CYCLIC-AMP INDUCES TRANSFORMING GROWTH-FACTOR-BETA-2 GENE-EXPRESSION AND GROWTH ARREST IN THE HUMAN ANDROGEN-INDEPENDENT PROSTATE CARCINOMA CELL-LINE PC-3

The standard therapy for advanced prostate cancer is androgen ablation. Despite transitory responses, hormonally treated patients ultimately relapse with androgen-independent disease that is resistant to further hormonal manipulation and cytotoxic chemotherapy. To develop an additional approach to the treatment of advanced prostate cancer, we have been studying the signal transductions controlling the growth of human androgen-independent prostate carcinoma cell lines. We report here that elevation of intracellular cAMP markedly inhibits the growth of the hormone-refractory cell line PC-3. To examine the mechanism of cAMP action in PC-3 cells, we tested the effect of the cAMP analog dibutyryl cAMP (Bt2-cAMP) on the regulation of the potent negative growth factor transforming growth factor-beta (TGF-beta). Bt2-cAMP selectively induced the secretion of TGF-beta-2 and not TGF-beta-1 by PC-3 cells. This TGF-beta-2 was shown to be bioactive by using the CCL-64 mink lung cell assay. TGF-beta-1 was not activated despite being present at 3-fold higher concentrations than TGF-beta-2. Northern analysis showed that Bt2-cAMP induced an increase in the five characteristic TGF-beta-2 transcripts and had no effect on the level of TGF-beta-1 or TGF-beta-3 transcripts. TGF-beta-2 induction was only weakly enhanced by cycloheximide and was completely inhibited by actinomycin D. These data show that Bt2-cAMP induces the expression of active TGF-beta-2 by PC-3 prostate carcinoma cells, suggesting a new approach to the treatment of prostate cancer and a new molecular mechanism of cAMP action.