MicroRNA-146a targets PRKCE to modulate papillary thyroid tumor development

MicroRNAs are single-stranded noncoding RNAs composed of approximately 22 nucleotides that suppress gene expression by selectively binding via base-pairing to the complementary 3′-untranslated region (3′-UTR) of messenger RNA transcripts. Protein kinase C epsilon (PKCe) is an important modulating member of the transducing Ras/Raf-1 signal pathway; a computational search revealed miR-146a putatively binds to the 3'-UTR of the PRKCE gene, and thus decreasing PKCe expression. Moreover, PKCe inhibits mitochondrial apoptosis and is associated with the Bcl family. However, it has been previously reported that miR-146a expression in papillary thyroid carcinoma (PTC) is slightly elevated. Thus, we hypothesized that because miR-146a expression depends on nuclear factor kappaB (NF-κB) activation and NF-κB expression is elevated in PTC, miR-146a is potentially upregulated in PTC via negative feedback of NF-κB, and thus suppressing PKCe expression. In our study, we investigated whether overexpression of miR-146a, a tumor-suppressing-miR, in PTC cells decreases cell survival and induces apoptosis. Luciferase reporter assay analysis confirmed the direct binding of miR-146a and PRKCE 3′-UTR. Specific overexpression of exogenous miR-146a significantly decreased PKCe levels in PTC cell line NPA-187 and increased apoptosis. Additionally, using stably expressing miR-146a thyroid carcinoma cells to establish subcutaneous tumors, the tumor growth exhibited significant inhibition. Our study confirmed the tumor-suppressing role of miR-146a in thyroid carcinoma cells and contributes to the knowledge regarding modulation of Ras/Raf-1 signal transduction and apoptosis via PKCe targeted by miR-146a in PTC; moreover, our findings confirmed that miR-146a is involved in the feedback system of the classical NF-κB signal pathway in PTC.