Medicine JournalFeeds

IRE1α activation protects mice against acetaminophen-induced hepatotoxicity.

J Exp Med. 2012 Jan 30;

Authors: Hur KY, So JS, Ruda V, Frank-Kamenetsky M, Fitzgerald K, Koteliansky V, Iwawaki T, Glimcher LH, Lee AH

Abstract

The mammalian stress sensor IRE1α plays a central role in the unfolded protein, or endoplasmic reticulum (ER), stress response by activating its downstream transcription factor XBP1 via an unconventional splicing mechanism. IRE1α can also induce the degradation of a subset of mRNAs in a process termed regulated IRE1-dependent decay (RIDD). Although diverse mRNA species can be degraded by IRE1α in vitro, the pathophysiological functions of RIDD are only beginning to be explored. Acetaminophen (APAP) overdose is the most frequent cause of acute liver failure in young adults in the United States and is primarily caused by CYP1A2-, CYP2E1-, and CYP3A4-driven conversion of APAP into hepatotoxic metabolites. We demonstrate here that genetic ablation of XBP1 results in constitutive IRE1α activation in the liver, leading to RIDD of Cyp1a2 and Cyp2e1 mRNAs, reduced JNK activation, and protection of mice from APAP-induced hepatotoxicity. A pharmacological ER stress inducer that activated IRE1α suppressed the expression of Cyp1a2 and Cyp2e1 in WT, but not IRE1α-deficient mouse liver, indicating the essential role of IRE1α in the down-regulation of these mRNAs upon ER stress. Our study reveals an unexpected function of RIDD in drug metabolism.

PMID: 22291093 [PubMed - as supplied by publisher]

Microbiota-induced IL-1β, but not IL-6, is critical for the development of steady-state TH17 cells in the intestine.

J Exp Med. 2012 Jan 30;

Authors: Shaw MH, Kamada N, Kim YG, Núñez G

Abstract

T(H)17 cells are a lineage of CD4(+) T cells that are critical for host defense and autoimmunity by expressing the cytokines IL-17A, IL-17F, and IL-22. A feature of T(H)17 cells at steady state is their ubiquitous presence in the lamina propria of the small intestine. The induction of these steady-state intestinal T(H)17 (sT(H)17) cells is dependent on the presence of the microbiota. However, the signaling pathway linking the microbiota to the development of intestinal sT(H)17 cells remains unclear. In this study, we show that IL-1β, but not IL-6, is induced by the presence of the microbiota in intestinal macrophages and is required for the induction of sT(H)17 cells. In the absence of IL-1β-IL-1R or MyD88 signaling, there is a selective reduction in the frequency of intestinal sT(H)17 cells and impaired production of IL-17 and IL-22. Myeloid differentiation factor 88-deficient (MyD88(-/-)) and germ-free (GF) mice, but not IL-1R(-/-) mice, exhibit impairment in IL-1β induction. Microbiota-induced IL-1β acts directly on IL-1R-expressing T cells to drive the generation of sT(H)17 cells. Furthermore, administration of IL-1β into GF mice induces the development of retinoic acid receptor-related orphan receptor γt-expressing sT(H)17 cells in the small intestine, but not in the spleen. Thus, commensal-induced IL-1β production is a critical step for sT(H)17 differentiation in the intestine, which may have therapeutic implications for T(H)17-mediated pathologies.

PMID: 22291094 [PubMed - as supplied by publisher]

FoxO1 induces Ikaros splicing to promote immunoglobulin gene recombination.

J Exp Med. 2012 Jan 30;

Authors: Alkhatib A, Werner M, Hug E, Herzog S, Eschbach C, Faraidun H, Köhler F, Wossning T, Jumaa H

Abstract

Somatic rearrangement of immunoglobulin (Ig) genes is a key step during B cell development. Using pro-B cells lacking the phosphatase Pten (phosphatase and tensin homolog), which negatively regulates phosphoinositide-3-kinase (PI3K) signaling, we show that PI3K signaling inhibits Ig gene rearrangement by suppressing the expression of the transcription factor Ikaros. Further analysis revealed that the transcription factor FoxO1 is crucial for Ikaros expression and that PI3K-mediated down-regulation of FoxO1 suppresses Ikaros expression. Interestingly, FoxO1 did not influence Ikaros transcription; instead, FoxO1 is essential for proper Ikaros mRNA splicing, as FoxO1-deficient cells contain aberrantly processed Ikaros transcripts. Moreover, FoxO1-induced Ikaros expression was sufficient only for proximal V(H) to DJ(H) gene rearrangement. Simultaneous expression of the transcription factor Pax5 was needed for the activation of distal V(H) genes; however, Pax5 did not induce any Ig gene rearrangement in the absence of Ikaros. Together, our results suggest that ordered Ig gene rearrangement is regulated by distinct activities of Ikaros, which mediates proximal V(H) to DJ(H) gene rearrangement downstream of FoxO1 and cooperates with Pax5 to activate the rearrangement of distal V(H) genes.

PMID: 22291095 [PubMed - as supplied by publisher]

Crucial role of SLP-76 and ADAP for neutrophil recruitment in mouse kidney ischemia-reperfusion injury.

J Exp Med. 2012 Jan 30;

Authors: Block H, Herter JM, Rossaint J, Stadtmann A, Kliche S, Lowell CA, Zarbock A

Abstract

Neutrophils trigger inflammation-induced acute kidney injury (AKI), a frequent and potentially lethal occurrence in humans. Molecular mechanisms underlying neutrophil recruitment to sites of inflammation have proved elusive. In this study, we demonstrate that SLP-76 (SH2 domain-containing leukocyte phosphoprotein of 76 kD) and ADAP (adhesion and degranulation promoting adaptor protein) are involved in E-selectin-mediated integrin activation and slow leukocyte rolling, which promotes ischemia-reperfusion-induced AKI in mice. By using genetically engineered mice and transduced Slp76(-/-) primary leukocytes, we demonstrate that ADAP as well as two N-terminal-located tyrosines and the SH2 domain of SLP-76 are required for downstream signaling and slow leukocyte rolling. The Tec family kinase Bruton tyrosine kinase is downstream of SLP-76 and, together with ADAP, regulates PI3Kγ (phosphoinositide 3-kinase-γ)- and PLCγ2 (phospholipase Cγ2)-dependent pathways. Blocking both pathways completely abolishes integrin affinity and avidity regulation. Thus, SLP-76 and ADAP are involved in E-selectin-mediated integrin activation and neutrophil recruitment to inflamed kidneys, which may underlie the development of life-threatening ischemia-reperfusion-induced AKI in humans.

PMID: 22291096 [PubMed - as supplied by publisher]

Inhibiting the HSP90 chaperone destabilizes macrophage migration inhibitory factor and thereby inhibits breast tumor progression.

J Exp Med. 2012 Jan 23;

Authors: Schulz R, Marchenko ND, Holembowski L, Fingerle-Rowson G, Pesic M, Zender L, Dobbelstein M, Moll UM

Abstract

Intracellular macrophage migration inhibitory factor (MIF) often becomes stabilized in human cancer cells. MIF can promote tumor cell survival, and elevated MIF protein correlates with tumor aggressiveness and poor prognosis. However, the molecular mechanism facilitating MIF stabilization in tumors is not understood. We show that the tumor-activated HSP90 chaperone complex protects MIF from degradation. Pharmacological inhibition of HSP90 activity, or siRNA-mediated knockdown of HSP90 or HDAC6, destabilizes MIF in a variety of human cancer cells. The HSP90-associated E3 ubiquitin ligase CHIP mediates the ensuing proteasome-dependent MIF degradation. Cancer cells contain constitutive endogenous MIF-HSP90 complexes. siRNA-mediated MIF knockdown inhibits proliferation and triggers apoptosis of cultured human cancer cells, whereas HSP90 inhibitor-induced apoptosis is overridden by ectopic MIF expression. In the ErbB2 transgenic model of human HER2-positive breast cancer, genetic ablation of MIF delays tumor progression and prolongs overall survival of mice. Systemic treatment with the HSP90 inhibitor 17AAG reduces MIF expression and blocks growth of MIF-expressing, but not MIF-deficient, tumors. Together, these findings identify MIF as a novel HSP90 client and suggest that HSP90 inhibitors inhibit ErbB2-driven breast tumor growth at least in part by destabilizing MIF.

PMID: 22271573 [PubMed - as supplied by publisher]

Pyruvate kinase M2-specific siRNA induces apoptosis and tumor regression.

J Exp Med. 2012 Jan 23;

Authors: Goldberg MS, Sharp PA

Abstract

The development of cancer-specific therapeutics has been limited because most healthy cells and cancer cells depend on common pathways. Pyruvate kinase (PK) exists in M1 (PKM1) and M2 (PKM2) isoforms. PKM2, whose expression in cancer cells results in aerobic glycolysis and is suggested to bestow a selective growth advantage, is a promising target. Because many oncogenes impart a common alteration in cell metabolism, inhibition of the M2 isoform might be of broad applicability. We show that several small interfering (si) RNAs designed to target mismatches between the M2 and M1 isoforms confer specific knockdown of the former, resulting in decreased viability and increased apoptosis in multiple cancer cell lines but less so in normal fibroblasts or endothelial cells. In vivo delivery of siPKM2 additionally causes substantial tumor regression of established xenografts. Our results suggest that the inherent nucleotide-level specificity of siRNA can be harnessed to develop therapeutics that target isoform-specific exons in genes exhibiting differential splicing patterns in various cell types.

PMID: 22271574 [PubMed - as supplied by publisher]

Genetic resistance to JAK2 enzymatic inhibitors is overcome by HSP90 inhibition.

J Exp Med. 2012 Jan 23;

Authors: Weigert O, Lane AA, Bird L, Kopp N, Chapuy B, van Bodegom D, Toms AV, Marubayashi S, Christie AL, McKeown M, Paranal RM, Bradner JE, Yoda A, Gaul C, Vangrevelinghe E, Romanet V, Murakami M, Tiedt R, Ebel N, Evrot E, De Pover A, Régnier CH, Erdmann D, Hofmann F, Eck MJ, Sallan SE, Levine RL, Kung AL, Baffert F, Radimerski T, Weinstock DM

Abstract

Enzymatic inhibitors of Janus kinase 2 (JAK2) are in clinical development for the treatment of myeloproliferative neoplasms (MPNs), B cell acute lymphoblastic leukemia (B-ALL) with rearrangements of the cytokine receptor subunit cytokine receptor-like factor 2 (CRLF2), and other tumors with constitutive JAK2 signaling. In this study, we identify G935R, Y931C, and E864K mutations within the JAK2 kinase domain that confer resistance across a panel of JAK inhibitors, whether present in cis with JAK2 V617F (observed in MPNs) or JAK2 R683G (observed in B-ALL). G935R, Y931C, and E864K do not reduce the sensitivity of JAK2-dependent cells to inhibitors of heat shock protein 90 (HSP90), which promote the degradation of both wild-type and mutant JAK2. HSP90 inhibitors were 100-1,000-fold more potent against CRLF2-rearranged B-ALL cells, which correlated with JAK2 degradation and more extensive blockade of JAK2/STAT5, MAP kinase, and AKT signaling. In addition, the HSP90 inhibitor AUY922 prolonged survival of mice xenografted with primary human CRLF2-rearranged B-ALL further than an enzymatic JAK2 inhibitor. Thus, HSP90 is a promising therapeutic target in JAK2-driven cancers, including those with genetic resistance to JAK enzymatic inhibitors.

PMID: 22271575 [PubMed - as supplied by publisher]

STAT5 is a potent negative regulator of TFH cell differentiation.

