title: Deletion of the extracellular membrane-distal cytokine receptor homology module of Mpl results in constitutive cell growth and loss of thrombopoietin binding.
abstract: The thrombopoietin receptor, Mpl, is a member of the cytokine receptor superfamily. The extracellular domain of Mpl contains two copies of the cytokine receptor homology module (CRM). Mpl is encoded by c-mpl, the cellular homologue of the oncogene v-mpl. The oncogenic potential of v-mpl may arise from deletion of all but the 43 most membrane-proximal amino acids of the extracellular domain of the wild-type receptor. To test the hypothesis that the extracellular domain of Mpl plays a role in controlling receptor activity, we created mutants of murine Mpl in which the membrane-distal CRM was either deleted or replaced by the membrane-proximal CRM. Introduction of these mutant receptors into factor-dependent BaF3 cells led to constitutive cell growth in the absence of growth factor. Both mutant receptors failed to bind 125I-Tpo. These results suggest that the membrane-distal CRM of Mpl acts as a brake on cell proliferation and that this region is required for ligand binding.
authors.affiliation: Department of Medicine, University of Washington, Seattle, WA 98195, USA. dfsabath@u.washington.edu
authors.forename: D F
authors.initials: DF
authors.lastname: Sabath
authors.forename: K
authors.initials: K
authors.lastname: Kaushansky
authors.forename: V C
authors.initials: VC
authors.lastname: Broudy
mesh_terms: D000818:Animals; D002455:Cell Division / Q000235:genetics; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D051379:Mice; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism*; D018121:Receptors, Cytokine / Q000235:genetics / Q000378:metabolism; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism; D053628:Receptors, Thrombopoietin; D017384:Sequence Deletion; D013926:Thrombopoietin / Q000378:metabolism*
chemical_list: D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D018121:Receptors, Cytokine; D011971:Receptors, Immunologic; D053628:Receptors, Thrombopoietin; C082218:MPL protein, human; D013926:Thrombopoietin