p38MAP kinase is a negative regulator for ERK1/2-mediated growth of AIDS-associated Kaposi's sarcoma cells.

AIDS-associated Kaposi's sarcoma (KS) is a cytokine-mediated tumor, at least in the early stages of this disease; however, there is at present no definitive consensus regarding the exact role of intracellular signaling pathways involved in growth of KS cells. We found that KS cell growth factors oncostatin M, sIL-6R/IL-6, TNFalpha, and IL-1beta all activate ERK1/2, and selective blockage of this kinase by PD98059 resulted in a profound inhibition of the cytokine-induced KS cell growth. Concurrently with activation of ERK1/2, these growth factors phosphorylated and activated p38MAPK. The selective inhibition of p38MAPK by SB203580 prominently enhanced the cytokine-induced proliferation of KS cells, thereby indicating that p38MAPK has a negative feedback on mitogenic signals. As these KS cell growth factors lead to simultaneous activation of ERK1/2 and p38MAPK signaling pathways, the concerted effects of these kinase activities may well determine the intensity of cellular proliferative responses to these growth factors.

Oncostatin M (OM) promotes the growth of DU 145 human prostate cancer cells, but not PC-3 or LNCaP, through the signaling of the OM specific receptor.

BACKGROUND: Oncostain M (OM) is a member of the interleukin-6 (IL-6) cytokine family and all members utilize gp130 as a common signal transducing receptor. Tyrosine phosphorylation of the transcription factor STAT3 plays an important role in IL-6 cytokine family-mediated reactions. OM signals are transduced through two different OM receptor complexes: a leukemia inhibitory factor (LIF)/OM receptor (a heterodimer of LIFR beta and gp130) and an OM specific receptor (a heterodimer of OMR beta and gp130). This study examined the expression of these two OM receptors as well as the effect of OM on the growth of prostate carcinoma cell lines. MATERIALS AND METHODS: PC-3, DU 145 and LNCaP cells were used. The expression of OMR beta and LIFR beta was determined by RT-PCR. Tyrosine phosphorylation of STAT3 was analyzed by Western blotting. RESULTS: OM promoted the growth of DU 145 but not that of PC-3 and LNCaP. LIF had no effect on the growth of any of these cell lines. DU 145 and PC-3 expressed much higher levels of OMR beta mRNA than those of LIFR beta mRNA. Neither OMR beta nor LIFR beta mRNA was detected in LNCaP. OM, but not LIF, induced rapid tyrosine phosphorylation of STAT3 in DU 145. PC-3 lacked STAT3 expression. CONCLUSIONS: OM has been known to be a cytostatic cytokine for tumor cells. Conversely, we show that OM promotes the growth of DU 145. Further, our findings suggest that the growth-promoting signals of OM is mediated through the OM specific receptor with subsequent activation of STAT3.

Sensitization of AIDS-Kaposi's sarcoma cells to Apo-2 ligand-induced apoptosis by actinomycin D.

Kaposi's sarcoma (KS) is the most frequent malignancy associated with HIV infection (AIDS-KS), a complication that leads to high mortality and morbidity. AIDS-KS cells are resistant to killing by chemotherapeutic drugs/NK cells and Fas-induced apoptosis, suggesting that the acquisition of antiapoptotic characteristics by AIDS-KS cells may contribute to their prolonged survival. Apo-2 ligand (Apo-2L)/TNF-related apoptosis-inducing ligand, a new member of the TNF family, has been identified as an apoptosis-inducing molecule. In this study we examined the sensitivity of 10 different AIDS-KS isolates to Apo-2L-mediated cytotoxicity. AIDS-KS cells were relatively resistant to Apo-2L; however, Apo-2L and actinomycin D (Act D) used in combination synergistically potentiated the induction of cell death in nine of the 10 isolates. Apo-2L induced apoptosis in >80% of AIDS-KS cells pretreated with Act D. The caspase inhibitors, zIETD-fmk and zDEVD-fmk, inhibited apoptosis in AIDS-KS by sApo-2L, suggesting that caspase 3-like and caspase 8 or 10 activities are essential for Apo-2L-mediated apoptosis. Act D treatment of AIDS-KS cells markedly and selectively down-regulated Bcl-xL expression, while the expressions of decoy receptors 1 and 2, Bax, cellular FLICE (Fas-associated death domain protein-like IL-1-converting enzyme) inhibitory protein, FADD (Fas-associated death domain protein), procaspase 8, and p53 were not affected. These findings suggest the possible involvement of Bcl-xL in Act D-induced sensitization of AIDS-KS cells to Apo-2L-mediated apoptosis. Furthermore, Act D did not sensitize PBMC or fibroblast cells to Apo-2L. Thus, Apo-2L and Act D used in combination may be of therapeutic value in the treatment of AIDS-KS.

