Cell cycle regulation of the human cdc2 gene.

Abstract

Transcription of the human cdc2 gene is cell cycle regulated and restricted to proliferating cells. Nuclear run‐on assays show that cdc2 transcription is high in S and G2 phases of the cell cycle but low in G1. To investigate transcriptional control further, genomic clones of the human cdc2 gene containing 5′ flanking sequences were isolated and shown to function as a growth regulated promoter in vivo when fused to a CAT reporter gene. In primary human fibroblasts, the human cdc2 promoter is negatively regulated by arrest of cell growth in a similar fashion to the endogenous gene. This requires specific 5′ flanking upstream negative control (UNC) sequences which mediate repression. The retinoblastoma susceptibility gene product (Rb) specifically represses cdc2 transcription in cycling cells via 136 bp of 5′ flanking sequence located between −245 and −109 within the UNC region. E2F binding sites in this region were shown to be essential for optimal repression. A model is proposed where Rb negatively regulates the cdc2 promoter in non‐cycling and cycling G1 cells.

Regulation of E2F-1 gene expression in avian cells

“…We report here the downregulation of E2F-1 gene expression itself in the developing retina. Since E2F-1 is a transactivator of the cdc2 promoter (North et al, 1996;Dalton, 1992), the disappearance of E2F-1 may participate in the de®nitive extinction of cdc2 expression in differentiating retinoblasts. Moreover, targeted overexpression of E2F-1 and DP-1 in the drosophila eye results in profound disorganization of photoreceptor layers, suggesting that the down-regulation of E2F activity is a necessary event in the developing retina (Du et al, 1996).…”

“…In particular, E2F-1 controls the expression of genes involved in G1 and S phase progression of the cell cycle, such as genes encoding B-myb, cyclin E, E2F-1, thymidine kinase, dihydrofolate reductase and DNA polymerase a (Slansky and Farnham, 1996). In addition, although p34 cdc2 lacks a clear role in the G1 to S transition, cdc2 gene expression is also induced at the G1/S boundary, via, at least in part, E2F binding sites (Dalton, 1992;North et al, 1996) existing in the promoter of cdc2.…”

Intratumoral injection of oligonucleotides to the NFκB binding site inhibits cachexia in a mouse tumor model

“…While E2F forms a complex with cyclin A and cdk 2, the major component of the complex during the early part of the cell cycle is the retinoblastoma protein (Rb). [22][23][24] As the cells enter S-phase, Rb is phosphorylated and leaves the complex, allowing E2F to induce cell cycle regulatory genes including c-myc, cmyb, cdc2, proliferating cell nuclear antigen (PCNA) and thymidine kinase, [25][26][27][28][29] resulting in the initiation of cell proliferation. Thus, we also hypothesize that transfection of tumor with sufficient quantities of the decoy ODN containing the E2F binding site would effectively bind E2F, and prevent it from transactivating the expression of cell cycle regulatory genes ( Figure 1) and thereby inhibit tumor growth in vivo.…”

pRb and p107 regulate E2F activity during lens fiber cell differentiation

“…Phosphorylation of pRb by cyclin D/cdk4 prevents formation of the pRb/E2F complex, permitting transcription of genes with E2F binding sites in their promoters (Nevins, 1992;Ikeda et al, 1996). Genes thought to be E2F targets include protooncogenes (Heibert et al, 1989;Lam and Watson, 1993), G1 cyclins (Muller et al, 1994;Henglein et al, 1994;Ohtani et al, 1995), enzymes required for DNA synthesis (Pearson et al, 1991;Means et al, 1992;Fridovich-Keil et al, 1993), and the G2-speci®c cdk, cdc2 (Dalton, 1992;Tommasi and Pfeifer, 1995). Several recent studies suggest that E2F may be primarily a negative regulator of transcription, directing the binding of repressors, such as pRb, to speci®c target genes (Tommasi and Pfeifer, 1995;Field et al, 1996;Yamasaki et al, 1996;Zwicker et al, 1996).…”