J. Biol. Chem., Vol. 261, Issue 18, 8309-8313, 06, 1986
Biochemical responses in activated human neutrophils mediated by protein kinase C and a Ca2+-requiring proteinase
S Pontremoli, E Melloni, M Michetti, O Sacco, F Salamino, B Sparatore and BL Horecker
Low concentrations of phorbol 12-myristate 13-acetate (PMA) elicit a
specific response in human neutrophils, characterized by the production of
oxygen radicals and the release into the medium of a membrane-bound serine
proteinase (Pontremoli, S., Melloni, E., Michetti, M., Sacco, O.,
Sparatore, B., Salamino, F., Damiani, G. and Horecker, B. L. (1986) Proc.
Natl. Acad. Sci. U. S. A., 83, 1685-1689). The following evidence indicates
that this response is mediated by membrane-bound protein kinase C: 1) it is
blocked by inhibitors of protein kinase C; and 2) it is enhanced in cells
preloaded with leupeptin which prevents proteolysis of protein kinase C and
its subsequent dissociation from the cell membrane. This response is not
accompanied by significant exocytosis of granule enzymes. With higher
concentrations of PMA, and more particularly on stimulation with
formylmethionyl-leucyl- phenylalanine (fMLP) plus cytochalasin B, a
substantial exocytosis of constituents of both specific and azurophil
granules is observed. With fMLP, exocytosis of granule enzymes is the
predominant event, with little production of H2O2 and negligible release of
membrane-bound serine proteinase. Exocytosis promoted either by a high
concentration of PMA or by fMLP is inhibited by leupeptin, indicating that
it is due to the action of an intracellular Ca2+-dependent thiol proteinase
(calpain), either directly or by conversion by calpain of membrane- bound
protein kinase C to the soluble Ca2+/phospholipid-independent form.
Intracellular mobilization of Ca2+ is also observed following stimulation
with either PMA or fMLP, but only the latter results in a net increase in
the intracellular concentration of free Ca2+; under these conditions
maximum exocytosis of granule contents is observed.