The ataxia-telangiectasia mutated gene product regulates the cellular acid-labile sulfide fraction

The ataxia-telangiectasia mutated (ATM) protein regulates cell cycle checkpoints, the cellular redox state, and double-stranded DNA break repair. ATM loss causes the disorder ataxia-telangiectasia (A-T), distinguished by ataxia, telangiectasias, dysregulated cellular redox and iron responses, and an increased cancer risk. We examined the sulfur pool in A-T cells, with and without an ATM expression vector. While free and bound sulfide levels were not changed with ATM expression, the acid-labile sulfide faction was significantly increased. ATM expression also increased cysteine desulfurase (NFS1), NFU1 iron-sulfur cluster scaffold homolog protein, and several mitochondrial complex I proteins' expression. Additionally, ATM expression suppressed cystathionine β-synthase and cystathionine γ-synthase protein expression, cystathionine γ-synthase enzymatic activity, and increased the reduced to oxidized glutathione ratio. This last observation is interesting, as dysregulated glutathione is implicated in A-T pathology. As ATM expression increases the expression of proteins central in initiating 2Fe-2S and 4Fe-4S cluster formation (NFS1 and NFU1, respectively), and the acid-labile sulfide faction is composed of sulfur incorporated into Fe-S clusters, our data indicates that ATM regulates aspects of Fe-S cluster biosynthesis, the transsulfuration pathway, and glutathione redox cycling. Thus, our data may explain some of the redox- and iron-related pathologies seen in A-T.