Cancer cells mainly uptake cystine through the xc− system, and the latter is catalyzed by thioredoxin reductase (TxrR) within the cells and reduced to cysteine by NADPH, thereby providing the most significant reducing precursor for the synthesis of GSH.[126] Cu2+ facilitated the nuclear translocation of HIF1A, thereby augmenting the expression of the functional subunit SLC7A11. This evidence concerns the gene SLC7A11 and cancer.