Publication Date:
2013-12-20
Description:
Ochratoxin A (OTA) is a carcinogen targeting proximal tubules at the renal outer medulla (ROM) in rodents. We previously reported that OTA increased mutant frequencies of the red / gam gene (Spi – ), primarily deletion mutations. In the present study, Spi – assays and mutation spectrum analyses in the Spi – mutants were performed using additional samples collected in our previous study. Spi – assay results were similar to those in our previous study, revealing large (〉1kb) deletion mutations in the red/gam gene. To clarify the molecular progression from DNA damage to gene mutations, in vivo comet assays and analysis of DNA damage/repair-related mRNA and/or protein expression was performed using the ROM of gpt delta rats treated with OTA at 70, 210 or 630 µg/kg/day by gavage for 4 weeks. Western blotting and immunohistochemical staining demonstrated that OTA increased -H2AX expression specifically at the carcinogenic target site. In view of the results of comet assays, we suspected that OTA was capable of inducing double-strand breaks (DSBs) at the target sites. mRNA and/or protein expression levels of homologous recombination (HR) repair-related genes ( Rad51 , Rad18 and Brip1 ), but not nonhomologous end joining-related genes, were increased in response to OTA in a dose-dependent manner. Moreover, dramatic increases in the expression of genes involved in G 2 /M arrest ( Chek1 and Wee1 ) and S/G 2 phase ( Ccna2 and Cdk1 ) were observed, suggesting that DSBs induced by OTA were repaired predominantly by HR repair, possibly due to OTA-specific cell cycle regulation, consequently producing large deletion mutations at the carcinogenic target site.
Print ISSN:
0267-8357
Electronic ISSN:
1464-3804
Topics:
Biology
,
Medicine
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