DNA lesions involved in chemotherapy responses and their repair

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The integrity of the human genome is constantly threatened by spontaneous DNA damage from products of normal metabolism, for example DNA oxidation, or environmental mutagens and carcinogens such as UV light. Improperly repaired DNA damage is a major contributing factor to the onset of cancer. To prevent this, human cells have a multitude of specialised DNA repair mechanisms to repair distinct lesions in the best possible way. As a consequence, mutations in DNA repair genes lead to increased cancer risk. Common examples for cancer-associated DNA repair gene mutations include the BRCA1 and BRCA2 breast cancer genes, and the MLH1 gene mutated in familial non-polyposis colorectal cancer. We have identified a novel human DNA repair protein termed ASCIZ that performs a function similar to BRCA1 and BRCA2 in that it regulates the concentration of the RAD51 repair protein in specific DNA repair centres in the cell nucleus. However, compared to BRCA1-BRCA2, ASCIZ performs this function in response to different types of DNA damage and acts in concert with the MLH1 protein. Here we want to investigate what the specific DNA lesions are that are repaired by ASCIZ, and we want to determine if the repair involves a copy mechanism that utilises intact genes as repair templates. In addition, we want to generate animals in which the ASCIZ gene is mutated, as a model to study its role in cancer development in humans. Cells that lack ASCIZ are dramatically hypersensitive to DNA damaging agents that are similar to clinically used chemotherapy drugs. We hope that our studies may identify possible approaches to develop drugs against ASCIZ and related proteins in order to kill cancer cells more efficiently.