Anti-inflammatory role of microRNA-429 in human gingival epithelial cells-inhibition of IL-8 production through direct binding to IKKβ mRNA

MicroRNAs (miRNAs), a family of small non-coding RNAs, serve a pivotal role in the regulation of the inflammation by modulating the expression of various genes. However, the molecular mechanism by which miRNAs regulate inflammation-associated molecules in oral epithelial cells remains to be elucidated. The present study examined the biological function of miR-429 by performing the gain-/loss-of-function studies of miR-429 in a gingival squamous cell carcinoma line Ca9-22 cells that either over- or under-expressed miR-429 through transient transfection with miR-429 mimic or miR-429 inhibitor, respectively. The results demonstrated that the over-expression of miR-429 suppressed the mRNA level of several interleukins, including IL-8. In addition, the over-expression of miR-429 reduced IL-8 secretion under the basal and TNF-α stimulated conditions, whereas the secretion of IL-8 was enhanced when miR-429 was under-expressed. The over-expression of miR-429 inhibited the activation of the transcription factor NF-κB. Furthermore, we found that miR-429 suppressed both mRNA and protein levels of IKKβ via its direct binding to the 3′-untranslated region of IKKβ mRNA. In addition, the downregulation of IKKβ by small interfering RNA reduced both NF-kB activity and IL-8 production in Ca9-22 cells. Taken together, the findings revealed the molecular mechanism of miR-429 to regulate the inflammatory mediator in gingival cells and suggested that it could be useful as a therapeutic target of oral inflammatory diseases.