SIGNAL TRANSDUCTION EVENTS AND THE REGULATION OF CELL GROWTH

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This project is designed to increase our understanding of the biology of prostate cancer and to develop a new approach to the treatment of advanced prostatic cancer through the study of the signal transduction events regulating the growth of human prostate carcinoma cell lines. This work is currently focused on (1) effects of cAMP on growth and differentiation, (2) cytotoxicity through activation of P2-purinergic receptors, and (3) the anticancer activity of the HMG-CoA reductase inhibitor lovastatin. We have found that elevation of intracellular cAMP is highly growth-inhibitory to all prostate carcinoma cell lines tested. To examine the mechanism of cAMP action in prostate carcinoma cells we tested the effect of the cAMP analog dibutyryl cAMP on the regulation of the potent negative growth factor TGF-beta. DbcAMP selectively induced the secretion of TGF-beta2 and not TGF-beta1 by prostate carcinoma cells. This TGF-beta2 was shown to be bioactive using the CCL-64 mink lung cell assay. Northern analysis showed that dbcAMP induced an increase in the five characteristic TGF-beta2 transcripts. Thus dbcAMP induces the expression of bioactive TGF-beta2 by prostate carcinoma cells, suggesting a new approach to the treatment of prostate cancer and a new molecular mechanism of cAMP action. P2-purinergic receptor studies demonstrated that androgen-independent prostate carcinoma cells express P2-purinergic receptors that are coupled to phospholipase C activation, acute Ca2+ mobilization, prolonged cytoplasmic and nuclear Ca2+ oscillations, growth arrest, and an increased rate of cell death. In contrast, androgen-sensitive cells have surface P2 receptors that are uncoupled from phospholipase C, Ca2+ mobilization and growth arrest. In collaboration with the Molecular Pathophysiology Branch we found that the androgen-sensitive cells lack expression of G protein alpha subunits that have been shown to couple to phospholipase C. These data strongly implicate phospholipase C activation and prolonged Ca2+ mobilization in the growth-inhibitory effect of P2 agonists, and provide a molecular mechanism for the uncoupling of the P2 receptor in androgen-sensitive cells. Studies with the HMG-CoA reductase inhibitor lovastatin showed that lovastatin is cytotoxic to human prostate carcinoma cells. We found that lovastatin treatment results in marked deregulation of TGF-beta2 mRNA synthesis and in deregulation of protein expression of the tumor suppressor gene product pRB.