REEXPRESSION OF THE TYPE-1 INSULIN-LIKE GROWTH-FACTOR RECEPTOR INHIBITS THE MALIGNANT PHENOTYPE OF SIMIAN-VIRUS-40 T-ANTIGEN IMMORTALIZED HUMAN PROSTATE EPITHELIAL-CELLS

Type 1 insulin-like growth factor receptor (IGF-IR) expression is decr eased in prostate cancer compared to that in noncancerous prostate epi thelium. We have demonstrated that as the simian virus 40 T antigen(SV 40T) immortalized human prostate epithelial cell line, P69SV40T, under goes transformation from a poorly tumorigenic to a malignant phenotype , the M12 subline, there is a significant decrease in IGF-1R expressio n. In the present study, we examine the effects of reexpression of the IGF-1R on the malignant phenotype of M12 cells. The IGF-1R was reexpr essed in M12 cells using a retroviral vector containing a 7-kilobase c oding sequence for the IGF-1R, LISN, to create several clones of the M 12-LISN cell line. As a control, M12 cells were also infected with a r etroviral vector (LNL6) without the 7-kilobase IGF-1R insert (M12-LNL6 clones. Functional assays were performed with two separate clones eac h of M12-LNLG and M12-LISN cells. Each clone of M12-LISN cells regaine d the proliferative response to IGF that was lost in the transition fr om P69SV40T cells to M12 cells. In addition, M12-LISN clones had a sig nificantly decreased growth rate compared to the M12-LNL6 cells when i njected sc in athymic/nude mice (P < 0.001). Tumorigenicity, as assess ed by anchorage-independent growth of colonies in soft agar, was also decreased by 75% in the M12-LISN clones compared to that in the M12-LN L6 control cells. These data demonstrate that reexpression of the IGF- IR in a malignant human prostate epithelial cell line results in decre ased tumor growth and decreased anchorage-independent colony formation independent of an increased proliferative response to IGF. Reexpressi on of the IGF-1R may be associated with reacquisition of the regulatio n of cellular proliferative and differentiation functions mediated by the IGF-1R that ar e lost as prostate epithelial cells undergo convers ion to a malignant phenotype.