A Truncated G-CSFR Inhibits Apoptosis Induced by Neutrophil Elastase G185R Mutant: Implication for Understanding CSF3R Mutations in Severe Congenital Neutropenia [Signal Transduction]

Mutations in ELANE encoding neutrophil elastase (NE) have been identified in the majority of patients with severe congenital neutropenia (SCN). The NE mutants have been shown to activate unfolded protein response (UPR) and induce premature apoptosis in myeloid cells. Patients with SCN are predisposed to acute myeloid leukemia (AML), and progression from SCN to AML is accompanied by mutations in CSF3R encoding the G-CSF receptor (G-CSFR) in approximately 80% patients. The mutations result in the expression of C-terminally truncated G-CSFRs that promote strong cell proliferation and survival. It is unknown why the CSF3R mutations, which are rare in de novo AML, are so prevalent in SCN/AML. We show here that a G-CSFR mutant, d715, derived from an SCN patient inhibited G-CSF-induced expression of NE in a dominant negative (DN) manner. Furthermore, G-CSFR d715 suppressed UPR and apoptosis induced by an SCN-derived NE mutant, which was associated with sustained activation of Akt and Stat5, and augmented expression of Bcl-xL. Thus, the truncated G-CSFRs associated with SCN/AML may protect myeloid precursor cells from apoptosis induced by the NE mutants. We propose that acquisition of CSF3R mutations may represent a mechanism by which myeloid precursor cells carrying the ELANE mutations evade the pro-apoptotic activity of the NE mutants in SCN patients.

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