DNA base excision repair (BER) is a ubiquitous and indispensable defense mechanism against cell death, mutagenesis, and carcinogenesis caused by spontaneously formed DNA damage, such as oxidation and alkylation. Apurinic/apyrimidinic endonuclease (APE1 in mammals) arguably determines the BER rate in cells and thus plays a central role in the repair pathway. Recent findings indicate that APE1 is essential for cellular viability, and that endogenous DNA damage is lethal if left unrepaired. Independently from its repair activity, APE1 interacts with histone deacetylase 1 (HDAC1) to suppress expression of many genes, including the parathyroid hormone gene. APE1 also regulates cJun/cFos and other crucial transcription factors. A high of APE1 is often in are expression observed malignant tumor cells, which more resistant to radio- and chemotherapeutic treatments, suggesting that APE1's repair function increases the chance of survival for cancer cells as well. Thus, APE1 may be either beneficial or harmful to humans, depending on the type of cells in which it is expressed. Understanding the mechanism for regulation of APE1 activity is therefore crucial for evaluating BER efficiency and its consequences in normal and cancer cells. Indeed, cancer predisposition by APE1 deficiency is known and p53 is an upstream regulator of APE1. We have discovered that APE1 is ubiquitinated by mouse double minute 2 (MDM2), and that the ubiquitination is induced by genotoxic stress in a p53-dependent manner. Ubiquitination occurs at specific Lys residues in the APE1 polypeptide, and appears to have significant effects on the functions of APE1 and other cellular proteins, including XRCC1 (X-ray cross-complementation 1), p53, and HDAC1, that interact directly with APE1. The central hypothesis of this project is that APE1 ubiquitination, regulated by MDM2 and p53, modulates the APE1 level and functions in DNA damage response. In order to elucidate the cellular defense mechanism involving this remarkably multifunctional protein, we will: (1) determine the effect of APE1 ubiquitination on its enzymatic and DNA binding activities;(2) unravel interaction of ubiquitinated APE1 with factors in BER and p53 signaling network;and (3) establish the regulation of APE1 ubiquitination in vivo. These parameters are crucial to predict susceptibility of cancer cells against therapeutic drugs that generates genomic instability. With the research facilities provided by Louisiana Cancer Research Consortium (LCRC), this project in the long-term should provide insights for developing new modalities for adjuvant cancer therapies and organ preservation, and for improving the management of other age-related pathophysiology.

Public Health Relevance

DNA is continuously damaged by environmental toxicants like smoke, and by reactive oxygen radicals generated inside of our bodies. Damaged DNA causes mutations and may ultimately lead to cancer and age- related diseases. This project will help us understand how to enhance natural healing of DNA damage, and will help to improve the current methodology for non-surgical cancer treatments, including radiotherapy and chemotherapy.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Cancer Etiology Study Section (CE)
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Okano, Paul
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University of Kentucky
Schools of Medicine
United States
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Wicker, Christina A; Izumi, Tadahide (2016) Analysis of RNA expression of normal and cancer tissues reveals high correlation of COP9 gene expression with respiratory chain complex components. BMC Genomics 17:983
Suganya, Rangaswamy; Chakraborty, Anirban; Miriyala, Sumitra et al. (2015) Suppression of oxidative phosphorylation in mouse embryonic fibroblast cells deficient in apurinic/apyrimidinic endonuclease. DNA Repair (Amst) 27:40-8
Li, Songhua; Izumi, Tadahide; Hu, Jane et al. (2014) Rescue of enzymatic function for disease-associated RPE65 proteins containing various missense mutations in non-active sites. J Biol Chem 289:18943-56
Scott, Timothy L; Rangaswamy, Suganya; Wicker, Christina A et al. (2014) Repair of oxidative DNA damage and cancer: recent progress in DNA base excision repair. Antioxid Redox Signal 20:708-26
Hegde, Muralidhar L; Izumi, Tadahide; Mitra, Sankar (2012) Oxidized base damage and single-strand break repair in mammalian genomes: role of disordered regions and posttranslational modifications in early enzymes. Prog Mol Biol Transl Sci 110:123-53
Jaiswal, Aruna S; Armas, Melissa L; Izumi, Tadahide et al. (2012) Adenomatous polyposis coli interacts with flap endonuclease 1 to block its nuclear entry and function. Neoplasia 14:495-508
Busso, Carlos S; Wedgeworth, Courtney M; Izumi, Tadahide (2011) Ubiquitination of human AP-endonuclease 1 (APE1) enhanced by T233E substitution and by CDK5. Nucleic Acids Res 39:8017-28
Busso, Carlos S; Lake, Michael W; Izumi, Tadahide (2010) Posttranslational modification of mammalian AP endonuclease (APE1). Cell Mol Life Sci 67:3609-20
Busso, C S; Iwakuma, T; Izumi, T (2009) Ubiquitination of mammalian AP endonuclease (APE1) regulated by the p53-MDM2 signaling pathway. Oncogene 28:1616-25
Mantha, Anil K; Oezguen, Numan; Bhakat, Kishor K et al. (2008) Unusual role of a cysteine residue in substrate binding and activity of human AP-endonuclease 1. J Mol Biol 379:28-37

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