AIDS-associated Kaposi's Sarcoma Cells Research Articles

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, TNFα, and IL-1β 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.

A possible role of multidrug resistance-associated protein (MRP) in basic fibroblast growth factor secretion by AIDS-associated Kaposi's sarcoma cells: a survival molecule?

Kaposi's sarcoma (KS) is considered a disorder of cytokines. Basic fibroblast growth factor (bFGF) is produced by AIDS-associated KS (AIDS-KS) cells and supports their growth in an autocrine and paracrine manner. bFGF lacks a signal sequence; therefore, its mechanism of secretion is unclear. In this study, we investigate the role of two important members of ATP-binding cassette transport proteins, the P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP), in the secretion of bFGF from AIDS-KS cells. Expression of P-gp and MRP was examined at both the protein and the mRNA levels by flow cytometry and RT-PCR respectively. Intracellular and secreted bFGF was measured by ELISA. AIDS-KS cells expressed MRP at both the mRNA and the protein levels; however, no P-gp expression was detected at either the mRNA or the protein level. Probenecid, a putative inhibitor of MRP efflux function, in a concentration-dependent manner, inhibited bFGF secretion, with a concomitant increase in intracellular bFGF, demonstrating that probenecid blocks bFGF secretion without inhibiting its synthesis. In addition, probenecid induced apoptosis in AIDS-KS cells. AIDS-KS cells expressed fas, bcl-2, and bcl-xL genes but lacked fasL and bax gene expression. These data suggest that bFGF is secreted from AIDS-KS cells via a probencid-sensitive transporter, most likely in MRP. Furthermore, probenecid appears to induce apoptosis in AIDS-KS cells by depriving them of the growth promoting activity of bFGF. These data suggest that MRP may play a role as a survival molecule in AIDS-KS 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.

AIDS-associated kaposi's sarcoma cells in culture express vascular endothelial growth factor

PCR cloning and cDNA sequencing have been used to identify mRNAs of two splice products of the vascular endothelial growth factor (VEGF) gene, VEGF121 and VEGF165, in cells isolated from Kaposi's sarcomas (KS) of AIDS patients (AIDS-KS). As demonstrated by Northern blot analysis, AIDS-KS cells as well as tumor cells show a high expression level of the VEGF gene as compared to primary human vascular cells like smooth muscle cells or endothelial cells. In addition to the lower expression of the gene, vascular cells express a 3.9 kb band together with a 3.2 kb band instead of a 3.9 kb and a 4.3 kb band in AIDS-KS cells. Our data suggest that the angiogenic properties of AIDS-KS cells might be mediated by the secretion of this growth factor and that this factor alone or in combination with other endothelial mitogens may be involved in endothelial proliferation associated with Kaposi's sarcoma.