ATM modulates transcription in response to histone deacetylase inhibition as part of its DNA damage response

Chromatin structure has a crucial role in a diversity of physiological processes, including development, differentiation and stress responses, via regulation of transcription, DNA replication and DNA damage repair. Histone deacetylase (HDAC) inhibitors regulate chromatin structure and activate the DNA damage checkpoint pathway involving Ataxia-telangiectasia mutated (ATM). Herein, we investigated the impact of histone acetylation/deacetylation modification on the ATM-mediated transcriptional modulation to provide a better understanding of the transcriptional function of ATM. The prototype HDAC inhibitor trichostain A (TSA) reprograms expression of the myeloid cell leukemia-1 (MCL1) and Gadd45alpha genes via the ATM-mediated signal pathway. Transcription of MCL1 and Gadd45alpha is enhanced following TSA treatment in ATM+ cells, but not in isogenic ATM- or kinase-dead ATM expressing cells, in the ATM-activated E2F1 or BRCA1-dependent manner, respectively. These findings suggest that ATM and its kinase activity are essential for the TSA-induced regulation of gene expression. In summary, ATM controls the transcriptional upregulation of MCL1 and Gadd45alpha through the activation of the ATM-mediated signal pathway in response to HDAC inhibition. These findings are important in helping to design combinatory treatment schedules for anticancer radio- or chemo-therapy with HDAC inhibitors.

DNA Damage Response Mediated through BRCA1 / Journal of the Korean Cancer Association, 대한암학회지

The BRCA1 gene was identified and cloned in 1994 based on its linkage to early onset breast and ovarian cancer syndromes in women. The tumor suppressor, BRCA1 is known as a major player in the DNA damage response. These are evident from its loss, which causes malignant transformation in breast and ovary, and renders cells to become sensitive to a wide variety of DNA damaging agents. Here, we have implications on functional coupling of the pleiotropic roles of BRCA1, including DNA damage signal networking, DNA repair, transcription, and checkpoint of cell cycle, to tumor suppression by examining the molecular mechanisms and functions of BRCA1. The breast cancer susceptibility 1 (BRCA1) gene was identified and mapped to chromosome 17q21 by analyzing families at high risk from breast and ovarian cancer, and was first cloned in 1994 (1). The BRCA1 gene encodes a large nuclear protein that is ubiquitously expressed in a number of tissues. BRCA1 shares little structural resemblance to the majority of other known proteins (Fig. 1). Its ortholog is only found in mammals but not in yeast, fly, worm, or zebra fish, indicating that BRCA1 may come later in evolution and it may have more specialized and tissue-specific functions in mammalian cells. Although a number of studies delineating and deciphering the real biological roles of BRCA1 have accumulated, understanding these BRCA1 unique features still remains to be challengingly elucidated.