title: Cell surface and serum protein phosphorylation by U-937 cell ectoprotein kinases.
abstract: Incubation of intact U-937 cells with 0.1 microM [gamma-32P]ATP for 10 min resulted in Mg(2+)-independent radiolabelling of about 40 cell surface proteins, some of which became more intensely labelled when cells were differentiated. Presence of 2% newborn calf serum revealed major labelling of three serum proteins with molecular weights of 170, 85 and 61 kDa. Out of several tested purified human serum proteins, complement factor 1s (C1s) exhibited specific labelling of the 28 kDa subunit. This capacity of monocytic cell ectokinases to phosphorylate cell surface and serum proteins may have significance for the regulation of interactions between these cells and their environment. In addition, phosphorylation of components of the complement system suggest a possible new means of regulating the immune response through the action of extracellular kinases.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Geberhiwot
authors.forename: G
authors.initials: G
authors.lastname: Skoglund
mesh_terms: D001798:Blood Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D003173:Complement C1s / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D009000:Monocytes / Q000201:enzymology*; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011494:Protein Kinases / Q000502:physiology*; D013379:Substrate Specificity
chemical_list: D001798:Blood Proteins; D008565:Membrane Proteins; D010761:Phosphorus Radioisotopes; D011494:Protein Kinases; C034454:ectoprotein kinase; D003173:Complement C1s