Translational control mechanisms in cutaneous malignant melanoma: the role of eIF2\u03b1

Immacolata Maida,Stefania Guida,Tiziana Cocco,Gabriella Guida,Stefania Tommasi,Anna Ferretta,Amalia Azzariti,Paola Londei,Paola Zanna,Giovanni Pellacani,Luigi Leonardo Palese,Dario Benelli,Michele Guida

doi:10.1186/s12967-019-1772-z

Abstract

BackgroundMelanoma cells develop adaptive responses in order to cope with particular conditions of tumor microenvironment, characterized by stress conditions and deregulated proliferation. Recently, the interplay between the stress response and the gene expression programs leading to metastatic spread has been reported.MethodsWe evaluated levels and localization of eIF2α/peIF2α in V600BRAF and wtBRAF metastatic melanoma cell lines by means of western blot and confocal microscopy analyses. Furthermore, we performed a sequence analyses and structure and dynamics studies of eIF2α protein to reveal the role of eIF2α and its correlations in different pathways involved in the invasive phase of melanoma.ResultsWe found peIF2α both in cytoplasm and nucleus. Nuclear localization was more represented in V600BRAF melanoma cell lines. Our studies on eIF2α protein sequence indicated the presence of a predicted bipartite NLS as well as a nuclear export signal NES and an S1 domain, typical of RNA interacting proteins. Furthermore, we found high levels of transcription factor EB (TFEB), a component of the MiT/TFE family, and low β-catenin levels in V600BRAF cells.ConclusionsBased on our results, we suggest that peIF2α nuclear localization can be crucial in ER stress response and in driving the metastatic spread of melanoma, through lysosomal signaling and Wnt/β-catenin pathway. In conclusion, this is the first evidence of nuclear localization of peIF2α, representing a possible target for future therapeutic approaches for metastatic melanoma.

Highlights

Melanoma cells develop adaptive responses in order to cope with particular conditions of tumor microenvironment, characterized by stress conditions and deregulated proliferation
Analysis of the Phosphorylated eIF2α (peIF2α), beyond the cytoplasmic localization, revealed a nuclear staining in all the melanoma cell lines (Fig. 1a). This nuclear localization was more evident in V600BRAF M3 and hmel1 melanoma cell lines (Fig. 1a), as compared to wtBRAF HBL
The western blotting analysis using total eIF2α or peIF2α antibody on the cytoplasmic and nuclear M3 cellular fractions confirmed that the peIF2α was present both in the nucleus and in the cytoplasm (Fig. 1b), even if the total eIF2α was more abundant in the cytoplasmic fraction

Summary

Introduction

Melanoma cells develop adaptive responses in order to cope with particular conditions of tumor microenvironment, characterized by stress conditions and deregulated proliferation. Tumor microenvironment conditions, characterized by stress stimuli and a push to fuel continue proliferation, induce the development of cellular adaptive responses. These stress signals induce the activation of the unfolded protein response (UPR) [2,3,4], and translational. The translational block is achieved through the phosphorylation of the alpha subunit of eukaryotic translation initiation factor 2 (eIF2α) which is one of the key regulator of the Integrated Stress Response (ISR). The phosphorylation of eIF2α determines an increase in the expression of the transcription factor ATF4, a key component of the ISR, in order to promote cellular recovery. ATF4 is a transcription factor of the ATF/CREB family that regulates the expression of genes involved in oxidative stress, amino acid synthesis, differentiation, metastasis and angiogenesis and it is induced by stress signals including anoxia/hypoxia, ER stress, amino acid deprivation, and oxidative stress [6]

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