Disruption of a cystine transporter downregulates expression of genes involved in sulfur regulation and cellular respiration

Abstract

Cystine and cysteine are important molecules for pathways such as redox signaling and regulation, and thus identifying cellular deficits upon deletion of the Saccharomyces cerevisiae cystine transporter Ers1p allows for a further understanding of cystine homeostasis. Previous complementation studies using the human ortholog suggest yeast Ers1p is a cystine transporter. Human CTNS encodes the protein Cystinosin, a cystine transporter that is embedded in the lysosomal membrane and facilitates the export of cystine from the lysosome. When CTNS is mutated, cystine transport is disrupted, leading to cystine accumulation, the diagnostic hallmark of the lysosomal storage disorder cystinosis. Here, we provide biochemical evidence for Ers1p-dependent cystine transport. However, the accumulation of intracellular cystine is not observed when the ERS1 gene is deleted from ers1-Δ yeast, supporting the existence of modifier genes that provide a mechanism in ers1-Δ yeast that prevents or corrects cystine accumulation. Upon comparison of the transcriptomes of isogenic ERS1+ and ers1-Δ strains of S. cerevisiae by DNA microarray followed by targeted qPCR, sixteen genes were identified as being differentially expressed between the two genotypes. Genes that encode proteins functioning in sulfur regulation, cellular respiration, and general transport were enriched in our screen, demonstrating pleiotropic effects of ers1-Δ. These results give insight into yeast cystine regulation and the multiple, seemingly distal, pathways that involve proper cystine recycling.

Cfs1p, a Novel Membrane Protein in the PQ-Loop Family, Is Involved in Phospholipid Flippase Functions in Yeast

“…We manually confirmed the synthetic genetic interaction of cfs1 Δ with ric1 Δ or rgp1 Δ. The ric1 Δ and rgp1 Δ mutants show temperature-sensitive growth (Mizuta et al 1997; Siniossoglou et al 2000) (Figure 8A). They grew as well as the wild-type strain at 30°, whereas the cfs1 Δ mutation caused severe growth defects in these mutants at this temperature (Figure 8A).…”

“…Ypt6p, the yeast counterpart of mammalian Rab6 GTPase, functions in endosome-to-TGN and intra-Golgi retrograde transport (Luo and Gallwitz 2003), together with its guanine nucleotide exchange factor (GEF), the Ric1p/Rgp1p complex (Siniossoglou et al 2000). We manually confirmed the synthetic genetic interaction of cfs1 Δ with ric1 Δ or rgp1 Δ.…”

Vacuolar hydrolysis and efflux: current knowledge and unanswered questions

“…Ers1 localizes to the vacuole membrane and whereas Ers1-deficient yeast cells show sensitivity to the antibiotic hygromycin B, expression of human CTNS in these cells can complement the hygromycin B sensitivity and confer resistance [198]. Recently, it was demonstrated that Ers1 can transport cystine, although intracellular cystine does not increase in ers1Δ cells [199], possibly indicating the presence of redundant, as yet unidentified, cystine transporters. Additional PQ-loop family members Ypq1, Ypq2, and Rtc2 also localize to the vacuole membrane, and it is proposed that they export basic amino acids such as lysine, arginine, and/or histidine [200].…”

Exacerbating and reversing lysosomal storage diseases: from yeast to humans

“…A comparative transcriptomic analysis of ers1Δ strains implicated sulfur homeostasis as aberrant, which was consistent with the gene expression profile of cystinotic cells from cystinosis patients. Additionally, energy production, oxidative stress, calcium and potassium transport and stress response were also awry in this mutant model 85 . A high copy suppressor screen in yeast identified that MEH1 , a gene critical for the process of microautophagy and the function of amino acid permease Gap1p that mediates cysteine uptake, suppressed hygB sensitivity in the ers1Δ yeast model 84 86 .…”