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Many anticancer drugs are targeted to the genomic DNA of cancer cells by generating interstrand cross-link (ICL) and blocking DNA replication. Mammalian cells also contain repair machinery that can overcome the ICL DNA lesion-mediated replication blockage by repairing or bypassing the ICL lesion and restoring normal function to the damaged cells. To provide a better understanding of ICL-mediated DNA repair and mutagenesis, we have studied DNA polymerase iota, an important error-prone DNA polymerase, for its role in DNA cross-linking reagent psoralen-generated ICL DNA repair and mutagenesis process. Overexpression of pol iota in normal human fibroblast (NF) cells does not affect the psoralen ICL-mediated mutation frequency or mutation spectrum. Overexpression of pol iota in xeroderma pigmentosum group F (XPF) cells, however, significantly altered the psoralen ICL-mediated mutation frequency and mutation spectrum. The results obtained from in vitro DNA repair assay also revaled the presence of pol iota overcame the psoralen ICL-meidated replication blockage. These results suggest that pol iota is not involved in the normal repair process of the psoralen ICL rather it is used to rescue DNA replication from unrepaired or incompletely repaired ICL-containing DNA template, which results in increased mutation accumulation around the ICL site. The increased mutations at the nearby sequence of the ICL site also suggest an important mechanism of pol iota in the psoralen ICL repair process. This data will have important clinical implications in cancer treatment and anticancer drug design and development.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]