Associate editor: Peter Molenaar
Structure, function and pathophysiology of protease activated receptors

https://doi.org/10.1016/j.pharmthera.2011.01.003Get rights and content

Abstract

Discovered in the 1990s, protease activated receptors1 (PARs) are membrane-spanning cell surface proteins that belong to the G protein coupled receptor (GPCR) family. A defining feature of these receptors is their irreversible activation by proteases; mainly serine. Proteolytic agonists remove the PAR extracellular amino terminal pro-domain to expose a new amino terminus, or tethered ligand, that binds intramolecularly to induce intracellular signal transduction via a number of molecular pathways that regulate a variety of cellular responses. By these mechanisms PARs function as cell surface sensors of extracellular and cell surface associated proteases, contributing extensively to regulation of homeostasis, as well as to dysfunctional responses required for progression of a number of diseases. This review examines common and distinguishing structural features of PARs, mechanisms of receptor activation, trafficking and signal termination, and discusses the physiological and pathological roles of these receptors and emerging approaches for modulating PAR-mediated signaling in disease.

Introduction

The four PAR family members (designated PAR1, PAR2, PAR3 and PAR4 (Hollenberg & Compton, 2002)2) belong to the broader G protein coupled receptor (GPCR) super family. In contrast with other GPCRs, PARs are not activated in vivo by binding of a soluble ligand but, instead, are triggered by proteases which cleave extracellularly within the PAR amino terminus. This cleavage exposes a new amino terminus that binds intramolecularly to activate the receptor and induce intracellular signal transduction. As described below, although the PARs are homologous and have overlapping tissue expression patterns, the functions of each receptor, and their roles in physiology and disease, are distinct and coordinated by an intricate array of binding proteins and post-translation modifications that regulate PAR trafficking, sub-cellular localization, signal transduction and termination, and receptor degradation.

Section snippets

Structural features and activation mechanisms

The PARs are encoded by genes that map to either a gene cluster on chromosome 5q13 (F2R encoding PAR1, F2RL1 encoding PAR2 and F2RL2 encoding PAR3) or chromosome 19p12 (F2RL3 encoding PAR4; Schmidt et al., 1997, Kahn et al., 1998a). Each gene spans two exons, the first encoding the signal peptide and the second the mature protein (Kahn et al., 1998a). As shown in Fig. 1, the PARs contain seven transmembrane (TM) helices, an extracellular amino terminal domain encompassing a signal peptide of

Agonists and antagonists

The various cellular effects stimulated in vivo via the PAR family are most often mediated by trypsin-like serine proteases that cleave on the carboxyl terminal side of arginine and lysine residues (Hansen et al., 2008, Ramsay et al., 2008b). Cleavage by these proteases, other than at this activation site, results in receptor inactivation (or disarming). In this section we describe the proteases so far known to function as PAR agonists and those that disarm these receptors. The general features

Molecular aspects of PAR function

PAR-mediated signal transduction occurs via ‘conventional’ intracellular coupling to specific G protein subunits and, also for PAR2, via G-protein independent pathways involving β-arrestin scaffolding (Sun et al., 2007, Defea, 2008). It is now apparent that these pathways are modulated at multiple levels including receptor translocation to, and localisation within, the plasma membrane, the properties of the agonist, molecular events following receptor activation including signal termination,

Physiological and pathological roles

Soon after PAR1 was cloned Coughlin and colleagues were able to establish that, in addition to activation by proteolytic cleavage and exposure and intramolecular binding of the TL, PAR1 could also be activated by a short synthetic peptide mimicking the sequence of the revealed TL (Vu et al., 1991, Scarborough et al., 1992). As described above, subtype-selective short synthetic peptides that activate each PAR are known (with the possible exception of PAR3) and have proven to be invaluable in

Conclusion

Much progress has been made over the last 20 years through molecular, biochemical, pharmacological and animal based studies in understanding aspects of the intricate mechanisms regulating PARs and the roles these receptors have in normal physiology and disease. This level of understanding has supported the first attempts to generate PAR1-targeted therapeutics designed to treat a number of cardiovascular ailments. Further effort is required to provide a more complete understanding of PAR biology

Acknowledgments

This work was supported by grants from the National Health and Medical Research Council of Australia (569595 (DPF), 614206 (JDH), APP1000745 (DPF)), the Cancer Council Queensland (JDH), the Australian Research Council (DP1093245 (DPF)) and the Canadian Institutes of Health Research (MDH), an ARC Federation Fellowship (DPF), and Australian Post-Graduate Award Scholarships (MNA and MKY), an Alberta Hertiage Foundation for Medical Research Post-Doctoral Fellowship (RR) and a University of

References (510)

  • M.L. Benka et al.

