IDENTIFICATION AND REGULATION OF PROTEIN-KINASE C-DELTA IN HUMAN NEUTROPHILS

The intracellular mechanisms that regulate the function of human neutr ophils are not well understood. Receptor-initiated signaling events re sult in the production of several second messengers (e.g., Ca2+, diacy lglycerol, phosphatidic acid, and arachidonic acid) with the potential to activate members of the protein kinase C (PKC) family of signaling enzymes, The mixture of second messenger signaling molecules produced usually varies, depending on the particular receptor engaged, Previou s work suggests that PKC has complex regulatory effects on neutrophil function, This may be due to the presence of multiple isoforms of the enzyme family, responding differentially to the second messengers prod uced, In studies to identify the PKC isoforms present in human neutrop hils, we discovered the presence of the PKC isoform delta in these cel ls. Like other previously identified isoforms (alpha, beta(I), beta(II ), and zeta), delta is a cytosolic enzyme in unstimulated neutrophils and partially translocates to membrane-containing fractions in cells s timulated by either the PKC activator PMA or the chemoattractant FMLP. Partial purification of cytosolic PKC gave two peaks of activity. The beta isoforms predominated in peak I, while the delta isoform predomi nated in peak II. The identification of delta indicates that neutrophi ls contain at least one member of the Ca2+-independent, diacylglycerol -dependent subfamily of PKC isoforms. Thus, this isoform may participa te in Ca2+-independent, but diacylglycerol-dependent signaling events in these cells.