Buhl A M, Osawa S, Johnson G L
Department of Chemistry, Aarhus University, Denmark.
J Biol Chem. 1995 Aug 25;270(34):19828-32. doi: 10.1074/jbc.270.34.19828.
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 G16 alpha subunit (alpha 16) results in the G16-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.
过敏毒素C5a受体可激活人中性粒细胞中的Ras/Raf/丝裂原活化蛋白（MAP）激酶信号通路。目前对于C5a及其他趋化因子受体激活Ras/Raf/MAP激酶信号通路所涉及的信号途径了解甚少。在HEK293细胞中表达的C5a受体受到刺激后会导致适度的MAP激酶激活，而百日咳毒素催化的G(i)的ADP核糖基化可抑制这种激活。C5a受体与G16α亚基（α16）共表达会导致G16介导的磷脂酶Cβ激活以及强烈的MAP激酶激活。用百日咳毒素处理C5a受体/α16共转染的细胞，相对于对照反应，C5a对MAP激酶活性的刺激作用会被抑制约60%。同样，蛋白激酶C抑制剂GF109203X可将C5a受体/α16共转染细胞中MAP激酶激活的活性抑制60%；在不存在α16表达的情况下，蛋白激酶C抑制剂不会影响C5a受体适度的反应。这些结果表明，G蛋白偶联受体对MAP激酶的最大激活需要两个独立的信号。
