ATG5 and ATG7 Expression Levels Are Reduced in Cutaneous Melanoma and Regulated by NRF1.

Živa Frangež,Philippe Lucarelli,S Morteza Seyed Jafari,Lasse Sinkkonen,Thomas Sauter,Shida Yousefi,Marios Gavriil,Hans-Uwe Simon,Yuniel Fernández-Marrero,Zhaoyue He,Deborah Gérard,Robert E Hunger

doi:10.3389/fonc.2021.721624

Abstract

Autophagy is a highly conserved cellular process in which intracellular proteins and organelles are sequestered and degraded after the fusion of double-membrane vesicles known as autophagosomes with lysosomes. The process of autophagy is dependent on autophagy-related (ATG) proteins. The role of autophagy in cancer is very complex and still elusive. We investigated the expression of ATG proteins in benign nevi, primary and metastatic melanoma tissues using customized tissue microarrays (TMA). Results from immunohistochemistry show that the expression of ATG5 and ATG7 is significantly reduced in melanoma tissues compared to benign nevi. This reduction correlated with changes in the expression of autophagic activity markers, suggesting decreased basal levels of autophagy in primary and metastatic melanomas. Furthermore, the analysis of survival data of melanoma patients revealed an association between reduced ATG5 and ATG7 levels with an unfavourable clinical outcome. Currently, the mechanisms regulating ATG expression levels in human melanoma remains unknown. Using bioinformatic predictions of transcription factor (TF) binding motifs in accessible chromatin of primary melanocytes, we identified new TFs involved in the regulation of core ATGs. We then show that nuclear respiratory factor 1 (NRF1) stimulates the production of mRNA and protein as well as the promoter activity of ATG5 and ATG7. Moreover, NRF1 deficiency increased in vitro migration of melanoma cells. Our results support the concept that reduced autophagic activity contributes to melanoma development and progression, and identifies NRF1 as a novel TF involved in the regulation of both ATG5 and ATG7 genes.

Highlights

Melanoma is one of the most aggressive and treatment-resistant cancers worldwide
In order to investigate the expression of ATG proteins and autophagic activity markers across several stages of melanoma biopsies, we constructed customized tissue microarrays (TMA) that contained tissue samples from benign nevi donors as well as from primary and metastatic melanoma patients
We detected a consistent decrease in ATG7 expression from benign nevi to primary melanomas and in contrast to ATG5, the levels of ATG7 were further reduced in metastatic tissues (Figure 1B)

Summary

Introduction

Despite new and promising therapeutic strategies, such as targeted therapies using BRAF and MEK inhibitors or novel immunotherapeutics, the prognosis of metastatic melanoma patients remains poor and is often associated with high tumor relapse rates. It is of increasing importance to develop new early-stage prognostic and diagnostic markers which help identify the patients at high risk of developing a more aggressive metastatic phenotype [1]. Through its recycling procedure it removes defective proteins and organelles, such as defective mitochondria, and prevents DNA damage and chromosomal instability, two attributes linked to cancer cell adaptation, enabling tumor progression and resistance to therapy [2]. A few years later, Qu and colleagues observed that monoallelic loss of Beclin-1 in mice correlates with high occurrence of tumors, such as hepatocellular carcinoma, lung adenocarcinoma and B cell lymphoma [4]

Methods

Results

Conclusion