Seck Thomas, Baron Roland, Horne William C
Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
J Biol Chem. 2003 Jun 20;278(25):23085-93. doi: 10.1074/jbc.M211280200. Epub 2003 Apr 9.
Numerous alternatively spliced transcripts are generated from the gene for the G protein-coupled calcitonin receptor, and some of the splice variants show differences in receptor-mediated signaling events. This study showed that the deltae13 splice variant of the rabbit calcitonin receptor is expressed together with the more common C1a in osteoclast-like cells. Since other G protein-coupled receptors form homo- or heterodimers, we examined whether heterodimerization of the calcitonin receptor splice variants occurs and, if so, whether it affects the function of the receptor. Homodimers of both isoforms and deltae13/C1a heterodimers were detected by co-immunoprecipitation and fluorescence resonance energy transfer analysis. In contrast to the C1a isoform, the deltae13 isoform was not efficiently transported to the cell surface. When co-expressed with the C1a splice variant, the deltae13 isoform colocalized with the C1a isoform within the cell but not at the cell surface. Furthermore, the overexpression of the deltae13 variant led to a significant reduction of the C1a surface expression and consequently a reduction of the cAMP response and Erk phosphorylation after ligand stimulation. We therefore suggest that the deltae13 variant of the rabbit calcitonin receptor acts to regulate the surface expression of the C1a isoform.
G蛋白偶联降钙素受体基因可产生众多可变剪接转录本，其中一些剪接变体在受体介导的信号转导事件中表现出差异。本研究表明，兔降钙素受体的deltae13剪接变体与破骨细胞样细胞中更常见的C1a共同表达。由于其他G蛋白偶联受体可形成同二聚体或异二聚体，我们研究了降钙素受体剪接变体是否会发生异二聚化，若发生，其是否会影响受体功能。通过免疫共沉淀和荧光共振能量转移分析检测到了两种异构体的同二聚体以及deltae13/C1a异二聚体。与C1a异构体不同，deltae13异构体不能有效地转运至细胞表面。当与C1a剪接变体共表达时，deltae13异构体在细胞内与C1a异构体共定位，但不在细胞表面。此外，deltae13变体的过表达导致C1a表面表达显著降低，进而导致配体刺激后cAMP反应和Erk磷酸化降低。因此，我们认为兔降钙素受体的deltae13变体可调节C1a异构体的表面表达。
