Kruglov Emma, Ananthanarayanan Meenakshisundaram, Sousa Pedro, Weerachayaphorn Jittima, Guerra Mateus T, Nathanson Michael H
Digestive Diseases Section, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520-8019, USA.
Digestive Diseases Section, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520-8019, USA.
Biochem Biophys Res Commun. 2017 May 6;486(3):659-664. doi: 10.1016/j.bbrc.2017.03.086. Epub 2017 Mar 19.
The type 2 inositol 1,4,5-trisphosphate receptor (IP3R2) is the principal intracellular Ca release channel in hepatocytes, and so is important for bile secretion and other functions. IP3R2 activity is regulated in part by post-translational modifications but little is known about transcriptional regulation of its expression. We found that both IP3R2 mRNA and protein levels in liver were increased during fasting. Treatment of hepatocytes with forskolin or 8-CPT-cAMP also increased IP3R2, and this was reduced by actinomycin D. Analysis of the IP3R2 promoter revealed five CREs, and CREB potently increased promoter activity. Mutation of CRE4 or CRE5 decreased induction by CREB, and ChIP assay showed recruitment of CREB to these sites. Adenylyl cyclase (AC) 6 and 9 were the principal AC isoforms detected in rat hepatocytes, and silencing either one decreased organic anion secretion, which depends on IP3R2. Secretion furthermore was increased by overnight but not acute treatment with forskolin or 8-CPT-cAMP. These findings provide evidence that IP3R2 expression is transcriptionally regulated by cAMP via CREB binding to CRE elements in its promoter. The findings furthermore suggest that this mechanism is relevant for hormonal regulation of bile secretion.
2型肌醇1,4,5-三磷酸受体（IP3R2）是肝细胞中主要的细胞内钙释放通道，对胆汁分泌和其他功能很重要。IP3R2的活性部分受翻译后修饰的调节，但其表达的转录调控知之甚少。我们发现，禁食期间肝脏中IP3R2的mRNA和蛋白质水平均升高。用福斯可林或8-CPT-cAMP处理肝细胞也会增加IP3R2，而放线菌素D可使其降低。对IP3R2启动子的分析揭示了五个CRE，CREB可有效增加启动子活性。CRE4或CRE5的突变会降低CREB的诱导作用，染色质免疫沉淀试验表明CREB被募集到这些位点。腺苷酸环化酶（AC）6和9是在大鼠肝细胞中检测到的主要AC亚型，沉默其中任何一种都会降低依赖于IP3R2的有机阴离子分泌。此外，过夜用福斯可林或8-CPT-cAMP处理可增加分泌，但急性处理则不然。这些发现提供了证据，表明IP3R2的表达通过CREB与启动子中的CRE元件结合而受到cAMP的转录调控。这些发现还表明，这种机制与胆汁分泌的激素调节有关。