Interleukin-6 induces G1 arrest through induction of p27(Kip1), a cyclin-dependent kinase inhibitor, and neuron-like morphology in LNCaP prostate tumor cells.

Prostate carcinoma cells express high levels of interleukin-6 (IL-6) and IL-6 receptor. In this study, we examined the effect of IL-6 on LNCaP human prostate carcinoma cells. IL-6 induces G1 growth arrest of LNCaP. Following IL-6 treatment of LNCaP, Western blot analysis showed that the protein levels of cyclin-dependent kinase-2 (CDK2), CDK4, and CDK6 were decreased, while accumulation of CDK inhibitor p27(Kip1) was rapidly and markedly induced. In vitro kinase assays revealed that the CDK-associated histone H1 and CDK4- and CDK6-associated pRb kinase activities were significantly inhibited in IL-6-treated LNCaP. Further, a significant amount of p27(Kip1) was co-precipitated with CDK2, CDK4 and CDK6, as detected in immunoprecipitation experiments. Thus, IL-6-induced G1 arrest appears to be due to the accumulation of p27(Kip1). In addition, IL-6-treated LNCaP cells induced neuron-like morphological changes. Since neuroendocrine differentiation is observed in most prostate carcinomas, these findings raise the possibility that IL-6 may be involved in neuroendocrine differentiation in vivo.

Implication of TNF receptor-I-mediated extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation in growth of AIDS-associated Kaposi's sarcoma cells: a possible role of a novel death domain protein MADD in TNF-alpha-induced ERK1/2 activation in Kaposi's sarcoma cells.

TNF-alpha is a key pathogenic mediator of infectious and inflammatory diseases. HIV infection stimulates and dysregulates the immune system, leading to abnormal production of TNF-alpha. Despite its cytotoxic effect on some tumor cell lines, TNF-alpha functions as a growth stimulator for Kaposi's sarcoma (KS), a common malignancy in HIV-infected patients. However, signaling pathways linked to TNF-alpha-induced mitogenic responses are not well understood. We found that extracellular signal-regulated kinases 1 and 2 (ERK1/2) in KS cells were significantly activated by TNF-alpha through tyrosine/threonine phosphorylation. Using neutralizing anti-TNFR-I and TNFR-II mAbs, we have now obtained evidence that TNF-alpha-induced KS cell growth and ERK1/2 activation are mediated exclusively by TNFR-I, not by TNFR-II. A selective inhibitor for ERK1/2 activator kinases, PD98059, profoundly inhibited not only the activation of ERK1/2, but also the TNF-alpha-induced KS cell proliferation. We therefore propose that the TNFR-I-ERK1/2 pathway plays a pivotal role in transmitting to KS cells the mitogenic signals of TNF-alpha. TNFR-I possesses no intrinsic kinase activity, suggesting that TNFR-I-associated proteins may provide a link between TNFR-I and ERK1/2 activation. We found that actinomycin D treatment of KS cells selectively abolished expression of mitogen-activated protein kinase-activating death domain protein (MADD), a novel TNFR-I-associated death domain protein. TNF-alpha failed to induce ERK1/2 activation in the actinomycin D-treated cells. MADD may couple TNFR-I with the ERK1/2 signaling pathway required for KS cell proliferation.

Endogenous basic fibroblast growth factor is essential for cyclin E-CDK2 activity in multiple external cytokine-induced proliferation of AIDS-associated Kaposi's sarcoma cells: dual control of AIDS-associated Kaposi's sarcoma cell growth and cyclin E-CDK2 activity by endogenous and external signals.

