title: Nuclear export of BRCA1 occurs during early S phase and is calcium-dependent.
abstract: Although the breast cancer susceptibility gene 1 (BRCA1) protein is predominantly nuclear, its localization can vary during the cell cycle in response to cellular insults. For example, in S-phase cells, BRCA1 forms subnuclear foci and localizes to the perinuclear region in response to DNA damage. The present study provides evidence that BRCA1 is transiently excluded from the nucleus during the early part of S phase in the absence of DNA damage. The percentage of MCF-7 human breast cancer cells predominantly expressing nonnuclear BRCA1 significantly correlates with the percentage of cells within early S phase. This redistribution of BRCA1 is partially sensitive to leptomycin B, indicating that CRM-1-mediated nuclear export is involved. Similar results were observed with MCF-12A nonmalignant human mammary cells. The abilities of BAPTA-AM, an intracellular calcium chelator, to inhibit the change in BRCA1 localization, and of A23187, a calcium ionophore, and of thapsigargin to mimic nuclear exclusion of BRCA1, provide evidence for the involvement of calcium in this process. The calcium-mediated change in BRCA1 localization occurs in several cell lines, indicating that this effect is not cell line specific. BRCA2 localization is not affected by A23187. Furthermore, inhibition of calcium-calmodulin interaction and calcium-calmodulin dependent protein kinase II attenuates the calcium-mediated change in BRCA1 localization. These data suggest that BRCA1 nuclear export can be cell cycle-regulated by a calcium-dependent mechanism.
authors.affiliation: Department of Cancer Biology, Meharry Medical College, Nashville, TN 37208-3599, USA. kglover01@mmc.edu
authors.forename: Katherine
authors.initials: K
authors.lastname: Glover-Collins
authors.forename: Marilyn E
authors.initials: ME
authors.lastname: Thompson
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins; D019313:BRCA1 Protein / Q000378:metabolism*; D024682:BRCA2 Protein / Q000378:metabolism; D001940:Breast / Q000166:cytology / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D045744:Cell Line, Tumor; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D005260:Female; D006801:Humans; D016196:S Phase; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D051017:Apoptosis Regulatory Proteins; C118024:BLID protein, human; D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D024682:BRCA2 Protein; C551750:BRCA2 protein, human; D005231:Fatty Acids, Unsaturated; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D000001:Calcimycin; D004533:Egtazic Acid; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D002118:Calcium; C038753:leptomycin B