The protein tyrosine kinase JAK2 is activated in neutrophils from patients with severe congenital neutropenia.
Severe congenital neutropenia (SCN; or Kostmann syndrome) is an autosomal recessive disorder characterized by a maturation arrest of myelopoiesis at the level of promyelocytes. Myeloid precursor cells from patients with SCN require pharmacological dosages of recombinant human granulocyte colony-stimulating factor (r-metHuG-CSF; Filgrastim; Amgen, Thousand Oaks, CA) to differentiate to normal neutrophils. Thus, it is hypothesized that the underlying defect responsible for SCN is based on an abnormal G-CSF-induced signal transduction pathway. Because JAK2, a nonreceptor tyrosine kinase, is involved in the signaling pathway of G-CSF, we examined the expression and activity of JAK2 in neutrophils from SCN patients during r-metHuG-CSF treatment. The immunoprecipitated JAK2 protein showed increased tyrosine phosphorylation in neutrophils from SCN patients as compared with that in neutrophils from healthy donors, suggesting that this kinase is activated. In vitro kinase assays of immunoprecipitated JAK2 confirmed that neutrophils from SCN patients show an increased autophosphorylation of JAK2 in comparison with that of neutrophils from healthy volunteers. These findings suggest that JAK2 is activated in SCN patients.
Department of Pediatric Hematology and Oncology, Medical School Hannover, Germany.
P
P
Rauprich
B
B
Kasper
N
N
Tidow
K
K
Welte
D000293:Adolescent; D000328:Adult; D002675:Child, Preschool; D004789:Enzyme Activation; D005260:Female; D000069585:Filgrastim; D016179:Granulocyte Colony-Stimulating Factor / Q000502:physiology / Q000627:therapeutic use*; D006801:Humans; D007155:Immunologic Factors / Q000627:therapeutic use*; D053614:Janus Kinase 2; D008297:Male; D009503:Neutropenia / Q000151:congenital* / Q000201:enzymology / Q000628:therapy; D009504:Neutrophils / Q000201:enzymology*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins / Q000627:therapeutic use; D015398:Signal Transduction
D007155:Immunologic Factors; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D016179:Granulocyte Colony-Stimulating Factor; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D000069585:Filgrastim