AIDS-associated Kaposi's sarcoma (KS) cell, a key element for development of KS lesions, proliferates in response to external cytokines, such as oncostatin M, the soluble IL-6R-IL-6 complex, TNF-alpha, and IL-1beta. In addition, the KS cell-produced basic fibroblast growth factor (bFGF) was reported to function as an autocrine growth factor. However, little is known of the exact roles of these external growth factors and endogenous bFGF on proliferation of KS cells, and underlying intracellular events have remained to be defined. We obtained evidence that anti-bFGF Ab abolished growth of KS cells by preventing S phase entry of the cell cycle, even in the presence of the external growth factors. Blockade of the FGF action profoundly inhibited cyclin E expression and cyclin-dependent kinase-2 (CDK2) activity, but not D-type cyclin expression and CDK4 activity. Exogenously added acidic FGF (aFGF), which generated a rapid tyrosine phosphorylation of FGFR1 and FGFR2 on KS cells, reversed the inhibitory effects of anti-bFGF Ab. Thus, FGF actions are essential for cyclin E-CDK2 activity and S phase entry. We also observed that the presence of external growth factors markedly induced cyclin E-CDK2 activity and S phase entrance, while the addition of aFGF or bFGF alone was insufficient to induce these responses. All this evidence shows that integration of the activities of external growth factors and endogenous bFGF is required for full activation of cyclin E-CDK2 activity and KS cell proliferation.

Differential regulation of human NK cell-associated gene expression following activation by IL-2, IFN-alpha and PMA/ionomycin.

Natural killer (NK) cells are important in host-defense mechanisms against infection and cancer and also participate in regulation of the immune response. The functions of NK cells as well as their maturation and differentiation are regulated by various stimuli such as interleukin-2 (IL-2) and interferon-alpha (IFN-alpha). The mechanisms by which these stimuli regulate distinct NK functions are not known. This study compared the patterns of gene expression for several NK-associated genes namely perforin (PEF), granzymes A and B (GA or B), IL-1beta, IFN-gamma, tumor necrosis factor-alpha (TNF-alpha), CD16 and NK-specific genes, NKG2A, NKG5 and NKG7 in both unstimulated and in IL-2-, IFN-alpha and PMA/Ionomycin (PMA/I)-stimulated NK cells purified from human peripheral blood. IFN-alpha enhanced mRNA expression for PEF, IFN-gamma, TNF-alpha and NKG2A, but did not affect NKG7 mRNA expression. IL-2 augmented mRNA expression for PEF, IFN-gamma, TNF-alpha, NKG2A and NKG7. PMA/I increased mRNA expression for IFN-gamma, TNF-alpha and NKG2A but did not affect mRNA expression for PEF and NKG7. Further, PMA/I inhibited the expression of CD16 mRNA. These findings demonstrate that the three NK-stimuli used share in common the regulation of several genes but each regulates specifically other genes. These findings suggest that stimuli-specific expression of NK-associated genes may underlie the molecular mechanisms responsible for distinct NK-mediated activities induced by different stimuli.

Dexamethasone enhances expression of membrane and soluble interleukin-6 receptors by prostate carcinoma cell lines.

BACKGROUND: Primary prostate carcinoma cells constitutively secrete interleukin-6 (IL-6), and high levels of IL-6 receptor are detected in prostate carcinoma tissues. These findings have implicated IL-6 in the growth and differentiation of prostate carcinomas. Herein, we examined the regulation of IL-6 receptor complex (IL-6R alpha/gpl30) in prostate carcinoma cell lines. We also analyzed the production of soluble IL-6R alpha (IL-6sR) because IL-6sR can confer the IL-6 responsiveness on IL-6R alpha-lacking cells. MATERIAL AND METHODS: Three established prostate carcinoma cell lines, PC-3, DU 145 and LNCaP, were analyzed. Protein tyrosine-phosphorylation was detected by immunoblotting. The expression of IL-6R alpha, gpl30 and IL-6sR was determined by RT-PCR, flow cytometry and ELISA. RESULTS: IL-6 induced tyrosine-phosphorylated proteins in LNCaP but not in PC-3 or DU 145, indicating that LNCaP cells express the functional IL-6 receptor. Dexamethasone (Dex)-treatment induced functional IL-6 receptors on DU 145 and PC-3 through upregulation of IL-6R alpha and gpl30. In addition, LNCaP, Dex-treated PC-3 and Dex-treated DU 145 secreted large amounts of IL-6sR. CONCLUSIONS: The expression of IL-6 receptor by prostate carcinoma cell lines was augmented by glucocorticoid. We propose prostate carcinomas as IL-6sR producing tumors, and IL-6sR may modulate the behavior of not only the tumor cells but also the surrounding cells.

