RGD Reference Report - Proteasomal activation mediates down-regulation of inositol 1,4,5-trisphosphate receptor and calcium mobilization in rat pancreatic islets. - Rat Genome Database

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Proteasomal activation mediates down-regulation of inositol 1,4,5-trisphosphate receptor and calcium mobilization in rat pancreatic islets.

Authors: Lee, B  Gai, W  Laychock, SG 
Citation: Lee B, etal., Endocrinology 2001 May;142(5):1744-51.
RGD ID: 68695
Web Url: http://endo.endojournals.org/cgi/content/abstract/142/5/1744
Pubmed: PMID:11316737   (View Abstract at PubMed)
DOI: DOI:10.1210/endo.142.5.8150   (Journal Full-text)

Inositol 1,4,5-trisphosphate receptor (IP3R) protein levels in isolated rat pancreatic islets were investigated in response to carbachol (CCh) and sulfated cholecystokinin 26-33 amide stimulation. Within 2 h, CCh reduced IP3R-I protein levels by 22% and IP3R-II and -III levels to 65% or more below basal. Sulfated cholecystokinin 26-33 amide decreased the levels of IP3R-I, -II, and -III by 34%, 60%, and 66% below basal, respectively. The effect of CCh was concentration- and time-dependent, with a persistent decline in IP3R levels for up to 6 h after the onset of stimulation. CCh-pretreated islets also showed an inhibition of glucose-stimulated insulin secretion. Proteasome inhibition completely blocked the down-regulatory effects of CCh on IP3Rs and significantly increased the insulin secretory response to glucose stimulation in the presence of CCH: Islet stimulation by glucose, alpha-ketoisocaproic acid, and tolbutamide completely protected IP3Rs against the down-regulatory effects of CCH: 2-deoxyglucose and 3-O-methyl glucose failed to affect CCh-induced IP3R down-regulation. The protective effects of glucose on IP3R down-regulation were completely inhibited by the Ca(2+) channel-blocking agent nimodipine. Intracellular Ca(2+) ([Ca(2+)](i)) levels in Fura-2 (fluorescent Ca(2+) indicator)-loaded islets, in the absence of extracellular Ca(2+), increased in response to glucose stimulation; but in islets pretreated with CCh, glucose did not increase [Ca(2+)](i) above basal levels. However, in islets pretreated with CCh and the proteasomal inhibitor MG-132 (carbobenzoxyl-leucinyl-leucinyl-leucinyl-H), the glucose-stimulated increase in [Ca(2+)](i) was significantly higher than the change observed for glucose-stimulated [Ca(2+)](i) in the absence of MG-132. The results suggest that muscarinic receptor stimulation modulates IP3R protein levels in islets through a proteasomal activation pathway, and that down-regulation of IP3Rs has a profound effect on Ca(2+) mobilization in islets that may relate to insulin secretory responsiveness.

Objects referenced in this article
Gene Asah2 N-acylsphingosine amidohydrolase 2 Rattus norvegicus
Gene Itpr1 inositol 1,4,5-trisphosphate receptor, type 1 Rattus norvegicus
Gene Itpr3 inositol 1,4,5-trisphosphate receptor, type 3 Rattus norvegicus

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