A lymphocyte molecule implicated in lymph node homing is a member of the cartilage link protein family

Monoclonal antibodies in the Hermes family recognize a lymphocyte structure that participates in lymphocyte adhesion to endothelium and has been suggested to be the human homolog of the murine Mel-14 lymph node homing receptor. Recently, antibodies against the Hermes antigen, the polymorphic glycoprotein Pgp-1 antigen, and the broadly expressed CDw44 antigen have been shown to recognize the same structure. In this work, cDNA clones encoding the CDw44 antigen were isolated and expressed in COS cells. Two forms were identified: a lymphoid form expressed in hematopoietic cells, and an epithelial form weakly expressed in normal epithelium but highly expressed in carcinomas. The extracellular domain of CDw44 bears homology to cartilage link proteins and a related segment of proteoglycan core protein. However, comparison with the recently identified sequence of the Mel-14 antigen shows that CDw44 and Mel-14 are unrelated.

The hematopoietic and epithelial forms of CD44 are distinct polypeptides with different adhesion potentials for hyaluronate-bearing cells

CD44 is a polymorphic integral membrane protein which recognizes hyaluronate and whose proposed roles encompass lymphocyte activation, matrix adhesion and the attachment of lymphocytes to lymph node high endothelial venules (HEVs). Immunochemical and RNA blot data have supported the existence of two forms of CD44: a hematopoietic form expressed by cells of mesodermal origin (and by some carcinoma cell lines) and an epithelial form weakly expressed by normal epithelium but highly expressed by carcinomas. This report describes the isolation of a cDNA encoding a distinct CD44 polypeptide expressed by epithelial cells. Re-expression of each form of CD44 in a B cell line allowed cells transfected with the hematopoietic but not the epithelial form to bind to viable rat lymph node HEV cells in primary culture.

Mcl-1 is overexpressed in multiple myeloma and associated with relapse and shorter survival

We and others have shown that Mcl-1 was essential for the survival of human myeloma cells in vitro. Furthermore, this antiapoptotic protein is upregulated by interleukin-6, which plays a critical role in multiple myeloma (MM). For these reasons, we have evaluated the expression of Mcl-1 in vivo in normal, reactive and malignant plasma cells (PC), that is, myeloma cells from 51 patients with MM and 21 human myeloma cell lines (HMCL) using flow cytometry. We show that Mcl-1 is overexpressed in MM in comparison with normal bone marrow PC. In total, 52% of patients with MM at diagnosis (P=0.017) and 81% at relapse (P=0.014 for comparison with diagnosis) overexpress Mcl-1. Of note, only HMCL but not reactive plasmacytoses have abnormal Mcl-1 expression, although both PC expansions share similar high proliferation rates. Of interest, Bcl-2 as opposed to Mcl-1, does not discriminate malignant from normal PC. Finally, the level of Mcl-1 expression is related to disease severity, the highest values at diagnosis being associated with the shortest event-free survival (P=0.002). In conclusion, Mcl-1, which has been shown to be essential for the survival of human myeloma cells in vitro, is overexpressed in vivo in MM in relation with relapse and shorter survival. Mcl-1 represents a potential therapeutical target in MM.

Sequence requirements for induction of cytolysis by the T cell antigen/Fc receptor zeta chain

The zeta chain of the T cell antigen receptor is a dimeric transmembrane protein with a very short extracellular domain and an extended cytoplasmic tail that triggers T cell effector function when aggregated by extracellular stimuli. We have reduced the active site of zeta to an 18 residue motif that can be appended to the intracellular domain of other transmembrane proteins to endow them with receptor-like activity. The compact size of the motif appears to eliminate zeta mechanisms based on enzymatic activity and suggests that one or at most a few cellular proteins interact with the zeta intracellular domain to initiate signal transduction. Analysis of individual amino acids within the 18 residue element reveals two phylogenetically conserved tyrosines that are absolutely required for activity and other residues that are less essential but contribute to the efficacy of receptor-directed cytolysis.

