the competition assay showed
that the NGF-treated cells exhibited profound binding of the
consensus or upstream and downstream NF-κB probes as com-
pared to the untreated control cells. A downstream NF-κB site
also evidenced stronger binding than the upstream NF-κB site
To investigate the effects of PI3K inhibitors on NF-κB activa-
tion, we evaluated the localization of the NF-κB subunits. As
shown in Fig. 4B, p65 and the phosphorylated form of p65
were polarized in the nuclear region. The NGF signal also in-
Regulation of Mac-2BP expression
Yuk Pheel Park, et al.
Fig. 3. Critical role of NGF signaling via a PI3K/Akt-dependent path-
way in Mac-2BP expression. (A) After NGF treatment for the indicated
amounts of time, the HEK293 cells were lysed and soluble cytosolic
proteins were immunoblotted with phospho-p140TrkA antibody. (B)
HEK293 cells were harvested at the indicated time points and the cy-
tosolic extracts were prepared. Total proteins of p42/44 MAP kinase,
Akt, or phosphorylated forms of these proteins were measured using
Western blot analysis. (C) Starved HEK293 cells were pre-treated with
PI3K inhibitors for 30 min prior to NGF treatment. RT-PCR was con-
ducted with Mac-2BP-specific primer. The relative values of the PCR
products were calculated using a densitometer (MAC-2BP/GAPDH).
(D) PI3K inhibited cells were lysed and the total Akt or phosphory-
lated Akt was determined using Western blotting. (E) Mac-2BP ex-
pression was assessed by Mac-2BP ELISA.
Fig. 4. Critical effect of NF-κB binding on Mac-2BP expression. (A)
EMSAs were conducted in order to assess NF-κB binding activity us-
ing commercial consensus or upstream (u) and downstream (d) puta-
tive NF-κB sequences of the Mac-2BP promoter. Competition assays
were conducted with a molar ratio of 20X or 40X cold probes. (B)
Starved HEK293 cells were pre-treated with PI3K inhibitors for 30
min, and were incubated with NGF for 24 h. The cells were pre-
pared as nuclear and cytosolic proteins. Western blotting was con-
ducted with the indicated antibodies.
creased the activation of the p65 NF-κB subunit, whereas it
was suppressed by LY294,002. Wortmannin increased phos-
phorylated p65 or p50 levels in the nuclear regions of the cells
indicating that wortmannin may regulate NF-κB activation oc-
curring via other pathways. Taken together, the results indicate
that NGF may increase Mac-2BP expression by the induction
of NF-κB binding on its promoter region, and is also depend-
ent on the PI3K/Akt/NF-κB pathway.
We have recently determined that Mac-2BP may prove useful
as a diagnostic and prognostic marker for gastric cancers (8). In
the current study, to evaluate the molecular basis of Mac-2BP
expression in HEK293, we assessed the effects of NGF on
Mac-2BP expression and dissected the signal pathway involv-
ing the binding of NGF to its receptor.
As shown in Fig. 1, NGF induced Mac-2BP expression in hu-
man embryonic kidney 293 cells. The Mac-2BP transcript level
achieved a peak at 6 h and then decreased slightly until 24 h.
NGF-induced Mac-2BP was also detected in a quantitative
Mac-2BP ELISA assay (Fig. 1B). NGF was shown to play roles in
the induction and secretion of Mac-2BP, and immunofluorescence
staining with Mac-2BP monoclonal antibody evidenced the up-
regulation of Mac-2BP as a result of NGF treatment. Because
Mac-2BP is known to be a highly glycosylated protein, we pre-
treated samples with 10 μg/ml tunicamycin for the easy detection
of Mac-2BP. Therefore, the sample containing NGF plus tunica-
mycin allowed for easier observation of Mac-2BP as compared to
the negative or NGF-treated samples (Fig. 1C).
We also demonstrated that the induction of Mac-2BP result-
ing from NGF treatment is regulated at the transcriptional level,
as shown in Fig. 2. Experiments in protein synthesis inhibition
and reporter assays demonstrated the regulation of Mac-2BP
expression upon transcription by NGF, and the DNA binding
activity of NF-κB was shown to be involved in the transcription
of Mac-2BP. To evaluate the signal cascades of Mac-2BP ex-
pression, we analyzed the activated states of the p140TrkA re-
ceptor, p42/44 MAP kinase, and Akt (Fig. 3). The NGF signal
induced an increase in the phosphorylated form of p140TrkA
within 1 h of NGF stimulation, and the activation of p42/44
MAP kinase and Akt were also increased as a consequence of
NGF treatment. This result also suggests that Mac-2BP is sub-
ject to control by NGF as a result of PI3K/Akt/NF-κB signaling.
In neuronal systems, the binding of NGF to p140TrkA or p75NTR
Regulation of Mac-2BP expression
Yuk Pheel Park, et al.
activates several signaling pathways, including the phosphoi-
nositide-3-kinase (PI3K) and mitogen-activated protein kinase
pathways. This also results in the activation of several transcrip-
tional factors (18, 19) including NF-κB (20). NGF activates
NF-κB and AP-1 in sympathetic neurons, and NGF-inducible
NF-κB is required for neuronal survival (21).
