The highest risk factor for prostate cancer is androgen action. Men castrated before puberty do not develop prostate cancer and the experimental induction of prostate carcinogenesis in animals requires androgen. Androgen could play a role in the process of carcinogenesis, progression to clinically manifest disease, progression from nonaggressive to aggressive disease, or simply the growth of prostate tumor cells. The androgen receptor (AR) could even play a role in androgen-independent tumors that continue to express AR if the AR could be activated in the absence of androgen. Our long term goal is to understand the role(s) of the AR in prostate cancer, and to determine whether this role is mediated by a normal AR or by abnormal AR. Our discovery of AR aggressive tumors.
Aim 1 is to expand our studies to specific subpopulations, and, in addition, determine whether tumors that lack gene mutations in the AR coding sequence nevertheless produce AR variants. We will screen for AR mutations in early stage tumors that had already progressed prior to radical prostatectomy, despite a lack of evidence of metastic spread, and in high grade/low volume tumors that may represent a more aggressive form of prostate cancer, having acquired a more ominous phenotype early in its course. In addition, we will determine whether AR mutations occur in prostate cancers from African-Americans; the higher incidence and mortality of prostate cancer in African-Americans than in Caucasians may be due to more aggressive disease. We will also determine whether prostate cancer produces AR mRNA splice variants that lack one or more exons, and truncated AR protein variants that arise from translation initiation at a downstream methionine. Tumors with such variants could manifest altered AR function despite a wild- type AR gene. If AR variants are found in prostate cancer, we will determine whether they also exist in normal prostate tissue.
Aim 2 is to characterize the properties of normal AR and abnormal AR variants found in prostate cancer. We will determine whether mutations found in early stage and late stage disease affect AR function in the same way, and whether even normal AR may exhibit altered activity under certain conditions. We will determine whether normal AR or AR variants can be activated by nonandrogenic steroids, antiandrogens, or activators of intracellular protein phosphorylation signaling pathways. Variants will include those that result from AR gene mutation, alternative mRNA splicing, and alternative translation initiation site utilization. We will determine whether glutamine and/or glycine repeat length modulates the properties of these variants. Variant AR expression vectors will be constructed and transfected into AR negative cells (e.g., prostate cancer cells, immortalized normal prostate epithelial cells). Transcriptional activity will be monitored by co- transfecting an androgen responsive reporter gene.
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