IL-6 up-regulates mcl-1 in human myeloma cells through JAK / STAT rather than ras / MAP kinase pathway

Mcl-1 is an anti-apoptotic member of the Bcl-2 family which is tightly regulated during myeloid and B cell differentiation. We have recently reported that Mcl-1 is expressed in human myeloma cells and that Mcl-1 and Bcl-x(L) expression are correlated. In the current study, we demonstrate that IL-6, a survival factor for the human myeloma cell line MDN, rapidly up-regulates Mcl-1 whereas it has no effect on Bcl-2 protein level. In MDN cells, IL-6 induces both extracellular signal-regulated protein kinase (ERK)1,2 and STAT3 activation whereas STAT1 and STAT5 activation remains undetectable. Furthermore, while investigating the IL-6 signaling pathway leading to Mcl-1 up-regulation, we show that a janus kinase (JAK)-2 inhibitor is able to inhibit both STAT3 activation and Mcl-1 up-regulation whereas an MAP/ERK kinase (MEK) inhibitor has no effect. In conclusion, our data suggest the involvement of the JAK / STAT pathway but not of the Ras / mitogen-activated protein (MAP) kinase pathway in IL-6-induced Mcl-1 up-regulation.

Zoledronate is a potent inhibitor of myeloma cell growth and secretion of IL-6 and MMP-1 by the tumoral environment

Bisphosphonates have recently been introduced in the therapeutic armamentarium for the long-term treatment of patients with multiple myeloma (MM). These pyrophosphate analogs not only reduce the occurrence of skeletal-related events but also provide patients with a clinical benefit and improve the survival of some of them. We investigated the effects of two bisphosphonates, pamidronate and zoledronate, on both myeloma cells and bone marrow stromal cells (BMSCs). We show here that both bisphosphonates induce both myeloma cell and BMSC apoptosis. Furthermore, at lower concentrations, they induce a significant inhibition (40% and 60%, respectively) of the constitutive production of interleukin-6 (IL-6) by BMSCs. We have recently shown that BMSCs produce MMP-1, the major metalloproteinase involved in the initiation of bone resorption, production up-regulated by IL-1beta. Here, we demonstrate that zoledronate significantly inhibits MMP-1 production by BMSCs stimulated with IL-1beta more efficiently than pamidronate. However, zoledronate and to a lesser extent pamidronate are responsible for an up-regulation of MMP-2 secretion by BMSCs. MMP-2 is involved both in bone resorption and in the metastatic process. In conclusion, the apoptosis of myeloma cells and BMSCs and the inhibition of both IL-6 and MMP-1 production induced by bisphosphonates, mainly zoledronate, could have antitumoral effects in patients with MM. However, the up-regulation of MMP-2 secretion observed in vitro suggests a putative risk of tumor cell dissemination in vivo when using these new potent bisphosphonates. This potentially deleterious effect could be abolished by combining bisphosphonates with metalloproteinase inhibitors.

The absence of CD56 (NCAM) on malignant plasma cells is a hallmark of plasma cell leukemia and of a special subset of multiple myeloma

In this study, we show that malignant plasma cells from patients with either primary (n=12) or secondary (n=15) plasma cell leukemia (PCL) do not express CD56 at all, neither in the bone marrow nor the peripheral blood in 81% of cases. On the other hand, multiple myeloma (MM) at diagnosis overexpress it in 63 of 94 (67%) cases (P=0.0001). In three secondary PCL evaluated serially, CD56 was also lacking at diagnosis showing that CD56 is not downregulated at the end stage of the disease but rather not upregulated in this subset of patients. This last concept is strengthened by the observation that 29% of MM patients lacking CD56 or weakly expressing it at diagnosis present a detectable leukemic phase vs 11% only in CD561 MM (P=0.06). Forty percent of all the CD56(-/weak) malignant plasma cell disorders present or develop a leukemic phase vs only 15% of CD56+ cases (P < 0.008). CD56(-/weak) MM subset is also associated with a significantly less aggressive osteolytic potential (P=0.012). We conclude that the lack or weak expression of CD56 is a characteristic feature of PCL but also delineates a special subset of MM at diagnosis mainly characterized by a lower osteolytic potential and a trend for malignant plasma cells to circulate in the peripheral blood more overtly.

Mcl-1 and Bcl-xL are co-regulated by IL-6 in human myeloma cells

Multiple myeloma (MM) is a slowly proliferative malignancy in which malignant plasma cells accumulate within the bone marrow. The expression of several anti-apoptotic proteins was evaluated by immunoblotting in human myeloma cell lines and in highly purified native myeloma cells. Expression of Bcl-xL, Mcl-1 and Bcl-2 was found in most of the samples; expression of Bcl-xL and Mcl-1 seemed to be related on myeloma cells. In a system of apoptosis by growth factor deprivation on myeloma cells, we showed that the effect of Bcl-2 seemed minimal whereas Mcl-1 and Bcl-xL were tightly regulated by interleukin (IL)-6. These findings underline the important role of Mcl-1 and Bcl-xL instead of Bcl-2 in IL-6-induced survival of myeloma cells.

A pivotal role for Mcl-1 in Bortezomib-induced apoptosis

Bortezomib is a proteasome inhibitor for the treatment of relapsed/refractory multiple myeloma (MM). Mechanisms of resistance to Bortezomib are undefined. Myeloid cell leukemia-1 (Mcl-1) is an antiapoptotic protein, which protects tumor cells against spontaneous and chemotherapy-induced apoptosis. In MM, specific downregulation of Mcl-1 induces apoptosis. Here, we examined the role of Mcl-1 in Bortezomib- and doxorubicin-induced apoptosis. We demonstrate that Bortezomib, but not doxorubicin, triggers caspase-dependent generation of a 28 kDa Mcl-1-fragment, in several MM cell lines, including MM.1S cells. Conversely, transient transfection of MM.1S cells with a previously reported 28 kDa Mcl-1(128-350) fragment, but not with the Mcl-1(1-127) fragment, induces apoptosis. Therefore, both downregulation of full-length antiapoptotic Mcl-1, as well as Bortezomib-induced generation of Mcl-1(128-350) cleaved protein, contribute to MM cell apoptosis. To verify further these findings, we next compared effects triggered by Bortezomib, doxorubicin and melphalan in Mcl-1(wt/wt) and Mcl-1(Delta/null) murine embryonic fibroblasts (MEFs). Our results show that Bortezomib, but not doxorubicin or melphalan, triggers Mcl-1 cleavage in Mcl-1(wt/wt), but not Mcl-1(Delta/null) MEFs and induces sub-G(1) phase cells; caspase-3 and -9, and PARP cleavage as well as morphological signs of apoptosis. Taken together, these results support an important role of Mcl-1 and a Mcl-1 fragment in Bortezomib-induced cell death in general, and in MM in particular. To prevent relapse of MM in patients treated with Bortezomib, we therefore recommend the combination of Bortezomib with agents that induce MM cell death independent of Mcl-1.

Plasma concentration of apolipoprotein E in intermediate-sized remnant-like lipoproteins in normolipidemic and hyperlipidemic subjects

Triglyceride-rich lipoprotein (TRL) remnants have been strongly implicated in the pathogenesis of atherosclerosis. To further investigate plasma remnant lipoprotein metabolism, we have determined the plasma concentration of apolipoprotein (apo) E (by polyclonal enzyme-linked immunoassay) in remnant-like lipoproteins, isolated by automated gel filtration chromatography as a fraction intermediate in size between VLDL and HDL. In normolipidemic subjects (n = 12), 1.2 +/- 0.11 mg/dL (33 +/- 2%, mean +/- SE) of total plasma apoE was associated with this fraction (termed ISL apoE). In hypercholesterolemic (type IIa, n = 12), hypertriglyceridemic (type IV, n = 12), and mixed hyperlipidemic (type IIb, n = 12) subjects, mean ISL apoE concentrations were 2.1 +/- 0.2, 2.5 +/- 0.2, and 3.8 +/- 0.4 mg/dL, respectively (P < .001 versus normal values) (45 +/- 2%, 32 +/- 2%, and 44 +/- 2% of total). ISL apoE was 8.7 +/- 1.4 mg/dL (42 +/- 3%) in type III dyslipidemic subjects (apoE2/2, n = 8). ISL apoE was positively correlated with plasma triglyceride (r = .41, P < .01), and at any given level of plasma triglyceride, subjects with an apoE2/2 or apoE3/2 phenotype tended to have a higher concentration of ISL apoE (P < .01) than apoE3/3 or E4/3 individuals. ISL apoE was also correlated (P < .001) with total plasma cholesterol (r = .66), TRL cholesterol (r = .49), TRL apoE (r = .47), LDL apoB (r = .42), and LDL+HDL triglyceride (r = .74). These results suggest that (1) a significant proportion of plasma apoE resides within an intermediate-sized remnant-like lipoprotein fraction in both normolipidemic and hyperlipidemic subjects; (2) plasma remnant lipoprotein accumulation is associated with an elevation in ISL apoE concentration; and (3) ISL apoE concentration is significantly correlated with various proatherogenic lipid parameters and may itself be a potentially important atherogenic index.

