Phosphatidylinositol metabolism and protein kinase C activation in leukocytes by lipopeptides

The synthetic lipopeptide Pam3Cys-Ser-Ser-Asn-Ala, an analogue of the N-terminal part of bacterial lipoprotein, constitutes a potent macrophage and B lymphocyte activator. In the macrophage cell-line P388D1 Pam3Cys-Ser-Ser-Asn-Ala stimulated phosphoinositol turnover, whereas in small resting lymphocytes no enhanced turnover was observed. Upon lipopeptide stimulation, a translocation of PKC from the cytosol to the plasma membrane was found in the cell line P388D1 but not in lymphocytes. Substituting lipopeptide for diacylglycerol shows that Pam3Cys-Ser-Ser-Asn-Ala leads to an activation of protein kinase C at Ca2+ concentrations of 0.5 mM. Thus, mitogenic lipopeptides constitute novel tools for investigating the molecular mechanism of transmembrane signaling in leukocyte activation.