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 MCF12A 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 calciumcalmodulin 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 calciumdependent mechanism.

Histone Methyltransferase EZH2 Induces Akt-Dependent Genomic Instability and BRCA1 Inhibition in Breast Cancer

“…While CAL51 controls exhibited predominantly cytoplasmic and perinuclear BRCA1 protein as previously reported (20), EZH2 KD cells accumulated BRCA1 in the nucleus (Figure 1C and D). We conclude that EZH2 influences the intracellular localization of BRCA1 protein in non-tumorigenic breast cells and in breast cancer cells.…”

“…Recent studies have provided information on the subcellular localization of BRCA1 protein during the cell cycle in normal breast cells and breast cancer cells (20–22). BRCA1 protein is exported from the nucleus transiently during the initial part of S phase.…”

“…BRCA1 protein is exported from the nucleus transiently during the initial part of S phase. By late S phase BRCA1 resumes being a predominantly nuclear protein (20–22). Activation of the protein kinase b (Akt) has been implicated in the nuclear/cytoplasmic shuttling of BRCA1 protein in breast cells (23–26).…”

Non-Selective Cation Channel-Mediated Ca²⁺-Entry and Activation of Ca²⁺/Calmodulin-Dependent Kinase II Contribute to G₂/M Cell Cycle Arrest and Survival of Irradiated Leukemia Cells

“…In osteosarcoma, CaMKII increases membrane-bound Tiam1 and GTP-bound Rac1 which decreases p21 gene expression [44]. Moreover, in breast cancer, CaMKII triggers the export of BRCA1 from the nucleus during the early part of the S phase [45]. This nuclear export decreases the BRCA1-dependent expression of p21.…”

Functional Interaction of the Ras Effector RASSF5 with the Tyrosine Kinase Lck: Critical Role in Nucleocytoplasmic Transport and Cell Cycle Regulation

“…[30][31][32][33][34] In order to understand the role of nucleocytoplasmic transport in RASSF5 function, we cotransfected wild type, export-defective mutant (ΔNES), proline mutant (RASSF5-M1), the Lck-interaction-defective mutant (Y262,281A) of RASSF5, and an empty vector with the pBABEpuro Fig. 9 (legend on next page) vector in A549 cells.…”