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Media type:
E-Article
Title:
cAMP-GEF cytoprotection by Src tyrosine kinase activation of phosphoinositide-3-kinase p110 β/α in rat hepatocytes
Contributor:
Gates, Anna;
Hohenester, Simon;
Anwer, M. Sawkat;
Webster, Cynthia R. L.
Published:
American Physiological Society, 2009
Published in:
American Journal of Physiology-Gastrointestinal and Liver Physiology, 296 (2009) 4, Seite G764-G774
Language:
English
DOI:
10.1152/ajpgi.90622.2008
ISSN:
0193-1857;
1522-1547
Origination:
Footnote:
Description:
Cyclic AMP protects against hepatocyte apoptosis by a protein kinase A-independent cAMP-GEF/phosphoinositide-3-kinase (PI3K)/Akt signaling pathway. However, the signaling pathway coupling cAMP-GEF with PI3K is unknown. The aim of this study was to investigate the role of Src tyrosine kinases (Src-TYK) and PI3K-p110 isoforms in this pathway. Studies were done in rat hepatocytes using the hydrophobic bile acid glycochenodeoxycholic acid (GCDC) to induce apoptosis. cAMP-binding guanine nucleotide exchange factors (cAMP-GEFs) were selectively activated by using 4-(4-chloro-phenylthio)-2′- O-methyladenosine-3′-5′-cyclic monophosphate (CPT-2-Me-cAMP), which sequentially phosphorylated Src-TYK (within 1 min) followed by Akt (within 5 min). The Src inhibitors PP2 and SU6656 inhibited basal and CPT-2-Me-cAMP-mediated Src and Akt phosphorylation. These inhibitors had no effect on CPT-2-Me-cAMP-mediated activation of Rap GTPases. CPT-2-Me-cAMP induced transient Src dependent autophosphorylation of the epidermal growth factor receptor (EGFR). Inhibition of the EGFR with AG 1478 partially inhibited the ability of CPT-2-Me to phosphorylate Akt. Whereas PP2 completely abolished the protective effect of CPT-2-Me-cAMP in GCDC induced apoptosis, AG 1478 partially inhibited the cytoprotective effect. CPT-2-Me-cAMP treatment resulted in Src-dependent activation of the p110 β and α subunits of PI3K, but only the latter was sensitive to inhibition with AG 1478. In conclusion, activation of cAMP-GEFs results in phosphorylation of Src-TYK and Akt and activation of the p110 β/α subunits of PI3K. Maximal cAMP-GEF-mediated Akt phosphorylation as well as protection from bile acid-induced apoptosis requires activation of Src-TYK and the EGFR. These studies support the existence of two pathways: cAMP-GEF/Rap/Src/PI3Kβ/Akt and cAMP-GEF/Rap/Src/EGFR/PI3Kα/Akt, both of which are necessary for maximal cytoprotective effect of cAMP-GEFs in hepatocytes.