title: Rapid agonist-induced desensitization and internalization of the A(2B) adenosine receptor is mediated by a serine residue close to the COOH terminus.
abstract: The G(s)-coupled rat A(2B) adenosine receptor (A(2B)-AR) was epitope-tagged at the NH(2) terminus with hemagglutinin (HA) and subjected to progressive deletions or point mutations of the COOH terminus in order to determine regions of the receptor that contribute to agonist-induced desensitization and internalization. When expressed stably in Chinese hamster ovary cells, a mutant receptor in which the final 2 amino acids were deleted, the Leu(330)-stop mutant, underwent rapid agonist-induced desensitization and internalization as did the wild type (WT) receptor. However, the Phe(328) and the Gln(325)-stop mutants were resistant to rapid agonist-induced desensitization and internalization. Co-expression of arrestin-2-green fluorescent protein (arrestin-2-GFP) with WT receptor or Leu(330)-stop mutant resulted in rapid translocation of arrestin-2-GFP from cytosol to membrane upon agonist addition. On the other hand, agonist activation of the Phe(328)-stop or Gln(325)-stop mutant did not result in translocation of arrestin-2-GFP from cytosol. A COOH terminus point mutant, S329G, was also unable to undergo rapid agonist-induced desensitization and internalization, indicating that Ser(329) is a critical residue for these processes. A further deletion mutant (Ser(326)-stop) unexpectedly underwent rapid agonist-induced desensitization and internalization. However, activation of this mutant did not promote translocation of arrestin-2-GFP from cytosol to membrane. In addition, whereas WT receptor internalization was markedly inhibited by co-expression of dominant negative mutants of arrestin-2 (arrestin-2-(319-418)), dynamin (dynamin K44A), or Eps-15 (EDelta95-295), Ser(326)-stop receptor internalization was only inhibited by dominant negative mutant dynamin. Taken together these results indicate that Ser(329), close to the COOH terminus of the rat A(2B)-AR, is critical for the rapid agonist-induced desensitization and internalization of the receptor. However, deletion of the COOH terminus also uncovers a motif that is able to redirect internalization of the receptor to an arrestin- and clathrin-independent pathway.
authors.affiliation: Department of Pharmacology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: A L
authors.initials: AL
authors.lastname: Matharu
authors.forename: S J
authors.initials: SJ
authors.lastname: Mundell
authors.forename: J L
authors.initials: JL
authors.lastname: Benovic
authors.forename: E
authors.initials: E
authors.lastname: Kelly
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019390:Arrestins / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D002966:Clathrin / Q000378:metabolism; D003001:Cloning, Molecular; D006224:Cricetinae; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D034281:Dynamins; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes; D020558:GTP Phosphohydrolases / Q000235:genetics; D017353:Gene Deletion; D005799:Genes, Dominant; D005973:Glutamine / Q000737:chemistry; D049452:Green Fluorescent Proteins; D007930:Leucine / Q000737:chemistry; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010649:Phenylalanine / Q000737:chemistry; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation; D051381:Rats; D043704:Receptor, Adenosine A2B; D018047:Receptors, Purinergic P1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000737:chemistry*; D013997:Time Factors; D014162:Transfection
chemical_list: D019390:Arrestins; D002966:Clathrin; D018076:DNA, Complementary; D000939:Epitopes; D008164:Luminescent Proteins; D010750:Phosphoproteins; D043704:Receptor, Adenosine A2B; D018047:Receptors, Purinergic P1; D011993:Recombinant Fusion Proteins; D005973:Glutamine; D049452:Green Fluorescent Proteins; D012694:Serine; D010649:Phenylalanine; D020558:GTP Phosphohydrolases; D034281:Dynamins; D007930:Leucine