N-acetyl-l-cysteine fosters inactivation and transfer to endolysosomes of c-Src

The non-receptor-protein tyrosine kinase c-Src is overexpressed and activated in a large number of human cancers, in which it is associated with tumor development and progression. Canonical regulation takes place by means of an alternative phosphorylation of tyrosine residues—Tyr419 for activation and Tyr530 for inactivation. An independent redox regulation mechanism, involving cysteine residues, has also been proposed, in which oxidation activates the enzyme. Here we present a kinetic analysis of the effect of N-acetyl-l-cysteine (NAC) on c-Src, demonstrating that reduction reverts the oxidation-driven activation. In cancer cells, we show that NAC treatment produces an increase in specifically labeled reduced thiols of c-Src cysteines, thus confirming a redox transition. In addition to a decrease in Tyr419 phosphorylation, this leads to a massive shift of c-Src from plasma membranes—where its active form is located—to endolysosomal compartments. With the objective of deciphering the complex issue of c-Src regulation and of devising new strategies to revert its activation in cancers, redox regulation thus emerges as a promising area for study.