Androgen-regulated expression of a cloned rat prostatic c3 gene transfected into mouse mammary tumor cells

The expression of the rat prostatic steroid binding protein gene C3 is androgen-responsive in vivo in the rat prostate. Recombinant transfection vectors were constructed containing a cloned C3 rat gene ligated directly into the dominant acting selection vector pSV2-gpt, and were used to transfect androgen-responsive mouse mammary tumor cells (S115 cells). Transformants containing intact copies of the C3 gene were isolated and shown by primer extension analysis to produce C3 transcripts that had authentic 5' termini. The steady state level of the transcripts was under androgen control in three cell lines tested which had low copy numbers of the intact C3 gene, but was not regulated in a cell line which had a very high C3 gene copy number. Despite this difference in the androgenic regulation of integrated C3 rat genes, both type of cell lines still demonstrated androgen-regulated growth characteristics.