    The thrombin receptor in human platelets is coupled to a GTP binding protein of the G alpha q family

    FEBS Lett

    (1995)
  • J.S. Blackburn et al.

    Matrix metalloproteinase-1 and thrombin differentially activate gene expression in endothelial cells via PAR-1 and promote angiogenesis

    Am J Pathol

    (2008)
  • A. Boire et al.

    PAR1 is a matrix metalloprotease-1 receptor that promotes invasion and tumorigenesis of breast cancer cells

    Cell

    (2005)
  • J. Buddenkotte et al.

    Agonists of proteinase-activated receptor-2 stimulate upregulation of intercellular cell adhesion molecule-1 in primary human keratinocytes via activation of NF-kappa B

    J Invest Dermatol

    (2005)
  • T.J. Bushell et al.

    Characterization of proteinase-activated receptor 2 signalling and expression in rat hippocampal neurons and astrocytes

    Neuropharmacology

    (2006)
  • E. Camerer et al.

    Genetic evidence that protease-activated receptors mediate factor Xa signaling in endothelial cells

    J Biol Chem

    (2002)
  • E. Camerer et al.

    Platelets, protease-activated receptors, and fibrinogen in hematogenous metastasis

    Blood

    (2004)
  • E. Camerer et al.

    Roles of protease-activated receptors in a mouse model of endotoxemia

    Blood

    (2006)
  • E. Camerer et al.

    Local protease signaling contributes to neural tube closure in the mouse embryo

    Dev Cell

    (2010)
  • R. Caruso et al.

    Protease-activated receptor-2 activation in gastric cancer cells promotes epidermal growth factor receptor trans-activation and proliferation

    Am J Pathol

    (2006)
  • N. Cenac et al.

    Induction of intestinal inflammation in mouse by activation of proteinase-activated receptor-2

    Am J Pathol

    (2002)
  • M.A. Ceruso et al.

    Thrombin receptor-activating peptides (TRAPs): investigation of bioactive conformations via structure-activity, spectroscopic, and computational studies

    Bioorg Med Chem

    (1999)
  • E.L. Chaikof et al.

    Growth-related responses in arterial smooth muscle cells are arrested by thrombin receptor antisense sequences

    J Biol Chem

    (1995)
  • C.H. Chen et al.

    Termination of protease-activated receptor-1 signaling by beta-arrestins is independent of receptor phosphorylation

    J Biol Chem

    (2004)
  • A.M. Coelho et al.

    Proteinases and proteinase-activated receptor 2: a possible role to promote visceral hyperalgesia in rats

    Gastroenterology

    (2002)
  • G.S. Cottrell et al.

    Trypsin IV, a novel agonist of protease-activated receptors 2 and 4

    J Biol Chem

    (2004)
  • G.S. Cottrell et al.

    Protease-activated receptor 2, dipeptidyl peptidase I, and proteases mediate Clostridium difficile toxin A enteritis

    Gastroenterology

    (2007)
  • S.R. Coughlin

    Protease-activated receptors in hemostasis, thrombosis and vascular biology

    J Thromb Haemost

    (2005)
  • L.A. Abraham et al.

    Expression of the thrombin receptor in developing bone and associated tissues

    J Bone Miner Res

    (1998)
  • A. Afkhami-Goli et al.

    Proteinase-activated receptor-2 exerts protective and pathogenic cell type-specific effects in Alzheimer's disease

    J Immunol

    (2007)
  • A. Agarwal et al.

    Targeting a metalloprotease-PAR1 signaling system with cell-penetrating pepducins inhibits angiogenesis, ascites, and progression of ovarian cancer

    Mol Cancer Ther

    (2008)
  • I.A. Akers et al.

