Detachment of cultured cells from the substratum induced by the neutrophil-derived oxidant NH2Cl: synergistic role of phosphotyrosine and intracellular Ca2+ concentration

The neutrophil-derived, membrane-permeating oxidant, NH2Cl, (but not the non-membrane-permeating chloramine, taurine-NHCl) induced detachment of fetal mouse cardiac myocytes and other cell types (fibroblasts, epithelial cells, and endothelial cells) from the culture dish, concomitant with cell shrinkage ("peeling off"). Stimulated human neutrophils also induced peeling off of cultured mouse cardiac myocytes when the latter were pretreated with inhibitors of .OH and elastase. Immunofluorescence microscopy revealed that the NH2Cl-induced peeling off of WI-38 fibroblasts is accompanied by disorganization of integrin alpha 5 beta 1, vinculin, stress fibers, and phosphotyrosine (p-Tyr)-containing proteins. Decrease in the content of the p-Tyr-containing proteins of the NH2Cl-treated cells was analyzed by immunoblotting techniques. Coating of fibronectin on the culture dish prevented both NH2Cl-induced peeling off and a decrease in p-Tyr content. Preincubation with a protein-tyrosine phosphatase inhibitor, sodium orthovanadate (Na3VO4), also prevented NH2Cl-induced peeling off, suggesting that dephosphorylation of p-Tyr is necessary for peeling off. NH2Cl-induced peeling off was accompanied by an increase in intracellular Ca2+ concentration ([Ca2+]i) in mouse cardiac myocytes and WI-38 fibroblasts. The absence of extracellular Ca2+ prevented both NH2Cl-induced peeling off and increased [Ca2+]i, both of which did occur on subsequent incubation of the cells in Ca2+-containing medium. These observations suggest that an increase in [Ca2+]i is also necessary for peeling off. Depletion of microsomal and cytosolic Ca2+ by incubation with the microsomal Ca2+-ATPase inhibitor 2',5'-di(tert-butyl)-1,4-benzohydroquinone (BHQ) plus EGTA prevented both NH2Cl-induced increases in [Ca2+]i and peeling off. Direct inhibition of microsomal Ca2+ pump activity by NH2Cl may participate in the NH2Cl-induced [Ca2+]i increment. A combination of p-Tyr dephosphorylation by genistein (an inhibitor of tyrosine kinase) and an increase in [Ca2+]i by BHQ could also induce peeling off. All these observations suggest a synergism between p-Tyr dephosphorylation and increased [Ca2+]i in NH2Cl-induced peeling off.