PHOSPHORYLATION OF T-LYMPHOCYTE PLASMA MEMBRANE-ASSOCIATED PROTEINS BY ECTOPROTEIN KINASES - IMPLICATIONS FOR A POSSIBLE ROLE FOR ECTOPHOSPHORYLATION IN T-CELL EFFECTOR FUNCTIONS

Extracellular adenosine triphosphate (ATPo) has been suggested to play a role in lymphocyte effector functions. Recently, it has been sugges ted that MgATP(2-) may be the molecular species which is involved in m odulating the lytic interaction between cytotoxic T-lymphocytes (CTL) and their target cells. In this study, we provide evidence that ATPo m ediates the phosphorylation of extracellular proteins on T-lymphocytes through the action of ectoprotein kinases. The ectophosphorylation is temperature-dependent, supported by Mg2+ and Mn2+, and both ATP and G TP, whereas kinase activity and/or substrates were removed by pretreat ment of intact lymphocytes with trypsin. We show the presence of extra cellular ATP/GTP-binding sites, indicating the presence of ectoenzymes on intact lymphocytes. The major ectoprotein kinase was identified as a casein kinase II-like protein kinase and could be inhibited by hepa rin, whereas its activity was enhanced by spermine. The ectoprotein ki nase showed remarkable substrate specificity, phosphorylating the seru m protein vitronectin, but not fibronectin. In experiments with the ce ll-impermeable protein kinase inhibitor K-252b, we demonstrate the pos sible functional importance of ectoprotein kinase in CTL-mediated cyto toxicity, i.e., target cell death was completely blocked by K-252b wit hout affecting intracellular phosphorylation. These results suggest th at ectoprotein phosphorylation may possibly be an important event in i mmunologically relevant cell-cell interactions. (C) 1997 Elsevier Scie nce B.V.