Specific interactions of chemoattractant factor receptors with G-proteins

T.T Amatruda,N.P Gerard,C Gerard,M.I Simon

doi:10.1016/s0021-9258(18)82183-4

T.T Amatruda, N.P Gerard + Show 2 more

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https://doi.org/10.1016/s0021-9258(18)82183-4

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Abstract

Stimulation of leukocytes with chemoattractant ligands activates phospholipid turnover and calcium release, ultimately leading to chemotaxis, degranulation, and the inflammatory response. The leukocyte response to these ligands is transduced by the interaction of transmembrane receptors with GTP-binding regulatory proteins (G-proteins). To examine the mechanisms of signal transduction by these receptors, we transfected cDNA clones encoding the receptors for the active cleavage product of the fifth component of complement (C5a) and platelet-activating factor (PAF) into COS-7 cells, then measured the production of inositol phosphates (IP) in response to stimulation with these chemoattractant ligands. Cells transfected with the C5a receptor showed no increase in IP production when stimulated with ligand (5-120 nM). However, in cells co-transfected with these receptors and with the cDNA for G alpha 16, a G-protein alpha subunit that is specific to cells of hematopoietic lineage, addition of ligand caused up to a 5-fold increase in IP production. This interaction was specific, as co-transfection of receptors with the G-proteins G alpha q or G alpha 11 did not allow ligand-dependent increase in IP production. In contrast, ligand-dependent activation of IP production was seen in COS cells transfected solely with the PAF receptor. These results indicate that the C5a receptor utilizes signaling pathways distinct from the PAF receptor and suggest that a pertussis toxin-resistant G-protein, G alpha 16, may play a role in the leukocyte response to inflammatory ligands.

Highlights

Stimulation of leukocytes with chemoattractant li- tidylinositol-phospholipase C (PI-PLC)’ and CaZ+ mobilizagands activatesphospholipid turnover andcalcium re- tion, and subsequent protein kinasCe activation, secretion of lease, leading to chemotaxis, degranulation,granular enzymes, activation of therespiratoryburst,and andtheinflammatory response
Two G-proteina subunits gand-dependent activation of IP production was seen that are substratesfor pertussis toxin ADP-ribosylation, Gia2 in COS cells transfected solely with theP A F receptor. and Gia3, are expressed inneutrophilsand monocytes (15, These results indicate that the C5a receptor utilizes 16)
Studies onfh4LP and C5a receptors isolated by biochemsignaling pathways distinct from PtAheF receptor and ical means havesuggested that these receptors areassociated suggest that a pertussistoxin-resistantG-protein, with G-protein heterotrimers, including Gia2 [17, 18].How-Gale,may play a roleintheleukocyteresponseto ever, the observation that the patterns of biochemical actiinflammatory ligands

Summary

Introduction

Stimulation of leukocytes with chemoattractant li- tidylinositol-phospholipase C (PI-PLC)’ and CaZ+ mobilizagands activatesphospholipid turnover andcalcium re- tion, and subsequent protein kinasCe activation, secretion of lease, leading to chemotaxis, degranulation,granular enzymes, activation of therespiratoryburst,and andtheinflammatory response. To examine the mecha- chemoattractant ligands through biochemical studies of the nisms of signal transduction by these receptors, we effects of G T P analogues on chemoattractant factor binding transfected cDNA clones encodingthe receptorsfor the and activation of phospholipases in permeabilized cells and active cleavage productof the fifthcomponent of com- membranes [2,3,4]. Caused up to a &fold increase in IP production This the involvementof G-proteins in the response to interaction wasspecific, as co-transfection of receptors chemoattractantfactorshas beenclearly established,the with the G-proteinsGo9 or Gall did not allow ligand- identification of which G-protein(s)transducetheinflamdependent increase in IP production. Studies onfh4LP and C5a receptors isolated by biochemsignaling pathways distinct from PtAheF receptor and ical means havesuggested that these receptors areassociated suggest that a pertussistoxin-resistantG-protein, with G-protein heterotrimers, including Gia2 [17, 18].How-

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