HORMONAL REGULATION OF ANDROGEN RECEPTOR EXPRESSION

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The long term objectives of the proposed research are to understand the effects of endocrine status on androgen receptor abundance in normal and diseased target tissues and to evaluate the physiologic significance of fluctuations in receptor number. In particular, the molecular mechanisms involved in androgen-mediated regulation of androgen receptor mRNA and protein levels will be investigated in cells expressing the androgen receptor cDNA. The capacity of receptors to be regulated by cognate ligand (autoregulation) is a feature common to virtually all members of the steroid/thyroid hormone receptor family. In many target tissues and androgen receptor-containing cell lines androgen treatment causes a reduction in receptor mRNA and protein. Preliminary results suggest that the expression of the human androgen receptor cDNA in transfected cells is also down-regulated by androgen. Since the heterologous promoter used to express the androgen receptor cDNA is insensitive to androgens, sequences within the receptor cDNA must be responsible for autoregulation of transfected androgen receptor mRNA. Experiments proposed here will test the hypothesis that androgen-mediated regulation of androgen receptor levels is achieved through the direct interaction of the androgen receptor with sequences within the receptor cDNA or mRNA. The specific aims of this proposal are: I. To evaluate the effects of androgens on steady state levels, transcription and stability of androgen receptor mRNA in cells transfected with the human androgen receptor cDNA. II. TO evaluate the effects of androgens on steady state levels and half-life of androgen receptor protein. III. To identify the intragenic down regulatory signals of the androgen receptor cDNA by (A) mapping androgen receptor binding to specific sequences within the androgen receptor cDNA (or mRNA); (B) in vitro mutagenesis (site directed or deletion) of receptor binding sites to ascertain the potential role of these sequences in down regulation. Since steroid receptor content has proven to be useful in predicting cellular responsiveness to steroid hormones, understanding how receptors are regulated is vital to the development of rational endocrine therapies. For example, modulation of androgen levels is a central component in the clinical management of prostate cancer. How cellular endocrine status affects androgen receptors should aid oncologists in arriving at more effective strategies for treatment of androgen-dependent tumors. Studies on steroid receptor down regulation will provide insight into mechanisms that attenuate cellular response to hormonal stimulation and that may be involved in the clinical problem of steroid-resistant neoplasia.