Our previous studies revealed a splicing variant (lacking a 42 base pair segment) within the 5'-UTR of the ERCC1 gene, a critical component of the nucleotide excision repair (NER) pathway that plays an important role in the development of chemoresistance in platinum-based anticancer therapy. This 42-bp segment seems to possess a regulatory function in ERCC1 expression and representing the level of clinical response to platinum-treatment in ovarian cancer patients. To confirm the existence of the 42-bp deletion and to investigate the 42-bp function, we performed several experiments and assays. Northern blot analysis and RNase protection assay provide evidence that the 42-bp deletion occurs at RNA level of ERCC1 5'-UTR in both ovarian cancer cell lines and ovarian cancer tissues. Luciferase assay suggests that this gene fragment possesses a regulatory function as an enhancer of ERCC1 gene expression in ovarian cancer cells. In Electrophoretic Mobility Shift Assay (EMSA), a shift band present in the ovarian cancer cell line extracts is consistent with the presence of an intracellular protein that recognizes this specific 42-bp sequence. Further, specific EMSA results with 42-bp probe mutated at the site of RFX-1 indicate different putative-DNA binding proteins, rather than RFX-1. We conclude that the 42-bp sequence within the 5'-UTR influences the expression of ERCC1 and hence can influence response to cisplatin in ovarian cancer therapy.

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