Ca2+ and phospholipid-dependent protein kinase (protein kinase C) activity
is not necessarily required for secretion by human neutrophils
KJ Balazovich, JE Smolen and LA Boxer
Ca2+-dependent and phospholipid-dependent protein kinase (PKC) is a
receptor for and is activated by phorbol esters. This enzyme is reportedly
involved in the mechanism of superoxide anion (O2-) production and the
release of intracellular granule contents from human neutrophils. As
previously reported by others, we found that greater than 75% of the total
cellular PKC activity existed in a soluble form in untreated neutrophils
and that this activity was enhanced in a dose- dependent manner by phorbol
12-myristate 13-acetate (PMA) and by phorbol 12,13-dibutyrate (PDBu).
Furthermore, mezerein, an analogue of PMA that is thought to be a
competitive inhibitor, did not activate PKC, and on the contrary, inhibited
PMA-stimulated activity in a dose- dependent manner. Pretreatment of intact
neutrophils with PMA or PDBu caused the "translocation" of PKC activity to
the insoluble cell fraction; PKC translocation was not detected after
mezerein stimulation at any of the tested concentrations. Neither did
mezerein cause an increase in intracellular Ca2+, as monitored by Quin 2
fluorescence. Both phorbol esters and mezerein stimulated intact
neutrophils to generate O2- and release lysosomal enzymes into the
extracellular medium. Finally sodium dodecyl sulfate-polyacrylamide gel
electrophoresis (SDS-PAGE) analysis demonstrated key differences in the
patterns of endogenous phosphoproteins of neutrophils stimulated with
phorbol as compared with mezerein. We therefore suggest that PKC activation
may not be the only pathway required to elicit neutrophil responses.
Volume 68,
Issue 4,
pp. 810-817,
10/01/1986
Copyright © 1986 by The American Society of Hematology
