Regulation of RB Transcription In Vivo by RB Family Members

Abstract

In cancer cells, the retinoblastoma tumor suppressor RB is directly inactivated by mutation in the RB gene or functionally inhibited by abnormal activation of cyclin-dependent kinase activity. While variations in RB levels may also provide an important means of controlling RB function in both normal and cancer cells, little is known about the mechanisms regulating RB transcription. Here we show that members of the RB and E2F families bind directly to the RB promoter. To investigate how the RB/E2F pathway may regulate Rb transcription, we generated reporter mice carrying an eGFP transgene inserted into a bacterial artificial chromosome containing most of the Rb gene. Expression of eGFP largely parallels that of Rb in transgenic embryos and adult mice. Using these reporter mice and mutant alleles for Rb, p107, and p130, we found that RB family members modulate Rb transcription in specific cell populations in vivo and in culture. Interestingly, while Rb is a target of the RB/E2F pathway in mouse and human cells, Rb expression does not strictly correlate with the cell cycle status of these cells. These experiments identify novel regulatory feedback mechanisms within the RB pathway in mammalian cells.

We are grateful to David MacPherson for his critical reading of the manuscript and the members of the Sage lab for helpful discussions throughout this work. We also thank Pauline Chu for her help with histology.

This work was supported by National Cancer Institute grant 5R01CA114102 and by the Damon Runyon Cancer Research Foundation (to J. Sage). D. L. Burkhart received a California Breast Cancer Research Program dissertation fellowship and P. Viatour a Human Frontier Science Program postdoctoral fellowship.

There are no potential conflicts of interest to disclose.