title: Defective internalization and sustained activation of truncated granulocyte colony-stimulating factor receptor found in severe congenital neutropenia/acute myeloid leukemia.
abstract: Acquired mutations truncating the C-terminal domain of the granulocyte colony-stimulating factor receptor (G-CSF-R) are found in about 20% of severe congenital neutropenia (SCN) patients, with this cohort of patients predisposed to acute myeloid leukemia (AML). In myeloid cells, such mutations act in a dominant-negative manner leading to hyperproliferation and lack of differentiation in response to G-CSF. However, why these truncated receptors are dominant in function over wild-type receptors has remained unclear. We report that ligand-induced internalization of truncated G-CSF-R is severely impaired compared with the wild-type receptor, which results in sustained activation of STAT proteins. Strikingly, in cells coexpressing both truncated and wild-type forms, the truncated receptors acted dominantly with regard to both internalization and sustained activation. Site-directed mutagenesis of the C-terminus showed that receptor tyrosines in this region were dispensable for internalization, whereas a di-leucine-containing motif in Box B3 played some role. However, loss of the di-leucine motif was not the critical determinant of the sustained activation status of truncated receptors. These data suggest that defective internalization, leading to extended receptor activation, is a major cause of the dominant hyperproliferative effect of truncated G-CSF receptors, which is only partially due to the loss of a di-leucine motif present in the Box B3 region of the full-length receptor.
authors.affiliation: Institute of Hematology, Erasmus University, Rotterdam, The Netherlands. ward@hema.fgg.eur.nl
authors.forename: A C
authors.initials: AC
authors.lastname: Ward
authors.forename: Y M
authors.initials: YM
authors.lastname: van Aesch
authors.forename: A M
authors.initials: AM
authors.lastname: Schelen
authors.forename: I P
authors.initials: IP
authors.lastname: Touw
mesh_terms: D000818:Animals; D015638:Cytochalasin D / Q000494:pharmacology; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000378:metabolism; D016179:Granulocyte Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D007930:Leucine; D015470:Leukemia, Myeloid, Acute / Q000235:genetics*; D051379:Mice; D008894:Milk Proteins; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009503:Neutropenia / Q000151:congenital* / Q000235:genetics*; D016188:Receptors, Granulocyte Colony-Stimulating Factor / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014443:Tyrosine
chemical_list: D004268:DNA-Binding Proteins; D008894:Milk Proteins; D016188:Receptors, Granulocyte Colony-Stimulating Factor; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D050799:STAT5 Transcription Factor; C494080:Stat1 protein, mouse; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D016179:Granulocyte Colony-Stimulating Factor; D015638:Cytochalasin D; D014443:Tyrosine; D007930:Leucine