Suppressor of cytokine signalling-3 is up-regulated by androgen in prostate cancer cell lines and inhibits androgen-mediated proliferation and secretion.

Suppressors of cytokine signalling (SOCS) are induced by interleukins (ILs) and various peptide hormones and may prevent sustained activation of signalling pathways. We have previously shown that SOCS-3 antagonizes regulation of cellular events by cAMP and is expressed in human prostate cancer. To investigate possible effects of androgen on SOCS-3 protein expression, two prostate cancer cell lines (PC3-AR and LAPC4) were treated with different concentrations of R1881. Western blot analyses revealed induction of SOCS-3 protein expression in both cell lines by androgen, an effect which can be blocked by the anti-androgen bicalutamide. To further characterize the effects of R1881 on the SOCS-3 gene, promoter-reporter assay and real-time PCR were performed. We found no influence of androgen on promoter activity or SOCS-3 mRNA levels, thus suggesting a post-transcriptional effect of androgen. Concordant with our previous findings, we show a significant increase of SOCS-3 protein after androgen treatment in cells in which transcription was blocked, but not in those with impaired translation. In order to understand implications of SOCS-3 regulation by androgen, we used SOCS-3-negative LNCaP-IL-6 cells and stably transfected them with a tetracycline-responsive SOCS-3 Tet-On plasmid. We report that androgenic effects on cell proliferation and prostate-specific antigen secretion are significantly diminished following up-regulation of SOCS-3. In conclusion, androgen up-regulates SOCS-3 protein via post-transcriptional effects. SOCS-3 inhibits androgen-stimulated proliferation by influencing cell cycle regulation. Taken together with previous findings showing androgen receptor activation by IL-6, our results imply that androgen and cytokine signalling pathways interact at multiple levels in prostate cancer.