Ligand Cross-reactivity within the Protease-activated Receptor Family*
- Brian D. Blackhart‡§,
- Kjell Emilsson¶,
- Dat Nguyen‡,
- Willy Teng‡,
- Arnold J. Martelli‡,
- Sverker Nystedt¶,
- Johan Sundelin¶ and
- Robert M. Scarborough‡
- From‡ COR Therapeutics, Inc., South San Francisco, California 94080 and the
- ¶ Division of Molecular Neurobiology, The Wallenberg Laboratory, Lund University, S-220 07 Lund, Sweden
- § To whom correspondence should be addressed: COR Therapeutics, Inc., 256 E. Grand Ave., South San Francisco, CA 94080. Tel.: 415-244-6800; Fax: 415-244-9270.
Abstract
Recently, a second member of the protease-activated receptor (PAR) family, named PAR-2, has been identified. Similar to the thrombin receptor, PAR-2 appears to be activated by proteolytic-mediated exposure of a “tethered ligand” sequence and can also be activated by the corresponding synthetic peptides. Similarities in the amino acid sequence of the receptors' tethered ligand sequences suggest that their respective agonist peptides might not be absolutely specific for their particular receptors. To test this, the receptor specificity of each agonist has been determined by measuring the responses of Xenopus oocytes expressing the thrombin receptor or PAR-2 to agonist peptides or enzymes. Thrombin receptors responded to thrombin, the human thrombin receptor-activating peptide SFLLRNP-NH2 (TRAP) (EC50 = 0.1 μM), and Xenopus TRAP, TFRIFD-NH2 (EC50 = 1 μM), but did not show any increase in calcium efflux over control levels with trypsin (50 nM) or PAR-2 agonist peptides (100 μM). Human and murine PAR-2 receptors responded comparably to human and murine PAR-2 agonist peptides (SLIGKVD and SLIGRL, respectively) (EC50 = 0.5-2.0 μM) and trypsin, but not to thrombin. PAR-2 was also found to be responsive to TRAP (EC50 = 1 μM) but was unresponsive to Xenopus TRAP (50 μM). Responses to additional peptide agonist analogs suggest that an amino-terminal serine is critical for PAR-2 agonist activity.
Footnotes
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↵* The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 The abbreviations used are:
- G protein
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guanine nucleotide-binding protein
- PAR
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protease-activated receptor
- TRAP
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thrombin receptor-activating peptide.
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- Received March 28, 1996.
- © 1996 by The American Society for Biochemistry and Molecular Biology, Inc.
