Hypoxia followed by re-oxygenation induces oxidation of tyrosine phosphatases.

Hypoxia and hypoxia/reoxygenation (H/R) are components of tissue ischemia and reperfusion implicated in myocardial infarction, organ transplantation, and tumor perfusion. H/R enhances production of reactive oxygen species (ROS). Candidate molecular targets of ROS are the catalytic site cysteine of protein tyrosine phosphatases (PTPs), which are major regulators of tyrosine kinase signaling. This study aimed at analyzing potential effects of H/R on PTP-oxidation in cultured cells and in heart tissue. Exposure of mouse NIH3T3 fibroblasts to H/R increased the oxidation of the PTPs SHP-2- and DEP-1. The catalytic pan-PTP- and SHP-2-activity after H/R were also decreased in rat cardiomyoblasts. In vivo dephosphorylation of the Platelet-derived Growth Factor (PDGF)-receptor in NIH3T3 fibroblasts was delayed following H/R. Erk1/2 displayed an antioxidant-sensitive increase in H/R. Furthermore, increased PDGF-induced cytoskeleton re-arrangements were evident following H/R and could be prevented by antioxidant pretreatment. Finally, decreased pan-PTP- and SHP-2 activity was demonstrated in tissue extracts from an ex vivo Langendorff-model of rat heart ischemia-reperfusion. This study thus demonstrates PTP-oxidation as a previously unrecognized molecular component of the cellular response to H/R in cells and tissues. The study additionally provides the first demonstration of increased PTP-oxidation in tissues under patho-physiological settings.