Prostate-Specific Membrane Antigen, PSMA is a highly expressed prostate antigen in human, which is increased in expression in the majority of human prostate cancers. We discovered that PSMA is a unique folate hydrolase. In addition to being a folate hydrolase with high affinity for polygammaglutamated folates, PSMA undergoes internalization and is transported to the lysosomal compartment, and thus may play a role in the binding and transport of polygammaglutamated folates as well. Folates provide methyl groups in the synthesis of DNA and RNA. Folate deficiencies are associated with chromosomal damage and increased sensitivity to carcinogens in carcinogenesis and folate can also alter the development of cancer in transgenic models expressing mutant genes associated with the development of cancers. The mouse homolog of PSMA is not expressed in the mouse prostate. The normal mouse prostate also has a low incidence of prostate cancer. We generated mice that strongly express PSMA in their prostates under the control of the PSA promoter/enhancer. We find a high incidence of hyperplasia and PIN in the prostates of these mice at about 9 months of age, especially in the ventral prostate and lateral prostate. Transgenic animals made to express a form of PSMA that lack the folate hydrolase activity do not demonstrate these changes. We hypothesize that PSMA's function as a folate hydrolase is responsible for the increased abnormal histologic architecture in the prostate and we propose a number of studies to determine to what extent manipulation of dietary folate will accentuate or attenuate these histologic changes. The prostate is a tissue with a low level of proliferation. Changes in folate are thought to have their major impact in cells that are proliferating. Recent studies in the human prostate suggest that conditions such as prostate intraepithelial atrophy, PIA, are in fact highly proliferative. Because a way to model PIA is not established for the mouse prostate, we will use transgenic animals which have dominate acting genes which drive proliferation, such as the large T antigen, or c-Myc. Both of these animals develop tumors in a reasonable time frame and we will determine the extent PSMA expression and folate modulation impact tumor formation in these prostate tumor models. In our proposed studies we will utilize transgenic animals that express PSMA, large T antigen, or c-Myc with or without dietary folate manipulation, with or without administration of highly specific high affinity inhibitors of PSMA. We will measure serum, RBC, and tissue folates, and extent of polygammglutamation, SAM/SAH, ratios and tissue uptake and retention of radio labeled folate. We will determine the changes in tissue histopathology and determine the effect of PSMA expression in the mouse prostate on prostate gene expression by array analysis. Those changes exhibiting the greatest changes will be verified and the cells of the prostate demonstrating those changes determined by in-situ hybridization. As PSMA may be enhancing the prostates susceptibility to develop cancer, these studies may indicate whether either PSMA inhibitors or folate manipulation may provide an approach to reducing the impact of PSMA as a factor in abnormal prostate growth.
