ACh and adenosine activate PI3-kinase in rabbit hearts through transactivation of receptor tyrosine kinases.
Adenosine and acetylcholine (ACh) trigger preconditioning through different signaling pathways. We tested whether either could activate myocardial phosphatidylinositol 3-kinase (PI3-kinase), a putative signaling protein in ischemic preconditioning. We used phosphorylation of Akt, a downstream target of PI3-kinase, as a reporter. Exposure of isolated rabbit hearts to ACh increased Akt phosphorylation 2.62 +/- 0.33 fold (P = 0.001), whereas adenosine caused a significantly smaller increase (1.52 +/- 0.08 fold). ACh-induced activation of Akt was abolished by the tyrosine kinase blocker genistein indicating at least one tyrosine kinase between the muscarinic receptor and Akt. ACh-induced Akt activation was blocked by the Src tyrosine kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) and by 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG-1478), an epidermal growth factor receptor (EGFR) inhibitor, suggesting phosphorylation of a receptor tyrosine kinase in an Src tyrosine kinase-dependent manner. ACh caused tyrosine phosphorylation of the EGFR, which could be blocked by PP2, thus supporting this receptor hypothesis. AG-1478 failed to block the cardioprotection of ACh, however, suggesting that other receptor tyrosine kinases might be involved. Therefore, G(i) protein-coupled receptors can activate PI3-kinase/Akt through transactivation of receptor tyrosine kinases in an Src tyrosine kinase-dependent manner.
Krieg
Thomas
T
Department of Physiology, University of South Alabama, Mobile 36688, USA.
Qin
Qining
Q
McIntosh
Elizabeth C
EC
Cohen
Michael V
MV
Downey
James M
JM
D000109:Acetylcholine / Q000494:pharmacology*; D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D005260:Female; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011799:Quinazolines; D011817:Rabbits; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015533:Transcriptional Activation / Q000187:drug effects; D020032:Tyrphostins / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology*; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
D000109:Acetylcholine; D000241:Adenosine; D004791:Enzyme Inhibitors; D066246:ErbB Receptors; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011799:Quinazolines; D020794:Receptor Protein-Tyrosine Kinases; D020032:Tyrphostins; D014665:Vasodilator Agents; D019061:src-Family Kinases; C101044:RTKI cpd