Expression of p16 induces transcriptional downregulation of the RB gene

The RB and p16INK4A tumor suppressor genes function in the same pathway of cell cycle control. Previous evidence indicates that the p16INK4A gene is transcriptionally repressed by the RB gene product, pRB. In this study using human ovarian cancer cell lines, we found that RB protein and mRNA were expressed at higher levels in cell lines lacking p16 than in those with normal p16. Since this suggests a potential role of p16 in regulating the cellular level of pRB, we studied the effect of wild-type p16INK4A on expression of the RB gene. Introduction of p16INK4A, carried by an adenovirus vector, into p16-negative cell lines dramatically decreased expression of RB protein and mRNA. Nuclei run-off assays demonstrated that p16 expression induced transcriptional downregulation of the RB gene. These results indicate that expression of RB is inversely regulated by p16. The findings reveal a new dimension of pRB-p16 interaction and should have implications for p16INK4A-mediated gene therapy.