Interaction between protein kinase C-dependent and G protein-dependent pathways in the regulation of natural killer cell granule exocytosis.
The binding of natural killer (NK) cells to either susceptible tumor cells or antibody-coated targets results in rapid activation of phospholipase C (PLC) in NK cells. PLC activation generates inositol-1,4,5-trisphosphate and sn-1,2-diacylglycerol as second messengers, which, in turn, increase intracellular free calcium concentrations ([Ca2+]i) and protein kinase C (PKC) activity, respectively. These proximal signals initiate a cascade of as yet undefined biochemical events, leading eventually to the exocytosis of preformed cytotoxic granules. To investigate the signal transduction pathways involved in granule exocytosis, we utilized streptolysin-O-permeabilized human NK cells as our experimental model. Our initial studies indicated that the separate activation of either PKC (using the phorbol ester, PMA) or G protein-dependent pathways (using guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S)) stimulated granule exocytosis in a time-, concentration-, and Ca(2+)-dependent manner. PMA-stimulated exocytosis was inhibited by staurosporine or a PKC pseudosubstrate antagonist peptide, but was not affected by GDP. In contrast, GTP gamma S-stimulated exocytosis was effectively inhibited by GDP, but not by staurosporine or the PKC pseudosubstrate antagonist. These observations suggest that NK cell exocytosis can be stimulated by at least two separate pathways; one involving PKC and the other involving a G protein. However, co-stimulation with PMA and GTP gamma S synergistically enhanced exocytosis, suggesting that even though the two exocytotic pathways were biochemically distinct, cross-talk between the two pathways may potently influence the exocytotic process. These results define a regulatory role for PKC- and G protein-dependent pathways during granule exocytosis from NK cells.
Ting
A T
AT
Department of Immunology, Mayo Clinic and Foundation, Rochester, Minnesota 55905.
Schoon
R A
RA
Abraham
R T
RT
Leibson
P J
PJ
D000470:Alkaloids / Q000494:pharmacology; D015703:Antigens, CD / Q000276:immunology; D002460:Cell Line; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology*; D004357:Drug Synergism; D004789:Enzyme Activation; D005089:Exocytosis / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D007694:Killer Cells, Natural / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D007700:Kinetics; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015290:Second Messenger Systems; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000470:Alkaloids; D015703:Antigens, CD; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate