Submitted November 9, 2006
Accepted August 23, 2007
Mutations of the ELA2 gene found in patients with severe congenital neutropenia induce the unfolded protein response and cellular apoptosis
David S Grenda, Mark Murakami, Jhuma Ghatak, Jun Xia, Laurence A Boxer, David Dale, Mary C Dinauer, and Daniel C Link*
Division of Oncology, Washington University School of Medicine, St. Louis, MO
Div of Pediatric Hematology/Oncology, Dept of Pediatrics, C.S. Mott Children's Hospital, University of Michigan, Ann Arbor, MI
Department of Medicine, University of Washington, Seattle, WA
Herman B Wells Center for Pediatric Research, Department of Pediatrics, Indiana University School of Medicine, Indiana, IN
* Corresponding author; email: dlink{at}im.wustl.edu.
Severe congenital neutropenia (SCN) is an inborn disorder of granulopoiesis. Mutations of the ELA2 gene encoding neutrophil elastase (NE) are responsible for most cases of SCN and cyclic neutropenia (CN), a related but milder disorder of granulopoiesis. However, the mechanisms by which these mutations disrupt granulopoiesis are unclear. We hypothesize that the ELA2 mutations result in the production of misfolded NE protein, activation of the unfolded protein response (UPR), and ultimately apoptosis of granulocytic precursors. Expression of mutant NE but not wild type NE strongly induced BiP/GRP78 mRNA expression and XBP1 mRNA splicing, two classic markers of the UPR. The magnitude of UPR activation by a specific ELA2 mutation correlated with its associated clinical phenotype. Consistent with the UPR model, expression of mutant NE in primary human granulocytic precursors increased expression of CHOP (DDITS) and induced apoptosis in a protease independent fashion. Most strikingly, UPR activation and decreased NE protein expression were detected in primary granulocytic precursors from SCN patients. Collectively, these data provide strong support for a UPR model of SCN disease pathogenesis and place SCN in a growing list of human disease caused by misfolded proteins.
