MiR-20a and miR-106b negatively regulate autophagy induced by leucine deprivation via suppression of ULK1 expression in C2C12 myoblasts

Autophagy is an evolutionarily conserved process responsible for degradation and recycling of cytoplasmic components through the lysosomal machinery. It has been proved to play pivotal roles in cellular homeostasis, cell growth and organism development. Moreover, abnormalities of autophagy have been linked to numerous human pathophysiologies. Emerging evidence has linked leucine deprivation induced protein breakdown to autophagy, but the underlying mechanisms controlling autophagic activity in this process are not fully understood. Here, we demonstrate that two members of the miR-17 microRNA family, miR-20a and miR-106b, may participate in regulating leucine deprivation induced autophagy via suppression of ULK1 expression in C2C12 myoblasts. We showed that leucine deprivation downregulated miR-20a and miR-106b expression via suppression of their transcription factor c-Myc. We discovered the essential autophagy gene ULK1 as cellular target of miR-20a and miR-106b. Treatment of C2C12 cells with the miR-20a or miR-106b mimic decreased the endogenous ULK1 protein levels. Dual luciferase reporter assay confirmed that the miRNA binding sequences in the 3' UTR of ULK1 contribute to the modulation of ULK1 expression by miR-20a and miR-106b. Furthermore, inhibition of ULK1 expression by the miR-20a or miR-106b mimic blunted activation of autophagy induced by leucine deprivation, while suppression of endogenous miR-20a or miR-106b by specific antagomir in C2C12 cells showed normal autophagic activity. Altogether, our data demonstrated that miR-20a and miR-106b regulated autophagy induced by leucine deprivation in C2C12 cells via targeting ULK1.