Alternative titles; symbols
HGNC Approved Gene Symbol: F2RL2
Cytogenetic location: 5q13.3 Genomic coordinates (GRCh38): 5:76,615,482-76,623,403 (from NCBI)
Thrombin (176930) is a coagulation protease that activates platelets, leukocytes, and endothelium and mesenchymal cells at sites of vascular injury, acting partly through an unusual proteolytically activated G protein-coupled receptor, coagulation factor II (thrombin) receptor (CF2R; 187930). Thrombin triggers cellular responses through protease-activated receptors (PARs), of which PAR3 is one. It is thought that PAR3 functions as a cofactor for the cleavage and activation of PAR4 (602779) by thrombin (Nakanishi-Matsui et al., 2000; Sambrano et al., 2001).
Using a PCR-based strategy, Ishihara et al. (1997) isolated a human cDNA encoding a putative G protein-coupled receptor with 27% amino acid sequence similarity to CF2R, which they referred to as PAR1 (187930), and 28% similarity to PAR2 (600933). PAR2 is a possible trypsin receptor. The N-terminal exodomain of the new receptor, designated PAR3 by the investigators, contains a possible thrombin cleavage site at residues lys38/thr39, followed by a sequence strikingly identical to a thrombin-binding sequence in the leech anticoagulant hirudin. Ishihara et al. (1997) showed that PAR3 mediates thrombin-triggered phosphoinositide hydrolysis and is expressed in a variety of tissues, including human bone marrow and mouse megakaryocytes, making it a candidate for the sought-after second platelet thrombin receptor. They commented that PAR3 provides a new tool for understanding thrombin signaling and a possible target for therapeutics designed selectively to block thrombotic, inflammatory, and proliferative responses to thrombin.
The human PAR1, PAR2, and PAR3 (Schmidt et al., 1997) genes were cloned and localized to 5q13, by in situ hybridization or use of radiation hybrid panels.
Kahn et al. (1998) independently identified PAR4 (602779) as a thrombin-activated receptor. Par4 mRNA was detected in mouse megakaryocytes, and a Par4-activating peptide caused secretion and aggregation of Par3-deficient mouse platelets. Thus, PAR3 is necessary for normal thrombin responses in mouse platelets, but a second PAR4-mediated mechanism for thrombin signaling exists. Studies performed by Kahn et al. (1998) with PAR-activated peptides suggested that PAR4 also functions in human platelets, which implies that an analogous dual-receptor system also operates in humans.
Nakanishi-Matsui et al. (2000) were unable to explain the failure of mouse Par3 to result in thrombin signaling on the basis of inability to reach the cell surface, inability to interact with thrombin, cloning artifacts, or alternative splicing. In situ hybridization to mouse tissues revealed mouse Par3 mRNA only in megakaryocytes. Expression of human PAR3 in heterologous expression systems reliably resulted in responsiveness to thrombin. Curiously, despite its importance for the activation of mouse platelets by thrombin, mouse Par3 did not lead to thrombin signaling even when overexpressed. Nakanishi-Matsui et al. (2000) reported that Par3 and Par4 interact in a novel way. Mouse Par3 does not itself mediate transmembrane signaling but instead functions as a cofactor for the cleavage and activation of Par4 by thrombin. This established a paradigm for cofactor-assisted PAR activation and for a G protein-coupled receptor acting as an accessory molecule to present ligand to another receptor.
Like PAR1, PAR3 is a potential thrombin receptor. Their similar gene structure, mechanism of activation, and colocalization to 5q13 raises the question of a common evolutionary origin and their characterization as a clustered gene family. By construction of a physical map of the 5q13 region by pulsed-field gel electrophoresis (PFGE), Duperat et al. (1998) identified 6 potential CpG islands and established linkage of the PAR genes. Southern blot analysis showed that they are in a cluster on a 560-kb AscI fragment, in the order PAR2, PAR1, and PAR3. The PAR1 and PAR2 genes were contained within the identical 240-kb NotI fragment, thus confirming a tight linkage between them. The localization of other CpG islands suggested that more PAR-family genes may be present.
Kahn et al. (1998) generated mice deficient in Par3 by targeted disruption. Thrombin responses in platelets from these mice were markedly delayed and diminished but not absent.
Sambrano et al. (2001) demonstrated that platelets from Par4-deficient mice failed to change shape, mobilize calcium, secrete ATP, or aggregate in response to thrombin. This result demonstrated that PAR signaling is necessary for mouse platelet activation by thrombin and supported the model that mouse Par3 does not by itself mediate transmembrane signaling but instead acts as a cofactor for thrombin cleavage and activation of Par4. Importantly, Par4-deficient mice had markedly prolonged bleeding times and were protected in a model of arteriolar thrombosis. Thus, Sambrano et al. (2001) concluded that platelet activation by thrombin is necessary for normal hemostasis and may be an important target in the treatment of thrombosis.
Guo et al. (2004) found that activated protein C protected mouse cortical neurons from NMDA- and staurosporine-induced apoptosis in vitro and in vivo. APC administration blocked nuclear translocation of apoptosis-inducing factor (AIF; 300169) and caspase-3 (CASP3; 600636) activation in response to NMDA and caspase-8 (CASP8; 601763) activation in response to staurosporine. Further studies with antibodies and mutant proteins showed that APC did not change the structure of or block NMDA receptors, that the APC active serine protease site was necessary for the effect, and that both PAR1 and PAR3 were required for APC-mediated neuronal protection.
Duperat, V. G., Jacquelin, B., Boisseau, P., Arveiler, B., Nurden, A. T. Protease-activated receptor genes are clustered on 5q13. Blood 92: 25-31, 1998. [PubMed: 9639495]
Guo, H., Liu, D., Gelbard, H., Cheng, T., Insalaco, R., Fernandez, J. A., Griffin, J. H., Zlokovic, B. V. Activated protein C prevents neuronal apoptosis via protease activated receptors 1 and 3. Neuron 41: 563-572, 2004. [PubMed: 14980205] [Full Text: https://doi.org/10.1016/s0896-6273(04)00019-4]
Ishihara, H., Connolly, A. J., Zeng, D., Kahn, M. L., Zheng, Y. W., Timmons, C., Tram, T., Coughlin, S. R. Protease-activated receptor 3 is a second thrombin receptor in humans. Nature 386: 502-506, 1997. [PubMed: 9087410] [Full Text: https://doi.org/10.1038/386502a0]
Kahn, M. L., Zheng, Y. W., Huang, W., Bigornia, V., Zeng, D., Moff, S., Farese, R. V., Jr., Tam, C., Coughlin, S. R. A dual thrombin receptor system for platelet activation. Nature 394: 690-694, 1998. [PubMed: 9716134] [Full Text: https://doi.org/10.1038/29325]
Nakanishi-Matsui, M., Zheng, Y.-W., Sulciner, D. J., Weiss, E. J., Ludeman, M. J., Coughlin, S. R. PAR3 is a cofactor for PAR4 activation by thrombin. Nature 404: 609-613, 2000. [PubMed: 10766244] [Full Text: https://doi.org/10.1038/35007085]
Sambrano, G. R., Weiss, E. J., Zheng, Y.-W., Huang, W., Coughlin, S. R. Role of thrombin signalling in platelets in haemostasis and thrombosis. Nature 413: 74-78, 2001. [PubMed: 11544528] [Full Text: https://doi.org/10.1038/35092573]
Schmidt, V., Wainer, J., Bahou, W. Identification and characterization of the human proteolytically activated receptor-3 (PAR-3) gene within the PAR gene cluster by positional mapping. (Abstract) Blood (suppl. 1) 90: 284a only, 1997.