When the fetal mouse urogenital sinus is grafted under the renal capsule of an isogenic mature male mouse, the graft differentiates into normal prostate. We introduced the ras and myc oncogenes, separately and in combination into the fetal urogenital sinus prior to grafting, using help-virus free recombinant retroviruses. Under these circumstances, instead of normal prostate, the grafts developed into premalignant phenotypes as well as frank carcinomas. This model of oncogene-induced prostatic malignancy offers a unique opportunity for an in vivo study of the fundamental processes of tumor initiation and progression. We plan to examine the effects of ras, myc and the ras+myc combination when introduced selectively into basal and luminal epithelial cells as well as into mesenchymal cells. By this approach, we hope to clarify the putative stem cell function of the prostatic basal epithelial cells and to establish whether these oncogenes demonstrate different activities in the different cell types. In addition, the exact role of androgens in the initiation and progression of these tumors will be assessed in a controlled in vivo environment. Modifications of the reconstitution protocol and additional retroviral constructs will be generated and used to specifically introduce the ras and myc oncogenes into the basal and luminal epithelial cells of the urogenital sinus. In addition, urogenital sinus epithelium from Tfm/y mice will be used as a recipient for these oncogenes. Since the tissue lacks functional androgen receptor, its contribution to the progression of ras+myc-induced carcinomas can be tested directly. We plan to identify cells containing the oncogene(s) either by using oncogene-specific antisera or staining for activity associated with the beta-galactosidase gene which is present and coexpressed along with the oncogene in the single-oncogene containing recombinant retroviral vectors. Additional immunohistochemical characterization will include staining for prostate specific antigens and extra cellular matrix components. A selected panel of growth factor and growth factor receptor sequences which includes the androgen receptor will be used to probe mRNA isolated from both normal control reconstitutions and oncogene-altered ones. Tumors and tumor-derived cell lines will be analyzed for amplification of growth factor receptor and androgen receptor genes. These studies should clarify certain steps and mechanisms involved in prostatic neoplasia and may provide clues to early diagnosis and rational approaches to prevention and therapy of human prostate cancer and benign prostatic hyperplasia.
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