Phosphorylation of serine 1387 in Brca1 is specifically required for the ATM-mediated S-phase checkpoint after ionizing irradiation

Department of Hematology-Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Cancer Research (Impact Factor: 9.33). 09/2002; 62(16):4588-91.
Source: PubMed

ABSTRACT Although it is well established that inheritance of mutations in the Brca1 gene significantly increases the chances of developing breast or ovarian cancers, the mechanisms underlying this specific tumor susceptibility remain to be clarified. It is clear that one of the roles of the Brca1 protein is to facilitate cellular responses to DNA damage. We recently reported that Brca1 function is required for appropriate cell cycle arrests after ionizing irradiation in both the S-phase and the G2 phase of the cell cycle. We also found that mutation of serine 1423 in Brca1, a target of Atm phosphorylation, abrogates the G2-M checkpoint but not the ionizing irradiation-induced S-phase checkpoint. Here we demonstrate that mutation of serine 1387 in Brca1, another target of Atm phosphorylation, conversely abrogates the radiation-induced S-phase arrest but does not affect the G2-M checkpoint. Thus, these two posttranslational modifications of Brca1 have two distinct functional roles in the protein. In addition, although mutation of this site abrogates the ionizing irradiation-induced S-phase arrest, it does not adversely affect cell survival after irradiation. This demonstrates that loss of this checkpoint function by itself does not affect cell survival and suggests that some other function of Brca1 alters cell survival after DNA damage.

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Available from: Seong-Tae Kim, Sep 26, 2015
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    • "Two tandem repeat globular domains termed BRCT, a common feature of proteins involved in the DNA damage repair and cell cycle control [5], lie at the C-terminus. Functionally, BRCA1 has been implicated in a diverse array of cellular functions, including ubiquitination [6]–[9], regulation of the G1/S [10], intra-S and G2/M-phase cell cycle checkpoint control [11]–[14], regulation of spindle pole body duplication[15], transcription [16]–[19], sex chromosome inactivation [20]–[23] and homologous recombination repair of double stranded DNA breaks [24], [25]. Taken together, these individual roles suggest a function for BRCA1 in the maintenance of genomic integrity [26], [27]. "
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    ABSTRACT: The assessment of BRCA1 and BRCA2 coding sequences to identify pathogenic mutations associated with inherited breast/ovarian cancer syndrome has provided a method to identify high-risk individuals, allowing them to seek preventative treatments and strategies. However, the current test is expensive, and cannot differentiate between pathogenic variants and those that may be benign. Focusing only on one of the two BRCA partners, we have developed a biological assay for haploinsufficiency of BRCA1. Using a series of EBV-transformed cell lines, we explored gene expression patterns in cells that were BRCA1 wildtype compared to those that carried (heterozygous) BRCA1 pathogenic mutations. We identified a subset of 43 genes whose combined expression pattern is a sensitive predictor of BRCA1 status. The gene set was disproportionately made up of genes involved in cellular differentiation, lending credence to the hypothesis that single copy loss of BRCA1 function may impact differentiation, rendering cells more susceptible to undergoing malignant processes.
    PLoS ONE 06/2014; 9(6):e100068. DOI:10.1371/journal.pone.0100068 · 3.23 Impact Factor
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    • "BRCA1 is implicated in the regulation of several cellular functions such as chromatin remodelling and DNA repair (105). BRCA1 becomes phosphorylated and, in turn, activated by ATM and ATR (106,107) and is involved in transcriptional activation of some DNA repair genes (see later in the text). BRCA1 was found to be associated with RNA polymerase II holoenzyme complex (108), thus having an impact on transcription in vitro (109). "
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    ABSTRACT: DNA repair is the first barrier in the defense against genotoxic stress. In recent years, mechanisms that recognize DNA damage and activate DNA repair functions through transcriptional upregulation and post-translational modification were the focus of intensive research. Most DNA repair pathways are complex, involving many proteins working in discrete consecutive steps. Therefore, their balanced expression is important for avoiding erroneous repair that might result from excessive base removal and DNA cleavage. Amelioration of DNA repair requires both a fine-tuned system of lesion recognition and transcription factors that regulate repair genes in a balanced way. Transcriptional upregulation of DNA repair genes by genotoxic stress is counteracted by DNA damage that blocks transcription. Therefore, induction of DNA repair resulting in an adaptive response is only visible through a narrow window of dose. Here, we review transcriptional regulation of DNA repair genes in normal and cancer cells and describe mechanisms of promoter activation following genotoxic exposures through environmental carcinogens and anticancer drugs. The data available to date indicate that 25 DNA repair genes are subject to regulation following genotoxic stress in rodent and human cells, but for only a few of them, the data are solid as to the mechanism, homeostatic regulation and involvement in an adaptive response to genotoxic stress.
    Nucleic Acids Research 07/2013; 41(18). DOI:10.1093/nar/gkt635 · 9.11 Impact Factor
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    • "A defect in this checkpoint results in continued DNA synthesis, also called radioresistant DNA synthesis following IR. This checkpoint was found to require an ATM-dependent phosphorylation of BRCA1 on serine-1387 as well as a functional NBS1 (Xu et al., 2002). In addition to DNA damage-responsive checkpoints, several studies indicate that BRCA1 also regulates the mitotic spindle checkpoint by regulating gene expression associated with orderly progression through mitosis (Wang et al., 2004; Bae et al., 2005). "
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    ABSTRACT: Mutations of the breast and ovarian cancer susceptibility gene 1 (BRCA1) account for about 40-45% of hereditary breast cancer cases. Moreover, a significant fraction of sporadic (non-hereditary) breast and ovarian cancers exhibit reduced or absent expression of the BRCA1 protein, suggesting an additional role for BRCA1 in sporadic cancers. BRCA1 follows the classic pattern of a highly penetrant Knudsen-type tumor suppressor gene in which one allele is inactivated through a germ-line mutation and the other is mutated or deleted within the tumor. BRCA1 is a multi-functional protein but it is not fully understood which function(s) is (are) most important for tumor suppression, nor is it clear why BRCA1-mutations confer a high risk for breast and ovarian cancers and not a broad spectrum of tumor types. Here, we will review BRCA1 functions in the DNA damage response (DDR), which are likely to contribute to tumor suppression. In the process, we will highlight some of the controversies and unresolved issues in the field. We will also describe a recently identified and under-investigated role for BRCA1 in the regulation of telomeres and the implications of this role in the DDR and cancer suppression.
    Frontiers in Genetics 06/2013; 4:85. DOI:10.3389/fgene.2013.00085
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