Androgen-induced proliferative quiescence in prostate cancer cells: The role of AS3 as its mediator

In the prostate gland of adult mammals, most epithelial cells are in a stat e of proliferative quiescence. Androgens regulate this effect by inducing c ell cycle arrest in the G(0)/G(1) phase. Potential mediators of this androg en-induced proliferative shutoff were identified by means of subtracted cDN A libraries. The expression pattern of one of these sequences, AS3, strongl y correlated with the expression of the androgen-induced proliferative shut off both temporally and dosewise. The AS3 gene is located on chromosome 13 q12.3, in close proximity to the BRCA2 gene. The loss of chromosomal region s where AS3 alleles are located correlates with various human cancers, incl uding prostate, The biological effect of AS3 was tested in two stable cell lines, one expressing sense and another expressing antisense AS3 constructs , both under tetracycline regulation. S9 cells were obtained by retroviral infection with virions containing a tetracycline-regulated sense AS3 constr uct. In these cells, sense AS3 was negatively regulated by tetracycline. Te tracycline withdrawal increased the expression of AS3 mRNA and protein. The expression of tetracycline-regulated AS3 resulted in inhibition of cell pr oliferation. A4 cells were obtained by retroviral infection with virions co ntaining a tetracycline-regulated antisense AS3 construct, Vector-driven ex pression of antisense-AS3 blocked the induction of androgen-induced endogen ous AS3 mRNA and blocked the inhibitory effect of androgens on cell prolife ration. Tetracycline-regulated expression of the empty vector control had n o effect on cell proliferation. These experiments strongly suggest that AS3 is a mediator of the androgen-induced proliferative shutoff.