The vitamin D receptor inhibits the respiratory chain, contributing to the metabolic switch that is essential for cancer cell proliferation.

Marco Consiglio,Gianpiero Pescarmona,Francesca Silvagno,Deborah Morena,Valentina Foglizzo,Mattia Forneris,Michele Destefanis,Makoto Makishima

doi:10.1371/journal.pone.0115816

Marco Consiglio, Gianpiero Pescarmona + Show 6 more

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https://doi.org/10.1371/journal.pone.0115816

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Abstract

We recently described the mitochondrial localization and import of the vitamin D receptor (VDR) in actively proliferating HaCaT cells for the first time, but its role in the organelle remains unknown. Many metabolic intermediates that support cell growth are provided by the mitochondria; consequently, the identification of proteins that regulate mitochondrial metabolic pathways is of great interest, and we sought to understand whether VDR may modulate these pathways. We genetically silenced VDR in HaCaT cells and studied the effects on cell growth, mitochondrial metabolism and biosynthetic pathways. VDR knockdown resulted in robust growth inhibition, with accumulation in the G0G1 phase of the cell cycle and decreased accumulation in the M phase. The effects of VDR silencing on proliferation were confirmed in several human cancer cell lines. Decreased VDR expression was consistently observed in two different models of cell differentiation. The impairment of silenced HaCaT cell growth was accompanied by sharp increases in the mitochondrial membrane potential, which sensitized the cells to oxidative stress. We found that transcription of the subunits II and IV of cytochrome c oxidase was significantly increased upon VDR silencing. Accordingly, treatment of HaCaT cells with vitamin D downregulated both subunits, suggesting that VDR may inhibit the respiratory chain and redirect TCA intermediates toward biosynthesis, thus contributing to the metabolic switch that is typical of cancer cells. In order to explore this hypothesis, we examined various acetyl-CoA-dependent biosynthetic pathways, such as the mevalonate pathway (measured as cholesterol biosynthesis and prenylation of small GTPases), and histone acetylation levels; all of these pathways were inhibited by VDR silencing. These data provide evidence of the role of VDR as a gatekeeper of mitochondrial respiratory chain activity and a facilitator of the diversion of acetyl-CoA from the energy-producing TCA cycle toward biosynthetic pathways that are essential for cellular proliferation.

Highlights

The vitamin D receptor (VDR), along with the other members of the steroid hormone receptor family, has generally been described as a classical ligandmodulated transcription factor
Many metabolic intermediates that support cell growth are provided by the mitochondria [15]; the identification of proteins that regulate mitochondrial metabolic pathways is of great interest, and we sought to understand whether the VDR may modulate these pathways
HaCaT cells represent a model of resistance to the differentiating properties of vitamin D, and there is not any incongruity between the nuclear antiproliferative role of vitamin D described in literature and the proliferative effects exerted by VDR in our cell model

Summary

Introduction

The vitamin D receptor (VDR), along with the other members of the steroid hormone receptor family, has generally been described as a classical ligandmodulated transcription factor. The differentiating effects of the VDR are triggered by ligand-induced nuclear translocation and binding to vitamin D responsive element (VDRE) sites on regulated genes, in association with heterodimerization partners, coactivators and corepressors. Resistance to the nuclear effects of vitamin D has been reported in several models of cancer, including prostate, breast and bladder cancers, in which increased corepressor expression and localization has been deemed to be responsible for the insensitivity to the hormone [2,3,4]. We recently described the mitochondrial localization of the VDR in a human proliferating keratinocyte cell line (HaCaT) for the first time and demonstrated that mitochondrial import of the receptor is mediated by the permeability transition pore complex [12]. Many metabolic intermediates that support cell growth are provided by the mitochondria [15]; the identification of proteins that regulate mitochondrial metabolic pathways is of great interest, and we sought to understand whether the VDR may modulate these pathways

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