We report here that two NF-κB binding sites on the Mac-2BP
promoter region are critical DNA-bound components for the
expression of Mac-2BP, and that the activity is regulated by the
PI3K/Akt pathway. The Mac-2BP transcripts or its secreted
products were regulated via the inhibition of PI3K inhibitors in-
cluding wortmannin and LY294,002, and its regulation was po-
tentially involved in NF-κB transactivation (Figs. 2C, 3C-E). The
identified sequence begins at the upstream position -1622/
-1611 and the downstream position -1580/-1589. NF-κB p50
usually binds to both positions containing the consensus se-
quence and promoter binding sites; however, p65-NF-κB dis-
played unique binding on the upstream site. Collectively, these
results suggest that p65-NF-κB binding is critical for Mac-2BP
expression, because p50-NF-κB lacks a transactivation domain.
The regulation of NF-κB activity by NGF and by Akt remains
a matter of some controversy, and the discrepancies among pre-
vious studies may be related in part to cell type specificity.
NGF-induced dissociation of the cytosolic p65/IκBα complex
via phosphorylation of IκBα at a tyrosine residue 42 has been
described (22). This mechanism results in nuclear translocation
of p65-NF-κB without significant degradation of IκBα. In addi-
tion, other cytokine signaling studies have shown that the tran-
scriptional activity of NF-κB is regulated independently of IκB.
For example, inhibition of IL-1 stimulated PI3K activity by pre-
treatment with LY294,002 or wortmannin also causes a dramatic
loss of NF-κB-dependent gene expression (23). Despite the dra-
matic decrease in NF-κB-induced gene expression, LY294,002
and wortmannin have no effects on interleukin-1 (IL-1) -stimulated
degradation of IκBα or the nuclear translocation or DNA bind-
ing of NF-κB itself in HepG2 cells (23).
Consistent with the evidence provided in the aforementioned
studies, our results also indicate that Mac-2BP is indeed regu-
lated via Akt expression or activation, and that NF-κB trans-
activation potential is crucial to the PI3/Akt-dependent pathway.
However, the nuclear localization of p65 is not inconsistent with
our prediction that NF-κB p65 and p50 proteins are localized at
the nuclear region even in unstimulated cells. In addition, wort-
mannin-pretreated cells, unlike LY294,002, evidenced higher
levels of nuclear phospho-p65-NF-κB than observed in the
NGF-treated cells (Fig. 4B). At this time, we do not have a clear
explanation for the differences in our results. However, these
findings reminded us that wortmannin could regulate NF-κB acti-
vation or transactivation occurring via multiple pathways. Our
results are similar to other reports that inhibitors of phophati-
dylcholine-specific phospholipase C and protein kinase C block
IL-1 and TNF-α-induced, NF-κB-dependent gene expression
without affecting cytokine-induced IκB degradation or the nu-
clear translocation or DNA binding of NF-κB (23,24).
Although the precise mechanism by which the regulation of
NF-κB by Mac-2BP occurs remains to be determined, the re-
sults of our study help to elucidate the manner in which NGF
and other signaling molecules regulate Mac-2BP. In summary,
we have uncovered new evidence indicating that Mac-2BP is
regulated by NGF at the transcriptional level, and that this oc-
curs in a PI3/Akt/NF-κB-dependent fashion.
MATERIALS AND METHODS
Cell culture and treatment
HEK293 cells were cultured in MEM-alpha (Gibco-BRL, Grand
Island, NY) with 10% heat-inactivated fetal bovine serum (FBS;
Hyclone, Road Logan, Utah) and antibiotics in a humidified 5%
CO2 incubator at 37oC. Signaling blockers were administered
including 100 nM wortmannin and 10 μM LY294, 002 (Sigma-
Aldrich, St, Louis, MO) for 30 min, followed by stimulation with
50 ng/ml of recombinant human β-NGF (R&D Systems,
Minneapolis, MN) for the indicated amounts of time.
Anti-Mac-2BP was purchased from Alexis (San Diego, CA); an-
ti-p50 and total p42/p44 MAP kinase were obtained from
Upstate (Charlottesville, VA); anti-total Akt and phospho-Akt
(Ser 473), phospho-p42/p44 MAP kinase (Thr202/Tyr204), and
total p65 and phopho-p65 were purchased from Cell Signaling
Technologies (Danvers, MA); anti-histone H3 was obtained
from Santa Cruz Biotechnology (Santa Cruz, CA); anti-heat
shock protein 70 was obtained from Stressgen Biotechnologies
(Ann Arbor, MI).
Total RNA of the cells was isolated using TRI Reagent
(Molecular Research Center, Cincinnati, OH) using the manu-
facturer's instructions. The first-strand cDNAs were synthe-
sized with a ProSTART First-Strand RT-PCR kit ST (Stratagene,
La Jolla, CA). The following primer pair for PCR was used:
Mac-2BP sense; 5'-ACACGGTCATCCTGACTGC-3', Mac-2BP
The cells were suspended in a cell lysis buffer (Cell Signaling
Technology, Beverly, MA) containing 1 mM PMSF and in-
cubated for 40 min on ice. The quantities of Mac-2BP in the cyto-
sol of the cells were measured via ELISA using an s90k/Mac-2BP
ELISA kit (Bender Med Systems GmbH, Vienna, Austria), in ac-
cordance with the instructions provided by the manufacturer.
