Functional synergy between DP-1 and E2F-1 in the cell cycle-regulating transcription factor DRTF1/E2F.

Abstract

It is widely believed that the cellular transcription factor DRTF1/E2F integrates cell cycle events with the transcription apparatus because during cell cycle progression in mammalian cells it interacts with molecules that are important regulators of cellular proliferation, such as the retinoblastoma tumour suppressor gene product (pRb), p107, cyclins and cyclin‐dependent kinases. Thus, pRb, which negatively regulates early cell cycle progression and is frequently mutated in tumour cells, and the Rb‐related protein p107, bind to and repress the transcriptional activity of DRTF1/E2F. Viral oncoproteins, such as adenovirus E1a and SV40 large T antigen, overcome such repression by sequestering pRb and p107 and in so doing are likely to activate genes regulated by DRTF1/E2F, such as cdc2, c‐myc and DHFR. Two sequence‐specific DNA binding proteins, E2F‐1 and DP‐1, which bind to the E2F site, contain a small region of similarity. The functional relationship between them has, however, been unclear. We report here that DP‐1 and E2F‐1 exist in a DNA binding complex in vivo and that they bind efficiently and preferentially as a heterodimer to the E2F site. Moreover, studies in yeast and Drosophila cells indicate that DP‐1 and E2F‐1 interact synergistically in E2F site‐dependent transcriptional activation.

Multiple Changes in E2F Function and Regulation Occur upon Muscle Differentiation

“…Recent evidence indicates that in human cells, E2F represents a transcription factor family (at least E2F-1 to E2F-4 and DP-1) (4,22,23,30,31,37,40,42,46,62). The E2F and DP families form heterodimeric complexes that are implicated in enhanced E2F-dependent transcriptional activation (2,31,42). There has been some characterization of murine E2Fs, but the list is probably not complete (23,48).…”

Methylseleninic acid inhibits microvascular endothelial G1 cell cycle progression and decreases tumor microvessel density

“…[28][29][30] The association of DP1 and E2F1 enhances and is critical for both the DNA binding and transcriptional activities of E2F1. 31,32 During the cell cycle, phosphorylation changes of Rb protein profoundly modulate E2F1 activity: at early-G 1 , hypophosphorylated Rb binds tightly to and disables the Growth factor-stimulated cell cycle progression of TIME cells; after 36 hr deprivation of growth factors including VEGF, EGF, bFGF and IGF-1, TIME cells were stimulated with these growth factors in the absence or presence of 3 lM MSeA; the average of 2 flasks at each data point was plotted; variability was within 3% of respective average values. (d) S-phase estimated by conventional flow cytometry versus by BrdU labeling; TIME cells were synchronized as in (c) and stimulated for 24 hr in the absence or presence of 3 lM MSeA; the cells were labeled with 1 lM BrdU for 1 hr and harvested for BrdU staining and propidium iodide staining followed by flow cytometry (mean 6 SD, n 5 3); * denotes significant difference from the respective control cells.…”

Control of E2F activity by p21Waf1/Cip1

“…Rabbit anti-DP1 polyclonal antibodies have been described previously (Bandara et al, 1993). The rabbit a nity puri®ed anti-p21 (AP8) antiserum was a kind gift from Dr J Gannon and T Hunt, and anti-p21 (C19), mouse E2F-1 (KH95) and Gal4 DBD antisera were obtained from Santa Cruz.…”

“…Extracts were precleared with 40 ml of glutathione beads for 2 h before incubation with 1 mg of the corresponding GST fusion proteins for a further 2 h. Beads were washed ®ve times in bu er containing 500 mM KCl and resuspended in two bead volumes of SDS loading bu er. Samples were then analysed by SDS ± PAGE followed by Western blotting using rabbit polyclonal anti-DP1 peptide antibodies (1/250) (Bandara et al, 1993) mouse monoclonal anti-E2F-1 KH95 (1/1000).…”