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, and (2) cytotoxicity through activation of P2- purinergic receptors. We found that elevation of intracellular cAMP is highly growth-inhibitory to all prostate carcinoma cell lines tested, and induces neuronal morphology in two of four cell lines. All of the cell lines expressed one or more markers of neuroendocrine differentiation, including dense core granules, NSE, S100, and neurofilament proteins. In collaboration with the Molecular Oncology Group, CPB, we tested for the expression and activity of the neuroendocrine marker pp60c-src and found high levels of src kinase activity that were increased after cAMP treatment. In collaboration with the Tumor Cell Biology Section, CPB, we found that two ansamycin antibiotics reported to inhibit src activity were highly potent cytotoxic agents in all prostatic carcinoma cell lines. Studies of the mechanism of cAMP-induced growth inhibition demonstrated that cAMP induces the secretion of bioactive TGF-Beta2, an increase in TGF-Beta2 transcription, and activation of cAMP response elements in the TGF-Beta2 promoter. P2-purinergic receptor studies demonstrated that androgen-independent prostate carcinoma cell lines express P2-purinergic receptors that are coupled to phospholipase C activation, acute Ca+ mobilization, the induction of prolonged Ca2+ oscillations, growth arrest, and cell death. In the androgen-sensitive cell line LNCaP, however, P2 agonists did not stimulate phospholipase C activity, did not induce Ca2+ release, and did not inhibit growth, while both cell types expressed specific P2 receptors, with comparable Kd and Bmax, These data strongly implicate phospholipase C activation and prolonged Ca2+ mobilization in the growth-inhibitory and cytotoxic effect of P2-purinergic receptor agonists.
