The Molecular Chaperone Activity of Simian Virus 40 Large T Antigen Is Required To Disrupt Rb-E2F Family Complexes by an ATP-Dependent Mechanism

Abstract

The simian virus 40 large T antigen (T antigen) inactivates tumor suppressor proteins and therefore has been used in numerous studies to probe the mechanisms that control cellular growth and to generate immortalized cell lines. Binding of T antigen to the Rb family of growth-regulatory proteins is necessary but not sufficient to cause transformation. The molecular mechanism underlying T-antigen inactivation of Rb function is poorly understood. In this study we show that T antigen associates with pRb and p130-E2F complexes in a stable manner. T antigen dissociates from a p130–E2F-4–DP-1 complex, coincident with the release of p130 from E2F-4–DP-1. The dissociation of this complex requires Hsc70, ATP, and a functional T-antigen J domain. We also report that the “released” E2F–DP-1 complex is competent to bind DNA containing an E2F consensus binding site. We propose that T antigen disrupts Rb-E2F family complexes through the action of its J domain and Hsc70. These findings indicate how Hsc70 supports T-antigen action and help to explain the cisrequirement for a J domain and Rb binding motif in T-antigen-induced transformation. Furthermore, this is the first demonstration linking Hsc70 ATP hydrolysis to the release of E2F bound by Rb family members.

ACKNOWLEDGMENTS

This work was supported by NIH grant CA40586.

We thank J. Brodsky, K. Sachsenmeier, R. Hendrix, A. McClellan, A. Slinskey, and L. Engler for their critical reading of the manuscript. We thank T. Harper for assistance with the figures.