Cross-talk between the circadian clock and the cAMP signaling pathway

描述（由申请人提供）：哺乳动物的摄食行为具有偶发性和昼夜性。因此，哺乳动物已经发展出暂时调节肝脏糖异生以维持葡萄糖稳态的机制。CREB/CRTC2通路通过顺式作用cAMP反应元件（CREs）调节糖异生基因的转录，以响应禁食和喂养。与此同时，自我维持的肝脏生物钟调节代谢基因表达的昼夜节律，其中许多由CREB和CRTC2调节，其峰值水平与一天中的适当时间一致。尽管生物钟和CREB/CRTC2通路之间的分子相互作用被认为塑造了对喂养方案的整体适应，但这些相互作用尚未得到很好的定义。核心生物钟基于一个转录反馈回路，其中clock /Bamal1转录激活因子与Per和Cry基因启动子中的顺式E-box结合，其蛋白产物反过来抑制clock /Bmal1功能，从而在Per和Cry蛋白中产生昼夜节律。目前的应用验证了生物钟和CREB通路通过Per/CRY抑制剂和CREB/CRTC2激活剂之间的相互调节作用促进代谢适应环境变化的假设。目的1至3探讨Cry蛋白在间歇性摄食对肝脏CREB和CRTC2活性的昼夜调节中的作用。特别是，我们将评估Crys在降低胰高血糖素依赖性cAMP生成增加中的作用。胞质Cry是否干扰G蛋白偶联受体信号？目的4-6探讨CREB/CRTC2通路对生物钟活动的反调控作用。特别是，我们将研究Per基因上CREB结合位点的调控重要性，它为同步Per转录提供了一个节点，从而使昼夜节律与日常摄食节律同步。最后，我们将测试这些相互作用如何塑造生物体对喂养方案的长期适应。

DESCRIPTION (provided by applicant): Feeding behavior in mammals is both episodic and circadian. Accordingly, mammals have developed mechanisms to temporally regulate liver gluconeogenesis to maintain glucose homeostasis. The CREB/CRTC2 pathway regulates transcription of gluconeogenic genes via cis-acting cAMP Response Elements (CREs) in response to fasting and feeding bouts. In parallel, the self sustaining hepatic circadian clock mediates circadian rhythm in expression of metabolic genes- a number of which are regulated by CREB and CRTC2- with peak levels aligned to appropriate time of the day. Although molecular interactions between the circadian clock and the CREB/CRTC2 pathway are thought to shape the overall adaptation to feeding regimen, these interactions are not well defined. The core circadian clock is based on a transcriptional feedback loop in which Clock/Bamal1 transcriptional activators bind to cis acting E-box in the promoters of Per and Cry genes, whose protein products in turn inhibit Clock/Bmal1 function, thus producing circadian rhythms in Per and Cry proteins. The current application tests the hypothesis that the circadian clock and CREB pathway promote metabolic adaptation to environmental changes through reciprocal regulatory interactions between the Per/CRY inhibitors and CREB/CRTC2 activators. Aims 1 to 3 address the role of Cry proteins in the circadian modulation of hepatic CREB and CRTC2 activities in response to episodic feeding. In particular, we will evaluate the proposed role of Crys in attenuating glucagon-dependent increases in cAMP production. Does cytoplasmic Cry interfere with G protein coupled receptor signaling? Aims 4-6 address counter-regulatory effects of the CREB/CRTC2 pathway on clock activity. In particular, we will examine the regulatory importance of CREB binding sites on Per genes, which offer a node for synchronizing Per transcription and consequently the circadian clock with the daily feeding rhythms. Finally, we will test how these interactions shape long term adaptation of the organism to feeding regimens. PUBLIC HEALTH RELEVANCE: The circadian clock is thought to promote energy homeostasis by modulating the expression of fasting and feeding programs in metabolically active tissues. Disturbances in clock function have been associated with an increased risk of insulin resistance and the metabolic syndrome, most notably in shift workers. The current application tests the importance of a newly identified interaction between the circadian clock and a cell surface receptor signaling pathway in maintaining glucose homeostasis.