Role of hMLH1 in sterigmatocystin-induced G₂ phase arrest in human esophageal epithelial Het-1A cells in vitro.

Sterigmatocystin (ST), a common environmental contaminant found across the world, is generally recognized as a potential carcinogen, mutagen and teratogen. Our previous epidemiological studies suggested that ST exposure might be a risk factor for esophageal cancer. However, the direct effects of ST on human esophageal epithelial cells are currently unknown. In the present study, we examined the effect of treating a human esophageal epithelial cell line (Het-1A) with ST on DNA damage, DNA repair mechanisms, and cell cycle distribution. We found that ST treatment could induce DNA damage and lead to a G₂ phase arrest, associated with a marked up-regulation of G₂/M regulatory proteins, including Cyclin B1, Cdc2/p-Cdc2, and Cdc25C/p-Cdc25C. Additionally, we found that the expression of two mismatch repair (MMR) proteins, hMLH1 and hMSH2, was up-regulated at both the mRNA and protein levels after ST treatment, suggesting that ST could induce the MMR system in Het-1A cells. Interestingly, ST-induced G₂ phase arrest was mediated by hMLH1 up-regulation, but was independent of hMSH2. Treatment with hMLH1-siRNA prevented the up-regulation of Cyclin B1, Cdc2/p-Cdc2 and Cdc25C/p-Cdc25C in ST-treated cells, thereby inhibiting the subsequent G₂ phase arrest of Het-1A cells. Moreover, we found that hMLH1 may act as a direct sensor of ST-mediated DNA damage. In conclusion, the study demonstrated that ST caused DNA damage and triggered G₂ phase arrest in Het-1A cells, and hMLH1 participated in the ST-induced G₂ phase arrest by up-regulating G₂/M regulatory proteins.
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