Department of Physiology, Xiangya Medicine School, Central South University, Changsha, Hunan, 410078, People's Republic of China.
J Mol Neurosci. 2012 Jan;46(1):88-99. doi: 10.1007/s12031-011-9675-3. Epub 2011 Nov 30.
The native ligand for the G protein-coupled bombesin receptor subtype-3 (BRS-3) has currently not been identified. Studies in mice showed robust BRS-3 expression in the hypothalamic satiety centers, and genetic receptor inactivation resulted in obesity, diabetes, and hypertension. BRS-3 was also detected in normal human pancreatic islet cells suggesting a critical role of BRS-3 in regulating energy metabolism and satiety via central and peripheral mechanisms of action. The cyclic AMP response element binding protein (CREB) is a main regulator of pancreatic β-cell gene expression required for glucose homeostasis and islet cell survival, and hypothalamic regulation of satiety. Therefore, in this study we examined whether agonist-dependent hBRS-3 stimulation mediates CREB activation. A selective hBRS-3 peptide agonist and two non-selective hBRS-3 peptide agonists were used to activate ectopically expressed hBRS-3. Stimulation with hBRS-3 peptide agonists resulted in transient calcium mobilization, whereby the selective peptide agonist acted exclusively via hBRS-3 but not through the gastrin-releasing peptide receptor (GRP-R). A selective high-affinity GRP-R antagonist did not inhibit hBRS-3-mediated calcium signals. We also found time-dependent CREB phosphorylation in response to the selective hBRS-3 activation, which was abrogated by pretreatment with protein kinase A and protein kinase C inhibitors. Human BRS-3 agonists also stimulated CREB transactivation and resulted in modest increases of CRE-dependent gene transcription. These changes were significantly reduced after pretreatment with inhibitors of PKA, PKC, and MEK-1. Thus, our results suggest that hBRS-3 agonist-dependent signaling mediates CREB phosphorylation and transactivation through partially PKA, PKC, and MEK-1 pathways.
B 型利钠肽受体亚型 3（BRS-3）的天然配体目前尚未确定。在小鼠中的研究表明，BRS-3 在下丘脑饱腹中心中表达旺盛，并且遗传受体失活导致肥胖、糖尿病和高血压。BRS-3 也在正常的人类胰岛细胞中被检测到，这表明 BRS-3 通过中枢和外周作用机制在调节能量代谢和饱腹感方面发挥着关键作用。环磷酸腺苷反应元件结合蛋白（CREB）是调节葡萄糖稳态和胰岛细胞存活所必需的胰腺β细胞基因表达的主要调节剂，也是下丘脑饱腹感的调节剂。因此，在这项研究中，我们研究了激动剂依赖性 hBRS-3 刺激是否介导 CREB 激活。使用选择性 hBRS-3 肽激动剂和两种非选择性 hBRS-3 肽激动剂来激活异位表达的 hBRS-3。hBRS-3 肽激动剂的刺激导致瞬时钙动员，其中选择性肽激动剂仅通过 hBRS-3 起作用，而不通过胃泌素释放肽受体（GRP-R）起作用。选择性高亲和力 GRP-R 拮抗剂不能抑制 hBRS-3 介导的钙信号。我们还发现，对选择性 hBRS-3 激活的 CREB 磷酸化具有时间依赖性，该作用可被蛋白激酶 A 和蛋白激酶 C 抑制剂预处理所阻断。人 BRS-3 激动剂还刺激 CREB 反式激活，并导致 CRE 依赖性基因转录适度增加。在用 PKA、PKC 和 MEK-1 抑制剂预处理后，这些变化显著减少。因此，我们的结果表明，hBRS-3 激动剂依赖性信号通过部分 PKA、PKC 和 MEK-1 途径介导 CREB 磷酸化和反式激活。
