miR-146a-5p Enhances Oncogenic Activities by Repressing TRAF6 and p-FADD-Ser194

Objectives: MicroRNAs are short non-coding RNAs that regulate gene expression and are increasingly implicated in carcinogenesis. miR-146a-5p is reported to have pleiotropic and conflicting functions in different cancer cell lines; this has led to controversy as to its role in carcinogenesis. Furthermore, the physiologic role of miR-146a-5p in human normal cells remains largely unknown. This study aimed to study the pathogenic implications of miR-146a-5p in oral carcinogenesis.
Methods: To investigate the role of miR-146a-5p in regulating the cellular responses of normal and transformed oral keratinocytes, we transfected the cells with miR-146a-5p pre-microRNAs or miR-146a-5p blocker and determined cell viability and apoptosis in the transfected cells using the EZ-Cytox Cell Viability Assay Kit and TUNEL assay, respectively. To assess the molecular mechanisms underlying the effects of miR-146a-5p on cell proliferation and apoptosis, we examined the expression levels of miR-146a-5p target genes by immunoblotting and qRT-PCR.
Results: Human papillomavirus (HPV)-immortalized and all thirteen oral squamous cell carcinoma (OSCC) cell lines tested exhibited higher levels of miR-146a-5p expression than normal oral keratinocytes. In addition, the plasma miR-146a-5p levels of patients were significantly higher than those of control subjects. Exogenous miR-146a-5p expression in normal oral keratinocytes harboring a low level of miR-146a-5p significantly enhanced oncogenic activities by increasing cell proliferation and by suppressing apoptosis through downregulation of TRAF6 and phosphorylated FADD at Ser194. In contrast, a miR-146a-5p blocker attenuated the proliferation of OSCC cells by upregulating TRAF6.
Conclusions: These findings support that miR-146a-5p enhances oncogenic activities by repressing TRAF6 and phosphorylated FADD at Ser194 in human oral keratinocytes. This study was granted by the Korea Healthcare Technology R&D Project, Republic of Korea (HI15C2455).