title: Phorbol ester PMA induces expression of the thrombopoietin receptor MPL in leukemia cells.
abstract: Thrombopoietin (TPO) is a major regulator of megakaryocytopoiesis both in vivo and in vitro. TPO initiates its biological effects by binding to the c-MPL receptor, which is a member of the hematopoietin receptor superfamily. To define the regulation of the MPL receptor, six continuous human leukemia cell lines with megakaryocytic properties were treated with the phorbol ester 12-myristate 13-acetate (PMA), TPO and transforming growth factor (TGF)-beta 1, a cytokine known to possess inhibitory effects. We used Northern blotting and flow cytometry analysis to determine MPL mRNA and protein levels. An increase of MPL mRNA and protein expression was observed in 2/6 PMA-exposed cell lines. There is no evidence from this study that TPO or TGF-beta 1 cause any decrease or increase in MPL expression. MPL upregulation triggered by PMA was accompanied by signs of induced differentiation such as increase in CD41, CD42 and CD61 expression, increase in cell size and cessation of proliferation. These data demonstrate that MPL can be upregulated in differentiating megakaryocytic cells via stimulation of protein kinase C, the intracellular target of PMA and a key kinase in one of the second messenger signal transduction pathways. These findings further the understanding of the regulation of this molecule, a cytokine receptor that, together with its ligand TPO, appears to represent a crucial element in megakaryocytopoiesis.
authors.affiliation: Department of Human and Animal Cell Cultures, DSMZ-German Collection of Microorganisms & Cell Cultures, Braunschweig, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Graf
authors.forename: M
authors.initials: M
authors.lastname: Zaborski
authors.forename: H
authors.initials: H
authors.lastname: Quentmeier
authors.forename: H G
authors.initials: HG
authors.lastname: Drexler
mesh_terms: D015415:Biomarkers; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D006801:Humans; D007938:Leukemia / Q000378:metabolism*; D008533:Megakaryocytes / Q000378:metabolism; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000187:drug effects*; D018121:Receptors, Cytokine / Q000096:biosynthesis / Q000187:drug effects*; D053628:Receptors, Thrombopoietin; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013926:Thrombopoietin; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
chemical_list: D015415:Biomarkers; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; C082218:MPL protein, human; D013926:Thrombopoietin; D013755:Tetradecanoylphorbol Acetate