Tumor Necrosis Factor-α Prevents Desensitization of Gα_s-Coupled Receptors by Regulating GRK2 Association with the Plasma Membrane

Abstract

We have reported previously that interleukin-1 and tumor necrosis factor (TNF)-␣ increase expression and function of adenosine A 2A receptors (A 2A Rs), although the increased function is disproportionate to the increment in expression. We therefore studied the effect of TNF-␣ on A 2A R function and desensitization in human monocytoid THP-1 cells. We observed that TNF-␣ regulates activity of A 2A Rs and other G protein-coupled receptors (GPCRs) by altering their ligand-mediated desensitization. Pretreatment of resting cells with the A 2A R agonist 2-[p-(2-carboxyethyl)phenethylamino]-5Ј-N-ethylcarboxamidoadenosine (CGS 21680) or the pan-adenosine receptor agonist 5Ј-N-ethylcarboxamidoadenosine quickly desensitized cAMP responses to CGS 21680 restimulation, but TNF-␣ treatment prevented A 2A R desensitization. As expected, A 2A R occupancy induced translocation of GPCR kinase-2 (GRK2) to the plasma membrane (PM). We were surprised to find that after TNF-␣ treatment, A 2A R occupancy not only failed to induce GRK2 translocation to PM but also decreased GRK2 association with PM. TNF-␣ altered GRK2 translocation in response to the ␤-adrenergic receptor agonist isoproterenol in a similar manner. Similar to GRK2, ␤-arrestin associated with PM after A 2A R stimulation in control cells but not in TNF-␣-treated cells. C 2 -ceramide, a downstream mediator in the sphingomyelinase (SMase)-dependent pathway, mimicked the effect of TNF-␣ on GRK2 translocation. Moreover, inhibitors of the SMases and an inhibitor of c-Jun NH 2 -terminal kinase, also a downstream effector in the SMase pathway, reversed TNF-␣-mediated effects on GRK2 translocation and A 2A R desensitization. These results suggest a novel form of cross-talk between TNF-␣ receptors and GPCRs; TNF-␣ enhances GPCR function by preventing agonist-induced desensitization of GPCRs by diminishing agonist-dependent recruitment of GRK2 and ␤-arrestin to PM by a SMase pathway-mediated mechanism.

Differential Expression of Adenosine A3 Receptors Controls Adenosine A2A Receptor-Mediated Inhibition of TLR Responses in Microglia

“…Biochemical studies using reporter cell lines transfected with different ADORAs might reveal possible interactions between A 2A R-and A 3 R-mediated signaling but are currently lacking. Although our data strongly suggest that the changes in ADORA expression patterns are responsible for the enhanced inhibition of TLR-induced cytokine production in activated microglia, we cannot exclude the possibility that other effects, such as altered coupling of ADORAs to intracellular signaling cascades (36,37), TNF-␣-induced prevention of A 2A R desensitization (38), or the altered expression of downstream signaling elements (39), play a role as well.…”

TNF-α potentiates lysophosphatidic acid-induced COX-2 expression via PKD in human colonic myofibroblasts

“…Evidence for cross talk between TNF-␣ and GPCRmediated signaling exists (6,15,19,62). Our laboratory previously identified signaling interactions between TNF-␣ and the specific GPCR BK, which also led to augmented COX-2 expression in colonic myofibroblasts through a PKDdependent process (62).…”

Local Glutamate Level Dictates Adenosine A2AReceptor Regulation of Neuroinflammation and Traumatic Brain Injury

“…The cAMP-PKA pathway has been identified as the main signaling cascade responsible for A 2A R-mediated inhibition of acute inflammation (Cronstein, 1994;Haskó and Cronstein, 2004;Sitkovsky et al, 2004;Fredholm et al, 2007). However, A 2A R activation can signal through cAMP-PKA independent pathways as well (Fredholm et al, 2007), including PKC (Lai et al, 1997;Cunha and Ribeiro, 2000;Pinto-Duarte et al, 2005), MAPK (mitogen-activated protein kinase) (Cheng et al, 2002;Schulte and Fredholm, 2003;Gianfriddo et al, 2004;Melani et al, 2006), ␤-arrestin (Khoa et al, 2006), and even Src-TrkA pathway (Malek et al, 1999). In addition, recent studies show that the C terminus of the A 2A R binds to several interacting proteins [actinin, ARNO (ARF nucleotide binding site opener), Usp4, and TRAX (Translin-associated factor X)] and might mediate the G-protein-independent function of A 2A Rs (for review, see Fredholm et al, 2007).…”