J Exp Med. 2012 Jan 23;

Authors: Johnston RJ, Choi YS, Diamond JA, Yang JA, Crotty S

Abstract

Follicular helper T cells (T(FH) cells) constitute the CD4(+) T cell subset that is specialized to provide help to germinal center (GC) B cells and, consequently, mediate the development of long-lived humoral immunity. T(FH) cell differentiation is driven by the transcription factor Bcl6, and recent studies have identified cytokine and cell-cell signals that drive Bcl6 expression. However, although T(FH) dysregulation is associated with several major autoimmune diseases, the mechanisms underlying the negative regulation of T(FH) cell differentiation are poorly understood. In this study, we show that STAT5 inhibits T(FH) cell differentiation and function. Constitutive STAT5 signaling in activated CD4(+) T cells selectively blocked T(FH) cell differentiation and GCs, and IL-2 signaling was a primary inducer of this pathway. Conversely, STAT5-deficient CD4(+) T cells (mature STAT5(fl/fl) CD4(+) T cells transduced with a Cre-expressing vector) rapidly up-regulated Bcl6 expression and preferentially differentiated into T(FH) cells during T cell priming in vivo. STAT5 signaling failed to inhibit T(FH) cell differentiation in the absence of the transcription factor Blimp-1, a direct repressor of Bcl6 expression and T(FH) cell differentiation. These results demonstrate that IL-2, STAT5, and Blimp-1 collaborate to negatively regulate T(FH) cell differentiation.

PMID: 22271576 [PubMed - as supplied by publisher]

TNF-induced osteoclastogenesis and inflammatory bone resorption are inhibited by transcription factor RBP-J.

J Exp Med. 2012 Jan 16;

Authors: Zhao B, Grimes SN, Li S, Hu X, Ivashkiv LB

Abstract

Tumor necrosis factor (TNF) plays a key role in the pathogenesis of inflammatory bone resorption and associated morbidity in diseases such as rheumatoid arthritis and periodontitis. Mechanisms that regulate the direct osteoclastogenic properties of TNF to limit pathological bone resorption in inflammatory settings are mostly unknown. Here, we show that the transcription factor recombinant recognition sequence binding protein at the J(κ) site (RBP-J) strongly suppresses TNF-induced osteoclastogenesis and inflammatory bone resorption, but has minimal effects on physiological bone remodeling. Myeloid-specific deletion of RBP-J converted TNF into a potent osteoclastogenic factor that could function independently of receptor activator of NF-κB (RANK) signaling. In the absence of RBP-J, TNF effectively induced osteoclastogenesis and bone resorption in RANK-deficient mice. Activation of RBP-J selectively in osteoclast precursors suppressed inflammatory osteoclastogenesis and arthritic bone resorption. Mechanistically, RBP-J suppressed induction of the master regulator of osteoclastogenesis (nuclear factor of activated T cells, cytoplasmic 1) by attenuating c-Fos activation and suppressing induction of B lymphocyte-induced maturation protein-1, thereby preventing the down-regulation of transcriptional repressors such as IRF-8 that block osteoclast differentiation. Thus, RBP-J regulates the balance between activating and repressive signals that regulate osteoclastogenesis. These findings identify RBP-J as a key upstream negative regulator of osteoclastogenesis that restrains excessive bone resorption in inflammatory settings.

PMID: 22249448 [PubMed - as supplied by publisher]

Age, microbiota, and T cells shape diverse individual IgA repertoires in the intestine.

J Exp Med. 2012 Jan 16;

Authors: Lindner C, Wahl B, Föhse L, Suerbaum S, Macpherson AJ, Prinz I, Pabst O

Abstract

Intestinal immunoglobulin A (IgA) ensures host defense and symbiosis with our commensal microbiota. Yet previous studies hint at a surprisingly low diversity of intestinal IgA, and it is unknown to what extent the diverse Ig arsenal generated by somatic recombination and diversification is actually used. In this study, we analyze more than one million mouse IgA sequences to describe the shaping of the intestinal IgA repertoire, its determinants, and stability over time. We show that expanded and infrequent clones combine to form highly diverse polyclonal IgA repertoires with very little overlap between individual mice. Selective homing allows expanded clones to evenly seed the small but not large intestine. Repertoire diversity increases during aging in a dual process. On the one hand, microbiota-, T cell-, and transcription factor RORγt-dependent but Peyer’s patch-independent somatic mutations drive the diversification of expanded clones, and on the other hand, new clones are introduced into the repertoire of aged mice. An individual’s IgA repertoire is stable and recalled after plasma cell depletion, which is indicative of functional memory. These data provide a conceptual framework to understand the dynamic changes in the IgA repertoires to match environmental and intrinsic stimuli.

PMID: 22249449 [PubMed - as supplied by publisher]