Distinct mechanisms of E2F regulation by Drosophila RBF1 and RBF2

Abstract

RBF1, a Drosophila pRB family homolog, is required for cell cycle arrest and the regulation of E2F-dependent transcription. Here, we describe the properties of RBF2, a second family member. RBF2 represses E2F transcription and is present at E2F-regulated promoters. Analysis of in vivo protein complexes reveals that RBF1 and RBF2 interact with different subsets of E2F proteins. dE2F1, a potent transcriptional activator, is regulated specifically by RBF1. In contrast, RBF2 binds exclusively to dE2F2, a form of E2F that functions as a transcriptional repressor. We find that RBF2-mediated repression requires dE2F2. More over, RBF2 and dE2F2 act synergistically to antagonize dE2F1-mediated activation, and they co-operate to block S phase progression in transgenic animals. The network of interactions between RBF1 or RBF2 and dE2F1 or dE2F2 reveals how the activities of these proteins are integrated. These results suggest that there is a remarkable degree of symmetry in the arrangement of E2F and RB family members in mammalian cells and in DROSOPHILA.

Retinoblastoma family genes

“…Furthermore, similar to the mammalian Rb protein that can bind to both the activating and the repressive E2F proteins, RBF can bind to both dE2F1 and dE2F2 proteins in Drosophila (Frolov et al, 2001). In contrast, RBF2 can only bind dE2F2 (Stevaux et al, 2002) analogous to the mammalian p107/p130 proteins that bind preferentially to the repressive E2F proteins (see Figure 3). Thus, the Rb-E2F pathway is well conserved and is much simpler in Drosophila than in the mammalian systems.…”

“…RB and E2F proteins in Drosophila There are two E2F (dE2F1 and dE2F2), one DP (dDP), and two Rb family (RBF and RBF2) genes in the Drosophila genome (Dynlacht et al, 1994a;Ohtani and Nevins, 1994;Du et al, 1996a;Sawado et al, 1998;Stevaux et al, 2002). Interestingly, the two Drosophila E2F proteins behave like the first two subgroups of the mammalian E2F proteins: dE2F1 mainly functions as a transcription activator (Du, 2000;Frolov et al, 2001), comparable to the mammalian-activating E2Fs 1-3, while dE2F2 primarily mediates active repression, similar to the mammalian-repressive E2Fs 4 and 5 (Frolov et al, 2001).…”

Functional antagonism between histone H3K4 demethylases in vivo

“…Cell culture and dsRNA S2 cells were cultured at 25°C in Schneider's insect medium (Sigma; 10% fetal bovine serum) and treated with dsRNA as described (Stevaux et al 2002).…”

Defects in a New Class of Sulfate/Anion Transporter Link Sulfur Acclimation Responses to Intracellular Glutathione Levels and Cell Cycle Control

“…Subsequently, E2F/DP-dependent transcription of cell cycle genes promotes S phase entry and cell cycle progression. Because of its central role in controlling the transcription of cell cycle genes, RB serves as a convergence point for regulating the cell cycle in response to internal and external mitogenic signals (Nakagami et al, 2002;Stevaux et al, 2002;Cobrinik, 2005;Dimova and Dyson, 2005;Wikenheiser-Brokamp, 2006;Jullien et al, 2008;van den Heuvel and Dyson, 2008;Borghi et al, 2010;Henriques et al, 2010;Johnston et al, 2010;Chen et al, 2011;Gutzat et al, 2011Gutzat et al, , 2012Weimer et al, 2012). Recent studies also provide evidence that RB depletion causes metabolic reprogramming and suggest that the RB pathway in animals exerts part of its effect on cell proliferation through the control of Gln metabolism (Nicolay et al, 2013;Reynolds et al, 2014).…”