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  • American Association for the Advancement of Science (AAAS)  (4)
  • 2010-2014  (4)
  • 2011  (4)
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  • American Association for the Advancement of Science (AAAS)  (4)
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  • 2010-2014  (4)
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  • 2011  (4)
  • 1
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    American Association for the Advancement of Science (AAAS) ; 2011
    In:  Science Signaling Vol. 4, No. 158 ( 2011-02)
    Details
    In: Science Signaling, American Association for the Advancement of Science (AAAS), Vol. 4, No. 158 ( 2011-02)
    Abstract: Circadian rhythms, which have a periodicity of ~24 hours, regulate many physiological and metabolic processes. From algae to humans, circadian rhythms are regulated by a transcription-translation feedback loop. The products of clock genes are transcriptional activators that drive the expression of repressor genes, whose products feed back to inhibit the activators (see Bass and Takahashi). O’Neill and Reddy investigated a role for nontranscriptional control of circadian rhythms in human red blood cells (RBCs), which lack nuclei and cannot support transcription. The authors monitored peroxiredoxins, proteins that protect RBCs from peroxides by becoming oxidized and forming dimers, which are then reduced to the monomeric form. The authors found that peroxiredoxins exhibited a circadian redox rhythm in RBCs kept in the dark at constant temperature. This cycle could be entrained by temperature and was not affected by inhibitors of transcription or translation. The equilibrium between dimeric hemoglobin (a source of peroxide) and tetrameric hemoglobin (which produces less peroxide) also exhibited a circadian rhythm, as did the reducing agents NADH and NADPH. The redox cycle of peroxiredoxins in mouse NIH 3T3 cells also exhibited a circadian rhythm, and this was altered in cells from mice deficient in clock genes. Conversely, knockdown of various peroxiredoxin-encoding genes in human cells had effects on circadian gene expression. In an accompanying study, O’Neill et al . examined circadian rhythms in the simple alga Ostreococcus tauri . When kept at constant temperature in the dark, circadian rhythms in the alga that are controlled by transcription-translation loops are suspended until it is reexposed to light. However, the cycles continue from the point at which darkness occurred, rather than becoming reset. The authors found that redox cycles of peroxiredoxins in the alga persisted in the dark in a transcription-independent manner and that inhibitors of clocks in mammalian cells had similar effects in the alga. Together, these studies suggest that nontranscriptional metabolic cycles couple with genetic oscillators to control rhythmic outputs. J. S. O’Neill, A. B. Reddy, Circadian clocks in human red blood cells. Nature 469 , 498–503 (2011). [Online Journal] J. S. O’Neill, G. van Ooijen, L. E. Dixon, C. Troein, F. Corellou, F.-Y. Bouget, A. B. Reddy, A. J. Millar, Circadian rhythms persist without transcription in a eukaryote. Nature 469 , 554–558 (2011). [Online Journal] J. Bass, J. S. Takahashi, Redox redux. Nature 469 , 476–478 (2011). [Online Journal]
    Type of Medium: Online Resource
    ISSN: 1945-0877 , 1937-9145
    URL: Article
    DOI: 10.1126/scisignal.4158ec29
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2011
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  • 2
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    Getting Choosy
    American Association for the Advancement of Science (AAAS) ; 2011
    In:  Science Signaling Vol. 4, No. 193 ( 2011-10-04)
    Details
    In: Science Signaling, American Association for the Advancement of Science (AAAS), Vol. 4, No. 193 ( 2011-10-04)