    Mast cell tryptase stimulates human lung fibroblast proliferation via protease-activated receptor-2

    Am J Physiol Lung Cell Mol Physiol

    (2000)
  • T. Akiyama et al.

    Activation of superficial dorsal horn neurons in the mouse by a PAR-2 agonist and 5-HT: potential role in itch

    J Neurosci

    (2009)
  • T. Akiyama et al.

    Scratching behavior and Fos expression in superficial dorsal horn elicited by protease-activated receptor agonists and other itch mediators in mice

    J Pharmacol Exp Ther

    (2009)
  • B. al-Ani et al.

    Detection of functional receptors for the proteinase-activated-receptor-2-activating polypeptide, SLIGRL-NH2, in rat vascular and gastric smooth muscle

    Can J Physiol Pharmacol

    (1995)
  • B. Al-Ani et al.

    Modified proteinase-activated receptor-1 and -2 derived peptides inhibit proteinase-activated receptor-2 activation by trypsin

    J Pharmacol Exp Ther

    (2002)
  • B. Al-Ani et al.

    Proteinase-activated receptor-2: key role of amino-terminal dipeptide residues of the tethered ligand for receptor activation

    Mol Pharmacol

    (2004)
  • K.A. Alier et al.

    Intrathecal administration of proteinase-activated receptor-2 agonists produces hyperalgesia by exciting the cell bodies of primary sensory neurons

    J Pharmacol Exp Ther

    (2008)
  • P. Andrade-Gordon et al.

    Design, synthesis, and biological characterization of a peptide-mimetic antagonist for a tethered-ligand receptor

    Proc Natl Acad Sci USA

    (1999)
  • P. Andrade-Gordon et al.

    Administration of a potent antagonist of protease-activated receptor-1 (PAR-1) attenuates vascular restenosis following balloon angioplasty in rats

    J Pharmacol Exp Ther

    (2001)
  • S. Antoniak et al.

    Protease-activated receptor 2 deficiency reduces cardiac ischemia/reperfusion injury

    Arterioscler Thromb Vasc Biol

    (2010)
  • P. Arora et al.

    Persistent transactivation of EGFR and ErbB2/HER2 by protease-activated receptor-1 promotes breast carcinoma cell invasion

    Oncogene

    (2008)
  • S. Asfaha et al.

    Proteinase-activated receptor-1 agonists attenuate nociception in response to noxious stimuli

    Br J Pharmacol

    (2002)
  • S. Asfaha et al.

    Protease-activated receptor-4: a novel mechanism of inflammatory pain modulation

    Br J Pharmacol

    (2007)
  • N. Asokananthan et al.

    Activation of protease-activated receptor (PAR)-1, PAR-2, and PAR-4 stimulates IL-6, IL-8, and prostaglandin E2 release from human respiratory epithelial cells

    J Immunol

    (2002)
  • N. Asokananthan et al.

    House dust mite allergens induce proinflammatory cytokines from respiratory epithelial cells: the cysteine protease allergen, Der p 1, activates protease-activated receptor (PAR)-2 and inactivates PAR-1

    J Immunol

    (2002)
  • L. Atzori et al.

    Absence of proteinase-activated receptor-1 signaling in mice confers protection from fMLP-induced goblet cell metaplasia

    Am J Respir Cell Mol Biol

    (2009)
  • C. Auge et al.

    Protease-activated receptor-4 (PAR 4): a role as inhibitor of visceral pain and hypersensitivity

    Neurogastroenterol Motil

    (2009)
  • V. Awasthi et al.

    Modulation of tissue factor-factor VIIa signaling by lipid rafts and caveolae

    Arterioscler Thromb Vasc Biol

    (2007)
  • M.A. Ayoub et al.

    Differential association modes of the thrombin receptor PAR1 with G{alpha}i1, G{alpha}12, and {beta}-arrestin 1

    FASEB J

    (2010)
  • Cited by (302)

    View all citing articles on Scopus
    1

    The term “protease activated receptor” is used in preference to “proteinase activated receptor”.

    View full text