OVEREXPRESSION OF TRANSFORMING-GROWTH-FACTOR (TGF) BETA-1 TYPE-II RECEPTOR RESTORES TGF-BETA-1 SENSITIVITY AND SIGNALING IN HUMAN PROSTATE-CANCER CELLS

TGF-beta 1 is a potent negative regulator of cell growth that transduc es signals through interaction with type I and type II receptors that form a heteroduplex. Abnormal expression and mutational alterations of these receptors have recently been shown in several human malignancie s, In previous studies, we have demonstrated reduced expression of bot h types of transforming growth factor (TGF) beta 1 receptors in human prostate tumors, In this study, using the human prostate cancer cell l ine, LNCaP, which is refractory to TGF-beta 1 and lacks type II recept or (R-II), we investigated whether overexpression of the R-II receptor can restore sensitivity to the negative growth effects of TGF-beta 1, LNCaP cells were transfected with plasmid containing the full length of human TGF-beta R-II receptor cDNA sequence, Stable transfectant clo nes were selected for R-II mRNA and protein expression by Northern and Western analyses, respectively, The effect of TGF-beta on LNCaP R-II overexpressing clones was examined on the basis of: (a) growth inhibit ion (cell number); (b) DNA synthesis using the [H-3]thymidine incorpor ation assay; (c) induction of cyclin-dependent-kinase inhibitors, p21( WAF-1/Cip1) p27(Kip1), and p15; and (d) colony-forming ability in soft agar, Both the cell number and the rate of DNA synthesis of R-II-over expressing clones were significantly suppressed by exogenous TGF-beta 1 in a dose-dependent manner, compared with control cell lines, Treatm ent of R-II cloned transfectants with TGF-beta 1 induced a G(1) arrest , which was accompanied by a transient increase in p21(WAF-1/Cip1) and p27(Kip1) expression at the mRNA and protein level, Furthermore, the LNCaP R-II transfectants analyzed exhibited a markedly reduced colony- forming ability. Our results indicate that overexpression of TGF-beta 1 R-II receptor in LNCaP prostate cancer cells caused tumor growth inh ibition by restoring the TGF-beta signaling mechanism and TGF-beta 1 s ensitivity.