Cellular responses to cysteine deprivation are mediated by the amino acid deprivation pathway but not the oxidative stress pathway.

Several genes in cysteine (Cys) metabolism are transcriptionally regulated in response to either Cys deprivation or oxidative stress. These include GCLC and GCLM , which encode glutamate:Cys ligase subunits that catalyze the first step of glutathione synthesis, and SLC7A11 , which encodes the cystine‐glutamate exchanger responsible for cystine uptake. In Cys‐deprived HepG2/C3A cells, GCLC , GCLM and SLC7A11 were upregulated as assessed by microarray analysis and qRT‐PCR. Expression of many genes with antioxidant response elements was not affected by Cys deprivation while genes with amino acid response elements (AAREs) were consistently upregulated, suggesting that Cys deprivation can induce the eIF2α kinase 4 mediated amino acid deprivation pathway without inducing oxidative stress. Induction of GCLC, GCLM and SLC7A11 was also observed in rats fed 10% (w/w) protein diets, and activation of the AARE‐mediated pathway was evidenced by phosphorylation of eIF2α and upregulation of mRNA and protein levels for genes with AAREs. The pattern of gene expression in growing rats fed diets marginally deficient in sulfur amino acids suggests that the amino acid deprivation response can be activated in response to mild, as well as severe, amino acid deficiencies. SLC7A11 contains an AARE and is likely a direct target, but the details of the regulation of GCLC and GCLM expression in response to Cys deficiency need further study. Funded by NIH Grant PHS DK0664303.