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The ability to introduce DNA into eucaryotic cells has provided a means to analyse the expression of cloned genes. By manipulating the genes in vitro using recombinant DNA techniques it is possible to identify regulatory DNA sequences which are important for individual steps in gene expression. This review will summarize how these techniques have been applied to study steroid-responsive genes and what we have learned about steroid hormone action.

The mechanisms whereby androgens modulate mRNA levels for the C1, C2 and C3 prostatic binding protein genes in the rat ventral prostate have been investigated. Transcription rates for the 3 genes were lowered 2-3-fold upon castration but found to increase again upon re-administration of testosterone. Although this demonstrated a direct effect of androgens at the transcriptional level for these genes, the rates of mRNA synthesis were insufficient to account for previously observed steady-state measurements. This was confirmed by analysis of the nuclear steady-state levels for each mRNA following hormonal manipulation of the rats in vivo. It is concluded that besides direct transcriptional regulation, androgens must also exert a major effect of the half-life of these mRNAs in the rat ventral prostate.

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.