Multiple Independent Functions of Arrestins in the Regulation of Protease-Activated Receptor-2 Signaling and Trafficking

Abstract

The irreversible proteolytic nature of protease-activated receptor-2 (PAR2) activation suggests that mechanism(s) responsible for termination of receptor signaling are critical determinants of the magnitude and duration of PAR2-elicited cellular responses. Rapid desensitization of activated G-protein-coupled receptors (GPCRs) involves both phosphorylation and binding of arrestins. Arrestins also function as scaffolds and transducers of mitogen-activated protein (MAP) kinase signaling cascades. The PAR2 cytoplasmic tail (C-tail) contains multiple sites of phosphorylation and may be an important determinant for arrestin interaction. Desensitization and internalization of activated PAR2 were markedly impaired in arrestin-deficient cells compared with wild-type control cells. PAR2 C-tail truncation mutants displayed normal agonist-induced internalization, caused rapid distribution of ␤arr2-GFP to the plasma membrane, and desensitized in an arrestin-dependent manner similar to that of wild-type PAR2. It is interesting that PAR2 C-tail mutants lost the capacity to stably associate with arrestins and consequently, redistributed to endocytic vesicles without ␤arr2-GFP, whereas internalized wild-type PAR2 remained stably associated with ␤arr2-GFP in endosomes. Moreover, activated PAR2 caused rapid and prolonged activation of endogenous extracellular signal-regulated kinase (ERK1/2). It was striking that in arrestin-deficient cells, activated PAR2 induced an initial peak in ERK1/2 activity that rapidly declined. The inability of internalized PAR2 C-tail mutants to stably associate with arrestins also resulted in loss of prolonged ERK2 activation. Thus, the PAR2 C-tail regulates the stability of arrestin interaction and kinetics of ERK1/2 activation but is not essential for desensitization or internalization. These findings further suggest that the diverse functions of arrestins in regulating PAR2 signaling and trafficking are controlled by multiple independent interactions involving both the intracellular loops and the C-tail.Protease-activated receptor-2 (PAR2) is activated by multiple trypsin-like serine proteases, including trypsin, tryptase, and coagulation proteases factors VIIa and Xa, but not by thrombin (Coughlin and Camerer, 2003). Because of the irreversible proteolytic nature of PAR2 activation and the generation of a tethered ligand that cannot diffuse away, mechanisms that contribute to the termination of signaling are critical determinants of the magnitude and kinetics of protease-elicited cellular responses. The regulation of PAR1 signaling has been extensively studied (Trejo, 2003), whereas considerably less is known about PAR2. G-protein-coupled receptors (GPCRs) are initially desensitized by rapid phosphorylation of agonist-occupied receptors by GPCR serine/ threonine kinases (GRKs) and other kinases (Krupnick and Benovic, 1998). In many cases, phosphorylation enhances receptor affinity for arrestin, and arrestin binding prevents receptor-G-protein interaction, thereby uncoupling the receptor fro...

Transactivation of the PAR1-PAR2 Heterodimer by Thrombin Elicits β-Arrestin-mediated Endosomal Signaling

“…We previously showed that activation of PAR1 results in transient ␤-arrestin association at the plasma membrane (28), whereas activated PAR2 and ␤-arrestin form a stable complex that co-internalizes to endocytic vesicles (21,29). Consistent with these studies, thrombinactivated PAR1 failed to remain associated with ␤-arrestin-2-GFP on endosomes in HeLa cells (Fig.…”

“…The cDNA plasmids encoding N-terminally FLAG-tagged human wild-type PAR1, N-terminally FLAG-tagged PAR2, and C-terminal tail truncation mutants were described previously (20,21). The N-terminally HA-tagged PAR2 construct was generated and cloned into the pcDNA3.1 vector.…”

“…Activation of PAR1 and PAR2 results in C-terminal tail phosphorylation and ␤-arrestin recruitment, although the receptors exhibit differences in ␤-arrestin-binding stability (21,28,32). To define the function of the PAR1 and PAR2 C-terminal tail domains in directing PAR1-PAR2 heterodimer recruitment of ␤-arrestins, we utilized C-terminal tail truncation mutants.…”

Biased Signaling Favoring Gi over β-Arrestin Promoted by an Apelin Fragment Lacking the C-terminal Phenylalanine

“…This dual signaling property of GPCRs has been reported for several receptors (35,48,(53)(54)(55)(56)(57)(58) and has given birth to the concept of biased agonists. This implies that a specific ligand might trigger distinct receptor conformations leading to different signaling pathways through interaction with different effector proteins.…”

The structural basis of arrestin-mediated regulation of G-protein-coupled receptors

“…However, for a surprising number of receptors phosphorylation is not required for arrestin binding. These include the lutropin receptor (Mukherjee et al, 1999a;Min & Ascoli, 2000;Min et al, 2002;Mukherjee et al, 2002), substance P receptor (Richardson et al, 2003), D6 non-signaling chemokine receptor (Galliera et al, 2004), orexin-1 receptor (Milasta et al, 2005), protease-activated receptor-2 (Stalheim et al, 2005), several splice variants of the serotonin 5-HT4 receptor , and leukotriene B4 receptor-1 (Jala et al, 2005). Although in some of these cases phosphorylation enhances the stability of the arrestin-receptor complex (Richardson et al, 2003;Milasta et al, 2005;Stalheim et al, 2005), arrestin binding to unphosphorylated receptors requires an explanation consistent with the known mechanism of arrestin activation.…”