title: E3 ligase-defective Cbl mutants lead to a generalized mastocytosis and myeloproliferative disease.
abstract: Somatic mutations of Kit have been found in leukemias and gastrointestinal stromal tumors. The proto-oncogene c-Cbl negatively regulates Kit and Flt3 by its E3 ligase activity and acts as a scaffold. We recently identified the first c-Cbl mutation in human disease in an acute myeloid leukemia patient, called Cbl-R420Q. Here we analyzed the role of Cbl mutants on Kit-mediated transformation. Coexpression of Cbl-R420Q or Cbl-70Z with Kit induced cytokine-independent proliferation, survival, and clonogenic growth. Primary murine bone marrow retrovirally transduced with c-Cbl mutants and transplanted into mice led to a generalized mastocytosis, a myeloproliferative disease, and myeloid leukemia. Overexpression of these Cbl mutants inhibited stem cell factor (SCF)-induced ubiquitination and internalization of Kit. Both Cbl mutants enhanced the basal activation of Akt and prolonged the ligand-dependent activation. Importantly, transformation was observed also with kinase-dead forms of Kit and Flt3 in the presence of Cbl-70Z, but not in the absence of Kit or Flt3, suggesting a mechanism dependent on receptor tyrosine kinases, but independent of their kinase activity. Instead, transformation depends on the Src family kinase Fyn, as c-Cbl coimmunoprecipitated with Fyn and inhibition abolished transformation. These findings may explain primary resistance to tyrosine kinase inhibitors targeted at receptor tyrosine kinases.
authors.affiliation: Department of Medicine, Hematology and Oncology and the Interdisciplinary Center for Clinical Research, University Hospital Muenster, Muenster, Germany.
authors.forename: Srinivasa Rao
authors.initials: SR
authors.lastname: Bandi
authors.forename: Christian
authors.initials: C
authors.lastname: Brandts
authors.forename: Marion
authors.initials: M
authors.lastname: Rensinghoff
authors.forename: Rebekka
authors.initials: R
authors.lastname: Grundler
authors.forename: Lara
authors.initials: L
authors.lastname: Tickenbrock
authors.forename: Gabriele
authors.initials: G
authors.lastname: Köhler
authors.forename: Justus
authors.initials: J
authors.lastname: Duyster
authors.forename: Wolfgang E
authors.initials: WE
authors.lastname: Berdel
authors.forename: Carsten
authors.initials: C
authors.lastname: Müller-Tidow
authors.forename: Hubert
authors.initials: H
authors.lastname: Serve
authors.forename: Bülent
authors.initials: B
authors.lastname: Sargin
mesh_terms: D000818:Animals; D016026:Bone Marrow Transplantation; D019556:COS Cells; D002471:Cell Transformation, Neoplastic; D002522:Chlorocebus aethiops; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D008024:Ligands; D008415:Mastocytosis / Q000209:etiology / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009196:Myeloproliferative Disorders / Q000209:etiology / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000090063:Proto-Oncogene Mas; D050721:Proto-Oncogene Proteins c-cbl / Q000235:genetics*; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism; D015398:Signal Transduction; D054875:Ubiquitination
chemical_list: D008024:Ligands; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D050721:Proto-Oncogene Proteins c-cbl; D019009:Proto-Oncogene Proteins c-kit; C067419:CBL protein, human; C493849:Cbl protein, mouse