Ku80 Deficiency Does Not Affect Particulate Chromate-Induced Chromosome Damage and Cytotoxicity in Chinese Hamster Ovary Cells

Abstract

Particulate hexavalent chromium ((Cr(VI)) compounds are human lung carcinogens. These compounds induce DNA damage, chromosome aberrations, and concentration-dependent cell death in human and Chinese hamster ovary (CHO) cells. The relationship between Cr(VI)-induced DNA damage and chromosome aberrations is poorly understood. Accordingly, this study focused on examining the role of Ku80, a gene involved in nonhomologous end-joining repair, in particulate chromate-induced cytotoxicity and chromosome damage in CHO cells. Three different cell lines were used: CHO-K1 (parental), xrs-6 (Ku80 deficient), and 2E (xrs-6 complemented with Ku80 gene). Levels of cell death were higher in xrs-6 cells when compared to wild type, suggesting that Ku80 was important for protecting cells from lead chromate. However, Ku80 played no role in protecting cells from particulate Cr(VI)-induced chromosome instability (CIN) as gene complementation with Ku80 (2E cells) studies and uptake experiments showed similar frequency and amounts of chromosome damage between the cell lines and that any observed difference based on administered concentration was actually due to differences in Cr(VI) uptake. The spectrum of chromosome damage was also unaffected by Ku80 deficiency. These data indicate that Ku80 protects cells from cytotoxicity but is not involved in protecting cells from particulate chromate-induced CIN.

Homologous recombination repair protects against particulate chromate-induced chromosome instability in Chinese hamster cells

“…These data are consistent with our previous reports showing that cells deficient in Ku80, FANCG and XRCC1 are also sensitive to the cytotoxic effects of particulate Cr(VI) [33,28,20]. They are also consistent with a previous study of soluble chromate showing that XRCC3-and BRCA2-deficient cells were more sensitive to its cytotoxicity [23].…”

“…This conclusion is supported by published data showing that Cr(VI)-induced DNA double strand breaks are preferentially formed after the S-phase of the cell cycle, likely during DNA replication, when HR repair is the most active [37][38][39]. Importantly, the role of HR in dealing with Cr(VI)-associated lesions is consistent with our recent data showing that a major alternative pathway for the repair of double strand breaks, NHEJ, does not protect cells from particulate Cr(VI)-induced CIN [20]. These data are the first to consider genes involved in HR repair and Cr(VI)-induced chromosome damage.…”

“…In this study, and in previous reports using DNA-repair defective cells, we find that DNA repair-deficient cells, including those deficient in Ku80, XRCC1, and FANCG, exhibited large differences in the levels of intracellular genotoxic chemicals compared to their parental and gene complemented control cells [33,20,28]. Such differences in uptake can potentially reverse the conclusions of the relative sensitivities of a cell strain to an agent based only on administered dose.…”

“…Thus, we hypothesize that DNA double strand break repair mechanisms play an important functional role in protecting cells from particulate Cr(VI)-induced CIN. Importantly, we have found previously that the DNA double strand break repair pathway of non-homologous end joining (NHEJ), a key mechanism used by the cell to repair DNA double strand breaks, plays no role in protecting the cell from particulate Cr(VI) induced chromosomal damage [20].…”

Homologous Recombination Repair Signaling in Chemical Carcinogenesis: Prolonged Particulate Hexavalent Chromium Exposure Suppresses the Rad51 Response in Human Lung Cells

“…Studies in Chinese hamster cells show loss of HR-mediated DNA double strand break repair results in increased Cr(VI)induced chromosome instability (Stackpole et al, 2007), whereas loss of NHEJ-mediated repair did not have this effect (Camyre et al, 2007). Studies in human lung cells show exposures to particulate Cr(VI) for over 24 h induces chromosome instability (Holmes et al, 2006a(Holmes et al, ,b, 2010Wise et al, 2006) suggesting HR repair might be affected after longer Cr(VI) exposures.…”