    Abstract: Members of the NOD-like receptor (NLR) family of cytosolic proteins respond to microbial components in the cytoplasm of infected cells by forming multiprotein complexes called inflammasomes, which stimulate the processing and activation of caspase 1. This protease then processes precursor forms of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18, which induce cell death. NLRC4-containing inflammasomes are formed in response to the bacterial proteins flagellin and PrgJ, a conserved component of the type-III secretion system (TTSS); however, how NLRC4 responds to specific stimuli is unclear (see commentary by Monack). Two groups now implicate NLR family members called NAIPs (NLR family, apoptosis inhibitory proteins) in determining the ligand specificity of NLRC4 inflammasome activation. Kofoed and Vance showed that mouse macrophages lacking NAIP2 failed to activate caspase 1 or undergo cell death in response to PrgJ; however, loss of NAIP2 had no effect on cell death induced by flagellin. In contrast, NAIP5 was required for flagellin-induced caspase 1 activation but was not necessary for cell death induced by PrgJ. Experiments in a reconstituted in vitro system showed that stimulation of NLRC4 inflammasome formation by flagellin required NAIP5, and NAIP5 and flagellin were also present in the complex. In contrast, PrgJ did not induce NAIP5-NLRC4 inflammasome formation but did stimulate complex formation between NAIP2 and NLRC4. Zhao et al . also demonstrated the ability of NAIP2 and NAIP5 to activate NLRC4 inflammasome formation in mouse cells in response to distinct ligands from various bacteria. In addition, they showed that CprI (a TTSS component from Chromobacterium violaceum ), but not flagellin, activated NLRC4 inflammasome formation in a human macrophage cell line and that CprI bound to NAIP, the sole human NAIP protein. Together, these data suggest that NAIP proteins bind directly to distinct microbial products and confer ligand specificity to NLRC4 inflammasomes. E. M. Kofoed, R. E. Vance, Innate immune recognition of bacterial ligands by NAIPs determines inflammasome specificity. Nature 477 , 592–595 (2011). [PubMed] Y. Zhao, J. Yang, J. Shi, Y.-N. Gong, Q. Lu, H. Xu, L. Liu, F. Shao, The NLRC4 inflammasome receptors for bacterial flagellin and type III secretion apparatus. Nature 477 , 596–600 (2011). [PubMed] D. M. Monack, Recognition of a unique partner. Nature 477 , 543–544 (2011). [Online Journal]
    Type of Medium: Online Resource
    ISSN: 1945-0877 , 1937-9145
    URL: Article
    DOI: 10.1126/scisignal.4193ec274
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2011
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  • 3
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    Food Fit for a Queen
    American Association for the Advancement of Science (AAAS) ; 2011
    In:  Science Signaling Vol. 4, No. 175 ( 2011-05-31)
    Details
    In: Science Signaling, American Association for the Advancement of Science (AAAS), Vol. 4, No. 175 ( 2011-05-31)
    Abstract: Royal jelly is a protein-, sugar-, lipid-, and mineral-containing food that is produced by worker bees of honeybee hives and that stimulates the development of a new queen bee (see Robinson for commentary). Kamakura noted that royal jelly lost its effectiveness after storage and isolated a protein, called royalactin, that was as effective as royal jelly in promoting the phenotypic changes associated with development of the queen—shortened developmental time, increased size of the adult, and increased ovary size. To explore the details of the pathways that might be responsible for these effects of royalactin, Kamakura fed royalactin to the fruit fly, Drosophila melanogaster , which does not have queens and workers, and found that the flies exhibited an increase in body weight and length, increased fecundity, and increased life span, which are all characteristics of the queen honeybee. Using flies with mutations or carrying RNA interference (RNAi) transgenes that disrupt various signaling pathways, Kamakura determined that royalactin signals through the epidermal growth factor receptor (EGFR) in the fat body. The effects on body size required EGFR-mediated signaling through PI3K-TOR-S6K (phosphatidylinositol 3-kinase to target of rapamycin to S6 kinase), a pathway known for stimulating protein synthesis and mediating growth. Activation of the mitogen-activated protein kinase (MAPK) pathway downstream of the EGFR was required for the shortened developmental time, and this was mediated by an increase in the production of the steroid hormone 20-hydroxyecdysone. EGFR signaling stimulated the production of juvenile hormone, transcription of the gene