Monash Institute of Pharmaceutical Sciences, 381 Royal Parade, Parkville, Victoria 3052, Australia.
J Biol Chem. 2013 Aug 9;288(32):22942-60. doi: 10.1074/jbc.M113.455774. Epub 2013 Jul 1.
TGR5 is a G protein-coupled receptor that mediates bile acid (BA) effects on energy balance, inflammation, digestion, and sensation. The mechanisms and spatiotemporal control of TGR5 signaling are poorly understood. We investigated TGR5 signaling and trafficking in transfected HEK293 cells and colonocytes (NCM460) that endogenously express TGR5. BAs (deoxycholic acid (DCA), taurolithocholic acid) and the selective agonists oleanolic acid and 3-(2-chlorophenyl)-N-(4-chlorophenyl)-N, 5-dimethylisoxazole-4-carboxamide stimulated cAMP formation but did not induce TGR5 endocytosis or recruitment of β-arrestins, as assessed by confocal microscopy. DCA, taurolithocholic acid, and oleanolic acid did not stimulate TGR5 association with β-arrestin 1/2 or G protein-coupled receptor kinase (GRK) 2/5/6, as determined by bioluminescence resonance energy transfer. 3-(2-chlorophenyl)-N-(4-chlorophenyl)-N, 5-dimethylisoxazole-4-carboxamide stimulated a low level of TGR5 interaction with β-arrestin 2 and GRK2. DCA induced cAMP formation at the plasma membrane and cytosol, as determined using exchange factor directly regulated by cAMP (Epac2)-based reporters, but cAMP signals did not desensitize. AG1478, an inhibitor of epidermal growth factor receptor tyrosine kinase, the metalloprotease inhibitor batimastat, and methyl-β-cyclodextrin and filipin, which block lipid raft formation, prevented DCA stimulation of ERK1/2. Bioluminescence resonance energy transfer analysis revealed TGR5 and EGFR interactions that were blocked by disruption of lipid rafts. DCA stimulated TGR5 redistribution to plasma membrane microdomains, as localized by immunogold electron microscopy. Thus, TGR5 does not interact with β-arrestins, desensitize, or traffic to endosomes. TGR5 signals from plasma membrane rafts that facilitate EGFR interaction and transactivation. An understanding of the spatiotemporal control of TGR5 signaling provides insights into the actions of BAs and therapeutic TGR5 agonists/antagonists.
TGR5 是一种 G 蛋白偶联受体，介导胆汁酸 (BA) 对能量平衡、炎症、消化和感觉的影响。TGR5 信号的机制和时空调控知之甚少。我们研究了转染 HEK293 细胞和内源性表达 TGR5 的结肠细胞 (NCM460) 中的 TGR5 信号转导和转运。BA（脱氧胆酸 (DCA)、牛磺胆酸）和选择性激动剂齐墩果酸和 3-(2-氯苯基)-N-(4-氯苯基)-N,5-二甲基异恶唑-4-甲酰胺刺激 cAMP 形成，但通过共聚焦显微镜评估，不会诱导 TGR5 内吞作用或β-arrestin 的募集。DCA、牛磺胆酸和齐墩果酸不会刺激 TGR5 与β-arrestin 1/2 或 G 蛋白偶联受体激酶 (GRK)2/5/6 结合，如生物发光共振能量转移所示。3-(2-氯苯基)-N-(4-氯苯基)-N,5-二甲基异恶唑-4-甲酰胺刺激 TGR5 与β-arrestin 2 和 GRK2 的低水平相互作用。DCA 通过基于交换因子直接调节的 cAMP（Epac2）的报告器在质膜和细胞质中诱导 cAMP 形成，但 cAMP 信号不会脱敏。表皮生长因子受体酪氨酸激酶抑制剂 AG1478、金属蛋白酶抑制剂 batimastat 以及阻断脂筏形成的甲基-β-环糊精和 filipin 阻止了 DCA 对 ERK1/2 的刺激。生物发光共振能量转移分析显示，TGR5 和 EGFR 相互作用被破坏脂筏形成所阻断。DCA 刺激 TGR5 重新分布到质膜微区，如免疫金电子显微镜定位的那样。因此，TGR5 不会与β-arrestin 相互作用、脱敏或转运到内体。TGR5 从质膜筏子发出信号，促进 EGFR 相互作用和转激活。对 TGR5 信号时空调控的理解为理解 BA 的作用和治疗性 TGR5 激动剂/拮抗剂提供了线索。
