Androgens repress expression of the F-box protein Skp2 via p107 dependent and independent mechanisms in LNCaP prostate cancer cells.

ABSTRACT

BACKGROUND: Androgens control homeostasis of the normal prostate and growth of prostate cancer (PCa) through the androgen receptor (AR) by regulating gene networks involving in cell proliferation, differentiation, and survival. We demonstrated previously that expression of Skp2, a key protein regulating cell entry into the S phase, is inhibited by androgens in an AR-dependent manner (Oncogene, 2004; 23(12) 2161-2176). However, the underlying mechanism of this regulation is unknown. METHODS: Using the LNCaP PCa cell line as a working model, the effect of androgens on the expression of Skp2 was examined by Western and Northern blot analyses. Cell cycle was measured by fluorescence-activated cell sorting (FACS). Gene transfection was performed by electroporation to manipulate the expression levels of proteins studied. RESULTS: At physiological levels androgens markedly repressed Skp2 expression but slightly induced Skp2 expression at subphysiological levels. Androgens modestly decreased the stability of the Skp2 protein. Androgenic repression of Skp2 expression was completely abolished by E1A-mediated inactivation of pocket proteins including RB, p130, and p107. Moreover, ectopic expression of p107 inhibited Skp2 expression, and silencing of p107 partially blocked androgenic repression of Skp2. CONCLUSIONS: Our data indicate that androgens repress Skp2 expression via p107-dependent and -independent pathways in PCa cells. These regulatory mechanisms may be targeted for the development of new therapeutics of androgen-refractory PCa.