Timing of cyclin E gene expression depends on the regulated association of a bipartite repressor element with a novel E2F complex

Abstract

Transient induction of the cyclin E gene in late G1 gates progression into S. We show that this event is controlled via a cyclin E repressor module (CERM), a novel bipartite repressor element located near the cyclin E transcription start site. CERM consists of a variant E2F-binding site and a contiguous upstream AT-rich sequence which cooperate during G0/G1 to delay cyclin E expression until late G1. CERM binds the protein complex CERC, which disappears upon progression through G0-G1 and reappears upon entry into the following G1. CERC disappearance correlates kinetically with the liberation of the CERM module in vivo and cyclin E transcriptional induction. CERC contains E2F4/DP1 and a pocket protein, and sediments faster than classical E2F complexes in a glycerol gradient, suggesting the presence of additional components in a novel high molecular weight complex. Affinity purified CERC binds to CERM but not to canonical E2F sites, thus displaying behavior different from known E2F complexes. In cells nullizygous for members of the Rb family, CERC is still detectable and CERM-dependent repression is functional. Thus p130, p107 and pRb function interchangeably in CERC. Notably, the CERC-CERM complex dissociates prematurely in pRb-/- cells in correspondence with the premature expression of cyclin E. Thus, we identify a new regulatory module that controls repression of G1-specific genes in G0/G1.

Cyclin D1/cdk4 can interact with E2F4/DP1 and disrupts its DNA‐binding capacity

“…Our results demonstrating the ability of E2F4 to disrupt the DNA-binding ability by cyclin D1/cdk4 suggest that E2F4 is cleared from promoters at the same time that the RB-related proteins are phosphorylated by cyclin D/cdk4. This model is consistent with the loss of E2F4 interactions with specific E2F sites during mid-G 1 in the promoters of several E2F-regulated genes (Zwicker et al, 1996;Tommasi and Pfeifer, 1997;LeCam et al, 1999;Takahashi et al, 2000). In some cases, mutation of these E2F sites results in derepression of the genes during G 0 and early G 1 without affecting expression at later times in the cell cycle suggesting that a repressor complex is released from the DNA during G 1 progression (reviewed in Dyson, 1998;Nevins, 1998).…”

“…One possibility is the elimination of E2F4 at the promoter element without replacement by another E2F family member. Evidence supporting this model has come from in vivo footprinting experiments examining E2F sites in the promoters of the cyclin E, B-myb, and cdc2 genes (Tommasi and Pfeifer, 1995;Zwicker et al, 1996;LeCam et al, 1999). E2F sites within the cyclin E, B-myb, and cdc2 promoters are occupied during G 0 and early in G 1 but remain unoccupied at later stages of the cell cycle when the genes are transcriptionally active.…”

Api5 Contributes to E2F1 Control of the G1/S Cell Cycle Phase Transition

“…MCM2-7, CDC6, TK), and checkpoints (e.g. BRCA1-2, TP53) [32] [34] [35] [36] (for review refer to [4]). In order to determine if Api5 may contribute to transcriptional activity of E2F1, HeLa cells were transiently transfected with Api5 or E2F1 siRNAs (Figure 2E) and the mRNA level of different E2F1-target cell cycle regulator genes was analyzed by quantitative RT-PCR (Figure 2F).…”

Molecular Basis for Viral Selective Replication in Cancer Cells: Activation of CDK2 by Adenovirus-Induced Cyclin E

“…Expression of cyclin E is strictly controlled in normal cells. The level of cyclin E rises at late G 1 phase, peaks at the G 1 /S phase to promote the S-phase entry, and decreases thereafter [35], [40]. Deregulation of cyclin E is frequently detected in many types of cancers, as cyclin E gene amplification [41], overexpression of cyclin E mRNA or protein levels [42], [43], decrease of cyclin E turnover [44], and the presence of more active forms of cyclin E [45]–[47].…”