T cells maintain a quiescent state prior to activation. As inappropriate T cell activation can cause disease, T cell quiescence must be preserved. Despite its importance, the mechanisms underlying the “quiescent state” remain elusive. Here, we identify BTG1 and BTG2 (BTG1/2) as factors responsible for T cell quiescence. BTG1/2-deficient T cells show an increased proliferation and spontaneous activation due to a global increase in messenger RNA (mRNA) abundance, which reduces the threshold to activation. BTG1/2 deficiency leads to an increase in polyadenylate tail length, resulting in a greater mRNA half-life. Thus, BTG1/2 promote the deadenylation and degradation of mRNA to secure T cell quiescence. Our study reveals a key mechanism underlying T cell quiescence and suggests that low mRNA abundance is a crucial feature for maintaining quiescence.

Summary To explore whether bacterial secreted 4‐hydroxy‐2‐alkylquinolines (HAQs) can regulate host innate immune responses, we used the extracts of bacterial culture supernatants from a wild‐type (PA14) and two mutants of Pseudomonas aeruginosa that have defects in making HAQs. Surprisingly, the extract of supernatants from the P. aeruginosa pqsA mutant that does not make HAQs showed strong stimulating activity for the production of innate cytokines such as tumour necrosis factor‐α and interleukin‐6 in the J774A.1 mouse monocyte/macrophage cell line, whereas the extract from the wild‐type did not. The addition of 4‐hydroxy‐2‐heptylquinoline (HHQ) or 2‐heptyl‐3,4‐dihydroxyquinoline (PQS, Pseudomonas quinolone signal) to mammalian cell culture media abolished this stimulating activity of the extracts of supernatants from the pqsA mutant on the expression of innate cytokines in J774A.1 cells and in the primary bronchoalveolar lavage cells from C57BL/6 mice, suggesting that HHQ and PQS can suppress the host innate immune responses. The pqsA mutant showed reduced dissemination in the lung tissue compared with the wild‐type strain in a mouse in vivo intranasal infection model, suggesting that HHQ and PQS may play a role in the pathogenicity of P. aeruginosa. HHQ and PQS reduced the nuclear factor‐κB (NF‐κB) binding to its binding sites and the expression of NF‐κB target genes, and PQS delayed inhibitor of κB degradation, indicating that the effect of HHQ and PQS was mediated through the NF‐κB pathway. Our results suggest that HHQ and PQS produced by P. aeruginosa actively suppress host innate immune responses.

Post-translational protein modification by the small ubiquitin-related modifier (SUMO) regulates numerous cellular pathways, including transcription, cell division, and genome maintenance. The SUMO protease Ulp2 modulates many of these SUMO-dependent processes in budding yeast. From whole-genome RNA sequencing (RNA-seq), we unexpectedly discovered that cells lacking Ulp2 display a twofold increase in transcript levels across two particular chromosomes: chromosome I (ChrI) and ChrXII. This is due to the two chromosomes being present at twice their normal copy number. An abnormal number of chromosomes, termed aneuploidy, is usually deleterious. However, development of specific aneuploidies allows rapid adaptation to cellular stresses, and aneuploidy characterizes most human tumors. Extra copies of ChrI and ChrXII appear quickly following loss of active Ulp2 and can be eliminated following reintroduction of ULP2, suggesting that aneuploidy is a reversible adaptive mechanism to counteract loss of the SUMO protease. Importantly, increased dosage of two genes on ChrI-CLN3 and CCR4, encoding a G 1 -phase cyclin and a subunit of the Ccr4-Not deadenylase complex, respectively-suppresses ulp2Δ aneuploidy, suggesting that increased levels of these genes underlie the aneuploidy induced by Ulp2 loss. Our results reveal a complex aneuploidy mechanism that adapts cells to loss of the SUMO protease Ulp2.

The Th2 locus control region (LCR) has been shown to be important in efficient and coordinated cytokine gene regulation during Th2 cell differentiation. However, the molecular mechanism for this is poorly understood. To study the molecular mechanism of the Th2 LCR, we searched for proteins binding to it. We discovered that transcription factor YY1 bound to the LCR and the entire Th2 cytokine locus in a Th2-specific manner. Retroviral overexpression of YY1 induced Th2 cytokine expression. CD4-specific knockdown of YY1 in mice caused marked reduction in Th2 cytokine expression, repressed chromatin remodeling, decreased intrachromosomal interactions, and resistance in an animal model of asthma. YY1 physically associated with GATA-binding protein-3 (GATA3) and is required for GATA3 binding to the locus. YY1 bound to the regulatory elements in the locus before GATA3 binding. Thus, YY1 cooperates with GATA3 and is required for regulation of the Th2 cytokine locus and Th2 cell differentiation. T h2 cytokine genes il4, il13, and il5 are clustered in chromosome 5 in human and chromosome 11 in mouse. The expression of the Th2 cytokine genes are coordinately regulated during Th2 cell differentiation. Several different regulatory elements have been shown to play an important role in Th2 cytokine gene expression, including promoters of Th2 cytokine genes, enhancers [conserved noncoding sequence 1 (CNS1)/hypersensitive site 1-3 (HSS1-3), hypersensitive site V (HSV)/CNS2, and intronic enhancer (IE)/ HSII], a silencer (HSIV), and a locus control region (LCR) (1, 2). The functions of these regulatory elements in Th2 cytokine expression in Th2 cells in vivo have been thoroughly investigated in transgenic mice and knockout mice that have targeted deletion in the regulatory elements (3-10). Among these regulatory elements, Th2 LCR has been shown to coordinately regulate Th2 cytokine genes, to induce chromatin remodeling, and to be required for chromosomal interactions (1, 2). The Th2 LCR is located in the introns of the Rad50 gene and is composed of four DNase I hypersensitive sites, including RHS4, RHS5, RHS6, and RHS7 (11,12). In previous studies, we have shown that the Th2 LCR is essential for Th2 cytokine expression and chromosome remodeling in the Th2 cytokine locus and in the pathogenesis of allergic asthma (7,11,13).The entire Th2 cytokine locus undergoes chromatin remodeling during Th2 cell differentiation (1, 2, 14). DNase I hypersensitive sites, which reflect accessibility of chromatin, are developed at the specific regulatory regions during Th2 cell differentiation (15, 16). Histone 3 lysine 9 (H3K9)-acetylation and histone 3 lysine 4 (H3K4)-methylation increase at specific regulatory regions in the Th2 cytokine locus during Th2 cell differentiation (17)(18)(19)(20). Th2 cytokine locus also undergoes DNA demethylation during Th2 cell differentiation (11,(21)(22)(23)(24)(25)(26). Treatment with drugs that cause chromatin modification such as 5-azacytidine or Trichostatin A induces Th2 cytokine expression upon T-cell recep...

