The human genome is subject to constant attack by endogenous and environmental DNA damaging agents. If unrepaired, DNA lesions will give rise to mutations that in turn may lead to cancer formation. Fortunately, a complex network of DNA repair pathways operates to remove DNA lesions. To assess the biological significance of exposure to environmental DNA damaging agents, it is necessary to understand the details of the complex cellular response to DNA damage. Unlike the conserved LIG1 and LIG4 genes, lower eukaryotes lack a homolog of the mammalian LIG3 gene, which encodes at least three distinct polypeptides. Interestingly, the DNA ligase III?-associated proteins, poly (ADP-ribose) polymerase 1 (PARP-1), XRCC1 and DNA polymerase (Pol) ?, each of which have been implicated in base excision repair and the repair of DNA single strand breaks, are also found only in higher eukaryotes. Using a modified yeast two hybrid assay, we have identified a series of XRCC1 mutants that are defective in specific protein-protein interactions.
In Specific Aim 1, we will utilize these mutants to delineate the functional and biological consequences of protein-protein interactions between DNA ligase III?/XRCC1 and other proteins involved in base excision and single strand break repair. Recent studies have increased the repertoire of DNA repair transactions in which DNA ligase III?/XRCC1 participates.
In Specific Aim 2, we will determine how DNA ligase III?/XRCC1 is recruited to the DNA nucleotide excision repair machinery and whether this involves an interaction between XRCC1 and PCNA. In preliminary studies, we have identified an interaction between DNA ligase III?/XRCC1 and hRad50/hMre11/Nbs.
In Specific Aim 3, we will determine how DNA damage regulates this interaction and whether these proteins act together in an error- prone non-homologous end-joining sub pathway that repairs DNA double strand breaks. Interestingly, this error-prone pathway is up-regulated in cancer cells and may contribute to their characteristic genomic instability.
In Specific Aim 4, we will identify and characterize small molecule inhibitors of DNA ligase III. We envision that that these inhibitors will not only be valuable reagents for elucidating the cellular functions of the LIG3 gene products but also may serve as lead compounds for the development of novel anti-cancer agents.

Public Health Relevance

Roles of DNA LIG3 and XRCC1 Genes in Genome Stability PI: Alan E. Tomkinson Public Health Relevance (Project Narrative) It is well established that genomic instability drives the progression from a normal cell into a cancer cell. Human cells have a complex network of pathways that act together to maintain genome stability. A mechanistic understanding of these pathways will provide fundamental insights into tumor suppression. In addition, genomic instability is a characteristic of tumor cells, indicating that there are differences in the pathways that normally maintain stability. These differences between normal and cancer cells offer an opportunity to develop therapeutic strategies that selectively target cancer cells.

National Institute of Health (NIH)
National Institute of Environmental Health Sciences (NIEHS)
Research Project (R01)
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Special Emphasis Panel (ZRG1-ONC-H (02))
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Mcallister, Kimberly A
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University of New Mexico Health Sciences Center
Internal Medicine/Medicine
Schools of Medicine
United States
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Sallmyr, Annahita; Tomkinson, Alan E (2018) Repair of DNA double-strand breaks by mammalian alternative end-joining pathways. J Biol Chem 293:10536-10546
Wiest, Nathaniel E; Tomkinson, Alan E (2017) Optimization of Native and Formaldehyde iPOND Techniques for Use in Suspension Cells. Methods Enzymol 591:1-32
Cannan, Wendy J; Rashid, Ishtiaque; Tomkinson, Alan E et al. (2017) The Human Ligase III?-XRCC1 Protein Complex Performs DNA Nick Repair after Transient Unwrapping of Nucleosomal DNA. J Biol Chem 292:5227-5238
Greco, George E; Matsumoto, Yoshihiro; Brooks, Rhys C et al. (2016) SCR7 is neither a selective nor a potent inhibitor of human DNA ligase IV. DNA Repair (Amst) 43:18-23
Sallmyr, Annahita; Matsumoto, Yoshihiro; Roginskaya, Vera et al. (2016) Inhibiting Mitochondrial DNA Ligase III? Activates Caspase 1-Dependent Apoptosis in Cancer Cells. Cancer Res 76:5431-41
Kukshal, Vandna; Kim, In-Kwon; Hura, Gregory L et al. (2015) Human DNA ligase III bridges two DNA ends to promote specific intermolecular DNA end joining. Nucleic Acids Res 43:7021-31
Ghezraoui, Hind; Piganeau, Marion; Renouf, Benjamin et al. (2014) Chromosomal translocations in human cells are generated by canonical nonhomologous end-joining. Mol Cell 55:829-842
Tomkinson, Alan E; Sallmyr, Annahita (2013) Structure and function of the DNA ligases encoded by the mammalian LIG3 gene. Gene 531:150-7
Tobin, L A; Robert, C; Rapoport, A P et al. (2013) Targeting abnormal DNA double-strand break repair in tyrosine kinase inhibitor-resistant chronic myeloid leukemias. Oncogene 32:1784-93
Tomkinson, Alan E; Howes, Timothy R L; Wiest, Nathaniel E (2013) DNA ligases as therapeutic targets. Transl Cancer Res 2:

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