pRB binds to and modulates the transrepressing activity of the E1A-regulated transcription factor p120E4F

pRB binds to and modulates the transrepressing activity of the E1A-regulated transcription factor p120^E4F

^*Institut de Génétique Moléculaire, Unité Mixte de Recherche 5535, IFR 24, Centre National de la Recherche Scientifique, 1919 Route de Mende, 34293, Montpellier cedex 5, France; and ^†Jordan Laboratory G03-647, Department of Hematology, University Hospital, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands

Communicated by Robert A. Weinberg, Whitehead Institute for Biomedical Research, Cambridge, MA (received for review January 19, 2000)

Abstract

The retinoblastoma protein pRB is involved in the transcriptional control of genes essential for cell cycle progression and differentiation. pRB interacts with different transcription factors and thereby modulates their activity by sequestration, corepression, or activation. We report that pRB, but not p107 and p130, binds to and facilitates repression by p120^E4F, a ubiquitously expressed GLI-Kruppel-related protein identified as a cellular target of E1A. The interaction involves two distinct regions of p120^E4F and the C-terminal part of pRB. In vivo pRB–p120^E4F complexes can only be detected in growth-arrested cells, and accordingly contain the hypophosphorylated form of pRB. Repression of an E4F-responsive promoter is strongly increased by combined expression of p120^E4F and pRB, which correlates with pRB-dependent enhancement of p120^E4F binding activity. Elevated levels of p120^E4F have been shown to block growth of mouse fibroblasts in G₁. We find this requires pRB, because RB ^−/− fibroblasts are significantly less sensitive to excess p120^E4F.

Footnotes

↵ ‡ To whom reprint requests should be address. E-mail: sardet{at}igm.cnrs-mop.fr.
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.130198397.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.130198397
Abbreviations:

C/EBP,

CCAAT/enhancer binding proteins;

AP-1,

activator protein-1;

GST,

glutathione S-transferase;

MEF,

mouse embryo fibroblast;

RT,

room temperature;

EMSA,

electrophoretic mobility shift assays