Secretagogues cause ubiquitination and down-regulation of inositol 1, 4,5-trisphosphate receptors in rat pancreatic acinar cells.
OBJECTIVE
The action of several exocrine pancreas secretagogues depends on the second messenger inositol 1,4, 5-trisphosphate (IP3), which, via endoplasmic reticulum-located IP3 receptors, mobilizes intracellular Ca2+ stores. Signaling pathways like this one are regulated at multiple loci. To determine whether IP3 receptors are one of these loci, we measured IP3 receptor concentration, distribution, and modification in secretagogue-stimulated rat pancreatic acinar cells.


METHODS
Isolated rat pancreatic acinar cells were exposed to cholecystokinin and other secretagogues, or rats were injected intraperitoneally with cerulein. Then samples of cells or pancreata were probed for IP3 receptor content and distribution as well as for ubiquitin association with IP3 receptors.


RESULTS
Secretagogues rapidly down-regulated acinar cell IP3 receptors both in vitro and in vivo. They also elicited receptor redistribution and caused receptors to become ubiquitinated, indicating that the ubiquitin/proteasome proteolytic pathway contributes to the down-regulation. Surprisingly, however, proteasome inhibitors did not block IP3 receptor down-regulation, and phospholipase Cbeta1 and protein kinase C also were down-regulated. Thus, secretagogues simultaneously activate an additional proteolytic pathway.


CONCLUSIONS
Secretagogues rapidly down-regulate IP3 receptors and other proteins involved in intracellular signaling by a mechanism that involves, but is not limited to, the ubiquitin/proteasome pathway. Loss of these proteins may account for the disruption of Ca2+ mobilization that occurs in models of acute pancreatitis, and may contribute to cell adaptation under physiological conditions.
Wojcikiewicz
R J
RJ
Department of Pharmacology, State University of New York Health Science Center at Syracuse, Syracuse, New York, USA. wojcikir@vax.cs.hscsyr.edu
Ernst
S A
SA
Yule
D I
DI
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D009097:Multienzyme Complexes / Q000378:metabolism; D010179:Pancreas / Q000187:drug effects* / Q000378:metabolism*; D054799:Phospholipase C beta; D046988:Proteasome Endopeptidase Complex; D011493:Protein Kinase C / Q000378:metabolism; D051744:Protein Kinase C-epsilon; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism; D014452:Ubiquitins / Q000378:metabolism*
D015220:Calcium Channels; D004791:Enzyme Inhibitors; D005765:Gastrointestinal Agents; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007527:Isoenzymes; D009097:Multienzyme Complexes; D018160:Receptors, Cytoplasmic and Nuclear; D014452:Ubiquitins; D019284:Thapsigargin; C497257:Prkce protein, rat; D011493:Protein Kinase C; D051744:Protein Kinase C-epsilon; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000262:Adenylyl Cyclases