Differential effects of transforming growth factor-beta-1 on a model of normal and tumorigenic renal epithelial cells

Abstract

During carcinogenesis, the ability to control cell growth or death is lost. Transforming growth factor beta-1 (TGFbeta1) inhibits epithelial cell growth and plays a role in multistage carcinogenesis. To better understand TGFbeta1 in carcinogenesis, we have studied TGFbeta1 effects on cell shape and its mediators, which are critical to cell growth. We have also characterized a cell model appropriate for our TGFbeta 1 studies. The NRK-52E rat kidney epithelial cell line and two H-ras oncogene-transfected NRK-52E cell lines, H/1.2 and H/6.1, were characterized. NRK-52E cells were differentiated, anchorage-dependent, non-tumorigenic, and contact-inhibited. H/1.2 and H/6.1 cells had increased growth rates, increased plasma membrane ruffling, altered cytoskeletal structure, anchorage-independent growth, and formed renal cell carcinoma-like tumors in vivo. H/6.1 cells formed more aggressive tumors in vivo than H/1.2, and were selected for further studies. Since Ras GTPases regulate cytoskeletal remodeling and we demonstrated H-ras oncogene-induced morphologic alterations, our cell model was validated for investigating the effects of TGFbeta1 on normal and tumorigenic cells. NRK-52E and H/6.1 cells had similar TGFbeta1 receptor expression and growth inhibition by TGFbeta1. NRK-52E treated with TGFbeta 1 showed cell flattening, actin protein expression, stress fiber formation, and increased vinculin fluorescence and expression. TGFbeta1 effects on NRK-52E cells induced talin fluorescence but not its expression. Biochemical analysis of F- and G-actin in NRK-52E cells showed significant TGFbeta1-induced increases. All of these effects were delayed, diminished, or absent in H1/6.1 cells. Since Rho GTPases are known to mediate stress fiber formation and TGFbeta1-induced transcription, we microinjected C3 transferase, a Rho inhibitor. C3 transferase depolymerized stress fibers in control cells but not in TGFbeta1-treated cells. Very high levels of C3 transferase eventually depolymerized all stress fibers in both treated and control cells. These results indicate that TGFbeta1 signaling in renal epithelial cells involves alterations in actin and focal adhesion proteins that differ between normal and H-ras-transformed cells. We suggest that TGFbeta1 modifies aspects of Rho GTPase signal transduction. Elucidating the mechanism by which TGFbeta1 induces cytoskeletal remodeling in tumor cells will reveal potential targets for cancer therapy.