B-Myb overcomes a p107-mediated cell proliferation block by interacting with an N-terminal domain of p107.
B-Myb is a cell-cycle regulated transcription factor which is implicated in cell proliferation and has an essential role in early embryonic development. In this study we examined the functions of B-Myb required to overcome G1 arrest in Saos-2 cells induced by the retinoblastoma-related p107 protein. Our results demonstrated that this activity was independent of B-Myb transactivation function, but correlated with its capacity to form an in vivo complex with p107. A large proportion of B-Myb formed complexes with p107 in cotransfected cells, however, B-Myb bound weakly to the related p130 protein and not at all to pRb. In contrast to the E2F transcription factors, which bind the p107 C-terminal pocket domain, B-Myb recognizes an N-terminal p107 region which overlaps the larger cyclin-binding domain. B-Myb and cyclin A2 formed mutually exclusive complexes with p107, and B-Myb enhanced the activity of co-transfected cyclin E kinase activity, implying that B-Myb affects the cell cycle by preventing sequestration of active cyclin/cdk2 complexes. This study defines a novel function of B-Myb and further suggests that the p107 N-terminus provides an interaction domain for transcription factors involved in cell cycle control.
Joaquin
Manel
M
Ludwig Institute for Cancer Research, Section of Virology and Cell Biology, Faculty of Medicine, Imperial College of Science, Technology and Medicine, Norfolk Place, London W2 1PG, UK.
Bessa
Maria
M
Saville
Mark K
MK
Watson
Roger J
RJ
D000595:Amino Acid Sequence; D001665:Binding Sites; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000502:physiology*; D019925:Cyclin A / Q000378:metabolism; D056751:Cyclin A2; D019927:Cyclin E / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D016193:G1 Phase / Q000502:physiology; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D011233:Precipitin Tests; D011485:Protein Binding; D050720:Retinoblastoma-Like Protein p107; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
C503721:CCNA2 protein, human; D018797:Cell Cycle Proteins; D019925:Cyclin A; D056751:Cyclin A2; D019927:Cyclin E; D004268:DNA-Binding Proteins; C064352:MYBL2 protein, human; D009687:Nuclear Proteins; C493844:RBL1 protein, human; D050720:Retinoblastoma-Like Protein p107; D015534:Trans-Activators