Journal of Biological Chemistry

Pontejo, Sergio M.;Alejo, Ali;Alcami, Antonio

doi: 10.1074/jbc.m115.650119pmid: 25940088

<p>The blockade of tumor necrosis factor (TNF) by etanercept, a soluble version of the human TNF receptor 2 (hTNFR2), is a well established strategy to inhibit adverse TNF-mediated inflammatory responses in the clinic. A similar strategy is employed by poxviruses, encoding four viral TNF decoy receptor homologues (vTNFRs) named cytokine response modifier B (CrmB), CrmC, CrmD, and CrmE. These vTNFRs are differentially expressed by poxviral species, suggesting distinct immunomodulatory properties. Whereas the human variola virus and mouse ectromelia virus encode one vTNFR, the broad host range cowpox virus encodes all vTNFRs. We report the first comprehensive study of the functional and binding properties of these four vTNFRs, providing an explanation for their expression profile among different poxviruses. In addition, the vTNFRs activities were compared with the hTNFR2 used in the clinic. Interestingly, CrmB from variola virus, the causative agent of smallpox, is the most potent TNFR of those tested here including hTNFR2. Furthermore, we demonstrate a new immunomodulatory activity of vTNFRs, showing that CrmB and CrmD also inhibit the activity of lymphotoxin β. Similarly, we report for the first time that the hTNFR2 blocks the biological activity of lymphotoxin β. The characterization of vTNFRs optimized during virus-host evolution to modulate the host immune response provides relevant information about their potential role in pathogenesis and may be used to improve anti-inflammatory therapies based on soluble decoy TNFRs.</p>

Loughney, John W.;Rustandi, Richard R.;Wang, Dai;Troutman, Matthew C.;Dick, Lawrence W.;Li, Guanghua;Liu, Zhong;Li, Fengsheng;Freed, Daniel C.;Price, Colleen E.;Van M. Hoang, ;Culp, Timothy D.;DePhillips, Pete A.;Fu, Tong-Ming;Ha, Sha

doi: 10.1074/jbc.m115.652230

Fonseca, Bruno D.;Zakaria, Chadi;Jia, Jian-Jun;Graber, Tyson E.;Svitkin, Yuri;Tahmasebi, Soroush;Healy, Danielle;Hoang, Huy-Dung;Jensen, Jacob M.;Diao, Ilo T.;Lussier, Alexandre;Dajadian, Christopher;Padmanabhan, Niranjan;Wang, Walter;Matta-Camacho, Edna;Hearnden, Jaclyn;Smith, Ewan M.;Tsukumo, Yoshinori;Yanagiya, Akiko;

Tsuboi, Tatsuhisa;Yamazaki, Reina;Nobuta, Risa;Ikeuchi, Ken;Makino, Shiho;Ohtaki, Ayumi;Suzuki, Yutaka;Yoshihisa, Tohru;Trotta, Christopher;Inada, Toshifumi

doi: 10.1074/jbc.m114.634592pmid: 25971974

<p>The tRNA splicing endonuclease (Sen) complex is located on the mitochondrial outer membrane and splices precursor tRNAs in <i>Saccharomyces cerevisiae</i>. Here, we demonstrate that the Sen complex cleaves the mitochondria-localized mRNA encoding Cbp1 (cytochrome <i>b</i> mRNA processing 1). Endonucleolytic cleavage of this mRNA required two <i>cis</i>-elements: the mitochondrial targeting signal and the stem-loop 652–726-nt region. Mitochondrial localization of the Sen complex was required for cleavage of the <i>CBP1</i> mRNA, and the Sen complex cleaved this mRNA directly <i>in vitro</i>. We propose that the Sen complex cleaves the <i>CBP1</i> mRNA, which is co-translationally localized to mitochondria via its mitochondrial targeting signal.</p>

Fleetwood, Andrew J.;O&apos;Brien-Simpson, Neil M.;Veith, Paul D.;Lam, Roselind S.;Achuthan, Adrian;Cook, Andrew D.;Singleton, William;Lund, Ida K.;Reynolds, Eric C.;Hamilton, John A.

doi: 10.1074/jbc.m115.645572pmid: 25979345

<p>Urokinase plasminogen activator (uPA) converts plasminogen to plasmin, resulting in a proteolytic cascade that has been implicated in tissue destruction during inflammation. Periodontitis is a highly prevalent chronic inflammatory disease characterized by destruction of the tissue and bone that support the teeth. We demonstrate that stimulation of macrophages with the arginine- and lysine-specific cysteine protease complex (RgpA-Kgp complex), produced by the keystone pathogen <i>Porphyromonas gingivalis</i>, dramatically increased their ability to degrade matrix in a uPA-dependent manner. We show that the RgpA-Kgp complex cleaves the inactive zymogens, pro-uPA (at consensus sites Lys¹⁵⁸-Ile¹⁵⁹ and Lys¹³⁵-Lys¹³⁶) and plasminogen, yielding active uPA and plasmin, respectively. These findings are consistent with activation of the uPA proteolytic cascade by <i>P. gingivalis</i> being required for the pathogen to induce alveolar bone loss in a model of periodontitis and reveal a new host-pathogen interaction in which <i>P. gingivalis</i> activates a critical host proteolytic pathway to promote tissue destruction and pathogen virulence.</p>

