MITF has a central role in regulating starvation-induced autophagy in melanoma

Katrin Möller,Valerie Fock,Matthias Wilmanns,Eirikur Steingrimsson,Ramile Dilshat,Asgeir O Arnthorsson,Helga M Ogmundsdottir,Vivian Pogenberg,Lionel Larue,Margret Bessadottir,Vesteinn Thorsson,Sara Sigurbjornsdottir,Anne Simonsen,Margret H Ogmundsdottir,Solveig H Brynjolfsdottir,Christian Bindesboll

doi:10.1038/s41598-018-37522-6

Abstract

The MITF transcription factor is a master regulator of melanocyte development and a critical factor in melanomagenesis. The related transcription factors TFEB and TFE3 regulate lysosomal activity and autophagy processes known to be important in melanoma. Here we show that MITF binds the CLEAR-box element in the promoters of lysosomal and autophagosomal genes in melanocytes and melanoma cells. The crystal structure of MITF bound to the CLEAR-box reveals how the palindromic nature of this motif induces symmetric MITF homodimer binding. In metastatic melanoma tumors and cell lines, MITF positively correlates with the expression of lysosomal and autophagosomal genes, which, interestingly, are different from the lysosomal and autophagosomal genes correlated with TFEB and TFE3. Depletion of MITF in melanoma cells and melanocytes attenuates the response to starvation-induced autophagy, whereas the overexpression of MITF in melanoma cells increases the number of autophagosomes but is not sufficient to induce autophagic flux. Our results suggest that MITF and the related factors TFEB and TFE3 have separate roles in regulating a starvation-induced autophagy response in melanoma. Understanding the normal and pathophysiological roles of MITF and related transcription factors may provide important clinical insights into melanoma therapy.

Highlights

Autophagy is a major intracellular degradation pathway that occurs at basal levels in all cells and is necessary for maintaining cellular homeostasis by degrading protein aggregates, long-lived proteins, lipids and malfunctioning organelles
Microphthalmia-associated transcription factor (MITF) binds to the promoters of MLANA as well as to several lysosomal and autophagosomal genes, such as LAMP1 and MAP1LC3B (LC3B), in these cells
As autophagy levels have been shown to be high in melanoma, we investigated the involvement of MITF in regulating expression of lysosomal and autophagosomal genes in these tumors

Summary

Introduction

Autophagy is a major intracellular degradation pathway that occurs at basal levels in all cells and is necessary for maintaining cellular homeostasis by degrading protein aggregates, long-lived proteins, lipids and malfunctioning organelles. MITF has been suggested to play a role in the regulation of lysosomal biogenesis and autophagy via transcriptional regulation of lysosomal and autophagosomal genes[20,21] These genes are expressed at higher levels in melanoma than in most other cancers and melanomas have been shown to be highly dependent on lysosomal and autophagic activity for both prevalence and progression[22,23,24]. MITF mRNA levels correlate with a subset of lysosomal and autophagosomal genes, that is different to the subset of genes regulated by TFEB and TFE3. These results suggest a distinct role for MITF in regulating stress-induced autophagy in melanoma cells

Methods

Results

Conclusion