WRN helicase promotes repair of DNA double-strand breaks caused by aberrant mismatch repair of chromium-DNA adducts

Abstract

Recent studies in yeast have found that processing of DNA-double strand breaks (DSB) for recombination repair involves Sgs1 helicase. Human cells have five Sgs1 homologues with unknown selectivity and significance for repair of different DSB types. Here we examined the importance of WRN helicase in repair of G2-specific DSB caused by abnormal mismatch repair (MMR) of ternary Cr-DNA adducts. We found that Cr(VI) induced a rapid dispersal of WRN from the nucleolus resulting in its prolonged retention in the nucleoplasm. The loss of MSH2 or MLH1 MMR proteins abolished the long-term but not the initial WRN relocalization. WRN-deficient fibroblasts were hypersensitive to Cr(VI)-induced clonogenic death and contained high levels of persistent DSB detected by γ-H2AX/53BP1 foci and pulsed-field gel electrophoresis. WRN was involved in recombination repair of Cr-induced DNA damage, as evidenced by WRN-RAD51 colocalization and defective formation of RAD51 foci in the absence of WRN. The accumulation of unrepaired DSB in WRN-depleted cells was rescued by the inactivation of MMR, indicating that MMR-generated DSB were a key substrate for WRN action in Cr(VI)-treated cells. Competition for the limited amounts of WRN in primary cells between G2 processes of telomere rebuilding and recombinational repair is expected to increase persistence of Cr-induced DSB and may cause telomeric abnormalities in tissues of chronically chromate-exposed workers. Our work provides the first demonstration of the major importance of WRN in repair of the specific class of DSB in human cells.

Persistent γH2AX: A promising molecular marker of DNA damage and aging

“…WRN interacts with several proteins involved in the repair of DNA DSB and localizes to the sites of laser-induced DSB in live cells [100]. A recent study reported a higher persistence of gH2AX/53BP1 foci in human WRN-deficient fibroblasts compared with controls for up to 24 h after being treated with 20 mM of the potent human carcinogen, chromium Cr(VI), indicating impaired DSB repair due to abnormal mismatched repair [101]. This result suggests that the WRN protein may play an important role in repairing a specific class of DSB in human cells.…”

Influence of Substrate Complexity on the Diastereoselective Formation of Spiroiminodihydantoin and Guanidinohydantoin from Chromate Oxidation

“…The unique unidirectional uptake of tetrahedral chromate through nonselective ion channels has been shown to result in high levels of chromate in exposed cells (3) and a variety of gross morphological changes in DNA structure. While many types of DNA lesions have been postulated to occur from chromate exposure, including DNA adducts (4), DNA-protein crosslinks (5), double-strand breaks (6), and oxidation of DNA bases (7), little structural data on the nature of these lesions, their mutagenic effects and their cellular prevalence have been forthcoming.…”

Variation in Extracellular Detoxification Is a Link to Different Carcinogenicity among Chromates in Rodent and Human Lungs

“…38−40 Mechanistically, DSBs arise from recognition and processing of Cr-DNA adducts by mismatch repair in replicated DNA. 38,39,41 Thus, formation of DSBs can serve as an important test for the assessment of genotoxic activity of Cr(VI) compounds and intracellular delivery of chromate anions either directly or as a result of particle dissolution inside the cell.…”