Ng G Y, Clark J, Coulombe N, Ethier N, Hebert T E, Sullivan R, Kargman S, Chateauneuf A, Tsukamoto N, McDonald T, Whiting P, Mezey E, Johnson M P, Liu Q, Kolakowski L F, Evans J F, Bonner T I, O'Neill G P
Merck Frosst Center for Therapeutic Research, Kirkland, Quebec H9H 3L1, Canada.
J Biol Chem. 1999 Mar 19;274(12):7607-10. doi: 10.1074/jbc.274.12.7607.
G protein-coupled receptors are commonly thought to bind their cognate ligands and elicit functional responses primarily as monomeric receptors. In studying the recombinant gamma-aminobutyric acid, type B (GABAB) receptor (gb1a) and a GABAB-like orphan receptor (gb2), we observed that both receptors are functionally inactive when expressed individually in multiple heterologous systems. Characterization of the tissue distribution of each of the receptors by in situ hybridization histochemistry in rat brain revealed co-localization of gb1 and gb2 transcripts in many brain regions, suggesting the hypothesis that gb1 and gb2 may interact in vivo. In three established functional systems (inwardly rectifying K+ channel currents in Xenopus oocytes, melanophore pigment aggregation, and direct cAMP measurements in HEK-293 cells), GABA mediated a functional response in cells coexpressing gb1a and gb2 but not in cells expressing either receptor individually. This GABA activity could be blocked with the GABAB receptor antagonist CGP71872. In COS-7 cells coexpressing gb1a and gb2 receptors, co-immunoprecipitation of gb1a and gb2 receptors was demonstrated, indicating that gb1a and gb2 act as subunits in the formation of a functional GABAB receptor.
G蛋白偶联受体通常被认为主要作为单体受体结合其同源配体并引发功能反应。在研究重组γ-氨基丁酸B型（GABAB）受体（gb1a）和一种GABAB样孤儿受体（gb2）时，我们观察到当在多个异源系统中单独表达时，这两种受体在功能上均无活性。通过大鼠脑中的原位杂交组织化学对每种受体的组织分布进行表征，发现gb1和gb2转录本在许多脑区共定位，这提示了gb1和gb2可能在体内相互作用的假说。在三个已建立的功能系统（非洲爪蟾卵母细胞中的内向整流钾通道电流、黑素细胞色素聚集以及HEK-293细胞中的直接cAMP测量）中，GABA在共表达gb1a和gb2的细胞中介导了功能反应，但在单独表达任一受体的细胞中则没有。这种GABA活性可以被GABAB受体拮抗剂CGP71872阻断。在共表达gb1a和gb2受体的COS-7细胞中，证实了gb1a和gb2受体的共免疫沉淀，表明gb1a和gb2在功能性GABAB受体的形成中作为亚基发挥作用。