encoding yolk protein, and fecundity, but these effects were not affected by disruption of the MAPK or PI3K-TOR-S6K pathways, suggesting that there is another arm of EGFR signaling that functions in this process. How royalactin promotes longevity also remains an open question. Armed with this information from the fruit fly, Kamakura returned to the honeybee and showed by RNAi and selective pathway inhibition that EGFR and the pathways identified in the flies were involved in the increase in body size and shortening of developmental time associated with development of the honeybee queen in response to royalactin. M. Kamakura, Royalactin induces queen differentiation in honeybees. Nature 473 , 478–483 (2011). [PubMed] G. E. Robinson, Royal aspirations. Nature 473 , 454–455 (2011). [Online Journal]
    Type of Medium: Online Resource
    ISSN: 1945-0877 , 1937-9145
    URL: Article
    DOI: 10.1126/scisignal.4175ec151
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2011
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  • 4
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    Tryptophan Fix
    American Association for the Advancement of Science (AAAS) ; 2011
    In:  Science Signaling Vol. 4, No. 195 ( 2011-10-18)
    Details
    In: Science Signaling, American Association for the Advancement of Science (AAAS), Vol. 4, No. 195 ( 2011-10-18)
    Abstract: Breakdown of tryptophan to kynurenine by the enzyme indoleamine-2,3-dioxygenase (IDO) inhibits T cell responses and promotes immune tolerance. Tryptophan degradation by IDO in tumor cells is associated with immune evasion and increased tumor growth (see commentary by Prendergast). Thus, better understanding of how tryptophan catabolism affects immune responses might help to develop anticancer therapies. Opitz et al . found that cultured human glioma cell lines and glioma-initiating cells degraded tryptophan and produced large quantities of kynurenine. Knockdown of IDO isoforms in these cells had no effect on tryptophan metabolism; rather, knockdown of another tryptophan-degrading enzyme, TDO, blocked production of kynurenine. Immunohistochemical analysis showed that the abundance of TDO correlated with malignancy in human brain tumors. The amount of kynurenine produced by glioma cells correlated with inhibition of the proliferation of cocultured T cells. Knockdown of TDO in glioma cells restored T cell proliferation, whereas T cell proliferation was inhibited by the addition of exogenous kynurenine. The growth of TDO knockdown tumors implanted in the brains of nude mice was impeded compared to that of tumors proficient in TDO . Microarray analysis of kynurenine-treated glioma cells revealed the enhanced expression of many aryl hydrocarbon receptor (AHR)–responsive genes. The AHR is a transcription factor that responds to xenobiotic compounds, such as dioxin, to suppress immune responses and stimulate tumorigenesis. AHR-responsive gene expression in glioma cells was decreased when TDO was knocked down, suggestive of autocrine AHR signaling. However, when injected into Ahr -deficient mice, Tdo -expressing tumor cells exhibited attenuated growth, suggesting that paracrine AHR signaling was also required for tumor progression. Microarray analysis showed that expression of TDO correlated with that of AHR-responsive genes in many different cancer types, and high expression of TDO , AHR , or the AHR-responsive gene CYP1B1 correlated with poor survival of glioma patients. Together, these data suggest that TDO-derived kynurenine acts in an autocrine and paracrine fashion through the AHR to promote tumor growth. C. A. Opitz, U. M. Litzenburger, F. Sahm, M. Ott, I. Tritschler, S. Trump, T. Schumacher, L. Jestaedt, D. Schrenk, M. Weller, M. Jugold, G. J. Guillemin, C. L. Miller, C. Lutz, B. Radlwimmer, I. Lehmann, A. von Deimling, W. Wick, M. Platten, An endogenous tumour-promoting ligand of the human aryl hydrocarbon receptor. Nature 478 , 197–203 (2011). [PubMed] G. C. Prendergast, Why tumours eat tryptophan. Nature 478 , 192–194 (2011). [Online Journal]
    Type of Medium: Online Resource
    ISSN: 1945-0877 , 1937-9145
    URL: Article
    DOI: 10.1126/scisignal.4195ec289
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2011
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