The Transcription Factor E2F-1 Is a Downstream Target of RB Action

Abstract

) cells causes a G 1 arrest and characteristic cellular swelling. Coexpression of the cellular transcription factor E2F-1 could overcome these effects. The ability of E2F-1 to bind to RB was neither necessary nor sufficient for this effect, and S-phase entry was not accompanied by RB hyperphosphorylation under these conditions. Furthermore, E2F-1 could overcome the actions of a nonphosphorylatable but otherwise intact RB mutant. These data, together with the fact that RB binds to E2F-1 in vivo, suggest that E2F-1 is a downstream target of RB action. Mutational analysis showed that the ability of E2F-1 to bind to DNA was necessary and sufficient to block the formation of large cells by RB, whereas the ability to induce S-phase entry required a functional transactivation domain as well. Thus, the induction of a G 1 arrest and the formation of large cells by RB in these cells can be genetically dissociated. Furthermore, the ability of the E2F-1 DNA-binding domain alone to block one manifestation of RB action is consistent with the notion that RB-E2F complexes actively repress transcription upon binding to certain E2F-responsive promoters. In keeping with this view, we show here that coproduction of an E2F1 mutant capable of binding to DNA, yet unable to transactivate, is sufficient to block RB-mediated transcriptional repression.

Cell cycle arrest and morphological alterations following microinjection of NIH3T3 cells with Puraα

“…This growth to large size may be likened to the e ect of reintroduction of Rb into SAOS2, Rb 7/7 cells. Rb causes a G1 block accompanied by characteristic cell swelling (Qin et al, 1995;Templeton et al, 1991). However, in the case of Pura it is primarily G2-arrested cells which become large.…”

Bistable biochemical switching and the control of the events of the cell cycle*

“…On the other hand, complexes of the retinoblastoma gene product (RB) or related proteins with E2F-1, may be active transcriptional repressors (Neuman et al, 1994;Qin et al, 1995;Johnson, 1995). Therefore E2F-1 can apparently have a biphasic e ect on its own transcription: low concentrations inhibit transcription by binding RB to the promoter, while concentrations exceeding [RB] competitively displace the RB-E2F complexes from the promoter and exert a positive (Figure 6).…”

Functional capabilities of molecular network components controlling the mammalian G1/S cell cycle phase transition

“…A family of cyclin-dependent kinases (cdk) hyperphosphorylates Rb in the complex with E2F, thereby destabilizing the complex and causing the release of active E2F. Ectopic expression of Rb can arrest cells in G1, and co-expression of E2F1 can overcome this arrest and allow cells to enter S-phase (Qin et al, 1995). The cdks are regulated by binding to a cyclin, which is required for kinase activity, and by phosphorylations which can be either stimulatory or inhibitory.…”