E3 ligase-defective Cbl mutants lead to a generalized mastocytosis and myeloproliferative disease.
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.
Bandi
Srinivasa Rao
SR
Department of Medicine, Hematology and Oncology and the Interdisciplinary Center for Clinical Research, University Hospital Muenster, Muenster, Germany.
Brandts
Christian
C
Rensinghoff
Marion
M
Grundler
Rebekka
R
Tickenbrock
Lara
L
Köhler
Gabriele
G
Duyster
Justus
J
Berdel
Wolfgang E
WE
Müller-Tidow
Carsten
C
Serve
Hubert
H
Sargin
Bülent
B
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
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