Regulation of inositol trisphosphate receptor isoform expression in glucose-desensitized rat pancreatic islets: role of cyclic adenosine 3',5'-monophosphate and calcium.
The regulation of inositol 1,4,5-trisphosphate receptor (IP3R) messenger RNA (mRNA) and protein expression was investigated in glucose-desensitized rat isolated pancreatic islets. Islets were cultured for 4 days with glucose (11 mM; G-treated) to induce desensitization; IP3R-I mRNA levels were similar to basal (5.5 mM glucose) values, whereas IP3R-II mRNA levels were increased and IP3R-III levels were reduced compared with basal levels. Somatostatin increased the expression of IP3R-II mRNA and reduced the expression of IP3R-III mRNA compared with basal values, but did not significantly affect G-treated islet IP3R expression. When forskolin (FSK), 8-bromo-cAMP, and glucagon-like peptide 1-(7-36) amide were added to G-treated islets after 4 days of culture, IP3R-II mRNA levels were reduced, whereas IP3R-III mRNA levels increased, to levels observed in control islets, within 3 h. The levels of IP3R-I mRNA were unaffected by either somatostatin or FSK. The protein kinase A inhibitor. H-89, and actinomycin D prevented the effects of FSK. A Ca2+ ionophore mimicked the effects of FSK on IP3R mRNA expression, whereas blockade of voltage-dependent Ca2+ channels or chelation of intracellular Ca2+ inhibited the actions of FSK. cAMP also increased IP3R-III mRNA in insulinoma cells. In G-treated islets, FSK slowed IP3R-III mRNA degradation. FSK, but not glucose, stimulated protein kinase A activation in G-treated islets. Thus, cAMP mediates changes in IP3R-II and -III mRNA transcription and stability in glucose-desensitized islets. The regulated expression of IP3R-II and -III mRNA is mediated in part by intracellular Ca2+ availability.
Lee
B
B
Department of Pharmacology and Toxicology, State University of New York, School of Medicine and Biomedical Sciences, Buffalo 14241, USA.
Laychock
S G
SG
D000818:Animals; D002118:Calcium / Q000502:physiology; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D046508:Culture Techniques; D000242:Cyclic AMP / Q000378:metabolism / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020871:RNA Stability / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D020033:Protein Isoforms; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D005947:Glucose; D002118:Calcium