V600EBRAF Inhibition Induces Cytoprotective Autophagy through AMPK in Thyroid Cancer Cells

Abstract

The dysregulation of autophagy is important in the development of many cancers, including thyroid cancer, where V600EBRAF is a main oncogene. Here, we analyse the effect of V600EBRAF inhibition on autophagy, the mechanisms involved in this regulation and the role of autophagy in cell survival of thyroid cancer cells. We reveal that the inhibition of V600EBRAF activity with its specific inhibitor PLX4720 or the depletion of its expression by siRNA induces autophagy in thyroid tumour cells. We show that V600EBRAF downregulation increases LKB1-AMPK signalling and decreases mTOR activity through a MEK/ERK-dependent mechanism. Moreover, we demonstrate that PLX4720 activates ULK1 and increases autophagy through the activation of the AMPK-ULK1 pathway, but not by the inhibition of mTOR. In addition, we find that autophagy blockade decreases cell viability and sensitize thyroid cancer cells to V600EBRAF inhibition by PLX4720 treatment. Finally, we generate a thyroid xenograft model to demonstrate that autophagy inhibition synergistically enhances the anti-proliferative and pro-apoptotic effects of V600EBRAF inhibition in vivo. Collectively, we uncover a new role of AMPK in mediating the induction of cytoprotective autophagy by V600EBRAF inhibition. In addition, these data establish a rationale for designing an integrated therapy targeting V600EBRAF and the LKB1-AMPK-ULK1-autophagy axis for the treatment of V600EBRAF-positive thyroid tumours.

LKB1 inhibits proliferation, metastasis and angiogenesis of thyroid cancer by upregulating SIK1

“…So far, there are only a few studies reporting the effect of LKB1 in thyroid cancer. One study showed that (V600E) BRAF inhibition could induce the cytoprotective autophagy via LKB1-AMPK signaling in thyroid cancer cells [14]. In the present study, the protein levels of p-LKB1 and LKB1 were remarkably lower in thyroid cancer tissues and cell lines, compared with the adjacent normal tissue and thyroid epithelial cell, respectively.…”

The new insights into autophagy in thyroid cancer progression

“…Treatment with PLX4720, the progenitor of vemurafenib, could activate AMPK signaling by phosphorylating the residue Thr172 and then phosphorylate ULK1 to induce autophagy in BHT101 ATC cells. The simultaneous treatment with BRAF V600E inhibitor and autophagy inhibitor (CQ) leads to increased apoptosis [ 98 ]. With the application of vemurafenib growing, some studies report the drug resistance, which limits its clinical prospects.…”

“…noticed that HMGB1 was perhaps one of the inducers that conferred cell resistance to vemurafenib. Upon vemurafenib exposure in BCPAP cells, knockdown of HMGB1 decreased autophagy but reversed the sensitivity to vemurafenib [ 98 ]. In K-1 and BCPAP cells, introduction of redox factor-1 (Ref-1) inhibitor E3330 can strikingly induce autophagy and senescence phenotype towards vemurafenib treatment, and strengthen drug sensitivity [ 99 ].…”

Research progress and application of single-cell sequencing in head and neck malignant tumors

“…In recent years, treatment strategies for BRAF V600E have been continuously developed. BRAF V600E reduces mTOR activity by regulating the activity of the AMPK pathway, thereby inhibiting the protective autophagy of thyroid cancer cells [ 135 ]. The combination of the BRAF inhibitor darafenib and the MEK inhibitor trametinib was the first therapy that showed strong clinical activity and good tolerability in the treatment of ATC with BRAF V600E mutation [ 136 ].…”