E2F6 negatively regulates ultraviolet-induced apoptosis via modulation of BRCA1

Abstract

E2F6 is believed to repress E2F-responsive genes and therefore plays an important role in cell-cycle regulation. However, the role of E2F6 in the control of apoptosis remains unknown. We show here that the expression of E2F6 was downregulated with a concurrent increase in BRCA1 mRNA and cleaved protein during ultraviolet (UV)-induced apoptosis in human embryonic kidney 293 cells. Moreover, E2F6 overexpression distinctly inhibited UV-induced apoptosis as well as UV-induced increases in BRCA1 expression and cleavage, accompanied with increases of the full-length BRCA1 and BRCA1 nuclear foci. In contrast, knockdown of E2F6 by small interfering RNA had opposite effects. Furthermore, these effects of E2F6 on BRCA1 depended upon the association of E2F6 with BRCA1 via its C-terminus in a UV-triggered manner and upon the transcriptional repression by E2F6 on the BRCA1 promoter. These findings provide the first demonstration of the important role for E2F6 in the control of apoptosis via targeting of BRCA1.

E2F6 Inhibits Cobalt Chloride-Mimetic Hypoxia-induced Apoptosis through E2F1

“…Ectopic expression of E2F6 significantly represses hypoxia-induced apoptosis, whereas RNAi-mediated E2F6 knockdown sensitizes cells to hypoxia-induced apoptosis (Figure 2). These observations are consistent with our recent findings of negative regulation of E2F6 in UV-induced apoptosis (Yang et al, 2007). Downregulation of E2F6 may play an important role in tumor suppression and in radiotherapy by sensitizing damaged cells to death responses.…”

“…These results confirm and extend our recent findings that E2F6 negatively regulates UV-induced apoptosis (Yang et al, 2007), and they provide new insight into the functional role and regulatory mechanisms of E2F6 in hypoxia-induced apoptosis.…”

“…It has also been shown that E2F6 increases the percentage of cells in S phase and, when overexpressed, it inhibits S phase entry of quiescent cells and induces subsequent proliferate arrest (Cartwright et al, 1998;Gaubatz et al, 1998;Kherrouche et al, 2001). We demonstrated recently that E2F6 can negatively regulate DNA damage-induced apoptosis via modulation of BRCA1 through its C terminus (Yang et al, 2007), whereas the implication of E2F6 in hypoxia-induced apoptosis remains to be identified. E2F1, the founding member of E2F family, has an apparently unique ability to induce apoptosis.…”

“…DNA fragmentation was determined according to previous methods, with slight modifications (Wyllie and Morris 1982;Yang et al, 2007). In brief, floating and attached cells (3-4 ϫ 10 6 ) were lysed in 500 l of TTE buffer (containing 10 mM Tris-HCl, pH 7.5, 1 mM EDTA, and 0.2% Triton X-100).…”

Type 3 inositol 1,4,5-trisphosphate receptor negatively regulates apoptosis during mouse embryonic stem cell differentiation

“…For cell cycle analysis, asynchronously growing ES cells were fixed with ethanol and stained with 50 mg/ml PI containing 0.1 mg/ml RNase A (both from Sigma-Aldrich). 54 Cells were analyzed by flow cytometry to determine G1, S, and G2/M cell cycle distribution (FACStar Plus Flow Cytometer, Becton-Dickinson).…”