Gastrointestinal growth factors and hormones have divergent effects on Akt activation.
Akt is a central regulator of apoptosis, cell growth and survival. Growth factors and some G-protein-coupled receptors (GPCR) regulate Akt. Whereas growth-factor activation of Akt has been extensively studied, the regulation of Akt by GPCR's, especially gastrointestinal hormones/neurotransmitters, remains unclear. To address this area, in this study the effects of GI growth factors and hormones/neurotransmitters were investigated in rat pancreatic acinar cells which are high responsive to these agents. Pancreatic acini expressed Akt and 5 of 7 known pancreatic growth-factors stimulate Akt phosphorylation (T308, S473) and translocation. These effects are mediated by p85 phosphorylation and activation of PI3K. GI hormones increasing intracellular cAMP had similar effects. However, GI-hormones/neurotransmitters [CCK, bombesin, carbachol] activating phospholipase C (PLC) inhibited basal and growth-factor-stimulated Akt activation. Detailed studies with CCK, which has both physiological and pathophysiological effects on pancreatic acinar cells at different concentrations, demonstrated CCK has a biphasic effect: at low concentrations (pM) stimulating Akt by a Src-dependent mechanism and at higher concentrations (nM) inhibited basal and stimulated Akt translocation, phosphorylation and activation, by de-phosphorylating p85 resulting in decreasing PI3K activity. This effect required activation of both limbs of the PLC-pathway and a protein tyrosine phosphatase, but was not mediated by p44/42 MAPK, Src or activation of a serine phosphatase. Akt inhibition by CCK was also found in vivo and in Panc-1 cancer cells where it inhibited serum-mediated rescue from apoptosis. These results demonstrate that GI growth factors as well as gastrointestinal hormones/neurotransmitters with different cellular basis of action can all regulate Akt phosphorylation in pancreatic acinar cells. This regulation is complex with phospholipase C agents such as CCK, because both stimulatory and inhibitory effects can be seen, which are mediated by different mechanisms.
Berna
Marc J
MJ
Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-1804, USA.
Tapia
Jose A
JA
Sancho
Veronica
V
Thill
Michelle
M
Pace
Andrea
A
Hoffmann
K Martin
KM
Gonzalez-Fernandez
Lauro
L
Jensen
Robert T
RT
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D045744:Cell Line, Tumor / Q000187:drug effects; D000242:Cyclic AMP / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005768:Gastrointestinal Hormones / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology*; D008297:Male; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000502:physiology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D043886:Receptor, Cholecystokinin A / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects; D012844:Sincalide / Q000494:pharmacology; D010738:Type C Phospholipases / Q000502:physiology; D019061:src-Family Kinases / Q000502:physiology
D002118:Calcium; D000242:Cyclic AMP; D004791:Enzyme Inhibitors; D005768:Gastrointestinal Hormones; D036341:Intercellular Signaling Peptides and Proteins; D018377:Neurotransmitter Agents; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D051057:Proto-Oncogene Proteins c-akt; D043886:Receptor, Cholecystokinin A; D012844:Sincalide; D010738:Type C Phospholipases; D019061:src-Family Kinases; C494920:Akt1 protein, rat