We analyzed the structure of the
granulocyte colony-stimulating factor (
G-CSF) receptor gene in a 6-year-old female patient with
severe congenital neutropenia (SCN) who experienced severe
recurrent infections since 1 month of age. There is no family history of any similar disease. When the patient was 4 months old, she began receiving treatment with recombinant human
G-CSF that resulted in a small increase in the neutrophil count sufficient for the prevention and treatment of
bacterial infection. An analysis of
complementary DNA for the patient's
G-CSF receptor revealed a 3-base pair deletion in the juxtamembrane intracellular sequence. This deletion at the beginning of exon 16 was thought to be caused by alternative splicing; analysis of the
DNA revealed a G-to-A point mutation of the final
nucleotide of intron 15. To evaluate the functional activity of the
G-CSF receptor with this 3-base pair deletion of the juxtamembrane region, we transfected this
G-CSF receptor mutant into an
interleukin 3-dependent cell line, BAF/3. BAF/3 cells expressing the mutant
G-CSF receptor showed augmented proliferation activity in response to
G-CSF compared with cells having the wild-type
G-CSF receptor. Although the proliferation signal of
G-CSF in normal hematopoiesis is transduced through the activation of MAP
kinases, this
G-CSF receptor mutant showed decreased activation of ERKI/2 in response to
G-CSF compared with the wild type, but the transduced sig-nal for Stat3 activation by
G-CSF was of the same magnitude as that of the wild-type
G-CSF receptor. This result means that the augmented proliferation activity in response to
G-CSF that we observed in cells having the
G-CSF receptor gene with the 3-base pair deletion is transduced through an intracellular signaling pathway other than MAP
kinase. Because SCN patients with a mutation in the
G-CSF receptor frequently develop
leukemia, this 3-base pair deletion in the juxtamembrane sequence of the
G-CSF receptor gene in this patient may be one step in the course of leukemic transformation.