Alteration of ROS Homeostasis and Decreased Lifespan inS. cerevisiaeElicited by Deletion of the Mitochondrial TranslocatorFLX1

Abstract

This paper deals with the control exerted by the mitochondrial translocator FLX1, which catalyzes the movement of the redox cofactor FAD across the mitochondrial membrane, on the efficiency of ATP production, ROS homeostasis, and lifespan of S. cerevisiae. The deletion of the FLX1 gene resulted in respiration-deficient and small-colony phenotype accompanied by a significant ATP shortage and ROS unbalance in glycerol-grown cells. Moreover, the flx1Δ strain showed H2O2 hypersensitivity and decreased lifespan. The impaired biochemical phenotype found in the flx1Δ strain might be justified by an altered expression of the flavoprotein subunit of succinate dehydrogenase, a key enzyme in bioenergetics and cell regulation. A search for possible cis-acting consensus motifs in the regulatory region upstream SDH1-ORF revealed a dozen of upstream motifs that might respond to induced metabolic changes by altering the expression of Flx1p. Among these motifs, two are present in the regulatory region of genes encoding proteins involved in flavin homeostasis. This is the first evidence that the mitochondrial flavin cofactor status is involved in controlling the lifespan of yeasts, maybe by changing the cellular succinate level. This is not the only case in which the homeostasis of redox cofactors underlies complex phenotypical behaviours, as lifespan in yeasts.

Riboflavin transport and metabolism in humans

“…Indeed, the existence of FADS in mitochondria has been a matter of debate for many years, as well as the direction of FAD movement across the mitochondrial translocator named Flx1p in S. cerevisiae and MFT in humans. Besides mediating FAD (or FMN) transport, Flx1p may have a role as a Bnutrient sensor^maintaining the normal status of mitochondrial FAD-binding enzymes such as lipoamide dehydrogenase and succinate dehydrogenase (Tzagoloff et al 1996;Bafunno et al 2004;Spaan et al 2005;Giancaspero et al 2008Giancaspero et al , 2014. This correlates well with the recent finding of a mitochondrial FAD transporter deficiency in a patient (Schiff et al 2016).…”

“…Studies on subcellular localization of FADSs are still in progress and represent the ongoing research efforts in our laboratory, especially related to neuronal biochemistry (Lin et al 2009). More recently, FADS was also found in the nucleus (Giancaspero et al 2015a); even if the nuclear isoform has not been characterized yet, nuclear FADS could concur, together with cytosolic and mitochondrial FADS, to the creation of a Bflavin network^, a scenario which is strictly in line with the recent literature demonstrating a fundamental role for cellular FAD biosynthesis in allowing for lysine demethylase1 (LSD1 or lysine-H3 histone demethylase 1, EC 1.14.11.B1) biogenesis and redox epigenetics (Hino et al 2012;Giancaspero et al 2015b;Giancaspero et al 2014). Moreover, very recently, using RNAseq analysis combined with protein mass spectrometry, novel FADS isoforms have been described, both at the protein and at the mRNA levels in the frame of the identification and description of flavin cofactor homeostasis derangements found in nine different patients suffering from multiple acyl-CoA dehydrogenase (MADD) and combined respiratory chain deficiency (Olsen et al 2016).…”

“…This feature was studied in some detail usingS. cerevisiae as a model (Giancaspero et al 2013b;Giancaspero et al 2014).…”

“…To validate the hypothesis that defects in flavin cofactor supply/delivery may cause flavoproteome-dependent derangements in mitochondrial bioenergetics and protein homeostasis, two novel model organisms, i.e. the yeast S. cerevisiae (Bafunno et al 2004;Giancaspero et al 2008) and the nematode Caenorhabditis elegans (Liuzzi et al 2012) have been established in which as a consequence of changing flavin cofactor metabolismalteration of complex II biogenesis, ATP production and ROS homeostasis and proteomic derangement were observed (Giancaspero et al 2014).…”

Succinate Dehydrogenase Loss in Familial Paraganglioma: Biochemistry, Genetics, and Epigenetics

“…These authors reported complete loss of covalent FAD incorporation into Sdh1 in flx1 mutant cells and inability of the mutant to grow on nonfermentable carbon sources. The flx1 mutant was also hypersensitive to hydrogen peroxide [ 37 ]. Interestingly, overexpression of Sdh5 (a protein required for flavination of SDH) partially restored SDH activity in the flx1 mutant.…”