The unfolded protein response sensor IRE1α is required at 2 distinct steps in B cell lymphopoiesis
Kezhong Zhang, … , Donalyn Scheuner, Randal J. Kaufman
Kezhong Zhang, … , Donalyn Scheuner, Randal J. Kaufman
Published February 1, 2005
Citation Information: J Clin Invest. 2005;115(2):268-281. https://doi.org/10.1172/JCI21848.
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The unfolded protein response sensor IRE1α is required at 2 distinct steps in B cell lymphopoiesis

Abstract

B lymphocyte differentiation is coordinated with the induction of high-level Ig secretion and expansion of the secretory pathway. Upon accumulation of unfolded proteins in the lumen of the ER, cells activate an intracellular signaling pathway termed the unfolded protein response (UPR). Two major proximal sensors of the UPR are inositol-requiring enzyme 1α (IRE1α), an ER transmembrane protein kinase/endoribonuclease, and ER-resident eukaryotic translation initiation factor 2α (eIF2α) kinase (PERK). To elucidate whether the UPR plays an important role in lymphopoiesis, we carried out reconstitution of recombinase-activating gene 2–deficient (rag2–/–) mice with hematopoietic cells defective in either IRE1α- or PERK-mediated signaling. IRE1α-deficient (ire1α–/–) HSCs can proliferate and give rise to pro–B cells that home to bone marrow. However, IRE1α, but not its catalytic activities, is required for Ig gene rearrangement and production of B cell receptors (BCRs). Analysis of rag2–/– mice transplanted with IRE1α trans-dominant-negative bone marrow cells demonstrated an additional requirement for IRE1α in B lymphopoiesis: both the IRE1α kinase and RNase catalytic activities are required to splice the mRNA encoding X-box–binding protein 1 (XBP1) for terminal differentiation of mature B cells into antibody-secreting plasma cells. Furthermore, UPR-mediated translational control through eIF2α phosphorylation is not required for B lymphocyte maturation and/or plasma cell differentiation. These results suggest specific requirements of the IRE1α-mediated UPR subpathway in the early and late stages of B lymphopoiesis.

Authors

Kezhong Zhang, Hetty N. Wong, Benbo Song, Corey N. Miller, Donalyn Scheuner, Randal J. Kaufman

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Figure 1

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Phenotype of ire1α–/– embryos. (A) Southern blot analysis of genomic DNA...
Phenotype of ire1α–/– embryos. (A) Southern blot analysis of genomic DNA from yolk sacs of ire1α+/+, ire1α+/–, and ire1α–/– embryos. The WT and knockout embryos have a 3-kb WT ire1α allele and a 4-kb recombinant allele, respectively. The heterozygous embryo has both the WT and the recombinant alleles. Rec. allele, ire1α recombinant allele; WT allele, WT ire1α allele. (B) Morphology of ire1α–/–, ire1α+/–, and ire1α+/+ embryos. The ire1α–/–, ire1α+/–, and ire1α+/+ embryos were from the same littermates at E12.5. Magnification, ×10. (C) Histological analysis of ire1α–/–, ire1α+/–, and ire1α+/+ embryos at E12.5. Paraffin-embedded sections (5 μM) of embryos were stained with H&E and visualized at magnification ×20.