XRCC1 Variant R280H: Search for Potential Role in Carcinogenesis

Rsrch Assoc Ther Radiology
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X-ray repair cross-complementing protein 1 (XRCC1) is a key player of both DNA base excision repair (BER) and single strand break repair (SSBR) pathways. XRCC1 is acting as a non-enzymatic scaffold protein by interacting with a large variety of proteins involved in BER/SSBR and localizing multiprotein complexes to the damaged DNA site. A number of single nucleotide polymorphisms (SNPs) in human XRCC1 were studied in relation with different types of cancer. The Arg280His (R280H) variant has been reported to be associated with an increased rate of breast cancer (in Asians but not Caucasians), prostate cancer, nasopharyngeal carcinoma, colorectal adenoma, and lung cancer (in conjunction with additional factors only). To induce expression of XRCC1 (R280H or WT) in mouse C127 or human MCF 10A cell lines, we used the tetracycline off system. Either of the two cell lines was infected with high titer retrovirus expressing WT or R280H XRCC1 under control of Tet-regulated promoter and single clones with similar levels of WT and R280H expression were selected for further study. C127 cells expressing the R280H variant were found to be more resistant to treatment with methylmethane sulfonate (MMS) or the base analog 5-fluorouracil (5-FU). A substantial increase in focus formation in two independent C127 clones expressing R280H suggested the ability of this variant to induce cellular transformation. This hypothesis is currently being tested by the anchorage independent growth assay in MCF10A clones expressing either R280H or WT XRCC1. The rate of cell growth is compared between XRCC1 expressing clones (R280H or WT) at early and late passages to reveal the possible cellular transformation effect of the variant. The level of chromosomal aberrations and the nature of accumulated BER intermediate substrates (if any) in MCF10A R280H and WT XRCC1 expressing clones are assessed to further characterize a potential role of R280H variant in carcinogenesis.