Dual regulation of proliferation and growth arrest in prostatic stromal cells by transforming growth factor-β1

In a preliminary study, we observed that TGF-β1 induced both proliferation and growth arrest in prostatic stromal cells, depending on the concentration of TGF-β1 used in the culture medium. In this study, we explored possible mechanisms of this dual effect of TGF-β. Primary cultures of prostatic stromal cells, established from clinical surgical specimens and treated with low doses of TGF-β1 (0.001-0.01 ng/ml), resulted in an increase in cell proliferation. The addition of neutralizing antibody against platelet-derived growth factor (PDGF)-BB, but not anti-PDGF-AA, abrogated this stimulatory effect of TGF-β1. TGF-β1 treatment resulted in a dose-related increase in PDGF-BB production as measured by ELISA. Cells underwent growth arrest at high concentrations of TGF-β1 (1.0 and 10 ng/ml). An inhibitor of cyclin-dependent kinase (cdk), p15^INK4b, was up-regulated at both transcript and protein levels in these cultures by TGF-β1 in a dose-related manner as determined by RT-PCR and Western blot analysis. The transcript, but not the protein, for another cdk inhibitor, p21^Cip1, was up-regulated with treatment of TGF-β1 to these cells. Levels of other cdk inhibitors, such as p16^INK4a and p27 ^Kip1, were constitutively expressed in prostatic stromal cells and were not significantly affected by TGF-β1 treatment. Finally, the growth arrest effect of TGF-β1 was abrogated when antisense oligonucleotides to p15^INH4b, but not p21^Cip1, were added to the culture medium. These data indicate that the dual effect of TGF-β1 is mediated, at least, by up-regulation of PDGF-BB and p15^INK4b, respectively.