The molecular chaperone activity of simian virus 40 large T antigen is required to disrupt Rb-E2F family complexes by an ATP-dependent mechanism

The simian virus 40 large T antigen (T antigen) inactivates tumor suppresso r proteins and therefore has been used in numerous studies to probe the mec hanisms that control cellular growth and to generate immortalized cell line s. Binding of T antigen to the Rb family of growth-regulatory proteins is n ecessary but not sufficient to cause transformation. The molecular mechanis m underlying T-antigen inactivation of Rb function is poorly understood. In this study me show that T antigen associates,vith pRb and p130-E2F complex es 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 a lso report that the "released" E2F-DP-1 complex is competent to bind DNA co ntaining 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 cis requirement for a J domain and Rb binding motif in T-antigen-induce d transformation. Furthermore, this is the first demonstration linking Hsc7 0 ATP hydrolysis to the release of E2F bound by Rb family members.