title: Biosynthesis of the third component of complement (C3) by the human monocytic-cell line U-937. Induction by phorbol myristate acetate.
abstract: Phorbol myristate acetate (PMA)-stimulated human monocyte-like cells (U-937) were found to synthesize the third component of complement (C3), as shown by enzyme-linked immunosorbent assay and immunoprecipitation from [35S]methionine-labelled culture supernatants. C3 synthesis occurred at a rate of about 160 ng of C3/24 h per 10(6) cells on day 7 after addition of PMA; it was blocked by cycloheximide treatment and was restored after removal of the inhibitor. SDS/polyacrylamide-gel-electrophoretic analysis of the immunoprecipitated protein showed that the size and subunit structure of the newly synthesized C3 were identical with those of plasma C3, and that a single-chain intracellular precursor was present in the cell lysates. Haemolytic assays showed that the synthesized C3 fully expressed functional activity in early culture within 4 h. After longer culture, a loss of haemolytic activity was observed. The possibility that newly secreted C3 is cleaved by U-937 cells themselves was suggested.
mesh_terms: D002460:Cell Line; D003176:Complement C3 / Q000096:biosynthesis*; D003513:Cycloheximide / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D003176:Complement C3; D003513:Cycloheximide; D013755:Tetradecanoylphorbol Acetate