Mitochondria in hematopoiesis and hematological diseases

Mitochondria are involved in hematopoietic cell homeostasis through multiple ways such as oxidative phosphorylation, various metabolic processes and the release of cytochrome c in the cytosol to trigger caspase activation and cell death. In erythroid cells, the mitochondrial steps in heme synthesis, iron (Fe) metabolism and Fe-sulfur (Fe-S) cluster biogenesis are of particular importance. Mutations in the specific delta-aminolevulinic acid synthase (ALAS) 2 isoform that catalyses the first and rate-limiting step in heme synthesis pathway in the mitochondrial matrix, lead to ineffective erythropoiesis that characterizes X-linked sideroblastic anemia (XLSA), the most common inherited sideroblastic anemia. Mutations in the adenosine triphosphate-binding cassette protein ABCB7, identified in XLSA with ataxia (XLSA-A), disrupt the maturation of cytosolic (Fe-S) clusters, leading to mitochondrial Fe accumulation. In addition, large deletions in mitochondrial DNA, whose integrity depends on a specific DNA polymerase, are the hallmark of Pearson's syndrome, a rare congenital disorder with sideroblastic anemia. In acquired myelodysplastic syndromes at early stage, exacerbation of physiological pathways involving caspases and the mitochondria in erythroid differentiation leads to abnormal activation of a mitochondria-mediated apoptotic cell death pathway. In contrast, oncogenesis-associated changes at the mitochondrial level can alter the apoptotic response of transformed hematopoietic cells to chemotherapeutic agents. Recent findings in mitochondria metabolism and functions open new perspectives in treating hematopoietic cell diseases, for example various compounds currently developed to trigger tumor cell death by directly targeting the mitochondria could prove efficient as either cytotoxic drugs or chemosensitizing agents in treating hematological malignancies.

Farnesyl transferase inhibitor R115777 induces apoptosis of human myeloma cells

R115777, a nonpeptidomimetic farnesyl transferase inhibitor has recently demonstrated a significant antileukemic activity in vivo in acute myeloid leukemia. Multiple myeloma (MM) is a fatal hematological malignancy characterized by an accumulation of long-lived plasma cells within the bone marrow. In the present study, we have investigated the effect of the R115777 on growth and survival of myeloma cells. We have found that R115777 induced (1) a significant and dose-dependent growth inhibition of the three myeloma cell lines tested; and (2) a significant and time-dependent apoptosis. R115777 also induced apoptosis in the bone marrow mononuclear cell population of four MM patients, being almost restricted to the malignant plasma cells. Finally, we have investigated the effect of the R115777 in the Ras/MAPK and JAK/STAT pathways which are implicated in survival and/or proliferation in MM. The phosphorylation of both STAT3 and ERK1/2 induced by IL-6 was totally blocked at 15 microM of R115777 and partially blocked when R115777 was used at 10 and 5 microM. The induction of apoptosis by R115777 in myeloma cells and its implication in the regulation of JAK/STAT signalling suggest that R115777 might be an interesting therapeutical approach in MM.

The human cell surface glycoprotein complex (gp 120,200) recognized by monoclonal antibody K20 is a component binding to phytohaemagglutinin on T cells

Monoclonal antibody K20 recognizes a human glycoprotein complex that is not restricted to haematopoietic lineages but is preferentially expressed on early haematopoietic cells, T cells, and monocytes. This glycoprotein complex is made of a constant 120,000-140,000 Mr subunit noncovalently associated at the cell surface with subunits of higher Mr ranging from 150,000 to 200,000 on different cell types. Internal labelling with [35S]methionine and pulse-chase experiments revealed that in the cell the 120,000 Mr glycoprotein of this complex is also noncovalently associated with a 100,000 Mr glycoprotein, and that both glycoproteins are independently biosynthesized. This glycoprotein complex is shown by immunoprecipitation by lectin plus antilectin antibodies and by sequential immunoprecipitations to be one of the cell surface structures bound by phytohaemagglutinin on the surface of normal T cells.

Interactions between cancer-associated fibroblasts and tumor cells promote MCL-1 dependency in estrogen receptor-positive breast cancers

Selective inhibition of BCL-2 is expected to enhance therapeutic vulnerability in luminal estrogen receptor-positive breast cancers. We show here that the BCL-2 dependency of luminal tumor cells is nevertheless mitigated by breast cancer-associated fibroblasts (bCAFs) in a manner that defines MCL-1 as another critical therapeutic target. bCAFs favor MCL-1 expression and apoptotic resistance in luminal cancer cells in a IL-6 dependent manner while their own, robust, survival also relies on MCL-1. Studies based on ex vivo cultures of human luminal breast cancer tissues further argue that the contribution of stroma-derived signals to MCL-1 expression shapes BCL-2 dependency. Thus, MCL-1 inhibitors are beneficial for targeted apoptosis of breast tumor ecosystems, even in a subtype where MCL-1 dependency is not intrinsically driven by oncogenic pathways.

Differential expression of Bcl-2 in human plasma cell disorders according to proliferation status and malignancy

Multiple myeloma (MM) is a malignancy characterized by a very slow proliferation of malignant plasma cells leading to their accumulation within the bone marrow. This suggests that resistance to apoptosis may play a critical role both in the pathogenesis and resistance to treatment of MM. Bcl-2 is a key protein for the regulation of apoptosis. However, it has been shown that this protein also regulates the state of proliferation. In the current study, we show that malignant plasma cells from both the bone marrow and peripheral blood express high levels of Bcl-2 and are slowly proliferating cells. In contrast, myeloma cells from extramedullary sites (ie pleural effusion, ascitis, mammary and gastric plasmacytoma) express Bcl-2 weakly while being highly proliferative. Normal non-dividing bone marrow plasma cells express high levels of Bcl-2 protein. In contrast, four highly proliferative reactive plasmacytosis express weak levels of Bcl-2. We conclude that there is an inverse correlation between Bcl-2 expression and the proliferation rate of both normal and malignant plasma cells. These data may be explained by the double function of Bcl-2, ie its well known function as an anti-apoptotic molecule and its intriguing function as an inhibitory molecule of cell proliferation.

The gp 130 family cytokines IL-6, LIF and OSM but not IL-11 can reverse the anti-proliferative effect of dexamethasone on human myeloma cells

In order to understand the mechanisms supporting steroid escape in patients with multiple myeloma (MM), three IL-6 autocrine human myeloma cell lines, LP1, OPM2 and L363, have been treated with dexamethasone in the presence or absence of cytokines belonging to the gp 130 family: IL-6, LIF, OSM and IL-11. With pharmacological doses of dexamethasone, a dramatic growth arrest was observed in all the cell lines. IL-6 completely reversed this inhibition. Of note, this IL-6 induced reversion was still seen with very low amounts of IL-6 (12 pg/ml). Finally, whereas LIF and OSM had clear growth-promoting effects on OPM2 only, both cytokines (but not IL-11) reversed the dexamethasone-induced growth arrest in all the cell lines. Therefore the high levels of IL-6 (ng/ml) observed in the MM intermediate milieu and the putative presence of LIF and OSM can easily counteract the effects of dexamethasone in vivo.

Interferon alpha extends the survival of human myeloma cells through an upregulation of the Mcl-1 anti-apoptotic molecule

We have recently reported that Mcl-1, an anti-apoptotic member of the Bcl-2 family, is upregulated by interleukin (IL)-6 in human myeloma cells through the janus kinase/signal transducers and activators of transduction (JAK/STAT) pathway. In the current study, we have explored the effects of interferon (IFN)-alpha, a cytokine which has been shown to increase myeloma cell survival. Our results demonstrate that IFN-alpha potently upregulates Mcl-1 on both myeloma cell lines and purified native myeloma cells. Of note, this upregulation is not due to an induction of an IL-6 autocrine loop. Furthermore, we showed that IL-6 and IFN-alpha had no additive effect on Mcl-1 upregulation, suggesting that both cytokines act through a common mechanism. Finally, the analysis of signalling transduction pathways strongly suggests that Mcl-1 upregulation induced by IFN-alpha depends on STAT3 activation. Altogether, our data show that IFN-alpha has an IL-6-like effect on human myeloma cells and suggest that it could be deleterious in some patients.

p53 dysregulation in B-cell malignancies: More than a single gene in the pathway to hell

TP53 deletion or mutation is frequent in B-cell malignancies and is associated with a low response rate. We describe here the p53 landscape in B-cell malignancies, from B-Acute Lymphoblastic Leukemia to Plasma Cell Leukemia, by analyzing incidence of gain or loss of function of actors both upstream and within the p53 pathway, namely MYC, RAS, ARF, MDM2, ATM and TP53. Abnormalities are not equally distributed and their incidence is highly variable among malignancies. Deletion and mutation, usually associated, of ATM or TP53 are frequent in Diffuse Large B-Cell Lymphoma and Mantle Cell Lymphoma. MYC gain, absent in post-GC malignancies, is frequent in B-Prolymphocytic-Leukemia, Multiple Myeloma and Plasma Cell Leukemias. RAS mutations are rare except in MM and PCL. Multiple Factorial Analysis notes that MYC deregulation is closely related to TP53 status. Moreover, MYC gain, TP53 deletion and RAS mutations are inversely correlated with survival. Based on this landscape, we further propose targeted therapeutic approaches for the different B-cell malignancies.

