Inactivation of retinoblastoma gene product RB or an RB-related protein by SV40 T antigen in MDCK epithelial cells results in massive apoptosis

SV40 T antigen (LT) transformation of renal MDCK epithelial cells resulted in massive apoptosis in the presence of serum. Cell death was dependent on the ability of LT to bind RB or a related protein, since MDCK cells expressing LT mutants unable to bind RB did not die. Apoptosis could be rescued by treatment of cells with EGF and TPA, a property linked to their ability to promote cell growth. Our results indicate an inverse correlation between proliferation and apoptosis. Thus LT transformation induced survival-factor dependence in epithelial cells, in contrast to its effect in fibroblasts. RB inactivation also resulted in a strong down-regulation of c-myc and c-fos, which were previously found to be highly and constitutively expressed in epithelial cells. RB gene transfer in MDCK(LT) cells restored cell viability and high c-myc expression. C-myc gene transfer in these cells also resulted in a significant survival effect. These results suggest that RB anti-cell death activity is at least partly mediated by up-regulation of c-myc. Overexpression of Bcl2 also protected cells against apoptosis. The role of RB and c-myc in cell survival is discussed and related to maintenance of the differentiation state rather than to their properties in cell cycle progression.