The microRNAs (miRNAs) are a class of small non-coding RNA molecules that play important roles in cellular processes by regulating gene expression at the post-transcriptional level. In skin biology, several miRNAs have been shown to be associated with differentiation, migration and apoptosis of keratinocytes, and regulation of the hair cycle. Although the biological role of miR-330-5p has been reported in several cancers and cells, the function and molecular mechanism of miR-330-5p in skin keratinocytes have not been identified. In this study, we found that miR-330-5p inhibited the proliferation and migration of mouse keratinocytes. Among the candidate target genes of miR-330-5p searched using microarray analysis, we found that the expression of Pdia3 was directly regulated by miR-330-5p in the mouse keratinocyte. Moreover, inhibition of Pdia3 expression caused decreased proliferation and migration ability of mouse keratinocytes. Additionally, expressions of miR-330-5p and Pdia3 displayed an inverse correlation with respect to the hair cycle stage. These results indicated that regulation of Pdia3 expression by miR-330-5p is important in maintaining the hair cycle through regulation of the proliferation and migration capability of keratinocytes.

Srpr is a gene encoding α subunit of the signal recognition particle receptor which is involved in the targeting and translocation of nascent secretory and membrane proteins to the endoplasmic reticulum. Previous studies showed aberrant expression of Srpr in several cell types with abnormal growth rate. Although Srpr is expressed in various tissues including skin, the role of Srpr in keratinocytes and regulation of its expression by miRNAs have not been studied. In this study, we investigated the role of SRPR and regulation of its expression by miRNA in skin keratinocytes. We found that SRPR was highly expressed in epidermal keratinocytes and regulated keratinocyte proliferation by affecting cell cycle progression. We also demonstrated that miR-330-5p directly inhibits Srpr expression. These data suggest that miR-330-5p-mediated regulation of the SRPR level is needed for the regulation of proliferation of epidermal keratinocytes.