Tyrosyl and phosphatidylinositol kinases of human erythrocyte membranes

Relationship between type II phosphatidylinositol 4-kinase activity and protein tyrosine phosphorylation in membranes from normal and sickle red cells

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. Biophs. 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 types 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 intrinsic tyrosine kinase activity.

Plasmodium falciparum gametocyte formation in vitro: its stimulation by phorbol diesters and by 8-bromo cyclic adenosine monophosphate

Phorbol 12-myristate 13-acetate increased the number of gametocytes by 50 to 100% in well or petri dish cultures of the HB-3 clone of Plasmodium falciparum. Phorbol dibutyrate had a similar effect. The optimal concentration for each of these agents was 20 ng/ml or approximately 30 nM. No effect of forskolin was found, other than a general inhibition of growth at concentrations over 10 microM. An inhibitor of phosphodiesterase, 8-bromo cyclic adenosine monophosphate (at concentrations of 0.1 and 1.0 microM) also significantly increased the number of gametocytes formed by this clone.