Tsu R C, Lai H W, Allen R A, Wong Y H
Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon.
Biochem J. 1995 Jul 1;309 ( Pt 1)(Pt 1):331-9. doi: 10.1042/bj3090331.
In neutrophils, activation of receptors for the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (fMLP) leads to changes in intracellular events such as phosphoinositide turnover and Ca2+ mobilization. Studies have shown that activation of the cloned fMLP receptor can also lead to inhibition of cyclic AMP (cAMP) accumulation [Lang, Boulay, Li and Wollheim (1993) EMBO J. 12, 2671-2679; Uhing, Gettys, Tomhave, Snyderman and Didsbury (1992) Biochem. Biophys. Res. Commun. 183, 1033-1039]. These responses are apparently mediated through pertussis toxin-sensitive Gi proteins. Since other chemotactic factor receptors can couple to multiple G proteins, we examined the ability of the fMLP receptor to utilize a pertussis toxin-insensitive G protein, Gz, in its signal transduction pathways. The human fMLP receptor was transiently expressed in 293 and Ltk- cells, and subsequently assayed for receptor-mediated inhibition of cAMP accumulation and stimulation of phosphoinositide-specific phospholipase C. In transfected 293 cells, fMLP inhibited choriogonadotropin-stimulated cAMP accumulation by 50% and the response could be abolished by pertussis toxin. Co-expression of the fMLP receptor with the alpha subunit of Gz rendered the fMLP response pertussis toxin-insensitive, indicating that the endogenous Gi proteins can be substituted efficiently by Gz. In contrast, Ltk- cells expressing the fMLP receptor were able to respond to fMLP with an increase in the production of inositol phosphates, but this response was completely abolished by pertussis toxin even in cells co-expressing the alpha subunit of Gz. Thus, although both signalling pathways appeared to utilize Gi-like proteins, Gz can only replace Gi in mediating inhibition of cAMP accumulation, and not in the stimulation of phospholipase C. Differential interaction with Gz might represent a novel mechanism by which fMLP receptors regulate intracellular events.
在中性粒细胞中，趋化肽N-甲酰甲硫氨酰-亮氨酰-苯丙氨酸（fMLP）受体的激活会导致细胞内事件的变化，如磷酸肌醇周转和Ca2+动员。研究表明，克隆的fMLP受体的激活也会导致环磷酸腺苷（cAMP）积累的抑制[朗、布莱、李和沃尔海姆（1993年）《欧洲分子生物学组织杂志》12卷，2671 - 2679页；乌欣、格蒂斯、汤姆哈夫、斯奈德曼和迪兹伯里（1992年）《生物化学与生物物理学研究通讯》183卷，1033 - 1039页]。这些反应显然是通过百日咳毒素敏感的Gi蛋白介导的。由于其他趋化因子受体可以与多种G蛋白偶联，我们研究了fMLP受体在其信号转导途径中利用百日咳毒素不敏感的G蛋白Gz的能力。人fMLP受体在293和Ltk -细胞中瞬时表达，随后检测受体介导的cAMP积累抑制和磷酸肌醇特异性磷脂酶C的刺激。在转染的293细胞中，fMLP将绒毛膜促性腺激素刺激的cAMP积累抑制了50%，且该反应可被百日咳毒素消除。fMLP受体与Gz的α亚基共表达使fMLP反应对百日咳毒素不敏感，表明内源性Gi蛋白可被Gz有效替代。相比之下，表达fMLP受体的Ltk -细胞能够对fMLP产生反应，肌醇磷酸的产量增加，但即使在共表达Gzα亚基的细胞中，该反应也完全被百日咳毒素消除。因此，尽管两条信号通路似乎都利用类Gi蛋白，但Gz只能在介导cAMP积累抑制方面取代Gi，而不能在刺激磷脂酶C方面取代Gi。与Gz的差异相互作用可能代表了fMLP受体调节细胞内事件的一种新机制。