High incidence of deletions but infrequent inactivation of the retinoblastoma gene in human myeloma cells

We have studied the retinoblastoma (RB-1) susceptibility gene status and pRB expression in 22 human myeloma cell lines (HMCL) and in 10 patients with advanced multiple myeloma (MM). Deletions of the RB-1 gene were observed in 81% (17/21) of the informative HMCL, regardless of their paracrine or autocrine interleukin-6 (IL-6) status. Among the deleted HMCL, only one (U266) had a biallelic deletion and lacked pRB expression. Monoallelic deletions had no consequence on the RB-1 gene activation and pRB expression. One patient of 10 presented the same biallclic deletion as U266 and six of 10 had monoallelic deletions. We conclude that monoallelic deletions of the RB-1 gene are frequent in HMCL and MM patients but have no consequence on gene activation and pRB expression.

The retinoblastoma susceptibility gene RB-1 in multiple myeloma

Genetic mechanisms leading to the development of multiple myeloma (MM) remain poorly understood. Given the frequency of chromosome 13 deletion in MM and the localization in 13q14 of the retinoblastoma susceptibility gene RB-1, an involvement of RB-1 in MM pathogenesis has been proposed. Moreover, interleukin-6 (IL-6) has been shown to be the main growth factor for MM in vitro and in vivo. The product of the RB-1 gene (pRB) can down-regulate IL-6 gene expression. Absence of pRB may then induce an autocrine IL-6 expression in myeloma cells and contribute to the autonomous growth of MM. As assessed in this review, heterozygous deletion of RB-1 is very common in MM but does not alter gene transcription and protein expression. Nevertheless, homozygous deletion of RB-1 has been identified in some MM patients with advanced disease and in the IL-6-autocrine human myeloma cell line U266. Thus, even if inactivation of RB-1 appears to be only a rare and late oncogenic event in MM and is not likely to represent the main mechanism involved in IL-6 up-regulation in MM, definitive assessment of the actual role played by RB-1 in MM pathogenesis still needs further investigation particularly the examination of pRB function.

Soluble IL-6R alpha upregulated IL-6, MMP-1 and MMP-2 secretion in bone marrow stromal cells

IL-6 mediates its activity through a cell surface receptor composed of a signal transducing protein, CD130, and a ligand-binding protein which exists in membrane-bound form (CD126) or in soluble form (sIL-6R alpha). Interestingly, sIL-6R alpha combined with IL-6 is able to interact with CD130 leading to the intracellular cascade of activation. In the present study, using flow cytometry, we show that stromal cells from human bone marrow (BMSC) express CD130 but not CD126. We demonstrate that BMSC are responsive to IL-6 only in the presence of exogenous sIL-6R alpha. Indeed, exogenous sIL-6R alpha induces in BMSC the production of its own ligand, IL-6, and of both MMP-1 and MMP-2, two matrix metalloproteinases involved in bone resorption and in tumour spreading, respectively. Since myeloma cells release sIL-6R alpha in the close vicinity of BMSC, these data suggest a role for this factor in the pathophysiology of multiple myeloma, a B-cell malignancy dependent on IL-6 for its growth and characterized by bone destruction.

IL-6 upregulates its own receptor on some human myeloma cell lines

Interleukin 6 (IL-6) is the major survival factor of myeloma cells. In this study, we demonstrate that IL-6, oncostatin M (OSM) and leukemia inhibitory factor (LIF) upregulate membrane IL-6 receptor alpha (IL-6Ralpha) on OPM-2 myeloma cell line at transcriptional level. In OPM-2 cells, IL-6, OSM and LIF induce both signal transducers and activators of transcription (STAT), mitogen activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI 3-K) activation. We show that the cytokine-induced upregulation of IL-6Ralpha can be abolished by a janus kinase (JAK)-2 specific inhibitor, i.e. AG490, suggesting an involvement of the JAK/STAT pathway in this process. Finally, IL-6Ralpha upregulation was also inhibited by wortmannin, an inhibitor of the PI 3-kinase pathway. In conclusion, IL-6 can upregulate its own receptor on OPM-2 cells probably through the JAK/STAT and PI 3-kinase pathways.