MiR-155 negatively regulates c-Jun expression at the post-transcriptional level in human dermal fibroblasts in vitro: implications in UVA irradiation-induced photoaging.

OBJECTIVE C-Jun plays a critical role in ultraviolet A (UVA) irradiation-induced photoaging. The exact mechanisms by which UVA irradiation up-regulates c-Jun expression in human dermal fibroblasts (HDFs) are still not completely understood. We undertook this study to investigate whether microRNA-155 (miR-155) directly regulates the expression of c-Jun in HDFs in vitro. METHODS Expression of c-Jun mRNA and protein and miR-155 in UVA-irradiated HDFs were detected using quantitative real-time RT-PCR and Western blotting. Luciferase reporter assays were performed to examine whether a miR-155 binding site in the 3'-untranslated region (3'-UTR) of the c-Jun gene is responsible for miR-155-mediated c-Jun regulation in HEK293A cells, and expression of c-Jun mRNA and protein in UVA non-exposed and exposed HDFs trasfected with a miR-155 mimic or a miR-155 inhibitor was detected by quantitative real-time RT-PCR and Western blotting. RESULTS Expression of miR-155 was markedly reduced and that of c-Jun mRNA and protein was significantly up-regulated in UVA-irradiated HDFs. Luciferase reporter assays indicated that c-Jun is a direct target of miR-155 in HEK293A cells. In both UVA non-exposed and exposed HDFs, miR-155 mimic decreased c-Jun protein levels, while miR-155 inhibitor increased c-Jun protein levels, but both had no effect on c-Jun mRNA expression, which suggest that miR-155-induced c-Jun inhibition occurs at the post-transcriptional level. CONCLUSIONS Our results demonstrate that miR-155 directly controls c-Jun expression in HDFs at the post-transcriptional level and might function as a protective miRNA in HDFs.