immunity-0

需无水印完整版本请发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com T s it M d e va l. n ith ip m the fused EGFP on the interaction of this case the role of Treg cells in immune postulated that the EGFP-Foxp3 fusion development. equal. Here, the studies by the two groups tion of the EGFP-fusion protein with IRF4 c w r stabilize Treg cell-specific transcriptional programs is rooted in its capacity for molecular interactions with transcriptional homeostasis, Bettini et al. found that the mutant allele also affected the generation of induced Treg (iTreg) cells, a subset that nizing HIF1a-dependent degradation of Foxp3, the EGFP moiety tipped the balance in favor of IRF4 interaction, re- partners. These interactions organize in modules in which different domains of Foxp3, including the N-terminal, zinc arises from naive conventional T cells in a TGF-beta-dependent manner and are required for tolerance (Haribhai et al., flected in a Treg cell transcriptome enriched in IRF4-regulated transcripts. Their proposal of subtle alterations in tolerance. The pivotal role of Foxp3 to effect and In addition to its impact on Treg cell development in the thymus and peripheral and HIF1a. By disfavoring the interaction with HIF1a, and consequently antago- N-terminal Foxp3domainwithother cofac- tors, disrupting some of those interactions while favoring others. These serendipitous findings shed new light on the biology of Foxp3 and the mechanisms by which it orchestrates distinct regulatory responses in immune tolerance. It also serves to emphasize both the power but also the limitations of genetic approaches to the study of complex biological systems, in protein altered the Treg cell transcriptional landscape and suppressive function. De- pendingon the tissueand themousestrain under study, both groups also tended to observe a decrease in the frequency of Treg cells expressing the mutant allele relative to control Treg cells, as well as an increase in the mutant protein. These changes began in the thymus, suggesting an impact of the mutant allele on Treg cell diverged to consider different potential mechanisms by which the Foxp3tm2Ayr allele alters Treg cell functions (Figure 1). Darce et al. focused on the apparent dichotomy that the Foxp3tm2Ayr allele pro- tected against antibodymediated autoim- munity in the K/BxN mouse model of arthritis even as it worsened the type 1 diabetes in NOD mice. They related both observations to alterations in the interac- Do w Immunity Previews Foxp3: Shades of Talal A. Chatila1,* and Calvin B. William 1Division of Immunology, the Children’s Hosp 2Section of Rheumatology, Department of Pe *Correspondence: talal.chatila@childrens.har DOI 10.1016/j.immuni.2012.05.011 In this issue of Immunity, Darce et a ations in the interaction of Foxp3 w immune phenotypes, worsening so The transcription factor Foxp3 controls myriad regulatory T (Treg) cell functions by virtue of its capacity to engage numerous other cofactors that array along the length of the protein in a series of molecular modules (Josefowicz et al., 2012). Disruption of one or more of those modules by missense mutations or in- frame deletions in FOXP3, as seen in human subjects with the IPEX syndrome, results in the emergence of systemic auto- immunity and inflammation (Torgerson and Ochs, 2007). In this issue of Immunity, two groups report that a commonly used murine Foxp3 reporter allele (Foxp3tm2Ayr), encoding a Foxp3 protein that is fused at its N-terminus to the enhanced green fluo- rescence protein (EGFP), exhibits distinct phenotypes on different murine genetic backgrounds prone to autoimmunity, thus accelerating some autoimmune diseases while suppressing others (Fontenot et al., 2005; Darce et al., 2012; Bettini et al., 2012). The altered function of the EGFP- Foxp3 chimera relates to the impact of uC 需无水印完整 olerance 2 al, and the Department of Pediatrics, Harvard iatrics, Medical College of Wisconsin, Milwauk rd.edu (2012) and Bettini et al. (2012) demo its transcriptional partners have a r e while ameliorating others. finger, leucine zipper, and DNA binding Forkheaddomain, interfacewith transcrip- tional factors and regulators to form large multiprotein complexes (Li et al., 2007). The N terminal domain of Foxp3 engages in interactions with transcription factors, including IRF4, HIF1a, and RORgt, and epigenetic regulators including TIP60 and HDAC7 (Josefowicz et al., 2012). Foxp3- IRF4 interactions enable Treg cells to control Th2 cell responses, whereas the interaction with HIF1a promotes the pro- teasomal degradation of Foxp3 (Zheng et al., 2009; Dang et al., 2011). The studies of Bettini et al. took off from the observation that Foxp3tm2Ayr allele dramatically accelerated the develop- ment of type 1 diabetes in disease-prone NOD mice. In contrast, Darce et al. first observed that the Foxp3tm2Ayr