ANDROGEN RECEPTOR FUNCTION IN PROSTATE CANCER

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Prostate cancer is the second leading cause of cancer death in American men. Patients succumb to androgen-independent metastatic disease. Androgens regulate the growth of prostate cancer through activation of the androgen receptor. Androgen-independent prostate cancer was thought to develop from prostate cancer cells lacking androgen receptors. However, androgen-independent prostate cancer expresses levels of androgen receptor proteins similar to those seen in benign prostate tissue and androgen- dependent prostate cancer. Androgen-independent growth could result from androgen receptor mutations that alter specificity or steroid binding or sensitivity to adrenal androgens. The frequency of mutations reported varies widely and only 6 mutations have been functionally analyzed. We will test the hypothesis that altered androgen receptor function is a critical event in the progression of prostate cancer. In Aim 1, molecular alterations in the androgen receptor gene will be searched for in androgen-dependent cancers that are organ-confined, locally invasive or metastatic and androgen-independent cancers that are locally recurrent or metastatic. An equal number of Caucasians and African Americans will be studied. The methods of denaturing gradient gel electrophoresis and single strand conformation polymorphism will be used to screen for point mutations in the androgen receptor. The glutamine and glycine repeat regions in exon A will be analyzed since polymorphisms or deletions may enhance androgen receptor mRNA or protein expression. RT-PCR will be used to search for abnormal splicing such as has been observed in estrogen and progesterone receptors in breast cancer but has not been reported in prostate cancer. In Aim 2, steroid binding and transient co-transfection assays will be used to determine the functional characteristics of mutant androgen receptors. In Aim 3, the expression and subcellular localization of wild-type and mutant androgen receptors in androgen-dependent and independent prostate cancer will be evaluated using immunohistochemistry and image analysis. Analysis of serial biopsies of prostate cancer from patients treated by castration will allow temporal comparison of androgen receptor protein expression with cellular proliferation. The role of androgen receptor gene amplification in the development of androgen independence will be determined using southern analysis and in situ hybridization. Insights gained should allow a more complete understanding of the role of the androgen receptor in the transition from androgen- dependent to independent prostate-cancer.