title: BRCA1-mediated G2/M cell cycle arrest requires ERK1/2 kinase activation.
abstract: Germline mutations in the BRCA1 gene are associated with an increased susceptibility to the development of breast and ovarian cancers. Evidence suggests that BRCA1 protein plays a key role in mediating DNA damage-induced checkpoint responses. Several studies have shown that ectopic expression of BRCA1 in human cells can trigger cellular responses similar to those induced by DNA damage, including G2/M cell cycle arrest and apoptosis. While the effects of ectopic BRCA1 expression on the G2/M transition and apoptosis have been extensively studied, the factors that dictate the balance between these two responses remain poorly understood. We have recently shown that ectopic expression of BRCA1 in MCF-7 human breast cancer cells resulted in activation of extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) and G2/M cell cycle arrest. Furthermore, inhibition of BRCA1-induced ERK1/2 activation using mitogen-activated protein kinase kinase 1 and 2 (MEK1/2)-specific inhibitors resulted in increased apoptosis, suggesting a potential role of ERK1/2 kinases in BRCA1-mediated G2/M checkpoint response. In this study, we assessed the role of ERK1/2 kinases in the regulation of BRCA1-mediated G2/M cell cycle arrest. Results indicate that BRCA1-induced G2/M cell cycle arrest and ERK1/2 activation correlate with changes in the level and/or activity of several key regulators of the G2/M checkpoint, including activation of Chk1 and Wee1 kinases, induction of 14-3-3, and down-regulation of Cdc25C. Furthermore, inhibition of ERK1/2 kinases using MEK1/2-specific inhibitors results in a marked attenuation of the BRCA1-induced G2/M arrest. Biochemical studies established that ERK1/2 inhibition abolished the effects of BRCA1 on components of the G2/M checkpoint, including regulation of Cdc25C expression and activation of Wee1 and Chk1 kinases. These results implicate a critical role of ERK1/2 signaling in the regulation of BRCA1 function on controlling the G2/M checkpoint responses.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 986805 Nebraska Medical Center, Omaha, NE 68198-6805, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Yan
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Spieker
authors.forename: Min
authors.initials: M
authors.lastname: Kim
authors.forename: Scott M
authors.initials: SM
authors.lastname: Stoeger
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Cowan
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D000256:Adenoviridae / Q000235:genetics; D017209:Apoptosis; D019313:BRCA1 Protein / Q000378:metabolism*; D015152:Blotting, Northern; D001943:Breast Neoplasms / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism; D002455:Cell Division; D045744:Cell Line, Tumor; D000071877:Checkpoint Kinase 1; D004247:DNA / Q000378:metabolism; D004249:DNA Damage; D015536:Down-Regulation; D004789:Enzyme Activation; D016195:G2 Phase; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014443:Tyrosine / Q000737:chemistry; D020687:cdc25 Phosphatases / Q000378:metabolism
chemical_list: D048948:14-3-3 Proteins; D019313:BRCA1 Protein; D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D014443:Tyrosine; D004247:DNA; D011494:Protein Kinases; C482128:MAP2K2 protein, human; D011505:Protein-Tyrosine Kinases; C499349:WEE1 protein, human; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C517009:CDC25C protein, human; D020687:cdc25 Phosphatases