SRP54 and a need for a new neutropenia nosology

Abstract

In this issue of Blood, Bellanné-Chantelot et al noted that mutations in signal recognition particle 54 (SRP54) cause an inherited neutropenia in 23 individuals with features of both severe congenital neutropenia (SCN) and Shwachman-Diamond syndrome (SDS).

Defects in the proteostasis pathway lead to inherited neutropenia. Molecular cloning of genetic lesions in individuals with moderate to severe neutropenias have centered on the biosynthetic pathway for proteins and their folding and trafficking (proteostasis for protein homeostasis). The most common genetic lesion in SDS is the biallelic mutation of SBDS. SBDS interacts with EFL1 to displace eukaryotic initiation factor 6 (eIF6). DNAJC21 stabilizes the 60S ribosome. As part of the SRP complex, SRP54 escorts the nascent polypeptide to the ER to complete translation and possible posttranslational modification. When defects arise in this prodigious and continuous process, unfolded protein response and ER stress follows. The most commonly mutated gene in SCN is ELANE, which encodes a serine protease. It is thought that mutated ELANE results in proteins that misfold and cause unfolded protein response. Through unknown mechanisms of apoptosis and/or differentiation impairment, granulopoiesis cannot be completed in SCN or sufficiently produced in SDS. How SCN and SDS transform frequently to MD or AML remains inadequately understood. GDP, guanosine diphosphate; GTP, guanosine triphosphate. Professional illustration by Somersault18:24.