IKK (cat), RAP-1A, CREB1, CDC42, Adenosine extracellular region, Adenosine A2a receptor, I-kB, Elk-1, G-protein alpha-s, MEKK1(MAP3K1), PKA-reg (cAMP-dependent), AKT(PKB), MEK2(MAP2K2), PKA-cat (cAMP-dependent), c-Jun, Adenylate cyclase type VI, PI3K cat class IA, PtdIns(3,4,5)P3, Erk (MAPK1/3), PtdIns(4,5)P2, 22.214.171.124, 126.96.36.199, p90Rsk, IKK-alpha, BAD, PDZ-GEF1, cAMP-GEFI, PDK (PDPK1), MEKK4(MAP3K4), BETA-PIX, cAMP, H-Ras, ATF-2, PKC-zeta, PAK1, B-Raf, MKK7 (MAP2K7), PARD6, MEK6(MAP2K6), p38 MAPK, MEK1(MAP2K1), NF-kB, JNK(MAPK8-10)
Adenosine A2A receptor signaling
Adenosine is a potent biological mediator that affects numerous cell types, including neuronal cells, platelets, neutrophils and smooth muscle cells. Currently, four adenosine receptor subtypes have been identified: A1, A2A, A2B and A3. Adenosine receptors belong to the G-protein-coupled receptor family of cell surface receptors. Adenosine A2A receptor is G-protein alpha-s coupled receptor that induces classical second messenger pathway such as modulation of cAMP production.
Adenosine A2A receptor interaction with the trimeric G-protein alpha-s/ beta/gamma causes the exchange of GDP to GTP bound to G protein alpha subunits and the dissociation of the beta/gamma heterodimers.
Activated G-protein alpha-s stimulates Adenylate cyclase 6 ( Adenylate cyclase type VI ) . Adenylate cyclase type VI increases level of cAMP in cells and activate Protein kinase, cAMP-dependent, regulatory ( PKA-reg (cAMP-dependent) ) that results in Protein kinase, cAMP-dependent, catalytic ( PKA-cat (cAMP-dependent) ) activation . In turn, PKA-cat (cAMP-dependent) phosphorylates and stimulates cAMP responsive element binding protein 1 ( CREB1 ) .
Adenosine A2A receptor facilitates protein secretion through the activation of PKA-cat (cAMP-dependent) and Phosphoinositide-3-kinase, catalytic ( PI3K cat class IA ). Activation of Adenosine A2A receptor transiently increases the phosphorylation of Mitogen-activated protein kinase 14 ( P38 MAPK ) and Mitogen-activated protein kinases 8-10 ( JNK(MAPK8-10) ), V-akt murine thymoma viral oncogene homolog 1 ( AKT(PKB) ), and Activating transcription factor 2 ( ATF-2 ) .
Stimulation of Adenosine A2A receptor prevents cells from the apoptosis via PKA-cat (cAMP-dependent) activation . PKA-cat (cAMP-dependent) phosphorylates and activates Rho guanine nucleotide exchange factor (GEF) 7 ( BETA-PIX ) that, in turn, activates Ras-related C3 botulinum toxin substrate 1 ( Rac1 ) and Cell division cycle 42 ( Cdc42 ). An effector of Cdc42, Par-6 partitioning defective 6 homolog ( PRAD6 ) interacts with Cdc42 in a GTP-dependent manner, and also directly binds to Protein kinase C, zeta ( PKC-zeta ), forming a stable ternary complex with Cdc42 and PKC-zeta. This association results in stimulation of PKC-zeta kinase activity. PKC-zeta prevents apoptosis via phosphorylation of Ribosomal protein S6 kinase, 90kDa ( p90Rsk ), which inhibits BCL2-associated agonist of cell death ( BAD ) protein . Stimulation of PKA-cat (cAMP-dependent) enhances nuclear PKC-zeta activity and cell survival .
Activation of Cdc42 increases the phosphorylation of P38 MAPK and JNK(MAPK8-10) as well as that of ATF-2 and Jun oncogene ( c-Jun ) via stimulation Mitogen-activated protein kinase kinase kinase 4 ( MEKK4(MAP3K4) )/ Mitogen-activated protein kinase kinase 6 MEK6(MAP2K6)/ P38 MAPK and p21 protein (Cdc42/Rac)-activated kinase 1 ( PAK1 )/ Mitogen-activated protein kinase kinase kinase 1 ( MEKK1 )/ Mitogen-activated protein kinase kinase 7( MEK7(MAP2K7)/ JNK(MAPK8-10) pathways .
Activated by cAMP guanine nucleotide exchange factor Rap guanine nucleotide exchange factor (GEF) 2 ( PDZ-GEF1 ) stimulates PI3K cat class IA activation via v-Ha-ras Harvey rat sarcoma viral oncogene homolog ( H-Ras ). PI3K cat class IA converts ( PtdIns(4,5)P2 ) to phosphatidylinositol 3,4,5-triphosphate ( PtdIns(3,4,5)P3 ) .
PtdIns(3,4,5)P3 is a second messenger that directly binds via pleckstrin homology (PH) domen with V-akt murine thymoma viral oncogene homolog 1 ( AKT(PKB) ), that activates Conserved helix-loop-helix ubiquitous kinase ( IKK-alpha )/ Nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor ( I-kB )/ Nuclear factor of kappa light polypeptide gene enhancer in B-cells ( NF-kB ) signaling , .
Activation of Adenosine A2a receptor stimulates nitric oxide production in human fetal umbilical vein endothelial cells via stimulation of Mitogen-activated protein kinase 1-3 ( ERK1/2 ) . cAMP binding to Rap guanine nucleotide exchange factor (GEF) 3 ( cAMP-GEFI ) activates transcription of Nitric oxide synthase 3 ( eNOS ) via RAP1A, member of RAS oncogene family ( RAP-1A )/ v-raf murine sarcoma viral oncogene homolog B1 ( B-Raf )/ Mitogen-activated protein kinase kinases 1 and 2 ( MEK1(MAP2K1) MEK2(MAP2K2) )/ ERK1/2/ ELK1, member of ETS oncogene family ( ELK1 ) pathway .