title: Plasma kallikrein enhances platelet aggregation response by subthreshold doses of ADP.
abstract: Human plasma kallikrein (huPK) potentiates platelet responses to subthreshold doses of ADP, although huPK itself, does not induce platelet aggregation. In the present investigation, we observe that huPK pretreatment of platelets potentiates ADP-induced platelet activation by prior proteolysis of the G-protein-coupled receptor PAR-1. The potentiation of ADP-induced platelet activation by huPK is mediated by the integrin αIIbβ3through interactions with the KGD/KGE sequence motif in huPK. Integrin αIIbβ3is a cofactor for huPK binding to platelets to support PAR-1 hydrolysis that contributes to activation of the ADP signaling pathway. This activation pathway leads to phosphorylation of Src, AktS473, ERK1/2, and p38 MAPK, and to Ca2+release. The effect of huPK is blocked by specific antagonists of PAR-1 (SCH 19197) and αIIbβ3(abciximab) and by synthetic peptides comprising the KGD and KGE sequence motifs of huPK. Further, recombinant plasma kallikrein inhibitor, rBbKI, also blocks this entire mechanism. These results suggest a new function for huPK. Formation of plasma kallikrein lowers the threshold for ADP-induced platelet activation. The present observations are consistent with the notion that plasma kallikrein promotes vascular disease and thrombosis in the intravascular compartment and its inhibition may ameliorate cardiovascular disease and thrombosis.
authors.affiliation: Department of Biochemistry, Universidade Federal de São Paulo, São Paulo 04044-020, Brazil.
authors.forename: Tatiana F
authors.initials: TF
authors.lastname: Ottaiano
authors.affiliation: Department of Gynecology, Universidade Federal de São Paulo, São Paulo 04024-002, Brazil; Charitable Association of Blood Collection - COLSAN São Paulo, SP, Brazil.
authors.forename: Sheila S
authors.initials: SS
authors.lastname: Andrade
authors.affiliation: Department of Biochemistry, Universidade Federal de São Paulo, São Paulo 04044-020, Brazil.
authors.forename: Cleide
authors.initials: C
authors.lastname: de Oliveira
authors.affiliation: Department of Biochemistry, Universidade Federal de São Paulo, São Paulo 04044-020, Brazil.
authors.forename: Mariana C C
authors.initials: MCC
authors.lastname: Silva
authors.affiliation: Department of Biophysics, Universidade Federal de São Paulo, São Paulo 04044-020, Brazil.
authors.forename: Marcus V
authors.initials: MV
authors.lastname: Buri
authors.affiliation: Department of Biophysics, Universidade Federal de São Paulo, São Paulo 04044-020, Brazil.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Juliano
authors.affiliation: Department of Gynecology, Universidade Federal de São Paulo, São Paulo 04024-002, Brazil; Charitable Association of Blood Collection - COLSAN São Paulo, SP, Brazil.
authors.forename: Manoel J B C
authors.initials: MJBC
authors.lastname: Girão
authors.affiliation: Department of Biochemistry, Universidade Federal de São Paulo, São Paulo 04044-020, Brazil.
authors.forename: Misako U
authors.initials: MU
authors.lastname: Sampaio
authors.affiliation: Case Western Reserve University and University Hospitals Cleveland Medical Center, Cleveland, OH, USA.
authors.forename: Alvin H
authors.initials: AH
authors.lastname: Schmaier
authors.affiliation: Macromolecular Crystallography Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Wlodawer
authors.affiliation: Department of Orthopedics and Surgery, Universidade Estadual Paulista, Botucatu, Brazil.
authors.forename: Francisco H A
authors.initials: FHA
authors.lastname: Maffei
authors.affiliation: Department of Biochemistry, Universidade Federal de São Paulo, São Paulo 04044-020, Brazil. Electronic address: olivaml.bioq@epm.br.
authors.forename: Maria Luiza V
authors.initials: MLV
authors.lastname: Oliva
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology*; D006801:Humans; D010766:Phosphorylation / Q000187:drug effects; D020842:Plasma Kallikrein / Q000494:pharmacology*; D010974:Platelet Aggregation / Q000187:drug effects*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D044463:Receptor, PAR-1 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D044463:Receptor, PAR-1; D000244:Adenosine Diphosphate; D020842:Plasma Kallikrein
keywords: ADP; Integrin alphaIIbbeta3; Plasma kallikrein; Platelet aggregation