1.X-Box-Binding Protein 1 and Innate Immune Responses of Human Cystic Fibrosis Alveolar Macrophages.
Lubamba BA1, Jones LC1, O'Neal WK1,2, Boucher RC1,2, Ribeiro CM1,2,3. Am J Respir Crit Care Med. 2015 Dec 15;192(12):1449-61. doi: 10.1164/rccm.201504-0657OC.
RATIONALE: Alveolar macrophages (AMs) play a key role in host defense to inhaled bacterial pathogens, in part by secreting inflammatory mediators. Cystic fibrosis (CF) airways exhibit a persistent, robust inflammatory response that may contribute to the pathophysiology of CF. Recent findings have linked endoplasmic reticulum stress responses mediated by inositol-requiring enzyme 1α-dependent messenger RNA splicing (activation) of X-box-binding protein-1 (XBP-1s) to inflammation in peripheral macrophages. However, the role of XBP-1s in CF AM function is not known.
2.IRE1 inhibition perturbs the unfolded protein response in a pancreatic β-cell line expressing mutant proinsulin, but does not sensitize the cells to apoptosis.
Zhang L, Nosak C, Sollazzo P, Odisho T, Volchuk A1. BMC Cell Biol. 2014 Jul 10;15:29. doi: 10.1186/1471-2121-15-29.
BACKGROUND: The Akita mutation (C96Y) in the insulin gene results in early onset diabetes in both humans and mice. Expression of mutant proinsulin (C96Y) causes endoplasmic reticulum (ER) stress in pancreatic β-cells and consequently the cell activates the unfolded protein response (UPR). Since the proinsulin is terminally misfolded ER stress is irremediable and chronic activation of the UPR eventually activates apoptosis in some cells. Here we analyzed the IRE1-dependent activation of genes in response to misfolded proinsulin production in an inducible mutant proinsulin (C96Y) insulinoma cell line.
3.The molecular basis for selective inhibition of unconventional mRNA splicing by an IRE1-binding small molecule.
Cross BC1, Bond PJ, Sadowski PG, Jha BK, Zak J, Goodman JM, Silverman RH, Neubert TA, Baxendale IR, Ron D, Harding HP. Proc Natl Acad Sci U S A. 2012 Apr 10;109(15):E869-78. doi: 10.1073/pnas.1115623109. Epub 2012 Feb 6.
IRE1 couples endoplasmic reticulum unfolded protein load to RNA cleavage events that culminate in the sequence-specific splicing of the Xbp1 mRNA and in the regulated degradation of diverse membrane-bound mRNAs. We report on the identification of a small molecule inhibitor that attains its selectivity by forming an unusually stable Schiff base with lysine 907 in the IRE1 endonuclease domain, explained by solvent inaccessibility of the imine bond in the enzyme-inhibitor complex. The inhibitor (abbreviated 4μ8C) blocks substrate access to the active site of IRE1 and selectively inactivates both Xbp1 splicing and IRE1-mediated mRNA degradation. Surprisingly, inhibition of IRE1 endonuclease activity does not sensitize cells to the consequences of acute endoplasmic reticulum stress, but rather interferes with the expansion of secretory capacity. Thus, the chemical reactivity and sterics of a unique residue in the endonuclease active site of IRE1 can be exploited by selective inhibitors to interfere with protein secretion in pathological settings.
4.The serine-threonine kinase inositol-requiring enzyme 1α (IRE1α) promotes IL-4 production in T helper cells.
Kemp KL1, Lin Z, Zhao F, Gao B, Song J, Zhang K, Fang D. J Biol Chem. 2013 Nov 15;288(46):33272-82. doi: 10.1074/jbc.M113.493171. Epub 2013 Oct 7.
The inositol-requiring enzyme 1α (IRE1α) is a serine-threonine kinase that plays crucial roles in activating the unfolded protein response. Studies suggest that IRE1α is activated during thymic T cell development and in effector CD8(+) T cells. However, its role in regulating T helper cell differentiation remains unknown. We find that IRE1α is up-regulated and activated upon CD4(+) T cell activation and plays an important role in promoting cytokine IL-4 production. CD4(+) T cells from IRE1α KO mice have reduced IL-4 protein expression, and this impaired IL-4 production is not due to the altered expression of Th2 lineage-specific transcription factors, such as GATA3. Instead, IL-4 mRNA stability is reduced in IRE1α KO T cells. Furthermore, treatment of T cells with an IRE1α-specific inhibitor, 4μ8C, leads to a block in IL-4, IL-5, and IL-13 production, confirming the role of IRE1α in the regulation of IL-4. This study identifies a regulatory function for IRE1α in the promotion of IL-4 in T cells.