title: The thrombopoietin receptor P106L mutation functionally separates receptor signaling activity from thrombopoietin homeostasis.
abstract: The interaction between thrombopoietin (THPO) and its receptor c-Mpl regulates downstream cytokine signaling and platelet homeostasis. Hereditary mutations of c-Mpl can either result in loss-of-function and thrombocytopenia or in gain-of-function and thrombocythemia (HT), and are important models to analyze the mechanism of c-Mpl activity. We have analyzed the effect of the c-Mpl P106L gain-of-function and the nearby loss-of-function R102P and F104S mutations, which cause HT or thrombocytopenia, respectively, on posttranslational processing, intracellular trafficking, cell surface expression, and cell proliferation. In contrast to R102P and F104S, the P106L mutant confers cytokine-independent growth and stimulates downstream signaling after THPO treatment in Ba/F3 cells. Despite their opposite function, R102P and P106L, both lead to abnormal subcellular receptor distribution, lack of membrane localization, impaired glycosylation, and elevated THPO serum levels in effected patients. These findings indicate that the activation of downstream signaling by c-Mpl P106L does not require correct processing, trafficking, and cell surface expression of c-Mpl, whereas the negative feedback loop controlling THPO serum levels requires cell surface expression of the receptor. Thus, we propose that the P106L mutation functionally separates the activity of c-Mpl in downstream signaling from that in maintaining platelet homeostasis.
authors.affiliation: Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, Heidelberg, Germany.
authors.forename: Clemens
authors.initials: C
authors.lastname: Stockklausner
authors.affiliation: Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, Heidelberg, Germany.
authors.forename: Anne-Christine
authors.initials: AC
authors.lastname: Klotter
authors.affiliation: Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, Heidelberg, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Dickemann
authors.affiliation: Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, Heidelberg, Germany.
authors.forename: Isabelle N
authors.initials: IN
authors.lastname: Kuhlee
authors.affiliation: Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, Heidelberg, Germany.
authors.forename: Christin M
authors.initials: CM
authors.lastname: Duffert
authors.affiliation: Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, Heidelberg, Germany.
authors.forename: Carolin
authors.initials: C
authors.lastname: Kerber
authors.affiliation: Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, Heidelberg, Germany.
authors.forename: Niels H
authors.initials: NH
authors.lastname: Gehring
authors.affiliation: Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, Heidelberg, Germany.
authors.forename: Andreas E
authors.initials: AE
authors.lastname: Kulozik
mesh_terms: D000328:Adult; D019943:Amino Acid Substitution; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D005190:Family; D005260:Female; D006367:HeLa Cells; D006706:Homeostasis / Q000235:genetics; D006801:Humans; D007930:Leucine / Q000235:genetics; D008297:Male; D020125:Mutation, Missense; D010375:Pedigree; D011392:Proline / Q000235:genetics; D053628:Receptors, Thrombopoietin / Q000235:genetics* / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics; D013921:Thrombocytopenia / Q000235:genetics* / Q000378:metabolism; D013922:Thrombocytosis / Q000235:genetics; D013926:Thrombopoietin / Q000378:metabolism*; D055815:Young Adult
chemical_list: D053628:Receptors, Thrombopoietin; C082218:MPL protein, human; D013926:Thrombopoietin; D011392:Proline; D007930:Leucine