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Title: Role of Poly (ADP-Ribose) Polymerase 1 and Copper Homeostasis Factor, Antioxidant Protein 1 in the Maintenance of Genomic Integrity
Keywords: PARP-1, Genotoxicity, ATOX1, Copper
Issue Date: 10-Jun-2010
Citation: LAKSHMIDEVI D/O BALAKRISHNAN (2010-06-10). Role of Poly (ADP-Ribose) Polymerase 1 and Copper Homeostasis Factor, Antioxidant Protein 1 in the Maintenance of Genomic Integrity. ScholarBank@NUS Repository.
Abstract: Telomeres are the terminal nucleoprotein structures of chromosomes, protecting chromosomal ends from nuclease attack and recombination. Dysfunctional telomeres trigger genomic instability that underlies tumourigenesis. Poly (ADP-Ribose) Polymerase 1 (PARP-1), an important player in the base excision repair pathway, is a regulator of telomere length and telomeric end-capping function. In this study, we wanted to investigate the role of PARP-1 at the telomeres under conditions of DNA damage. Sodium arsenite, the DNA damaging agent used in this study, is a potent environmental toxicant and a known inducer of oxidative damage. We identified that PARP-1 is a critical factor required for mouse cells to withstand arsenite-induced chromosomal aberrations and cell death. PARP-1 was also observed to have an essential function in defence against telomere attrition and resultant genomic instability. Interestingly, our microarray analysis revealed differential expression of copper metabolism and copper binding proteins following arsenite-induced DNA damage. Additionally, a link between copper metabolism and PARP-1 has been recently demonstrated where, copper was able to inhibit PARP-1 activity. Copper is a key component of enzymatic anti-oxidative defence systems yet under conditions of copper excess, it can be a key inducer of ROS. Defects in copper homeostasis are implicated in pathophysiologies such as cancer. Gene set enrichment analysis indicated that genes involved in copper metabolism were significantly differentially expressed in the absence of PARP-1 and following arsenite treatment. We thus investigated if copper metabolism may directly have a role in DNA damage response in mammalian cells. Copper supplementation reduced the levels of double strand breaks induced by genotoxicants in normal MEFs. Yet, in copper metabolism disease conditions such as Menkes and Wilson¿s diseases, patient lymphoblastoid cells displayed increased levels of DSBs and genomic instability. These findings reiterate the importance of tight regulation of copper levels in the cellular milieu for proper biological function. We then further explored if specific factors in the copper metabolism pathway may affect the susceptibility to DNA damage. Antioxidant protein 1 (ATOX1), a copper chaperone, was down regulated in PARP-1 deficient MEFs. Furthermore, ATOX1 was recently established to be a copper-dependent transcription factor. While the antioxidant effects of ATOX1 have been demonstrated, its role in DNA damage response or the maintenance of genomic stability has not been clearly elucidated. We identified that Atox1 mRNA levels rose in response to hydrogen peroxide and arsenite exposure. Hence, we investigated the effect of ATOX1 deficiency in MEFs under conditions of genotoxicant-induced DNA damage. Increased DNA damage was observed in Atox1 deficient MEFs when challenged with sodium arsenite and radiation. The absence of ATOX1 was also responsible for increased levels of ROS as well as DSB sustained by the cells. In addition, genes in the DNA damage signalling, oxidative stress and anti-oxidant defence pathways were differentially expressed in the absence of ATOX1. Given that oxidative processes are major sources of DNA damage, we propose that the antioxidant properties of ATOX1 may protect genomic integrity. Although the nature of PARP-1 and ATOX1 interaction has not yet been elucidated, this study proposes a new paradigm for how copper metabolism impacts cellular oxidation state and genome stability.
Appears in Collections:Ph.D Theses (Open)

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