EPIDERMAL GROWTH-FACTOR INDUCES CYCLIN D-1 IN A HUMAN PROSTATE-CANCERCELL-LINE

BACKGROUND. The human prostate carcinoma cell line, LNCaP, proliferate s under stimulation by a limited number of mitogenic signals, which in clude members of the growth factor and steroid hormone families. Andro gens and epidermal growth factor (EGF) are among the LNCaP cell mitoge ns. We tested the hypothesis that these mitogens stimulate LNCaP cell proliferation at least in part through the induction of cyclin D-1, a protein requisite for cell cycle progression, which is expressed in th e G(1) phase of the cell cycle. METHODS. LNCaP cells were grown in ser um-free medium with 10 ng/ml or 100 ng/ml EGF, 0.1 nM or 1.0 nM mibole rone (a potent androgen agonist), or vehicle (distilled water or 0.01% ethanol). Expression of cyclin D, mRNA, and protein were assessed by Northern and Western blot analyses. Transcription regulation was asses sed by nuclear runoff assay. RESULTS. Western analyses demonstrated th at EGF stimulated cyclin D-1 protein expression 4-fold over 12 hr. Nor thern analyses showed a 4-fold increase in mRNA expression, peaking wi thin 4 hr of EGF stimulation. There were no effects on cyclin D-1 prot ein or mRNA expression with mibolerone treatments. We further Explored the mechanism of cyclin D-1 induction. LNCaP cells stimulated for 1 h r with EGF demonstrated a 2-fold increase in cyclin D-1 message, as as sayed by nuclear runoff transcription assay. IN addition, we demonstra ted the involvement of the protein kinase C pathway in mediating the E GF induction of cyclin D-1. CONCLUSIONS. We conclude that one of the m echanisms by which growth factors such as EGF may stimulate prostate c ell proliferation is through the direct induction of cyclin proteins, which are necessary for entry of cells into mitosis. (C) 1998 Wiley-Li ss, Inc.