allele pro- tected mice from autoimmune arthritis in the K/BxN model. This prompted the later group to examine the effects of the allele in NOD mice, where they too observed accelerated diabetes. Both groups then om PDF w.pd fwiz a Immunity 版本请发邮件：wzxidian edical School, Boston MA 02115, USA e, Wisconsin 53226, USA strate that seemingly subtle alter- ple effect on the outcome of auto- 2011; Bilate and Lafaille, 2012). In a related observation, Darce et al. found that the mutant allele decreased the frequency of Th17 cells in the small intes- tinal lamina propria, an effect that may be linked to an altered capacity of Treg cells expressing the Foxp3tm2Ayr allele to suppress Th17 cell generation. These observations have relevance to studies that employ the Foxp3tm2Ayr allele in the analysis of inflammatory and tolerogenic responses to exogenous antigens and the microbial flora at the environmental interfaces. In examining the impact of the Foxp3tm2Ayr allele on Treg cell function in the context of autoimmune responses, an unusually nuanced picture emerged. Although it accelerated the autoimmune diabetes in NOD mice and bowel inflam- mation in lymphopenia-colitis models, the Foxp3tm2Ayr allele proved to be protec- tive against experimental autoimmune arthritis in the K/BN model, reinforcing the dictum that not all tolerance is created Tria l d.co m 36, May 25, 2012 ª2012 Elsevier Inc. 693 @gmail.com L L u F be an T la ed ra (e. N-terminal Zinc finger Hif1a Tip60 HAT HDAC7 p300 HAT Eos IRF-4 Zinc finger EGFP p300 HAT Eos IRF-4 Figure 1. Altered Functions of EGFP-Foxp3 F Interactions of the N-terminal domain of the native Foxp3 proteins interact at their N-termini with a num among others the transcription factors Hif1a, IRF4, and p300, and the histone deacetylase HDAC7. dependent transcriptional circuitries and help regu domain interactions and Treg cell responses induc introduction of an N-terminal EGFP alters the inte different co-factors, invigorating some interactions Foxp3-cofactor interaction resulting in a dramatic impact on the regulation by Treg cells of different modalities of auto- immunity, such as Th1 cell-dependent type 1 diabetes versus Th2 and Th17 cell-dependent autoantibody-dependent arthritis, is very provocative and will prob- ably pique further interest in how different transcriptional modules of Foxp3 regulate distinct facets of autoimmunity. Bettini et al. also observed altered inter- action of the N-terminal domain of the EGFP-Foxp3 chimera, with decreased interaction with a number of cofactors involved in the regulation of gene ex- pression by Foxp3, including the zinc finger-type transcription factor Eos, the histone acetyl transferases Tip60 and p300, and the histone deacetylase HDAC7. They hypothesized that impair- ment of these interactions affected the stability of Foxp3 at sites of inflammation, in part by instigating decreased acetyla- tion and increased polyubiquitination of the EGFP-Foxp3 fusion protein. The failure of these cofactors to effectively engage the N-terminus of the EGFP- Foxp3 fusion protein also altered the Treg cell transcriptome in a manner that impaired the Treg cell response at those (e.g., those with HATs, Eos, and Hif1a). These altera cells, potentiating their capacity to enforce tolerance antibody production in the K/BxN arthritis model) Th1-driven type 1 diabetes in the NOD mouse). 694 Immunity 36, May 25, 2012 ª2012 Elsevi 需无水印完整 Doc uC w C-terminal eucine zipper Fork-head AML-1 NF-AT eucine zipper Fork-head AML-1 NF-AT Foxp3 EGFP-Foxp3 Cofactor-dependent transcriptional program Altered epigenetic signature Biased transcriptional program Increased EGFP-Foxp3 protein expression sion Protein oxp3 protein with different cofactors (top). Dimeric r of transcriptional factors and regulators, including d Eos, the histone acetyltransferases (HATs) Tip60 hese interactions enable a number of cofactor- te the levels of Foxp3 protein. Altered N-terminal by the EGFP-Foxp3 fusion protein (bottom). The ction of the EGFP-Foxp3 fusion protein with the g., with IRF4) while weakening or abolishing others DF inflammatory sites. Although the pro- posed mechanisms for the Treg cell dysfunction associated with the EGFP- Foxp3 fusion protein are not exclusive, more studies are required to clarify the relative contribution of the respective mechanism(s) to the observed pheno- types associated with the mutant protein. More broadly, these findings suggest potentially wider perturbations in the function of other subsets of Treg cells, such as lymph node follicular Treg cells and mucosal iTreg cells, that may be rele- vant to the observed phenotypes. Previous studies employing the Foxp3tm2Ayr allele have been instrumental in illuminating the biology of Treg cells and in probing the various functions of Foxp3 in transcriptional regulations. Many of these findings have been independently confirmed by several groups using other genetic and reporter allele models of Foxp3 function. Nevertheless, the over- whelming majority of the studies employ- ing the Foxp3tm2Ayr allele were carried out on the non-autoimmune prone C57BL/6 background, and the results discussed herein indicate that caution should be ex- ercised when extending some of those studies to other genetic strains. Addi- tions impact the transcriptional landscape of Treg against some autoimmune responses (e.g., auto- while weakening their response to others (e.g., er Inc. 版本请发邮件：wzxidian@ om P ww .pdf wiza r tionally, earlier results obtained with the Foxp3tm2Ayr allele need to be carefully considered in at least two other situations. The first is in regards to the employment of the EGFP-Foxp3 chimera in studies on iTreg cells, whose development it may impair. The second relates to studies on compound mutations that are either in cis at other sites in the Foxp3 locus or in trans with other genes (e.g., combination of the Foxp3tm2Ayr allele and other knockin- knockout alleles such as those targeting transcription factors relevant to Treg cell function). Unaccounted interac- tions between such mutations, although interesting in their own right, may cloud the interpretations of the resultant phenotypes. Finally, it is worth recalling that the deri- vationofanygeneticallyengineeredanimal model entails a compromise between faithfully reproducing the phenomenon under study while acknowledging an impact, however minor, of the alterations introduced by the genetic engineering on the results thus obtained. This reenact- ment of the uncertainty principle should not be far from the mind of investigators employing those models in their studies. REFERENCES Bettini, M.L., Pan, F., Bettini, M., Finkelstein, D., Rehg, J.E., Floess, S., et al. (2012). Immunity 36, this issue, 717–730. Bilate, A.M., and Lafaille, J.J. (2012). Annu. Rev. Immunol. 30, 733–758. Dang, E.V., Barbi, J., Yang, H.Y., Jinasena, D., Yu, H., Zheng, Y., Bordman, Z., Fu, J., Kim, Y., Yen, H.R., et al. (2011). Cell 146, 772–784. Darce, J., Rudra, D., Li, L., Nishio, J., Cipolletta, C., Rudensky, A.Y., et al. (2012). Immunity 36, this issue, 731–741. Fontenot, J.D., Rasmussen, J.P., Williams, L.M., Dooley, J.L., Farr, A.G., and Rudensky, A.Y. (2005). Immunity 22, 329–341. Haribhai, D., Williams, J.B., Jia, S., Nickerson, D., Schmitt, E.G., Edwards, B., Ziegelbauer, J., Yas- sai, M., Li, S.H., Relland, L.M., et al. (2011). Immu- nity 35, 109–122. Josefowicz, S.Z., Lu, L.F., and Rudensky, A.Y. (2012). Annu. Rev. Immunol. 30, 531–564. Li, B., Samanta, A., Song, X., Iacono, K.T., Brennan, P., Chatila, T.A., Roncador, G., Banham, A.H., Riley, J.L., Wang, Q., et al. (2007). Int. Immu- Immunity Previews Tria l d.co m nol. 19, 825–835. Torgerson, T.R., and Ochs, H.D. (2007). J. Allergy Clin. Immunol. 120, 744–750, quiz 751–752. Zheng, Y., Chaudhry, A., Kas, A., deRoos, P., Kim, J.M., Chu, T.T., Corcoran, L., Treuting, P., Klein, U., and Rudensky, A.Y. (2009). Nature 458, 351–356. gmail.com t r ar us l, b . ( R a io dent pathways are of the utmost impor- tance in protecting from viruses, the factors that act primarily to prevent immune effector protein kinase R (PKR), which inhibits the cytoskeleton, blocking catalyzes the actin cleavage and nucle- answering this is the fact that transcrip- tion of PKR is regulated by IFN, which a logical extension from this work, exactly r viruses from accessing the cytosol and usurping the host machinery required for ation required for cytoskeletal rearrange- ments in lammelopodia extension and how effective this mechanism of basal defense is during the systemic antiviral reality is that they are only triggered after the fact—when the sanctity of the cell has already been breached. A preferable strategy would surely be for the host to simply prevent the invasion of viruses in the first place. An emerging paradigm in antiviral immunity suggest that this is the case and points to an important role of potential actin-dependent routes of viral entry (Figure 1). They observed that cells from PKR-deficient mice have an altered cytoskeleton, with less filamentous actin and more active membrane processes, resulting in increased endocytosis. A search for PKR-binding proteins found gelsolin, an actin binding protein that both increased PKR expression and the amounts of F actin in the cell. Therefore, because PKR is upregulated by IFN, it would be predicted that the systemic anti- viral response might increase the cell- autonomous resistance of bystander uninfected cells, and thus acts to limit viral spread. Although this hypothesis is Do w Penetration Resis Adam Lacy-Hulbert1 and Lynda M. Stu 1Developmental Immunology/CCIB Massach 2The Broad Institute of Harvard and MIT, Cam *Correspondence: lstuart@partners.org DOI 