The downregulation of ATG4B mediated by microRNA-34a/34c-5p suppresses rapamycin-induced autophagy.

Objectives: Autophagy-related 4B (ATG4B) plays an important role in the process of autophagy induction. However, the molecular events that govern the expression of ATG4B in this process are not well known.

Materials and Methods: Human ATG4B 3'-UTR region (1377 nt) containing miR-34a/miR-34c-5p binding site was amplified by PCR. Luciferase assay was used to assess the activity of reporter genes. Real-time PCR was used to detect the levels of miR-34a and miR-34c-5p. Western blot was used toanalyze the protein levels of ATG4B, LC3 and p62.

Results: Both miR-34a and miR-34c-5p could directly target the 3'-UTR of ATG4B mRNA at same site. Overexpression of either miR-34a or miR-34c-5p significantly down-regulated ATG4B at both mRNA and protein levels and this effect can be reversed by ATG4B overexpression. Moreover, Rapamycin-induced autophagy is accompanied with the upregulation of ATG4B and the downregulation of miR-34a/miR-34c-5p. Ectopic expression of either miR-34a or miR-34c-5p markedly suppressed rapamycin-triggered autophagy.

Conclusion: In the present study, we found that miR34/ATG4B signaling axis involves in rapamycin-triggered autophagy. This study may provide a new insight for understanding the mechanisms of ATG4B regulation and autophagy induction.