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DNA polmerase theta and its potential role in cancer

Investigator: Jamie Towle-Weicksel

Scientific Theme: Cancer

Abstract: Cancer is a devastating disease that results from the uncontrollable growth of certain cells in the body and is one of the leading causes of death in the United States. DNA is randomly damaged on daily basis by many factors including environmental exposure, random error, or genetic inheritance. This damaged DNA can lead to genomic instability and eventually cancer. Depending on the damage, the cell handles the stress in different ways. Double stranded breaks are resolved by three potential end-joining pathways: homologous recombination (HR); canonical non-homologous end joining (cNHEJ); or microhomology-mediated end joining (MMEJ). HR typically occurs in S and G2 phases of the cell cycle and requires a sister chromosome to provide a template for DNA synthesis. NHEJ occurs throughout the cell cycle, but results in loss of nucleotides at the site of the break. An alternative pathway, that is also active throughout the cell cycle, is MMEJ. The ends of the double-stranded DNA are resected exposing single-stranded DNA on either ends of the break. Any homology within the DNA ends are aligned by the enzyme DNA polymerase θ, which is thenable to fill in nucleotides at the gaps in the DNA. XRCC1-Ligase III α seals the remaining nick in the DNA.This results in little loss in genetic information, but can be mutagenic. This proposed study focuses on the A-family DNA polymerase theta (Pol θ or POLQ). It is a DNA repair enzyme that is able to perform single base, template directed, low fidelity repair (Arana et al., 2008; Maga et al., 2002; Prasad et al., 2009). POLQ gene expression has been shown to be upregulated in breast and colorectal cancer (Lemée et al., 2010; Pillaire et al., 2009). We have also identified Pol θ mutations from patient derived melanomas in collaboration with the Tissue Resource Core of the Yale SPORE in Skin Cancer. We hypothesize that aberrant Pol θ may be aid cancer cells during its growing stages. This study would provide a mechanism of mutagenesis by understanding 1) how cancer-associated variants have impaired fidelity and might contribute to carcinogenesis and 2) how the dynamics of the Pol θ is involved in nucleotide selection and overall fidelity.

Human Health Relevance: DNA polymerases are necessary for maintaining DNA fildelity as increased mutagenesis has been associated with cancer. Pol θ may play an important role in overall genomic stability due to its DNA repair capabilities. By identifying and characterizing cancer-associated variants of Pol θ that have reduced DNA repair abilities, our studies will provide fundamental insight as to the mechanism of mutagenesis and cancer.

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