Ohkawa, Yuki;Momota, Hiroyuki;Kato, Akira;Hashimoto, Noboru;Tsuda, Yusuke;Kotani, Norihiro;Honke, Koichi;Suzumura, Akio;Furukawa, Keiko;Ohmi, Yuhsuke;Natsume, Atsushi;Wakabayashi, Toshihiko;Furukawa, Koichi

doi: 10.1074/jbc.m114.635755pmid: 25940087

<p>There have been a few studies on the ganglioside expression in human glioma tissues. However, the role of these gangliosides such as GD3 and GD2 has not been well understood. In this study we employed a genetically engineered mouse model of glioma to clarify the functions of GD3 in gliomas. Forced expression of platelet-derived growth factor B in cultured astrocytes derived from p53-deficient mice resulted in the expression of GD3 and GD2. GD3-positive astrocytes exhibited increased cell growth and invasion activities along with elevated phosphorylation of Akt and Yes kinase. By enzyme-mediated activation of radical sources reaction and mass spectrometry, we identified PDGF receptor α (PDGFRα) as a GD3-associated molecule. GD3-positive astrocytes showed a significant amount of PDGFRα in glycolipid-enriched microdomains/rafts compared with GD3-negative cells. Src kinase family Yes was co-precipitated with PDGFRα, and its pivotal role in the increased cell invasion of GD3-positive astrocytes was demonstrated by silencing with anti-Yes siRNA. Direct association between PDGFRα and GD3 was also shown, suggesting that GD3 forms ternary complex with PDGFRα and Yes. The fact that GD3, PDGFRα, and activated Yes were colocalized in lamellipodia and the edge of tumors in cultured cells and glioma tissues, respectively, suggests that GD3 induced by platelet-derived growth factor B enhances PDGF signals in glycolipid-enriched microdomain/rafts, leading to the promotion of malignant phenotypes such as cell proliferation and invasion in gliomas.</p>

Svensson, Kristoffer;Schnyder, Svenia;Albert, Verena;Cardel, Bettina;Quagliata, Luca;Terracciano, Luigi M.;Handschin, Christoph

doi: 10.1074/jbc.m114.590653pmid: 25987562

<p>Resveratrol (RSV) and SRT1720 (SRT) elicit beneficial metabolic effects and are postulated to ameliorate obesity and related metabolic complications. The co-activator, peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α), has emerged as a major downstream effector responsible for metabolic remodeling of muscle and other metabolic tissues in response to RSV or SRT treatment. However, the requirement of PGC-1α in skeletal muscle for the systemic metabolic effects of these compounds has so far not been demonstrated. Using muscle-specific PGC-1α knock-out mice, we show that PGC-1α is necessary for transcriptional induction of mitochondrial genes in muscle with both RSV and SRT treatment. Surprisingly, the beneficial effects of SRT on glucose homeostasis and of both compounds on energy expenditure occur even in the absence of muscle PGC-1α. Moreover, RSV and SRT treatment elicit differential transcriptional effects on genes involved in lipid metabolism and mitochondrial biogenesis in liver and adipose tissue. These findings indicate that RSV and SRT do not induce analogous metabolic effects <i>in vivo</i>. Our results provide important insights into the mechanism, effects, and organ specificity of the caloric restriction mimetics RSV and SRT. These findings are important for the design of future therapeutic interventions aimed at ameliorating obesity and obesity-related metabolic dysfunction.</p>

Najyb, Ouafa;Brissette, Louise;Rassart, Eric

doi: 10.1074/jbc.m115.644302pmid: 25918162

<p>Apolipoprotein D (apoD), a member of the lipocalin family, is a 29-kDa secreted glycoprotein that binds and transports small lipophilic molecules. Expressed in several tissues, apoD is up-regulated under different stress stimuli and in a variety of pathologies. Numerous studies have revealed that overexpression of apoD led to neuroprotection in various mouse models of acute stress and neurodegeneration. This multifunctional protein is internalized in several cells types, but the specific internalization mechanism remains unknown. In this study, we demonstrate that the internalization of apoD involves a specific cell surface receptor in 293T cells, identified as the transmembrane glycoprotein basigin (BSG, CD147); more particularly, its low glycosylated form. Our results show that internalized apoD colocalizes with BSG into vesicular compartments. Down-regulation of BSG disrupted the internalization of apoD in cells. In contrast, overexpression of basigin in SH-5YSY cells, which poorly express BSG, restored the uptake of apoD. Cyclophilin A, a known ligand of BSG, competitively reduced apoD internalization, confirming that BSG is a key player in the apoD internalization process. In summary, our results demonstrate that basigin is very likely the apoD receptor and provide additional clues on the mechanisms involved in apoD-mediated functions, including neuroprotection.</p>

