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The C1q-binding cell membrane proteins cC1q-R and gC1q-R are released from activated cells: subcellular distribution and immunochemical characterization.
Peterson, K L; Zhang, W; Lu, P D; Keilbaugh, S A; Peerschke, E I; Ghebrehiwet, B.
Afiliação
  • Peterson KL; Department of Medicine, State University of New York, Stony Brook 11794-8161, USA.
Clin Immunol Immunopathol ; 84(1): 17-26, 1997 Jul.
Article em En | MEDLINE | ID: mdl-9191880
Two types of widely coexpressed cell surface C1q-binding proteins (C1q-R): a 60-kDa calreticulin-homolog which binds to the collagen-like "stalk" of C1q and a 33-kDa protein with affinity for the globular "heads" of the molecule, have been described. In this report, we show that the two molecules are also secreted by Raji cells and peripheral blood lymphocytes and can be isolated in soluble form from serum-free culture supernatant by HPLC purification using a Mono-Q column. The two purified soluble proteins had immunochemical and physical characteristics similar to their membrane counterparts in that both bound to intact C1q and to their respective C1q ligands, cC1q and gC1q. In addition, N-terminal amino acid sequence analyses of the soluble cC1q-R and gC1q-R were found to be identical to the reported sequences of the respective membrane-isolated proteins. Ligand blot analyses using biotinylated membrane or soluble cC1q-R and gC1q-R showed that both bind to the denatured and nondenatured A-chain and moderately to the C-chain of C1q. Moreover, like their membrane counterparts, the soluble proteins were found to inhibit serum C1q hemolytic activity. Although cC1q-R was released when both peripheral blood lymphocytes and Raji cells were incubated in phosphate-buffered saline for 1 hr under tissue culture conditions, gC1q-R was releasable only from Raji cells, suggesting that perhaps activation or transformation leading to immortalization is required for gC1q-R release. Subcellular fractionation of Raji cells and analyses by enzyme-linked immunosorbent assay and Western blotting showed that the two molecules are present in the cytosolic fractions as well as on the membrane. The data suggest that soluble forms of both C1q-binding molecules are released from cells and that these molecules may play important roles in vivo as regulators of complement activation.
Assuntos
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Coleções: 01-internacional Base de dados: MEDLINE Assunto principal: Glicoproteínas de Membrana / Ativação Linfocitária / Linfócitos / Receptores de Complemento / Complemento C1q / Receptores de Hialuronatos / Proteínas de Membrana Limite: Humans Idioma: En Revista: Clin Immunol Immunopathol Ano de publicação: 1997 Tipo de documento: Article País de afiliação: Estados Unidos País de publicação: Estados Unidos
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Coleções: 01-internacional Base de dados: MEDLINE Assunto principal: Glicoproteínas de Membrana / Ativação Linfocitária / Linfócitos / Receptores de Complemento / Complemento C1q / Receptores de Hialuronatos / Proteínas de Membrana Limite: Humans Idioma: En Revista: Clin Immunol Immunopathol Ano de publicação: 1997 Tipo de documento: Article País de afiliação: Estados Unidos País de publicação: Estados Unidos