The complexity of mitochondrial outer membrane permeability and VDAC regulation by associated proteins

Aleksandr Klepinin,Laura Truu,Marju Puurand,Igor Shevchuk,Kersti Tepp,Vladimir Chekulayev,Tuuli Kaambre,Kati Mado,Lyudmila Ounpuu,Anu Planken

doi:10.1007/s10863-018-9765-9

Abstract

Previous studies have shown that class II β-tubulin plays a key role in the regulation of oxidative phosphorylation (OXPHOS) in some highly differentiated cells, but its role in malignant cells has remained unclear. To clarify these aspects, we compared the bioenergetic properties of HL-1 murine sarcoma cells, murine neuroblastoma cells (uN2a) and retinoic acid - differentiated N2a cells (dN2a). We examined the expression and possible co-localization of mitochondrial voltage dependent anion channel (VDAC) with hexokinase-2 (HK-2) and βII-tubulin, the role of depolymerized βII-tubuline and the effect of both proteins in the regulation of mitochondrial outer membrane (MOM) permeability. Our data demonstrate that neuroblastoma and sarcoma cells are prone to aerobic glycolysis, which is partially mediated by the presence of VDAC bound HK-2. Microtubule destabilizing (colchicine) and stabilizing (taxol) agents do not affect the MOM permeability for ADP in N2a and HL-1 cells. The obtained results show that βII-tubulin does not regulate the MOM permeability for adenine nucleotides in these cells. HL-1 and NB cells display comparable rates of ADP-activated respiration. It was also found that differentiation enhances the involvement of OXPHOS in N2a cells due to the rise in their mitochondrial reserve capacity. Our data support the view that the alteration of mitochondrial affinity for ADNs is one of the characteristic features of cancer cells. It can be concluded that the binding sites for tubulin and hexokinase within the large intermembrane protein supercomplex Mitochondrial Interactosome, could be different between muscle and cancer cells.

Highlights

Malignant transformation of cells leads to reprogramming in numerous signaling and metabolic pathways, especially in regard to energy metabolism
It was demonstrated that the mitochondrial outer membrane (MOM) voltage-dependent anion channel (VDAC) is the main switch between mitochondrial oxidative phosphorylation (OXPHOS) and glycolysis in malignant cells and it chould be a good target for a new generation of cancer therapy (Carre et al 2002; Maldonado 2017)
The mitochondrial respiration in all studied permeabilized cell types was activated with 2 mM ADP and the rate of O2 consumption was increased by about 3–4 times (Supplementary Fig. 1)

Summary

Introduction

Malignant transformation of cells leads to reprogramming in numerous signaling and metabolic pathways, especially in regard to energy metabolism. It was reported that in brain and tumor cells, some hexokinase isoforms can bind to the VDAC in the MOM thereby suppressing cytochrome c release and apoptotic cell death (Arzoine et al 2009). This channel is involved in the transport of respiratory substrates, Ca2+, ATP, ADP and inorganic phosphate across the external mitochondrial membranes supporting the high efficiency of OXPHOS and the Krebs cycle (Noskov et al 2013; Rostovtseva and Colombini 1997; Shoshan-Barmatz et al 2018)

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