Functional significance of platelet membrane glycoprotein p62 (GP VI), a putative collagen receptor.
We previously suggested that platelet 62 kDa protein (p62, GP VI) is a putative collagen receptor by the studies on platelets and antiplatelet antibody in a patient (YA) with idiopathic thrombocytopenic purpura (ITP) who showed defective collagen-induced platelet function. Herein, we confirm that p62/p57 (reduced/unreduced conditions) is a specific membrane protein recognized by YA antibody using an improved immunoprecipitation technique. To further study the functional role of this protein, a crude p57 fraction ('p57') was obtained from human platelets by serial chromatography including DEAE-Sepharose CL-6B and WGA-agarose followed by preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). This 'p57' diminished the platelet-aggregating activity of collagen and of YA immunoglobulin G (IgG). N-terminal amino acid sequence analysis of 'p57' showed that it contained intercellular adhesion molecule 2 (ICAM-2). Immunoprecipitation experiments using platelet lysates and anti-ICAM-2 monoclonal antibody demonstrated that ICAM-2 molecules had a molecular weight similar to p62 on SDS-PAGE. However, ICAM-2 was also expressed on YA's p62-deficient platelets both on immunoprecipitation and flow cytometric analysis. Thus, ICAM-2 seems to be different from p62.
Ishibashi
T
T
Department of Internal Medicine, Faculty of Medicine, Kyoto University, Japan.
Ichinohe
T
T
Sugiyama
T
T
Takayama
H
H
Titani
K
K
Okuma
M
M
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology; D000918:Antibody Specificity; D015703:Antigens, CD / Q000737:chemistry / Q000276:immunology; D001792:Blood Platelets / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000276:immunology; D003094:Collagen / Q000378:metabolism*; D000939:Epitopes / Q000276:immunology; D005434:Flow Cytometry; D006801:Humans; D008969:Molecular Sequence Data; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins / Q000235:genetics / Q000302:isolation & purification*; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000097:blood*
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D015815:Cell Adhesion Molecules; D000939:Epitopes; C065289:ICAM2 protein, human; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D003094:Collagen