STRUCTURE, FUNCTION AND REGULATION OF BOMBESIN RECEPTORS

哺乳动物蛙皮素样神经肽，胃泌素释放肽(GRP) 和神经介素B(NMB)，在正常情况下介导一系列生物反应 细胞，包括促进某些人的旁分泌或自分泌生长 小细胞肺癌(SCLC)细胞。最近，我们报道了克隆 以及三种药理上不同的啮齿动物和人类的特征 蛙皮素多肽受体胃泌素释放多肽受体(GRP-R)， 神经介素B受体(NMB-R)和蛙皮素受体亚型3(BRS-3)， 在正常和恶性细胞中有不同的表达模式。这些 受体由7个假定的跨膜结构域组成，由 短的细胞内和细胞外环路，它们耦合到 磷脂酶C激活、肌醇磷酸代谢与钙 通过百日咳毒素不敏感的G蛋白动员。GRP-R结合 GRP高亲和力，NMB-R高亲和力结合NMB，BRS-3高亲和力结合 两种多肽的亲和力都相对较低。建造和建造 GRP-R/NMB-R嵌合受体的特性表明 跨膜结构域5是NMB高亲和力结合的关键 NMB-R，特别是Ile216。定点突变研究强调 C末端一个或多个丝氨酸和苏氨酸的重要性 GRP-R的尾部结构域，用于快速有效的受体内化。 这些残基似乎被迅速磷酸化，当受体 与其同源的异源三聚体GTP结合蛋白偶联。 相似受体突变分析显示，15个氨基酸立即 C-末端到跨膜区7，形成一个基本的结构基序 对于效应器连接，结合特定的保守氨基酸 第二个(精氨酸139)和第三个(赖氨酸263)细胞内环中的酸 GRP-R的结构域。

The mammalian bombesin-like neuropeptides, gastrin releasing peptide (GRP) and neuromedin B (NMB), mediate a range of biological responses in normal cells, including promotion of paracrine or autocrine growth in some human small cell lung carcinoma (SCLC) cells. Recently we reported the cloning and characterization of three pharmacologically distinct rodent and human bombesin peptide receptors gastrin releasing peptide receptor (GRP-R), neuromedin-B receptor (NMB-R) and bombesin receptor subtype 3 (BRS-3), with distinct patterns of expression in normal and malignant cells. These receptors consist of seven putative membrane-spanning domains separated by short intracellular and extracellular loops, which are coupled to phospholipase C activation, inositol phosphate metabolism and calcium mobilization through pertussis toxin insensitive G-proteins. GRP-R binds GRP at high affinity, NMB-R binds NMB at high affinity and BRS-3 binds both peptides at relatively low affinity. Construction and characterization of GRP-R/NMB-R chimeric receptors indicates that transmembrane domain 5 is critical for high affinity binding of NMB by NMB-R, in particular Ile216. Site directed mutagenesis studies highlight the importance of one or more serines and threonines in the C-terminal tail domain of the GRP-R for rapid and efficient receptor internalization. These residues appear to be rapidly phosphorylated when the receptor becomes coupled to its cognate heterotrimeric GTP-binding protein. Similar receptor mutagenesis analysis show that 15 amino acids immediately C-terminal to transmembrane domain 7, form a structural motif essential for the effector coupling, in conjunction with specific conserved amino acids in the second (Arginine139) and third (Lysine263) intracellular loop domains of the GRP-R.