Western blot analysis
Proteins were separated by 12-15% sodium dodecyl sulfate-
polyacrylamide gel electrophoresis (SDS-PAGE) and were trans-
ferred to Hybond-P PVDF membranes (Amersham Biosciences,
Buckinghamshire, UK). The nuclear and cytosolic fractions were
separated using a commercially available kit according to the
Regulation of Mac-2BP expression
Yuk Pheel Park, et al.
protocol of the manufacturer (Pierce Biotechnology, Rockford,
IL). The membranes were blocked with 5% non-fat dry milk in
TBST (50 mM Tris-HCl, pH7.6, 150 mM NaCl, 0.1% Tween-20),
and were incubated for 2 h with the appropriate primary and
horseradish peroxidase (HRP)-conjugated secondary antibodies
at room temperature. After extensive washing, the protein
bands were visualized with an ImmobilonTM Western Chemilu-
miscent HRP substrate (Millipore, Billerica, MA).
Immunofluorescence confocal microscopy
Two million HEK293 cells were grown on 3-glycopropyl trime-
thoxysilane (Sigma-Aldrich) coated coverslips under starvation
conditions for 18 h. NGF (50 ng/ml) and NGF plus tunicamycin
(10 μg/ml) were administered for 24 h. The cells were then
washed with PBS, fixed, and permeabilized in BD Cytofix
/CytopermTM (BD Biosciences Pharmingen, San Diego, CA) for
20 min. After washing, the cells were blocked for 10 min in 1%
bovine serum albumin (BSA)/PBS at room temperature, washed,
and stained overnight with an anti-Mac-2BP monoclonal anti-
body (Alexis, San Diego, CA) at 4oC, followed by incubation
with fluorescein isothiocyanate (FITC)-conjugated anti- mouse
IgG and 4',6-diamidino-2-phenylindole (DAPI; Calbiochem,
San Diego, CA) staining. Cell-containing coverslips were
mounted onto glass slides using Dakocytomation mounting me-
dium (Produktionsvej 42, Glostrup, Denmark) and visualized
with a LSM510META Zeiss confocal microscope (Carl Zeiss,
Jena, Germany) at a magnification of 40X. The confocal images
were captured by the Zeiss LSM Image Browser program.
Luciferase reporter assay
The -2377 bp DNA fragment (nucleotide positions -2377 to
+61) including the 5' flanking region was inserted into the
pGL3-basic luciferase vector (Promega, Madison, WI). The in-
serted sequences were verified via DNA sequence analysis
(Genotech, Daejeon, Korea). For transient transfection, the
cells were plated at a density of 5 × 105 cells /12 wells on day
1. One day later, 0.5 μg of pGL3-Mac pro-2377 vector and 0.2
μg of Renillar vector as an internal control were co-transfected
with Lipofectamine PlusTM Reagent (Invitrogen). After 3 h of in-
cubation, the transfection media was changed with 1% fetal
bovine serum (FBS)/MEM-α, and the next day, NGF was ad-
ministered for an additional 24 h. The cells were lysed and a
luciferase assay was conducted using the Dual-LuciferaseR re-
porter assay system, in accordance with the instructions pro-
vided by the manufacturer (Promega). Luciferase activity was
determined using a Microlumat Plus luminometer (Berthold
Technologies, Bad Wildbad, Germany) by measuring light
emission for 10 s.
Preparation of nuclear extracts and electro mobility shift assay
Nuclear extract (5-7 μg) of nuclear extracts were incubated
with 32P-labeled probe in binding buffer (100 mM KCl, 30 mM
HEPES, 1.5 mM MgCl2, 0.3 mM EDTA, 10% glycerol, 1 mM
DTT, 1 mM PMSF, and protease inhibitor cocktail) in the pres-
ence or absence of competitor or antibodies for 20 min at room
temperature. The mixtures were then run on 6% polyacrylamide
gels in 0.5 ×TBE, and were dried and analyzed via autoradio-
graphy. The following probes that had been constructed through
the annealing of single-stranded oligonucleotides were utilized
for the EMSAs: upstream NF-κB site (NF-κBu -1622/-1611)
sense '-GGCCTCTGGGTTTTCCATTT-3', antisense, 5'-GGAGA
CCCAAAAGGTAAAAT-3'; downstream NF-κB site (NF-κBd-
1580/-1589) sense, 5'-GGATGGCTTAGGACTTTCCC-3', anti-
sense, 5'-TACCGAATCCTGAAAGGGCC-3'. The NF-κB con-
sensus oligonucleotides were purchased from Promega.
This work was supported by FG08-12-01 of the 21C Frontier
Functional Human Genome Project from the Ministry of
Science & Technology in the Republic of Korea, and by the
KRIBB Research Initiative Program.
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