E2F-4 switches from p130 to p107 and pRB in response to cell cycle reentry.
The E2F transcription factor couples the coordinate expression of cell cycle proteins to their appropriate transition points. Its activity is controlled by the cell cycle regulators pRB, p107, and p130. These bind to E2F at defined but distinct stages of the cell cycle. Using specific antisera, we have identified the DP and E2F components of each of these species. Although present at very different levels, DP-1 and DP-2 are evenly distributed among each of these complexes. In contrast, the individual E2Fs have distinctly different binding profiles. Consistent with previous studies, E2F-1, E2F-2, and E2F-3 bind specifically to the retinoblastoma protein. In each case, their expression and DNA binding activity are restricted to post-G1/S fractions. Surprisingly, E2F-1 and E2F-3 make unequal contributions to the pRB-associated and free E2F activity, suggesting that these proteins perform different cell cycle functions. Most significantly, this study showed E2F-4 accounts for the vast majority of the endogenous E2F activity. In arrested cells, E2F-4 is sequestered by the p130 protein. However, as the cells pass the G1-to-S transition, the levels of pRB and p107 increase and E2F-4 now associates with both of these regulators. Despite this, a considerable amount of E2F-4 exists as free E2F. In G1 cells, this accounts for almost all of the free activity. Once the cells enter S phase, free E2F is composed of an equal mixture of E2F-4 and E2F-1.
Moberg
K
K
Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, 02139, USA.
Starz
M A
MA
Lees
J A
JA
D000911:Antibodies, Monoclonal; D001483:Base Sequence; D015153:Blotting, Western; D002352:Carrier Proteins; D002453:Cell Cycle / Q000235:genetics*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050703:E2F2 Transcription Factor; D050699:E2F3 Transcription Factor; D050704:E2F4 Transcription Factor; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000096:biosynthesis*; D015345:Oligonucleotide Probes; D010750:Phosphoproteins / Q000096:biosynthesis*; D011506:Proteins; D016160:Retinoblastoma Protein / Q000096:biosynthesis*; D056465:Retinoblastoma-Binding Protein 1; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000096:biosynthesis*; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D050703:E2F2 Transcription Factor; C493761:E2F2 protein, human; D050699:E2F3 Transcription Factor; C098319:E2F3 protein, human; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D009687:Nuclear Proteins; D015345:Oligonucleotide Probes; D010750:Phosphoproteins; D011506:Proteins; C493844:RBL1 protein, human; C493837:RBL2 protein, human; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; C493735:TFDP1 protein, human; D050680:Transcription Factor DP1; D014157:Transcription Factors