FIG. 9.

C/EBPα regulates E2F complexes in HT1 cultured cells. (A) Composition of E2F complexes in dividing HT1 cells. Nuclear extracts (5 μg) from HT1 cells were incubated with the E2F oligomer in the presence of antibodies (indicated at the top) and analyzed by gel shift assay. (B) Induction of C/EBPα by IPTG (36) leads to the disruption of E2F-p107 and E2F-Rb complexes. Cytoplasmic (C) and nuclear (N) proteins of HT1 cells were isolated 24 h after IPTG or glucose (Gl) (control) addition and analyzed by gel shift assay. Free probe was run off the gel. (C) The E2F homology region of C/EBPα (Y-DLF) is sufficient to disrupt E2F-p107 and E2F-Rb complexes. Y-DLF peptide and control peptide (C.pept.) were preincubated with nuclear extracts from dividing HT1 cells and added to the E2F binding reaction mixture.