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High Expression of Membrane Cofactor Protein of Complement (CD46) in Human Leukaemia Cell Lines: Implication of an Alternatively Spliced Form Containing the ST A Domain in CD46 Up‐Regulation
Author(s) -
HARA T.,
SUZUKIt Y.,
SEMBAJ T.,
HATANAKA M.,
MATSUMOTO M.,
SEYA T.
Publication year - 1995
Publication title -
scandinavian journal of immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.934
H-Index - 88
eISSN - 1365-3083
pISSN - 0300-9475
DOI - 10.1111/j.1365-3083.1995.tb03700.x
Subject(s) - cd46 , domain (mathematical analysis) , microbiology and biotechnology , human cell , biology , cell , complement (music) , cofactor , cell culture , chemistry , gene , biochemistry , genetics , complement system , antibody , enzyme , phenotype , mathematical analysis , mathematics , complementation
Human membrane cofactor protein (MCP, CD46) is a receptor for the measles virus and serves as a complement regulator which protects host cells from autologous complement attack. MCP is highly polymorphic due to a variety of mRNA splice products. The levels of MCP expression on T and myeloid cell lines are usually two‐eightfold higher than those on their normal counterparts, whereas Burkitt's lymphoma B cell lines express less MCP than B cell lineages carrying no EB virus. The molecule has a Ser/Thr‐rich (ST) domain adjacent to the functional domain, namely short consensus repeats (SCR). The ST domain and a cytoplasmic tail (CYT) contribute to the MCP polymorphism. The ST domain is encoded by three exons (A, B and C) and major ST iscforms are ST ABC , ST BC and ST C . The authors investigated the relationship between the expression levels and isoform usage of MCP by flow cytometry using specific antibodies against ST A and ST C , by reverse transcriptase‐polymerase chain reaction (RT‐PCR) with size markers for each splice variant, and by RT‐PCR/Southern blotting using a specific probe for ST A . The results were (1) the profiles of mean shifts of myeloid and T cell lines were ST C < ST A on flow cytometry while those of B cell lines and normal blood cells were ST a < ST C ; (2) all cell lines tested by RT‐PCR expressed the messages for the isoforms ST BC /CYTl, ST C /CYTl, ST BC /CYT2, and ST C /CYT2. The band for ST ABC /CYT2 overlapped that for ST C /CYTl, and the band for ST ABC /CYTl was marginal in all cell lines examined; (3) semi‐quantitative analysis of the ST ABC isoforms by Southern blotting indicated the presence of high levels of the ST ABC messages in myeloid and T‐cell lines in comparison with B lymphoid cells and normal leucocytes. Thus, the quantity of MCP expressed parallels the ST ABC message level, which is up‐regulated in T and myeloid leukaemia cell lines.