Relationship between Type II Phosphatidylinositol 4‐kinase Activity and Protein Tyrosine Phosphorylation in Membranes from Normal and Sickle Red Cells

Publisher Website
Google Scholar
Abstract
To assess the origin of the previously reported higher type II phosphatidylinositol 4‐kinase (PtdIns 4‐kinase) activity of sickle‐red‐cell membranes [Rhoda‐Hardy‐Dessources, M. D., de Neef, R. S., Mérault, G. & Giraud, F. (1993) Biochim. Biophys. Acta 1181, 90–96], we have investigated the possible involvement of protein kinase C and tyrosine kinases in the regulation of the lipid kinase activity. Both protein kinase activities were found to be markedly higher in membranes from the pathological cells. When isolated normal‐red‐cell or sickle‐red‐cell membranes were assayed, phosphatidylinositol phosphorylation activity was not significantly modified after phorbol ester modulation of protein kinase C. In contrast, stimulation (with sodium orthovanadate) or inhibiton (by tyrphostin) of tyrosine phosphorylation led, respectively, to increased or decreased PtdIns 4‐kinase activity in membranes from both cell types. Moreover, immunoprecipitations of membrane extracts from normal and sickle red cells with anti‐PtdIns 4‐kinase antibody 4C5G, followed by immunoblotting with an anti‐phosphotyrosine Ig, revealed a 56‐kDa band migrating with PtdIns 4‐kinase activity. Taken together, these findings indicate that PtdIns 4‐kinase in red blood cells is a phosphotyrosine‐containing protein and could be regulated by a mechanism involving tyrosine phosphorylation, and the increase in PtdIns 4‐kinase activity of sickle‐red‐cell membranes is at least in part mediated by their high intrinsic tyrosine kinase activity.