Interleukin-6 activates phosphatidylinositol-3 kinase, which inhibits apoptosis in human prostate cancer cell lines

BACKGROUND. A number of recent studies have identified interleukin (IL)- 6 as an important regulator of prostate cancer growth. Here, we investigate the potential interaction of IL-6 with phosphatidylinositol (PI)-3 kinase, a key growth regulatory enzyme, in prostate cancer cell lines. METHODS. Tyrosine phosphorylation of p85, the regulatory subunit of PI-3 kinase, in the human prostate cancer cell lines LNCaP and PC-3 was assessed by sequential immunoprecipitation with anti-p85 antibody and immunoblotting with anti-phosphotyrosine. The effects of wortmannin, an inhibitor of PI-3 kinase, and/or IL-6 on cell growth were assessed by MTT assays. DNA laddering experiments were performed to assay for programmed cell death. RESULTS. Tyrosine phosphorylation of p85 is upregulated by IL-6 in both LNCaP and PC- 3. IL-6 promotes coprecipitation of p85 with gp130, the signal-transducing component of the IL-6 receptor. Inhibition of PI-3 kinase with wortmannin induces programmed cell death in PC-3 cells. In contrast, wortmannin has no effect on LNCaP growth when used alone; however, combined with IL-6, wortmannin promotes apoptosis in these cells. CONCLUSIONS. PI-3 kinase is involved in IL-6 signal transduction and delivers an anti-apoptotic signal in human prostate cancer cell lines.