THE CONVENTIONAL TRANSFORMING-GROWTH-FACTOR-BETA (TGF-BETA) RECEPTOR-TYPE-I IS NOT REQUIRED FOR TGF-BETA-1 SIGNALING IN A HUMAN PROSTATE-CANCER CELL-LINE, LNCAP

LNCaP is an androgen-responsive human prostate cancer cell line that h as a defective gene for ALK-B, the conventional TGF-beta receptor type I. Yet, these cells respond to exogenous TGF-beta 1 under appropriate concentrations of dihydrotestosterone (DHT). Because a heteromeric co mplex composed of type I and type II receptor is required for TCF-beta signaling, the expression of these receptors was investigated in LNCa P cells at following concentrations of DHT-O, 0.1, and 100 nM. These c oncentrations were selected because they represent the zero DHT contro l in which LNCaP cells are not sensitive to TGP-beta 1, the proliferat ive dose of DHT in which these cells are sensitive to exogenous TGF-be ta 1, and the growth-arrest dose of DHT in which LNCaP exhibits signs of TGF-beta signaling but are insensitive to exogenous TGF-beta 1, res pectively. Results of Western blot analysis showed that LNCaP cells ex press an increased level of type II receptor at 0.1 nM DHT, the TGF-be ta 1-sensitive dose, However, results of competitive quantitative RT-P CR demonstrated that DHT did not significantly change the level of typ e II receptor mRNA, suggesting that DHT modulates the level of type II receptor at the posttranscriptional level. In contrast, ALK-B was not detected in these cells by either Western blot analysis or RT-PCR at all concentrations of DHT used in this study. Subsequently, the expres sion of ALK-1, -2, and -4 in LNCaP cells was examined because these pr oteins have been shown to bind TGF-beta 1 in vitro. ALK-1 and -2 were detected in these cells. Further analysis by competitive quantitative RT-PCR and Western blot demonstrated that DHT did not affect the level of expression of ALK-1 and -2 in LNCaP cells. These observations, tak en together, demonstrate that ALK-B is not required for TGF-beta 1 sig naling and that there may be alternative mechanism(s) for TGF-beta 1 s ignal transduction in some systems. (C) 1998 Academic Press.