Molecular cloning of a functional thrombin receptor reveals a novel proteolytic mechanism of receptor activation.
We isolated a cDNA encoding a functional human thrombin receptor by direct expression cloning in Xenopus oocytes. mRNA encoding this receptor was detected in human platelets and vascular endothelial cells. The deduced amino acid sequence revealed a new member of the seven transmembrane domain receptor family with a large amino-terminal extracellular extension containing a remarkable feature. A putative thrombin cleavage site (LDPR/S) resembling the activation cleavage site in the zymogen protein C (LDPR/I) was noted 41 amino acids carboxyl to the receptor's start methionine. A peptide mimicking the new amino terminus created by cleavage at R41 was a potent agonist for both thrombin receptor activation and platelet activation. "Uncleavable" mutant thrombin receptors failed to respond to thrombin but were responsive to the new amino-terminal peptide. These data reveal a novel signaling mechanism in which thrombin cleaves its receptor's amino-terminal extension to create a new receptor amino terminus that functions as a tethered ligand and activates the receptor.
Vu
T K
TK
Department of Medicine, University of California, San Francisco 94143-0524.
Hung
D T
DT
Wheaton
V I
VI
Coughlin
S R
SR
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001792:Blood Platelets / Q000378:metabolism; D002460:Cell Line; D003001:Cloning, Molecular; D004727:Endothelium / Q000378:metabolism; D006801:Humans; D008533:Megakaryocytes / Q000378:metabolism; D008845:Microinjections; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D015539:Platelet Activation / Q000502:physiology*; D011061:Poly A / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000502:physiology; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018179:Receptors, Thrombin; D013917:Thrombin / Q000502:physiology*; D014982:Xenopus laevis
D010446:Peptide Fragments; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D011061:Poly A; D013917:Thrombin