The participation of the Fas-mediated cytotoxic pathway by natural killer cells is tumor-cell-dependent.

Cytotoxic T lymphocytes and natural killer (NK) cells kill target cells by two main mechanisms, namely, the perforin/granzymes and the Fas ligand (Fas-L) pathways. The preferential activation of either of these two mechanisms by target cells is not known. This study examined whether various NK stimuli regulate preferentially the perforin/granzyme or the Fas pathways during the NK-cell-mediated cytotoxic reaction (NK-CMC). Purified peripheral-blood-derived NK cells were stimulated with interleukin-2 (IL-2), IL-12, or interferon alpha (IFN alpha) and their response was analyzed by the reverse transcriptase/polymerase chain reaction (RT-PCR) for NK-associated gene expression and by the 51Cr-release assay for cytotoxic function. RT-PCR data revealed that the perforin, granzyme A and granzyme B mRNAs were constitutively expressed in unstimulated NK cells and the level of perforin mRNA was augmented following activation. IL-2 enhanced the level of Fas-L mRNA in NK cells; however, the Fas-L level was much lower than that obtained in activated T cells. NK-CMC against Fas-sensitive cells was examined in the presence of neutralizing anti-(Fas antigen receptor) (Fas-R) antibody (ZB-4) or EGTA/Mg2+, which inhibits the perforin/granzyme pathway but not the Fas Fas-L interaction. The human colon adenocarcinoma HT-29 cells were sensitized to anti-Fas-R antibody (CH-11) cytotoxicity following treatment with IFN gamma. NK-CMC against untreated HT-29 cells was completely inhibited by EGTA/Mg2+ and was unaffected by ZB-4, while both EGTA/Mg2+ and ZB-4 partially inhibited NK-CMC against IFN gamma-treated HT-29 cells. Similar findings to those obtained with untreated NK cells were observed with NK cells stimulated with IL-2, IL-2 plus IL-12 or IFN alpha. In contrast to IFN gamma-treated HT-29 cells, the neutralizing anti-Fas antibody ZB-4 did not inhibit NK-CMC against Fas-sensitive U937, CEM or Jurkat tumor cells. These findings demonstrate that the Fas pathway is involved in NK-CMC against certain target cells but not all. Further, the data demonstrate that activation of NK cells by IL-2, IL-2 plus IL-12 or IFN alpha does not preferentially modulate the Fas-L-mediated killing by NK cells.

Enhancement of gp130-mediated tyrosine phosphorylation of STAT3 and its DNA-binding activity in dexamethasone-treated AIDS-associated Kaposi's sarcoma cells: selective synergy between dexamethasone and gp130-related growth factors in Kaposi's sarcoma cell proliferation.

The soluble IL-6R (slL-6R alpha)/IL-6 complex and oncostatin M (OM), which exert biologic activities through the signal-transducing protein gp130, are potent growth factors for AIDS-associated Kaposi's sarcoma (KS) cells. Clinical observations indicate that glucocorticoid therapy is a possible risk factor in KS; however, little is known of specific interactions in KS cells between glucocorticoid and gp130-related growth factors. We obtained evidence that dexamethasone (Dex), in a synergistic manner, enhances gp130-mediated growth of KS cells. Anti-gp130 Abs or the glucocorticoid antagonist RU-486 abolished this synergistic effect. In addition, Dex had additive but not synergistic effects on stimulation of KS cell growth with IL-1beta or TNF-alpha, the signals of which are not mediated through gp130. Immunoblot analysis revealed sIL-6R alpha/IL-6- or OM-induced tyrosine phosphorylation of a similar set of proteins in KS cells, and which was augmented significantly in Dex-treated KS cells. Stimulation of KS cells with sIL-6R alpha/IL-6 or OM induced rapid tyrosine phosphorylation of the transcription factor STAT3, and Dex significantly enhanced the accumulation of tyrosine-phosphorylated STAT3. Electrophoretic mobility shift assays showed sIL-6R alpha/IL-6- or OM-induced DNA-binding activity of STAT3 in KS cells, and Dex further increased this activity. Thus, Dex appears to participate in the gp130-STAT3 signaling and transcriptional events by enhancing STAT3 activation, thereby leading to selective synergistic stimulation of KS cell growth with Dex and the gp130-related growth factors.

Vascular endothelial growth factor is a potent angiogenic factor in AIDS-associated Kaposi's sarcoma-derived spindle cells.

