title: Tumor necrosis factor-alpha prevents desensitization of Galphas-coupled receptors by regulating GRK2 association with the plasma membrane.
abstract: We have reported previously that interleukin-1 and tumor necrosis factor (TNF)-alpha increase expression and function of adenosine A2A receptors (A2ARs), although the increased function is disproportionate to the increment in expression. We therefore studied the effect of TNF-alpha on A2A R function and desensitization in human monocytoid THP-1 cells. We observed that TNF-alpha regulates activity of A2A Rs and other G protein-coupled receptors (GPCRs) by altering their ligand-mediated desensitization. Pretreatment of resting cells with the A2AR agonist 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosine (CGS 21680) or the pan-adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine quickly desensitized cAMP responses to CGS 21680 restimulation, but TNF-alpha treatment prevented A2AR desensitization. As expected, A2A R occupancy induced translocation of GPCR kinase-2 (GRK2) to the plasma membrane (PM). We were surprised to find that after TNF-alpha treatment, A2AR occupancy not only failed to induce GRK2 translocation to PM but also decreased GRK2 association with PM. TNF-alpha altered GRK2 translocation in response to the beta-adrenergic receptor agonist isoproterenol in a similar manner. Similar to GRK2, beta-arrestin associated with PM after A2A R stimulation in control cells but not in TNF-alpha-treated cells. C2-ceramide, a downstream mediator in the sphingomyelinase (SMase)-dependent pathway, mimicked the effect of TNF-alpha on GRK2 translocation. Moreover, inhibitors of the SMases and an inhibitor of c-Jun NH2-terminal kinase, also a downstream effector in the SMase pathway, reversed TNF-alpha-mediated effects on GRK2 translocation and A2A R desensitization. These results suggest a novel form of cross-talk between TNF-alpha receptors and GPCRs; TNF-alpha enhances GPCR function by preventing agonist-induced desensitization of GPCRs by diminishing agonist-dependent recruitment of GRK2 and beta-arrestin to PM by a SMase pathway-mediated mechanism.
authors.affiliation: Division of Clinical Pharmacology, Department of Medicine, New York University School of Medicine, 550 First Ave., New York, NY 10016, USA.
authors.forename: Nguyen D
authors.initials: ND
authors.lastname: Khoa
authors.forename: Michael
authors.initials: M
authors.lastname: Postow
authors.forename: Jennifer
authors.initials: J
authors.lastname: Danielsson
authors.forename: Bruce N
authors.initials: BN
authors.lastname: Cronstein
mesh_terms: D019390:Arrestins / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D021381:Protein Transport; D058906:Purinergic P1 Receptor Agonists; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D000071557:beta-Arrestins
chemical_list: D019390:Arrestins; D047428:Protein Kinase Inhibitors; D058906:Purinergic P1 Receptor Agonists; D043562:Receptors, G-Protein-Coupled; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D000071557:beta-Arrestins; D013108:Sphingomyelin Phosphodiesterase; D019204:GTP-Binding Proteins