Grimsey Neil, Lin Huilan, Trejo JoAnn
Department of Pharmacology, School of Medicine, University of California, La Jolla, California, USA.
Department of Pharmacology, School of Medicine, University of California, La Jolla, California, USA.
Methods Enzymol. 2014;535:389-401. doi: 10.1016/B978-0-12-397925-4.00022-5.
Protease-activated receptors (PARs) are a family of G protein-coupled receptors (GPCRs) that are uniquely activated by proteolysis. There are four members of the PAR family including: PAR1, PAR2, PAR3, and PAR4. PARs are expressed primarily in the cells of the vasculature and elicit cellular responses to coagulant and anticoagulant proteases. PAR1 exemplifies the unusual proteolytic mechanism of receptor activation. Thrombin binds to and cleaves the N-terminal exodomain of PAR1, generating a new N-terminus that functions as a tethered ligand. The N-terminal tethered ligand domain of PAR1 binds intramolecularly to the receptor to trigger transmembrane signaling and cannot diffuse away. Similar to other GPCRs, activation of PARs promotes coupling to heterotrimeric G proteins at the plasma membrane. After activation, PARs are rapidly internalized to endosomes and then sorted to lysosomes and degraded. Internalization functions to uncouple PARs from heterotrimeric G proteins at the cell surface. However, recent studies indicate that activated internalized PARs signal from endosomes through the recruitment of β-arrestins and potentially other pathways. Here, we provide an overview of methods and strategies used to examine endosomal signaling by PARs.
蛋白酶激活受体（PARs）是一类G蛋白偶联受体（GPCRs），其独特之处在于通过蛋白水解作用被激活。PAR家族有四个成员，包括：PAR1、PAR2、PAR3和PAR4。PARs主要在脉管系统的细胞中表达，并引发细胞对凝血和抗凝蛋白酶的反应。PAR1体现了受体激活的异常蛋白水解机制。凝血酶与PAR1的N端胞外结构域结合并将其切割，产生一个新的N端，该N端作为一个拴系配体发挥作用。PAR1的N端拴系配体结构域与受体内分子结合以触发跨膜信号传导，且不能扩散离开。与其他GPCRs类似，PARs的激活促进其在质膜上与异源三聚体G蛋白偶联。激活后，PARs迅速内化至内体，然后被分选至溶酶体并降解。内化作用使PARs在细胞表面与异源三聚体G蛋白解偶联。然而，最近的研究表明，激活的内化PARs通过募集β - 抑制蛋白以及可能的其他途径在内体中发出信号。在此，我们概述了用于检测PARs内体信号传导的方法和策略。
