Overexpression of Transforming Growth Factor (TGF) β1 Type II Receptor Restores TGF-β1 Sensitivity and Signaling in Human Prostate Cancer Cells

TGF-β1 is a potent negative regulator of cell growth that transduces 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 malignancies. In previous studies, we have demonstrated reduced expression of both types of transforming growth factor (TGF) β1 receptors in human prostate tumors. In this study, using the human prostate cancer cell line, LNCaP, which is refractory to TGF-β1 and lacks type II receptor (R-II), we investigated whether overexpression of the R-II receptor can restore sensitivity to the negative growth effects of TGF-β1. LNCaP cells were transfected with plasmid containing the full length of human TGF-β R-II receptor cDNA sequence. Stable transfectant clones were selected for R-II mRNA and protein expression by Northern and Western analyses, respectively. The effect of TGF-β on LNCaP R-II overexpressing clones was examined on the basis of: (a) growth inhibition (cell number); (b) DNA synthesis using the [³H]thymidine incorporation 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-overexpressing clones were significantly suppressed by exogenous TGF-β1 in a dose-dependent manner, compared with control cell lines. Treatment of R-II cloned transfectants with TGF-β1 induced a G₁ 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-β1 R-II receptor in LNCaP prostate cancer cells caused tumor growth inhibition by restoring the TGF-β signaling mechanism and TGF-β1 sensitivity.