Alcohol-induced protein kinase Calpha phosphorylation of Munc18c in carbachol-stimulated acini causes basolateral exocytosis.
OBJECTIVE
Acute or chronic alcohol treatment does little to the exocrine pancreas but predisposes the pancreas to postprandial cholinergic stimulation that triggers cellular events leading to pancreatitis. This alcohol-induced susceptibility mechanism of pancreatitis is unknown.


METHODS
We employed alcohol-treated dispersed rat pancreatic acini and alcohol diet-fed rats to examine the effects of submaximal carbachol-induced changes in exocytosis (FM1-43 epifluorescence imaging and electron microscopy), Munc18c cellular translocation (confocal microscopy and subcellular fractionation), and protein kinase C (PKC) alpha-induced phosphorylation in relation to pancreatitis.


RESULTS
Acute low-dose alcohol (20 mmol/L) in vitro exposure or chronic alcohol diet reduces postprandial cholinergic-stimulated amylase secretion from rat pancreatic acinar cells by blocking apical exocytosis and redirecting exocytosis to less efficient basolateral plasma membrane sites. This ectopic exocytosis is mediated by PKCalpha-induced phosphorylation of Munc18c, causing Munc18c displacement from the basolateral plasma membrane into the cytosol in which it undergoes proteolytic degradation; these processes can be blocked by PKCalpha inhibition.


CONCLUSIONS
We conclude that sequential low-dose alcohol and postprandial cholinergic stimulation can induce PKCalpha-mediated Munc18c plasma membrane displacement. This relieves cognate SNARE proteins on zymogen granules and basolateral membrane to complex and consummate pathologic ectopic exocytosis at the basolateral surface. This change in vesicle trafficking may be related to the pathogenesis of pancreatitis.
Cosen-Binker
Laura I
LI
Department of Medicine, University Health Network, University of Toronto, Toronto, Ontario, Canada.
Lam
Patrick P L
PP
Binker
Marcelo G
MG
Gaisano
Herbert Y
HY
D000681:Amylases / Q000378:metabolism; D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D018679:Cholinergic Agonists / Q000494:pharmacology; D004247:DNA / Q000235:genetics*; D000431:Ethanol / Q000633:toxicity; D005089:Exocytosis / Q000235:genetics*; D005456:Fluorescent Dyes; D015870:Gene Expression; D015151:Immunoblotting; D047468:Immunoprecipitation; D008297:Male; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D051938:Munc18 Proteins / Q000187:drug effects / Q000235:genetics*; D010179:Pancreas / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure; D019512:Pancreatitis, Alcoholic / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009195:Peroxidase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051571:Protein Kinase C-alpha / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D051381:Rats; D017208:Rats, Wistar; D012997:Solvents / Q000633:toxicity; D014178:Translocation, Genetic
D018679:Cholinergic Agonists; C073804:FM1 43; D005456:Fluorescent Dyes; D051938:Munc18 Proteins; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D012997:Solvents; D000431:Ethanol; D002217:Carbachol; D004247:DNA; D009195:Peroxidase; D051571:Protein Kinase C-alpha; D000681:Amylases