Analysis of assembly and trafficking of native P2X4 and P2X7 receptor complexes in rodent immune cells.
P2X4 and P2X7 are the predominant P2X receptor subtypes expressed in immune cells. Having previously shown a structural and functional interaction between the two recombinant receptors, our aims here were to identify the preferred assembly pathway of the endogenous receptors in macrophage-like cells and to investigate the trafficking of these receptors between the plasma membrane and intracellular sites. We exploited the difference in size between the two subunits, and we used a combination of cross-linkers and blue native-PAGE analysis to investigate the subunit composition of complexes present in primary cultures of rat microglia and macrophages from wild type and P2X7(-/-) mice. Our results indicate that the preferred assembly pathway for both receptors is the formation of homotrimers. Homotrimers of P2X7 were able to co-immunoprecipitate with P2X4, suggesting that an interaction occurs between rather than within receptor complexes. In both macrophages and microglia, P2X7 receptors were predominantly at the cell surface, whereas P2X4 receptors were predominantly intracellular. There were clear cell type-dependent differences in the extent to which P2X4 receptors trafficked to and from the surface; trafficking was much more dynamic in microglia than in the macrophages, and further activation of cultured microglia with relatively short (3-h) incubations with lipopolysaccharide caused an approximately 4-fold increase in the fraction of receptors at the surface with only a 1.2-fold increase in total expression. The redistribution of intracellular receptors is thus an efficient means of enhancing the functional expression of P2X4 at the plasma membrane of microglia.
Boumechache
Miyyada
M
Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD.
Masin
Marianela
M
Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD.
Edwardson
J Michael
JM
Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD.
Górecki
Dariusz C
DC
School of Pharmacy and Biomedical Sciences, University of Portsmouth, Portsmouth PO1 2DT, United Kingdom.
Murrell-Lagnado
Ruth
R
Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD. Electronic address: rdm1003@cam.ac.uk.
D000818:Animals; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000276:immunology / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D017628:Microglia / Q000276:immunology / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000276:immunology / Q000378:metabolism*; D058848:Receptors, Purinergic P2X4; D058486:Receptors, Purinergic P2X7; D013997:Time Factors
D008070:Lipopolysaccharides; C548227:P2rx4 protein, mouse; C548228:P2rx4 protein, rat; C546469:P2rx7 protein, mouse; C546470:P2rx7 protein, rat; D018048:Receptors, Purinergic P2; D058848:Receptors, Purinergic P2X4; D058486:Receptors, Purinergic P2X7