Regulation of prostate-specific antigen (PSA) gene expression and release in LNCaP prostate cancer by antagonists of growth hormone-releasing hormoneand vasoactive intestinal peptide

BACKGROUND. Prostate-specific antigen (PSA) is the best tumor marker for di agnosis and prognosis of prostatic carcinoma. The secretion of PSA from LNC aP human prostate cancer cells is influenced by acute stimuli such as vasoa ctive intestinal peptide (VIP), growth hormone-releasing hormone (GHRH), an d chronic stimuli like androgens. METHODS. To study the regulation of basal and VIP/GHRH or androgen-stimulat ed secretion from LNCaP cells, we used a superfusion system, which allowed us to simultaneously measure PSA gene expression, PSA secretion, and cAMP r elease from the same cancer cells. LNCaP cancer cells were also implanted o rtho topically into nude mice. RESULTS. VIP (30 pM-3 nM), GHRH (3 nM-300 nM), and dihydrotestosterone (100 nM) induced a significant increase in PSA gene expression, PSA secretion, and cAMP release. The dose and time-dependent effects of peptides were mani fested only in the presence of androgens. At the end of continuous stimulat ion of cells with 1 nM VIP for 2 hr, large amounts of stored immunoreactive PSA still remained in the cells. Adenylate cyclase activator, forskolin (F SK), significantly increased PSA secretion and gene expression, and potassi um, which causes nonspecific depolarization of membranes, augmented gene ex pression, and secretion of PSA, but did not influence cAMP release. This su ggests that PSA secretion is regulated by cAMP-dependent as well as cAMP-in dependent pathways. In superfusion system, stimulatory effects of VIP and G HRH on PSA secretion were inhibited by VIP antagonist JV-1-53, and less by GHRH antagonist JV-1-38. In cell cultures, JV-1-38 had a stronger inhibitor y effect on proliferation, indicating an involvement of the recently discov ered tumoral GHRH receptors in this process. In nude mice, with orthotopica lly implanted LNCaP cancer cells, GHRH antagonist JV-1-38 alone or androgen ablation by castration had no effect on tumor growth and PSA levels. Howev er, castration combined with treatment with GHRH antagonist, significantly decreased tumor growth and PSA secretion. CONCLUSIONS. Our findings suggest that the secretion of PSA is regulated ra ther than constitutive, contrary to previous reports. In addition, the effe ct of GHRH and VIP antagonists on PSA secretion from prostate cancer cells is not correlated with their antiproliferative action.