MiR-23a regulates DNA damage repair and apoptosis in UVB-irradiated HaCaT cells

Abstract

MiRNAs remain at a constant level under physiological conditions. However, how the expression of miRNAs is regulated and what are the roles of miRNAs in response to UVB damage to skin cells is still not fully understood. In our preliminary study, we observed that miR-23a was upregulated following a treatment with a DNA repair agent and UVB exposure. To investigate the regulation and function of miR-23a in response to UVB-induced injury in human keratinocyte cell line (HaCaT) cells. The changes in expression of miR-23a after UVB irradiation of HaCaT cells were measured by qRT-PCR. The level of miR-23a expression was also modulated by transfecting with a miR-23a mimic or an inhibitor. Cell viability was assessed by the CCK-8 assay. Immunofluorescence staining and Southwestern dot blotting were used to detect the levels of cyclobutane pyrimidine dimers (CPDs). Flow cytometry, Hoechst staining, and measurements of caspase-3 activity were employed to measure the incidence of apoptosis. The mRNA and protein expression levels of genes related to DNA reparation and apoptosis, such as topoisomerase-1, caspase-7, and STK4, were analyzed by qRT-PCR and Western blotting, respectively. MiR-23a expression was remarkably up-regulated at 4 h and 24 h after the UVB irradiation of HaCaT cells. UVB-induced apoptosis was increased by down-regulation of miR-23a. UVB-induced removal of CPDs was accelerated by miR-23a up-regulation and delayed by miR-23a down-regulation. Forced over-expression of miR-23a decreased the expression of UVB-induced topoisomerase-1\caspase7\STK4 at both the mRNA and protein levels, and these effects were reversed by down-regulation of miR-23a. The protection of HaCaT cells against UVB damage is afforded by miR-23a through regulation of topoisomerase-1\caspase7\STK4, and this miRNA may be a novel therapeutic target in skin diseases related to UVB radiation.