MITOGEN-ACTIVATED PROTEIN-KINASE ACTIVATION REQUIRES 2 SIGNAL INPUTS FROM THE HUMAN ANAPHYLATOXIN C5A RECEPTOR

The anaphylatoxin C5a receptor activates the Ras/Raf/mitogen-activated protein (MAP) kinase pathway in human neutrophils. The signal pathways involved in Ras/Raf/MAP kinase activation in response to C5a and other chemoattractant receptors is poorly understood. Stimulation of the C5a receptor expressed in HEK293 cells results in modest MAP kinase activation which is inhibited by pertussis toxin-catalyzed ADP-ribosylation of G(i). Coexpression of the C5a receptor and the G(16) alpha subunit (alpha(16)) results in the G(16)-mediated activation of phospholipase C beta and a robust MAP kinase activation. Pertussis toxin treatment of C5a receptor/alpha(16)-cotransfected cells inhibits C5a stimulation of MAP kinase activity approximately 60% relative to the control response. Similarly, the protein kinase C inhibitor, GF109203X inhibits activation of MAP kinase activation in C5a receptor/alpha(16)-cotransfected cells by 60%; the protein kinase C inhibitor does not affect the modest C5a receptor response in the absence of alpha(16) expression. These results demonstrate that two independent signals are required for the maximal activation of MAP kinase by G protein-coupled receptors.