miR-216b enhances the efficacy of vemurafenib by targeting Beclin-1, UVRAG and ATG5 in melanoma

Autophagy maintains cells survival in many stressful conditions including starvation, growth factor deprivation and misfolded protein accumulation. Additionally, autophagic survival mechanisms are used by transformed tumor cells to inhibit cell death, limit drug effectiveness and possibly generate drug resistance. However, the mechanism of how cells utilize autophagy during drug resistance is not fully understood. Here, we demonstrate that miR-216b plays an important role in alleviating drug resistance by regulating autophagy in melanoma. We show that miR-216b attenuates autophagy by directly targeting three key autophagy genes Beclin-1, UVRAG and ATG5. Overexpression of these genes from miRNA immune cDNA constructs rescue autophagic activity in the presence of miR-216b. Antagomir-mediated inactivation of endogenous miR-216b led to an increase of Beclin-1, UVRAG, ATG5, and subsequent autophagic activity. More importantly, we have discovered that BRAF(V600E) inhibitor vemurafenib suppresses miR-216b activity, which in turn activates autophagy to generate drug resistance in both BRAFi-sensitive and -resistant cells. Strikingly, ectopic expression of miR-216b increases the efficacy of vemurafenib both in vitro and in vivo. Taken together, these data indicate that miR-216b regulates autophagy by suppressing three key autophagy genes, and enhances the antitumor activity of vemurafenib in BRAF(V600E) melanoma cells.