Lee B, Laychock S G
Department of Pharmacology and Toxicology, State University of New York, School of Medicine and Biomedical Sciences, Buffalo 14241, USA.
Endocrinology. 2000 Apr;141(4):1394-402. doi: 10.1210/endo.141.4.7421.
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.
在葡萄糖脱敏的大鼠分离胰岛中研究了肌醇1,4,5-三磷酸受体（IP3R）信使核糖核酸（mRNA）和蛋白质表达的调节。胰岛用葡萄糖（11 mM；G处理）培养4天以诱导脱敏；与基础（5.5 mM葡萄糖）值相比，IP3R-I mRNA水平相似，而IP3R-II mRNA水平升高，IP3R-III水平降低。与基础值相比，生长抑素增加了IP3R-II mRNA的表达并降低了IP3R-III mRNA的表达，但对G处理的胰岛IP3R表达没有显著影响。培养4天后，当向G处理的胰岛中加入福斯可林（FSK）、8-溴环磷酸腺苷（8-bromo-cAMP）和胰高血糖素样肽1-（7-36）酰胺时，IP3R-II mRNA水平降低，而IP3R-III mRNA水平在3小时内升高至对照胰岛中观察到的水平。IP3R-I mRNA水平不受生长抑素或FSK的影响。蛋白激酶A抑制剂H-89和放线菌素D可阻止FSK的作用。钙离子载体模拟了FSK对IP3R mRNA表达的影响，而电压依赖性钙通道的阻断或细胞内钙的螯合则抑制了FSK的作用。环磷酸腺苷（cAMP）也增加了胰岛素瘤细胞中IP3R-III mRNA的表达。在G处理的胰岛中，FSK减缓了IP3R-III mRNA的降解。FSK而非葡萄糖刺激了G处理的胰岛中蛋白激酶A的激活。因此，cAMP介导了葡萄糖脱敏胰岛中IP3R-II和-III mRNA转录及稳定性的变化。IP3R-II和-III mRNA的调节表达部分由细胞内钙的可用性介导。