10.1016/j.immuni.2012.05.010 In this issue of Immunity, Irving et al interaction with gelsolin. This altern Over the past ten years, the field of innate immunity has made substantial progress in better understanding how the host recognizes and responds to viruses. It is now evident that this is accomplished by the collaboration of certain Toll-like receptors, which monitor the endosomal compartments of cells for the presence of viral nucleic acids, and cytosol viral sensors such as RIG-I andMDA-5. Down- stream of these, and of major importance to anti-viral immunity, is the production of interferons (IFNs), which have potent antiviral activity and act through the upre- gulation of a complex network of IFN- stimulated genes. Additionally, engage- ment of receptors such as AIM2 can result in the activation of caspase-1 and pro- duction of the mature form of the proin- flammatory cytokines IL-1b and IL-18, as well as induction of a form of defensive cell death termed ‘‘pyroptosis.’’ Together, these classic pattern recognition recep- tors (PRRs) trigger immune signaling pathways that make a vital contribution to antiviral immunity. However, although these PRR-depen- Immunity Previews cuC their replication. Indeed, it is now apparent that such factors can afford a significant advantage to the host and that there are strong evolutionary pres- sures to maintain such proteins or to favor mutant alleles that have these restrictive 需无水印完整 ance: PKR’s Othe t1,2,* etts General Hospital/Harvard Medical Schoo ridge, MA 02142, USA 2012) show that protein kinaseR (PK tive role for PKR prevents penetrat properties. One of the first examples of this was the discovery of restrictive alleles of the HIV coreceptors CCR5 and CCR2 that protect from infection andwere found to offer a major advantage in areas where HIV is endemic (Kostrikis et al., 1998). Similarly, studies of New World monkeys found that simian TRIM5a, but not human TRIM5a, protected against HIV by accel- erating the uncoating of the virus (Strem- lau et al., 2004). More recently, the IFN-induced transmembrane proteins were identified as a new family of antiviral molecules that protect against a number of viruses, particularly those that enter via acidic endolysosomal compartments (Brass et al., 2009). Thus, in a manner analogous to the epithelial barriers that protect the organism from pathogen inva- sion, there appear to also be cell autono- mous barriers that restrict viral entry. In this issue of Immunity, Irving et al. (2012) describe a mechanism of resis- tance to viral infection that is active under basal conditions and increased in response to interferon. This mechanism of immune resistance involves the innate om PDF ww .pdf wiza retraction, as well as particle uptake. Notably, PKR binding inhibited the ability of gelsolin to bind and sever actin fila- ments in both in vitro and in vivo assays. From these observations, the authors hypothesized that PKR-mediated inhibi- Immunity 版本请发邮件：wzxidian Talent Boston, MA 02144, USA ) regulates the cytoskeleton via an n of virions into the cell. tion of gelsolin normally serves to inhibit entry of viral particles in the basal state. Supporting this theory, silencing of gelso- lin reduced viral entry and infection into cells, whereas deletion of PKR increased infection. Furthermore, knockdown of gelsolin in mice reduced adenovirus infection. These results therefore add regulation of viral entry to the already es- tablished functions of PKR in inhibiting viral and host protein translation and promoting immune responses. Curiously, the interaction of PKR and gelsolin occurred only with inactive PKR, whereas PKR’s other antiviral roles require PKR activation by binding double-stranded RNA. Confirming this process, Irving et al. (2012) activated PKR by the viral nu- cleic acid mimic polyI:polyC and showed that this activation released gelsolin inhi- bition, increasing membrane ruffling. Thus, once an individual cell is infected this mechanism is no longer active and the cells become permissive for infection. How does this work during an active infection and what advantage might it have for the host? An important clue to Tria l d.co m immune responses remains to be fully defined and will require further and more in depth in vivo studies. Placing these findings in their broader context, it is well recognized that patho- gens often target the cytoskeleton by the 36, May 25, 2012 ª2012 Elsevier Inc. 695 @gmail.com R PKR Gelsolin Virion IFN + PKR PR - - - + Resistant liberation of virulence factors thatmanipu- late it to their advantage and for their own gain (Aktories et al., 2011). As a mecha- nism of counterdefense it is also clear, from this work and the work of others, that the cytoskeleton, their binding proteins, and their regulators can play unusual and unexpected roles immune defense. An interesting example