Angiogenesis is one of the most important features of AIDS-associated Kaposi's sarcoma (AIDS-KS). Our studies suggested that spindle-shaped AIDS-KS cells from various AIDS-KS lesions play important roles in the development of KS lesions. Basic fibroblast growth factor (bFGF) has been reported to be a predominant angiogenic factor expressed in AIDS-KS cells. However, our data from ELISA revealed the presence of the vascular endothelial growth factor (VEGF) molecule in large quantities in AIDS-KS cell-derived conditioned medium (AIDS-KS-CM) (12.1-21.4 ng/ml). In contrast, small amounts of bFGF were detected in AIDS-KS-CM (76-245 pg/ml). The combination of anti-VEGF and anti-bFGF IgGs completely inhibited endothelial cell growth-promoting activities in AIDS-KS-CM, while activities partially remained in the presence of anti-bFGF IgG or anti-VEGF IgG alone. VEGF and bFGF in AIDS-KS-CM were distinguished by heparin-affinity chromatography. Furthermore, the combination of VEGF and bFGF synergistically augmented the growth of endothelial cells. Both VEGF and bFGF revealed an angiogenic property that was inhibited by specific Abs, when applied to the rabbit cornea and chicken chorioallantoic membrane. On Western blots, anti-VEGF IgG gave two major bands of 22 and 24 kDa, similar to those of recombinant VEGF165. As detected on Northern blots, AIDS-KS cells expressed major 3.9-kb VEGF-specific mRNA. Thus, VEGF, in concert with bFGF, may play a crucial role in the angiogenesis of AIDS-KS lesions.

Short report: herpes-like DNA sequences in African-endemic and acquired immunodeficiency syndrome-associated Kaposi's sarcoma.

Recently, the unique nucleic acid closely related to the herpes-like sequences has been found in acquired immunodeficiency syndrome (AIDS)-associated Kaposi's sarcoma (KS). We have confirmed the presence of herpes-like DNA sequences in six cases of AIDS-associated KS and three of the nine cases of African-endemic KS in adults, but not in eight cases of KS in children from the same area. These sequences were seen in a histologically early stage of KS. Our results suggest that herpes-like DNA sequences may play an important role in the pathogenesis of AIDS-associated KS.

Resistance of AIDS-associated Kaposi's sarcoma cells to Fas-mediated apoptosis.

Escape of tumor cells from apoptotic-mediated stimuli results in tumor cell survival and resistance to cytotoxic mechanisms. Kaposi's sarcoma (KS) is the most common malignancy associated with AIDS, although its pathogenesis is not known. It is clinically important to determine whether AIDS-KS cells are resistant to apoptosis via the Fas system. Three isolates of AIDS-KS cells were studied. Although all KS cells express Fas on the cell surface, these cells were resistant to cytotoxic anti-Fas antibody (IgM, CH-11). Treatment of AIDS-KS cells with actinomycin D sensitized the tumor cells to anti-Fas cytotoxicity and apoptosis. Apoptosis was assessed by morphological changes and DNA fragmentation analysis. Three possible mechanisms related to AIDS-KS cells, resistance to anti-Fas cytotoxicity were examined. First, synthesis and secretion of soluble Fas by the tumor cells can neutralize antibody-induced cytotoxicity. However, none of the three types of KS cells expressed soluble Fas mRNA as determined by reverse transcription (RT)-PCR. Second, the expression of the proto-oncogene bcl-2 can protect cells from apoptotic signals. Analysis of bcl-2 mRNA by RT-PCR revealed that all three AIDS-KS cells express very low levels of bcl-2 mRNA. Third, the Fas-associated phosphatase-1 (FAP-1) is an antiapoptotic molecule reported to interact with Fas and can block transduction of the apoptotic signal. RT-PCR analysis revealed that all three types of AIDS-KS cells express high levels of FAP-1 mRNA, and treatment of KS cells with actinomycin D reduced the levels of FAP-1 mRNA significantly. These findings demonstrate that AIDS-KS cells are resistant to Fas-mediated apoptosis and suggest that FAP-1 may be involved in the acquisition of resistance of AIDS-KS to anti-Fas antibody-mediated apoptosis.

The soluble form of the IL-6 receptor (sIL-6R alpha) is a potent growth factor for AIDS-associated Kaposi's sarcoma (KS) cells; the soluble form of gp130 is antagonistic for sIL-6R alpha-induced AIDS-KS cell growth.

