Pertussis toxin-sensitive activation of phospholipase C by the C5a and fMet-Leu-Phe receptors

Signal transduction pathways that mediate C5a and fMet-Leu-Phe (fMLP)-induced pertussis toxin (PTx)-sen-sitive activation of phospholipase C (PLC) have been investigated using a cotransfection assay system in COS-7 cells. The abilities of the receptors for C5a and fMLP to activate PLC b2 and PLC b3 through the Gbg subunits of endogenous Gi proteins in COS-7 cells were tested because both PLC b2 and PLC b3 were shown to be activated by the bg subunits of G proteins in in vitro reconstitution assays. Neither of the receptors can acti-vate endogenous PLC b3 or recombinant PLC b3 in transfected COS-7 cells. However, both receptors can clearly activate PLC b2 in a PTx-sensitive manner, sug-gesting that the receptors may interact with endoge-nous PTx-sensitive G proteins and activate PLC b2 prob