title: Fc gamma receptor activation induces the tyrosine phosphorylation of both phospholipase C (PLC)-gamma 1 and PLC-gamma 2 in natural killer cells.
abstract: Crosslinking of the low affinity immunoglobulin G (IgG) Fc receptor (Fc gamma R type III) on natural killer (NK) cells initiates antibody-dependent cellular cytotoxicity. During this process, Fc gamma R stimulation results in the rapid activation of phospholipase C (PLC), which hydrolyzes membrane phosphoinositides, generating inositol-1,4,5-trisphosphate and sn-1,2-diacylglycerol as second messengers. We have recently reported that PLC activation after Fc gamma R stimulation can be inhibited by a protein tyrosine kinase (PTK) inhibitor. Based on the paradigm provided by the receptor tyrosine kinases, we investigated whether PLC-gamma 1 and/or PLC-gamma 2 are expressed in NK cells, and whether the PLC-gamma isoforms are tyrosine phosphorylated in response to Fc gamma R stimulation. Immunoblotting analyses with PLC-gamma 1- and PLC-gamma 2-specific antisera demonstrate that both isoforms are expressed in human NK cells. Furthermore, Fc gamma R crosslinking triggers the tyrosine phosphorylation of both PLC-gamma 1 and PLC-gamma 2 in these cells. Phosphorylation of both isoforms is detectable within 1 min, and returns to basal level within 30 min. Pretreatment with herbimycin A, a PTK inhibitor, blocked the Fc gamma R-induced tyrosine phosphorylation of PLC-gamma 1 and PLC-gamma 2, and the subsequent release of inositol phosphates. These results suggest that Fc gamma R-initiated phosphoinositide turnover in human NK cells is regulated by the tyrosine phosphorylation of PLC-gamma. More broadly, these observations demonstrate that nonreceptor PTK(s) activated by crosslinkage of a multisubunit receptor can phosphorylate both PLC-gamma isoforms.
mesh_terms: D000920:Antibody-Dependent Cell Cytotoxicity; D016227:Benzoquinones; D002460:Cell Line; D004789:Enzyme Activation; D006801:Humans; D015151:Immunoblotting; D007527:Isoenzymes / Q000378:metabolism*; D007694:Killer Cells, Natural / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology*; D007700:Kinetics; D047029:Lactams, Macrocyclic; D010766:Phosphorylation; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011809:Quinones / Q000494:pharmacology; D017452:Receptors, IgG / Q000378:metabolism*; D017828:Rifabutin / Q000031:analogs & derivatives; D010738:Type C Phospholipases / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis
chemical_list: D016227:Benzoquinones; D007527:Isoenzymes; D047029:Lactams, Macrocyclic; D011809:Quinones; D017452:Receptors, IgG; D017828:Rifabutin; D019000:Phosphotyrosine; D014443:Tyrosine; C020754:herbimycin; D011505:Protein-Tyrosine Kinases; D010738:Type C Phospholipases