title: Proteolytic cleavage of platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) is regulated by a calmodulin-binding motif.
abstract: Homophilic engagement of platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) induces 'outside-in' signal transduction that results in phosphorylation events and recruitment and activation of signalling molecules. The formation of signalling scaffolds with PECAM-1 are important signalling events that modulate platelet secretion, aggregation and platelet thrombus formation. In this study, we describe a novel interaction between PECAM-1 and cytosolic calmodulin (CaM) in platelets. Reciprocal co-immunoprecipitation studies revealed that cytosolic CaM is constitutively associated with PECAM-1 in resting, thrombin activated and aggregated human platelets. Our studies demonstrate that CaM directly interacts with a PECAM-1 peptide (594-604) C595A containing the sequences (594)KAFYLRKAKAK(604). This CaM:PECAM-1 interaction has a threefold higher affinity than CaM:GPVI interaction. It is potentiated by the addition of calcium ions, and dissociated by the CaM inhibitor, trifluoperazine. Treatment of platelets with CaM inhibitors triggers cleavage of PECAM-1 in a time- and dose-dependent manner. Furthermore, this membrane proximal portion of PECAM-1 is conserved across mammalian species and the helical representation of basic/hydrophobic residues reveals a charge distribution analogous to other CaM-binding motifs in other proteins. Taken together, these results suggest that this highly charged cluster of amino acids in the PECAM-1 cytoplasmic domain directly interacts with CaM and this novel interaction appears to regulate cleavage of PECAM-1.
authors.affiliation: Kronheimer Building, Austin Research Institute, Austin Hospital, Heidelberg, Vic., Australia.
authors.forename: Mae-Xhum
authors.initials: MX
authors.lastname: Wong
authors.forename: Stacey N
authors.initials: SN
authors.lastname: Harbour
authors.forename: Janet L
authors.initials: JL
authors.lastname: Wee
authors.forename: Lai-Man
authors.initials: LM
authors.lastname: Lau
authors.forename: Robert K
authors.initials: RK
authors.lastname: Andrews
authors.forename: Denise E
authors.initials: DE
authors.lastname: Jackson
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D006868:Hydrolysis; D008969:Molecular Sequence Data; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D002147:Calmodulin; D019408:Platelet Endothelial Cell Adhesion Molecule-1