title: Up-regulation of surface CD34 is associated with protein kinase C-mediated hyperphosphorylation of CD34.
abstract: CD34 is a transmembrane sialoglycoprotein expressed by early hematopoietic progenitor cells as well as endothelial cells. Previously we found that CD34 is rapidly and stoichiometrically phosphorylated by activated protein kinase C (PKC) (Fackler, M.J., Civin, C.I., Sutherland, D.R., Baker, M.A., and May, W.S. (1990) J. Biol. Chem. 265, 11056-11061). In the present study, we find dose-dependent up-regulation of CD34 surface expression following treatment of normal human CD34+ bone marrow progenitor cells, cord blood-derived KMT-2, or KG1 a myeloid leukemia cells with the PKC activator 12-O-tetradecanoylphorbol-13-acetate. Up-regulation begins within 1 min of treatment, is maximal by 30 min, is maintained for at least 3 h, and is associated with CD34 hyperphosphorylation. A specific inhibitor of PKC, 2,6-diamino-N-(1[1-(1-oxotridecyl)-2-piperadinyl]methyl)h exan-amide (NPC 15437), blocks both up-regulation and hyperphosphorylation of CD34. CD34 up-regulation is independent of transcription and/or translation and results from the recruitment of preformed intracellular CD34. The endocytosis rate of surface CD34 is unaltered by 12-O-tetradecanoylphorbol-13-acetate. Thus, activation of PKC mediates increased surface expression of the CD34 molecule possibly as a result of phosphorylation of CD34.
authors.affiliation: Johns Hopkins Oncology Center, Baltimore, Maryland 21231.
authors.forename: M J
authors.initials: MJ
authors.lastname: Fackler
authors.forename: C I
authors.initials: CI
authors.lastname: Civin
authors.forename: W S
authors.initials: WS
authors.lastname: May
mesh_terms: D015703:Antigens, CD / Q000378:metabolism*; D018952:Antigens, CD34; D001854:Bone Marrow Cells; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D005312:Fetal Blood; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D010748:Phosphopeptides / Q000302:isolation & purification; D010766:Phosphorylation; D014176:Protein Biosynthesis; D011493:Protein Kinase C / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014158:Transcription, Genetic
chemical_list: D015703:Antigens, CD; D018952:Antigens, CD34; D010748:Phosphopeptides; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate