Haematologica 2003 - Supplements

or LY 294002 did not influence MAPK activation, suggesting
that there is no cross talk between MIP-1α-dependent activation
of the PI3-K/AKT and MAPK pathway.
Our data suggest that besides the role of development of
osteolytic bone destruction, MIP-1α also directly affects cell
signaling pathways mediating growth, survival and migration in
MM cells and provide evidence that MIP-1α might play a pivotal
role in the pathogenesis of MM.
115
Regulation of Hypoxia-Inducible Factor-1-Mediated
VEGF Expression in Human Multiple Myeloma Cells
Rena Feinman, Billy Abungu, Jennifer Chan, Jadd Koury,
Pranoti Gangurde and David Siegel
Department of Surgery, UMDNJ-New Jersey Medical School,
Newark, NJ 07013; Myeloma and Lymphoma Program,Cancer
Center at Hackensack University Medical Center, Hackensack, NJ
07601
Constitutive expression of the transcription factor, hypoxia-inducible
factor-1 (HIF-1), has been associated with tumor angiogenesis and
higher mortality in solid tumors such as breast, ovarian, prostate and
colon. HIF-1 is composed of a HIF-1α subunit, which is degraded
under normoxic conditions but stabilized under hypoxic conditions,
and a constitutive HIF-1β subunit. To date, very little is known about
the role of HIF-1 activation in hematological malignancies. Our
studies demonstrate that multiple myeloma (MM) cells express
constitutive HIF-1α protein under normoxic conditions. HIF-1 has
recently emerged as a critical determinant in the pathophysiological
response to hypoxia and regulates angiogenic factors such as vascular
endothelial growth factor (VEGF). Hypoxia further increases HIF-1α
protein levels in several MM cell lines as well as HIF-1 dependent
transcriptional activity in ARP-1 cells. Furthermore, treatment of
MM cells with insulin-like growth factor-1 (IGF-1) and interleukin-6
(IL-6), two major growth and survival factors for MM cells, induced
HIF-1 DNA binding and HIF-1α protein levels in several MM cell
lines. Induction of HIF-1α protein levels by IGF-1 and IL-6
correlated with VEGF transcription. Pharmacological inhibitors of
phosphatidylinositol-3 kinase/Akt kinase (PI3-K/Akt), mammalian
target of rampamycin (mTOR), and MAP kinase (MAPK) signaling
pathways blocked IGF-1 and IL-6-induced HIF-1α protein and
VEGF mRNA levels in ARP-1 cells. This study suggests an
important role for HIF-1 in IGF-1 and IL-6 -induced MM cell growth
and survival as well as a central role in the regulation of VEGF
expression. The elucidation of the HIF-1 signaling pathway may
therefore identify novel therapeutic targets.
116
Essential Role of Caveolae in IL-6- and IGF-I- Triggered
Akt-1- Mediated Survival of Multiple Myeloma Cells
Podar-K*, Tai-YT*, Cole-CE*†, Hideshima-T*, Sattler-M*,
Hamblin-A*, Mitsiades-N*, Schlossman-R*, Davies-FE,
Morgan-GJ, Munshi-NC*, Chauhan-D*, and Anderson-KC*
*The Jerome Lipper Multiple Myeloma Center, Department of
Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical
School; †Department of Internal Medicine, University of Michigan,
Medical Center; Leeds General Infirmary; ‡the VA Healthcare
Center
Caveolae, specialized flask-shaped lipid rafts on the cell surface,
are composed of cholesterol, sphingolipids and structural proteins
termed caveolins; functionally, these plasma membrane
microdomains have been implicated in signal transduction and
transmembrane transport. In the present study, we examined the
role of caveolin-1 in multiple myeloma cells. We show for the
first time that caveolin-1, which is usually absent in blood cells,
is expressed in multiple myeloma cells. Interestingly, Cav-1 was
up-regulated in MM (158+/-36) versus MGUS (49+/-24)
samples, suggesting a possible role for caveolae in the transition
of MGUS to MM. Analysis of myeloma cell-derived plasma
membrane fractions shows that caveolin-1 is co-localized with
interleukin-6 receptor signal transducing chain gp130 and with
insulin-like growth factor-I- receptor, but not with ERK.
Cholesterol depletion by β-cyclodextrin results in the loss of
caveolae structure in myeloma cells, as shown by transmission
electron microscopy, and loss of caveolin-1 function. Interleukin-
6 and insulin-like growth factor- I, growth and survival factors in
multiple myeloma, induce caveolin-1 phosphorylation, which is
abrogated by pre-treatment with β-cyclodextrin. Importantly,
inhibition of caveolin-1 phosphorylation blocks both interleukin-
6- induced protein complex-formation with caveolin-1 and
downstream activation of the phosphatidylinositol 3-kinase/ Akt-
1 pathway. β-cyclodextrin also blocks insulin-like growth factor-
I- induced tyrosine phosphorylation of insulin responsive
substrate-1 and downstream activation of the phosphatidylinositol
3-kinase / Akt-1 pathway. Therefore cholesterol depletion by β-
cyclodextrin abrogates both interleukin-6- and insulin-like growth
factor-I- triggered multiple myeloma cell survival via negative
regulation of caveolin-1. Taken together, this study identifies
caveolin-1 and other structural membrane components as
potential new therapeutic targets in multiple myeloma.
117
Multiple Bone Marrow Derived Cytokines Stimulate
Signaling Cascades and Mediate Survival and
Proliferation in Multiple Myeloma (MM)
S. Lentzsch, M. Chatterjee, St. Mathas, H. Gollasch, M.Y.
Mapara, B. Dorken and R. Bargou
Humboldt University of Berlin, Charite Campus Buch, Robert-
Roessle-Klinik, 13125 Berlin, Germany, Tel.: +49-30-94171370,
FAX:+49-30-94171209, e-mail: lentzsch@rrk-berlin.de
Interleukin-6 (IL-6) has been reported to play a central role in
malignant growth and survival of Multiple Myeloma (MM) cells.
Several studies have demonstrated IL-6-dependent activation of
STAT-3 signaling pathways regulating proliferation and survival of
MM cells. However, recently we have shown that in the presence of
bone marrow stromal cells survival of MM cells becomes
independent of the IL-6-gp130-STAT3 pathway and IL-6 antibody
therapies have failed to induce remissions in patients with MM
questioning the singular role of IL-6 in MM. Therefore, it was the
aim of this study to identify additional factors and their corresponding
signaling pathways contributing to the growth of MM cells.
We found that besides IL-6 a number of various bone marrow
derived cytokines such as LIF, VEGF, βFGF, MIP-1α, SDF-1α,
IL-1β, SCF, and IL-3 redundantly activates the PI3K/Akt
pathway and its downstream target FKHR and the MAPK
pathway. Inhibition of these pathways by specific small
compound inhibitors induces apoptosis in both MM cell lines and
primary MM cells. Furthermore LIF, VEGF, βFGF, MIP-1α,
SDF-1α, IL-1β, SCF, and IL-3 induces proliferation of MM cell
lines and mediates survival of primary human MM cells.
Thus, we provide evidence that in addition to IL-6 a number of
different factors secreted by the bone marrow microenvironment
might redundantly trigger a few important growth promoting
pathways thereby supporting proliferation and survival of MM
cells. Therefore, blocking of such pathways rather than blocking
a single factor might be a promising approach to develop novel
treatment strategies in MM.
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