A Cellular Repressor of E1A-Stimulated Genes That Inhibits Activation by E2F

ABSTRACT

The adenovirus E1A protein both activates and represses gene expression to promote cellular proliferation and inhibit differentiation. Here we report the identification and characterization of a cellular protein that antagonizes transcriptional activation and cellular transformation by E1A. This protein, termed CREG for cellular repressor of E1A-stimulated genes, shares limited sequence similarity with E1A and binds both the general transcription factor TBP and the tumor suppressor pRb in vitro. In transfection assays, CREG represses transcription and antagonizes 12SE1A-mediated activation of both the adenovirus E2 and cellular hsp70 promoters. CREG also antagonizes E1A-mediated transformation, as expression of CREG reduces the efficiency with which E1A and the oncogeneras cooperate to transform primary cells. Binding sites for E2F, a key transcriptional regulator of cell cycle progression, were found to be required for repression of the adenovirus E2 promoter by CREG, and CREG was shown to inhibit activation by E2F. Since both the adenovirus E1A protein and transcriptional activation by E2F function to promote cellular proliferation, the results presented here suggest that CREG activity may contribute to the transcriptional control of cell growth and differentiation.

ACKNOWLEDGMENTS

We thank Amelia Tung for technical assistance. Studies ofDrosophila CREG were initiated in the laboratory of Robert Tjian at the University of California, Berkeley. We are grateful to Jennifer Dowhanick for help in setting up the BRK transformation assays. Reagents used in this study were kindly provided by Rene Bernards, Nicholas Dyson, Bill Kaelin, Karl Munger, Joseph Nevins, Bill Sellers, and Yang Shi. We also thank Keith Blackwell, Mike Carey, Phil Hinds, Karl Munger, and Yang Shi for helpful comments on the manuscript.

This work was supported in part by a grant from The Jessie B. Cox Charitable Trust and The Medical Foundation to G.G.