UV-induced DNA methyltransferase 1 promotes hypermethylation of tissue inhibitor of metalloproteinase 2 in the human skin.

Abstract Background Ultraviolet (UV) radiation has been reported to influence epigenetic regulation by affecting the expression of genome regulators such as DNA methyltransferase 1 (DNMT1). DNMT1 is a “gene silencer,” that is responsible for the maintenance of DNA methylation and contribution to de novo methylation. Implications of DNMT1′s involvement in the expression of UV-induced proteins have been previously reported. Objective To investigate for changes in DNA methylation-associated gene expressions by UV and to analyze the role of DNA methylation in the suppression of TIMP2 in UV-irradiated human skin. Methods The expression of DNA methylation-associated proteins and TIMP2 were analyzed in UV-irradiated human skin in vivo and in human dermal fibroblasts in vitro . To investigate the relationship between DNMT1 and TIMP2, we assessed the effect of DNMT1 knockdown, inhibition and overexpression on TIMP2 levels in human dermal fibroblasts. Lastly, methylation-specific PCR was used to confirm increased DNA methylation in TIMP2 promoter in response to UV. Results DNMT1 expression significantly increased whereas TIMP2 expression decreased in UV-irradiated human skin in vivo and in vitro . Downregulation of DNMT1 by knockdown or inhibition resulted in increased TIMP2 expression, whereas the overexpression of DNMT1 resulted in decreased TIMP2 expression. Lastly, methylation-specific PCR confirmed increased methylation on the CpG island residing in TIMP2 promoter in UV-irradiated human dermal fibroblasts. Conclusion These findings suggest that UV-induced expression of DNMT1 may be responsible for mediating DNA hypermethylation in TIMP2, and thus, silencing its expression, in UV-exposed human skin.