Characterization of novel splice variants of LGR7 and LGR8 reveals that receptor signaling is mediated by their unique low density lipoprotein class A modules
Characterization of novel splice variants of LGR7 and LGR8 reveals that receptor signaling is mediated by their unique low density lipoprotein class A modules
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DOI：
10.1074/jbc.m602728200
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发表时间：
2006-11-17
影响因子：
4.8
通讯作者：
Bathgate, Ross A. D.
中科院分区：
文献类型：
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作者：
Scott, Daniel J.;Layfield, Sharon;Bathgate, Ross A. D.
松弛素和胰岛素样肽3受体，LGR 7和LGR 8，分别是富含亮氨酸重复的G蛋白偶联受体（LGR）家族的独特成员，因为它们具有与低密度脂蛋白A类（LDLa）模块同源的N-末端基序。通过表征几种LGR 7和LGR 8剪接变体，我们揭示了LDLa模块指导配体激活的cAMP信号传导。LGR 8短变体编码缺乏LDLa模块的LGR 8受体，而LGR 7截短体、LGR 7截短体-2和LGR 7截短体-3均编码保留LGR 7 LDLa模块的截短分泌蛋白。LGR 8-短和缺失其LDLa模块的工程化LGR 7变体LGR 7-短以高亲和力结合至它们各自的配体，但失去了它们通过刺激细胞内cAMP积累而发出信号的能力。相反，具有LDLa模块的分泌的LGR 7截短蛋白能够阻断松弛素诱导的LGR 7 cAMP信号传导，并且这样做不会损害LGR 7结合松弛素或在细胞膜上表达的能力。尽管LGR 7的LDLa模块在位置Asn-14处被N-糖基化，但LGR 7 N14 Q突变体保留松弛素结合亲和力和cAMP信号传导，这意味着糖基化对于最佳LDLa功能不是必需的。实时荧光定量PCR检测到LGR 7截短体在孕鼠子宫中有高表达，且特异性表达于孕鼠子宫。LGR 7截短体的差异表达和进化保守性进一步表明它在体内也可能发挥重要作用。这项研究强调了LDLa模块在LGR 7和LGR 8功能中的重要作用，并介绍了一种新的GPCR调控模型。
The relaxin and insulin-like peptide 3 receptors, LGR7 and LGR8, respectively, are unique members of the leucine-rich repeat-containing G-protein-coupled receptor (LGR) family, because they possess an N-terminal motif with homology to the low density lipoprotein class A (LDLa) modules. By characterizing several LGR7 and LGR8 splice variants, we have revealed that the LDLa module directs ligand-activated cAMP signaling. The LGR8-short variant encodes an LGR8 receptor lacking the LDLa module, whereas LGR7-truncate, LGR7-truncate-2, and LGR7-truncate-3 all encode truncated secreted proteins retaining the LGR7 LDLa module. LGR8-short and an engineered LGR7 variant missing its LDLa module, LGR7-short, bound to their respective ligands with high affinity but lost their ability to signal via stimulation of intracellular cAMP accumulation. Conversely, secreted LGR7-truncate protein with the LDLa module was able to block relaxin-induced LGR7 cAMP signaling and did so without compromising the ability of LGR7 to bind to relaxin or be expressed on the cell membrane. Although the LDLa module of LGR7 was N-glycosylated at position Asn-14, an LGR7 N14Q mutant retained relaxin binding affinity and cAMP signaling, implying that glycosylation is not essential for optimal LDLa function. Using real-time PCR, the expression of mouse LGR7-truncate was detected to be high in, and specific to, the uterus of pregnant mice. The differential expression and evolutionary conservation of LGR7-truncate further suggests that it may also play an important role in vivo. This study highlights the essential role of the LDLa module in LGR7 and LGR8 function and introduces a novel model of GPCR regulation.