Wei, An-Chi;Liu, Ting;O&apos;Rourke, Brian

doi: 10.1074/jbc.m114.628446pmid: 25963147

<p>The large inner membrane electrochemical driving force and restricted volume of the matrix confer unique constraints on mitochondrial ion transport. Cation uptake along with anion and water movement induces swelling if not compensated by other processes. For mitochondrial Ca²⁺ uptake, these include activation of countertransporters (Na⁺/Ca²⁺ exchanger and Na⁺/H⁺ exchanger) coupled to the proton gradient, ultimately maintained by the proton pumps of the respiratory chain, and Ca²⁺ binding to matrix buffers. Inorganic phosphate (P_i) is known to affect both the Ca²⁺ uptake rate and the buffering reaction, but the role of anion transport in determining mitochondrial Ca²⁺ dynamics is poorly understood. Here we simultaneously monitor extra- and intra-mitochondrial Ca²⁺ and mitochondrial membrane potential (ΔΨ_m) to examine the effects of anion transport on mitochondrial Ca²⁺ flux and buffering in P_i-depleted guinea pig cardiac mitochondria. Mitochondrial Ca²⁺ uptake proceeded slowly in the absence of P_i but matrix free Ca²⁺ ([Ca²⁺]_mito) still rose to ∼50 μm. P_i (0.001–1 mm) accelerated Ca²⁺ uptake but decreased [Ca²⁺]_mito by almost 50% while restoring ΔΨ_m. P_i-dependent effects on Ca²⁺ were blocked by inhibiting the phosphate carrier. Mitochondrial Ca²⁺ uptake rate was also increased by vanadate (V_i), acetate, ATP, or a non-hydrolyzable ATP analog (AMP-PNP), with differential effects on matrix Ca²⁺ buffering and ΔΨ_m recovery. Interestingly, ATP or AMP-PNP prevented the effects of P_i on Ca²⁺ uptake. The results show that anion transport imposes an upper limit on mitochondrial Ca²⁺ uptake and modifies the [Ca²⁺]_mito response in a complex manner.</p>

Dai, Xin;Chen, Xi;Chen, Qun;Shi, Lei;Liang, Hongwei;Zhou, Zhen;Liu, Qian;Pang, Wenjing;Hou, Dongxia;Wang, Cheng;Zen, Ke;Yuan, Yaozong;Zhang, Chen-Yu;Xia, Lu

doi: 10.1074/jbc.m115.659318pmid: 25931122

<p>Intestinal inflammation is characterized by epithelial disruption, leading to the loss of barrier function, recruitment of immune cells, and host immune responses to gut microbiota. PepT1, a di/tripeptide transporter that uptakes bacterial products, is up-regulated in inflamed colon tissue, which implies its role in bacterium-associated intestinal inflammation. Although microRNA (miRNA)-mediated gene regulation has been found to be involved in various processes of inflammatory bowel disease (IBD), the biological function of miRNAs in the pathogenesis of IBD remains to be explored. In this study we detected miRNA expression patterns in colon tissues during colitis and investigated the mechanism underlying the regulation of colonic PepT1 by miRNAs. We observed an inverse correlation between PepT1 and miR-193a-3p in inflamed colon tissues with active ulcerative colitis, and we further demonstrated that miR-193a-3p reduced PepT1 expression and activity as a target gene and subsequently suppressed the NF-κB pathway. Intracolonic delivery of miR-193a-3p significantly ameliorated dextran sodium sulfate-induced colitis, whereas the overexpression of colonic PepT1 via PepT1 3′-untranslated region mutant lentivirus vector abolished the anti-inflammatory effect of miR-193a-3p. Furthermore, antibiotic treatment eliminated the difference in the dextran sodium sulfate-induced inflammation between the presence and absence of miR-193a-3p. These findings suggest that miR-193a-3p regulation of PepT1 mediates the uptake of bacterial products and is a potent mechanism during the colonic inflammation process. Overall, we believe miR-193a-3p may be a potent regulator of colonic PepT1 for maintaining intestinal homeostasis.</p>