Compensatory role of Neuroglobin in nervous and non-nervous cancer cells in response to the nutrient deprivation.

Marco Fiocchetti,Manuela Cipolletti,Maria Marino,Ferdinando Auricchio

doi:10.1371/journal.pone.0189179

Abstract

Environmental factors or adverse growth conditions that may reduce cell function or viability are considered stress. The cell ability to sense and respond to environmental stresses determine its function and survival destiny. We recently defined Neuroglobin (NGB), a heme-protein, as a compensatory protein in the 17β-Estradiol (E2) anti-apoptotic activity and as a sensor of oxidative stress in both neurons and breast cancer cells. Here, the possibility that NGB levels could represent a pivotal regulator of integrated response of cancer cells to stress has been evaluated. Data obtained in neuroblastoma and in breast cancer cell lines evidence that nutrient deprivation significantly up-regulated NGB levels at different time points. However, the analysis of autophagy activation led to exclude any possible role of stress- or E2-induced NGB in the upstream regulation of general autophagy. However, the over-expression of Flag-NGB in ERα stable transfected HEK-293 cells completely affects nutrient deprivation-induced decrease in cell number. In addition, reported results indicate that modulation of the anti-apoptotic Bcl-2 level may play a key role in the protective NGB function against energetic stress. Overall, these data define a role of NGB as compensatory protein in the cell machinery activated in response to stress and as general stress adaptation marker of cancer cells susceptible to oxidative stress, oxygen and, as demonstrated here for the first time, even to nutrient willingness. Despite the lacking of any direct NGB role on autophagic flux activated by energetic stress, NGB upregulation appears functional in delaying stress-related cell death allowing an appropriate cell response and adaptation to the changing extracellular conditions.

Highlights

During their life, cells may encounter unfavorable environmental conditions, which beyond a certain threshold became “stressors” activating the so-called stress response pathway, which, in turn, attempt to reduce cell damage and to maintain or re-establish cell homeostasis, or eventually eliminate damaged cells [1,2]
E2, Pen-Strep solution, RPMI-1640 media without phenol red, Dulbecco’s modified Eagle medium (DMEM) without phenol red, Earle’s Balanced Salt Solution (EBSS), charcoalstripped fetal calf serum, protease inhibitor cocktail, bovine serum albumin fraction V (BSA), Bafilomycin A1, anti-Tubulin and anti-Microtubule associated protein light chain 3 (LC3) antibodies and G418 (Geneticin) selection antibiotic were purchased from Sigma-Aldrich
The effects of nutrient deprivation on the expression of NGB levels has been evaluated in human neuroblastoma cells (SK-N-BE) [8], breast cancer cells (MCF-7) [24] and the estrogen receptor (ER) devoid HEK-293 [26] stable transfected with ERα plasmid (ERα-HEK-293)

Summary

Introduction

Cells may encounter unfavorable environmental conditions, which beyond a certain threshold became “stressors” activating the so-called stress response pathway, which, in turn, attempt to reduce cell damage and to maintain or re-establish cell homeostasis, or eventually eliminate damaged cells [1,2]. Autophagy (macro-autophagy), an intracellular degradation pathway that occurs at basal levels in all cells during nutrient rich conditions, is one of the key cellular response upregulated in response to the nutrient withdrawal [4,5]. This process provides the cell with nutrients and energy by degrading cell components, by reducing the nutrient requirement, and decline of general functions; autophagy allows cells to adapt themselves and function properly and coherently within the new environment. Pathological conditions, like solid cancer growth, are mainly linked to cells full adaption to the critical condition and escaping from the extracellular controls [6,7]

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Results

Conclusion