Mutations in neutrophil elastase causing congenital neutropenia lead to cytoplasmic protein accumulation and induction of the unfolded protein response.
Severe congenital neutropenia (SCN) and cyclic neutropenia (CyN) are sporadic or inherited hematologic disorders of myelopoiesis. Heterozygous mutations in the gene encoding neutrophil elastase (ELA2) have been reported in both diseases. We used an inducible system to express a panel of ELA2 mutations and found for almost all mutants disruption of intracellular neutrophil elastase (HNE) protein processing at different levels. This disruption resulted in cytoplasmic accumulation of a nonfunctional protein, thereby preventing its physiologic transport to azurophil granules. Furthermore, the secretory capacity of the mutant proteins was greatly diminished, indicating alteration of the regulated and the constitutive pathways. Through analysis of primary granulocytes from SCN patients carrying ELA2 mutations, we found an identical pattern of intracellular accumulation of mutant HNE protein in the cytoplasm. Moreover, cells expressing mutant HNE protein exhibited a significant increase in apoptosis associated with up-regulation of the master ER chaperone BiP, indicating that disturbance of intracellular trafficking results in activation of the mammalian unfolded protein response.
Institute of Cell and Molecular Pathology, the Institute of Virology, the Department of Pediatric Hematology and Oncology, Hannover Medical School, Germany.
Inga
I
Köllner
Beate
B
Sodeik
Sabine
S
Schreek
Holger
H
Heyn
Nils
N
von Neuhoff
Manuela
M
Germeshausen
Cornelia
C
Zeidler
Martin
M
Krüger
Brigitte
B
Schlegelberger
Karl
K
Welte
Carmela
C
Beger
D017209:Apoptosis; D003593:Cytoplasm / Q000737:chemistry; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins / Q000235:genetics; D006801:Humans; D019272:Leukocyte Elastase / Q000235:genetics* / Q000378:metabolism; D018832:Molecular Chaperones / Q000235:genetics; D050505:Mutant Proteins; D009154:Mutation; D009503:Neutropenia / Q000151:congenital* / Q000209:etiology*; D017510:Protein Folding; D021381:Protein Transport; D015854:Up-Regulation / Q000235:genetics
D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D050505:Mutant Proteins; D019272:Leukocyte Elastase