Involvement of mitogen protein kinase cascade in agonist-mediated human A(3) adenosine receptor regulation.
It has been suggested that A(3) adenosine receptors (ARs) play a role in the pathophysiology of cerebral ischemia with dual and opposite neuroprotective and neurodegenerative effects. This could be due to a receptor regulation mediated by rapid phosphorylation and desensitization carried out by intracellular kinases. In this study, we investigated the involvement of extracellular regulated kinase (ERK 1 and 2), members of the mitogen-activated protein kinase (MAPK) family, in A(3) AR phosphorylation. A(3) AR mediated the activation of ERK 1/2 with a typical transient monophasic kinetics (5 min). The activation was not affected by hypertonic sucrose cell pre-treatment, suggesting that this effect occurred independently of receptor internalization. The involvement of MAPK cascade in the A(3) AR regulation process was evaluated using two well-characterized MAPK kinase inhibitors, PD98059 (2-(2'-amino-3'-methoxyphenyl)oxanaphthalen-4-one) and U0126 (1,4-diamino-2,3-dicyano-1,4-bis (aminophenylthio) butadiene). The exposure of cells to PD98059 prevented MAPK activation and inhibited homologous A(3) AR desensitization and internalization, impairing agonist-mediated receptor phosphorylation. PD98059 inhibited the membrane translocation of G protein-coupled receptor kinase (GRK(2)), which is involved in A(3) AR homologous phosphorylation, suggesting this kinase as a target for the MAPK cascade. On the contrary, the chemically unrelated inhibitor of the MAPK cascade, U0126, did not significantly affect GRK(2) membrane translocation or receptor internalization. Nevertheless, the inhibitor induced a significant impairment of receptor phosphorylation and desensitization. These results suggested that the MAPK cascade is involved in A(3) AR regulation by a feedback mechanism which controls GRK(2) activity and probably involves a direct receptor phosphorylation.
Dipartimento di Psichiatria, Neurobiologia, Farmacologia e Biotecnologie, Università di Pisa, Via Bonanno 6, 56126 Pisa, Italy.
M Letizia
ML
Trincavelli
Daniela
D
Tuscano
Matteo
M
Marroni
Karl-Norbert
KN
Klotz
Antonio
A
Lucacchini
Claudia
C
Martini
D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004705:Endocytosis; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D058906:Purinergic P1 Receptor Agonists; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D015398:Signal Transduction
D004791:Enzyme Inhibitors; D005419:Flavonoids; D058906:Purinergic P1 Receptor Agonists; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1; D019830:Adenosine-5'-(N-ethylcarboxamide); D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one