Deoxygenation of sickle cells stimulates Syk tyrosine kinase and inhibits a membrane tyrosine phosphatase

Polymerization of hemoglobin S in sickle red cells, in deoxygenated conditi ons, is associated with K+ loss and cellular dehydration. It was previously reported that deoxygenation of sickle cells increases protein tyrosine kin ase (PTK) activity and band 3 tyrosine phosphorylation and that PTK inhibit ors reduce cell dehydration. Here, the study investigates which PTKs are in volved and the mechanism of their activation. Deoxygenation of sickle cells induced a 2-fold increase in Syk activity, measured by autophosphorylation in immune complex assays, but had no effect on Lyn. Syk was not stimulated by deoxygenation of normal red cells, and stimulation was partly reversibl e on reoxygenation of sickle cells. Syk activation was independent of the i ncrease in intracellular Ca++ and Mg2+ associated with deoxygenation. Lecti ns that promote glycophorin or band 3 aggregation did not activate Syk. In parallel to Syk stimulation, deoxygenation of sickle cells, but not of norm al red cells, decreased the activity of both membrane-associated protein ty rosine phosphatase (PTPs) and membrane protein thiol content. In vitro pret reatment of Syk immune complexes with membrane PTP inhibited Syk autophosph orylation. It is suggested that Syk activation in vivo could be mediated by PTP inhibition, itself resulting from thiol oxidation, as PTPs are known t o be inhibited by oxidants. Altogether these data indicate that Syk could b e involved in the mechanisms leading to sickle cell dehydration. (C) 2001 b y The American Society of Hematology.