Kaposi's sarcoma (KS) is most frequently associated with HIV-infected individuals (AIDS-KS). While AIDS-KS-derived spindle cells (AIDS-KS cells) contribute to the development of KS lesions, growth regulation of these cells in vivo is poorly understood. AIDS-KS cells express considerable amounts of the signal transducing subunit (gp130) of the IL-6 receptor, but only a scanty amount of its binding subunit (IL-6R alpha). This phenotype can account for the lack of IL-6 responsiveness of AIDS-KS cells. We now report that the soluble form of IL-6R alpha (sIL-6R alpha), lacking transmembrane and cytoplasmic regions, functions as a potent growth factor for AIDS-KS cells by making these cells responsive to IL-6. After exposure to sIL-6R alpha together with IL-6 in culture, AIDS-KS cells assumed a spindle-shaped morphology and showed a remarkable augmentation of growth, while IL-6 alone did not induce AIDS-KS cell growth. Even without the addition of IL-6, sIL-6R alpha induced significant growth levels of AIDS-KS cells. Since AIDS-KS cells express high levels of IL-6, it is likely that, in the presence of sIL-6R alpha, these cells acquire an IL-6 autocrine growth loop. Anti-gp130 antibodies blocked the action of sIL-6R alpha on AIDS-KS cells; hence, we refer to sIL-6R alpha as a gp130-related AIDS-KS cell growth factor. In contrast, the soluble form of gp130 (sgp130) had inhibitory effects on AIDS-KS cell growth, thereby suggesting that a complex regulatory system is involved in the modulation of the gp130-mediated AIDS-KS cell growth. In recent years, soluble forms of IL-6R alpha and gp130 have been detected in the sera of healthy individuals and increased levels of sIL-6R alpha as well as IL-6 have been noted in the sera of HIV-infected patients. It seems reasonable to assume that perturbed production of sIL-6R alpha and sgp130 may play a crucial role in the development and regression of AIDS-KS lesions by directly acting on growth of KS cells through the gp130-mediated pathway.

AIDS-associated Kaposi's sarcoma (KS) cells express oncostatin M (OM)-specific receptor but not leukemia inhibitory factor/OM receptor or interleukin-6 receptor. Complete block of OM-induced KS cell growth and OM binding by anti-gp130 antibodies.

Oncostatin M (OM), which shares functional similarity and structural homology to leukemia inhibitory factor (LIF) and interleukin-6 (IL-6), functions as a potent growth factor for AIDS-associated Kaposi's sarcoma-derived cells (AIDS-KS cells). OM was also suggested to bind to the LIF receptor (LIF/OM receptor), which consists of a signal transducing subunit for LIF and IL-6 (gp130) and a LIF receptor alpha-subunit. Recent studies indicate that IL-6 has growth-stimulating activity for AIDS-KS cells. However, we find that AIDS-KS cell growth is exclusively induced by OM and not by LIF or IL-6. We also observed the lack of binding properties of AIDS-KS cells for LIF and IL-6. Scatchard plots revealed the existence of two affinity classes of OM receptor sites on AIDS-KS cells, with Kd values of 6-12 pM (high affinity) and 521-815 pM (low affinity). In competition binding studies, we find that the OM-specific receptor, but not the LIF/OM receptor, contributes to the OM-specific growth stimulation of AIDS-KS cells. We also noted that anti-gp130 antibodies can completely abolish OM-induced growth stimulation of AIDS-KS cells as well as OM binding to AIDS-KS cells. PCR amplification clearly revealed high levels of gp130 expression in AIDS-KS cells, while the transcript of LIF receptor alpha-subunit or IL-6 receptor alpha-subunit was not observed. Therefore, we conclude that (a) AIDS-KS cells express the OM-specific receptor with high and low affinity, but not the LIF/OM receptor; (b) gp130 on AIDS-KS cells plays a key role in OM binding and signaling on the OM-specific receptor; and (c) the lack of biological response of AIDS-KS cells to IL-6 and LIF can be explained by the absence of the IL-6 and LIF/OM receptors. All this evidence shows the correlation of OM-specific biological activity with expression of the OM-specific receptor and the involvement of gp130 on this receptor, as based on findings in in vitro growth assays and binding experiments for AIDS-KS cells.