Previous studies have shown that Th2 cytokine genes on mouse chromosome 11 are coordinately regulated by the Th2 locus control region (LCR). To examine the in vivo function of Th2 LCR, we generated CD4-specific Th2 LCR-deficient (cLCR KO) mice using CreLoxP recombination. The number of CD4 T cells in the cLCR KO mouse was comparable to that in wild-type mice. The expression of Th2 cytokines was dramatically reduced in in vitro-stimulated naïve CD4 T cells. Deletion of the LCR led to a loss of general histone H3 acetylation and histone H3-K4 methylation, and demethylation of DNA in the Th2 cytokine locus. Upon ovalbumin challenge in the mouse model of allergic asthma, cLCR KO mice exhibited marked reduction in the recruitment of eosinophils and lymphocytes in the bronchoalveolar lavage fluid, serum IgE level, lung airway inflammation, mucus production in the airway walls, and airway hyperresponsiveness. These results directly demonstrate that the Th2 LCR is critically important in the regulation of Th2 cytokine genes, in chromatin remodeling of the Th2 cytokine locus, and in the pathogenesis of allergic asthma.chromatin remodeling | differentiation | locus control region C D4 T cells play an essential role in the activation and regulation of a variety of immune responses. Effector CD4 T cells are composed of several different subsets including Th1, Th2, and Th17 cells (1-5). The expression of subset-specific cytokines is critical for the differentiation and function of T helper cells (6, 7). The Th2 cytokine genes, il4, il5, and il13, are clustered on human chromosome 5 and mouse chromosome 11. The Th2 cytokine locus undergoes structural changes in its chromatin upon Th2 cell differentiation to accommodate the high level expression of Th2 cytokine genes. The changes include acquisition of DNase I hypersensitivity (8, 9), restriction enzyme accessibility (10), histone acetylation (11-16), histone methylation (17), and DNA demethylation (8,13,18,19). Chromatin remodeling and enhancement of transcription of a gene are regulated by trans-acting factors that bind to specific DNA regulatory elements. Many laboratories including ours have shown that the Th2 cytokine locus is regulated by a number of regulatory elements including enhancers [CNS-1/ HSS (9, 20-22), CNS-2/HSV (20, 23), IE/HSII (20)], a silencer (HSIV) (20,24), and a locus control region (LCR) (25).We have shown previously that the expression of Th2 cytokines is coordinately regulated by the Th2 LCR that is located in the 3′ region of the rad50 gene (25). The Th2 LCR is composed of four DNase I-hypersensitive sites, namely RHS4, RHS5, RHS6, and RHS7 (13, 26). We have shown that deletion of RHS7 causes marked reduction of Th2 cytokine genes under Th0 conditions and partial reduction under Th2 conditions (27), suggesting that RHS7 is important for Th2 cytokine expression. The Th2 LCR interacts with the promoters of Th2 cytokine genes through intrachromosomal associations (28). Deletion of RHS7 disrupts these (27), suggesting that RHS7 is critical for these int...

Th17 cells mediate inflammation and autoimmunity. Although it was known that cytokine IL-2 inhibits Th17 cell differentiation, how it does so was elusive. Using IL-17–specific PTEN-deficient mice, Kim et al. show that phosphatase PTEN inhibits IL-2 production and thus promotes Th17 cell differentiation.

Peroxisome proliferator-activated receptor gamma (PPARγ) is a transcription factor that regulates lipid and glucose metabolism. Although studies of PPARγ ligands have demonstrated its regulatory functions in inflammation and adaptive immunity, its intrinsic role in T cells and autoimmunity has yet to be fully elucidated. Here we used CD4-PPARγKO mice to investigate PPARγ-deficient T cells, which were hyper-reactive to produce higher levels of cytokines and exhibited greater proliferation than wild type T cells with increased ERK and AKT phosphorylation. Diminished expression of IκBα, Sirt1, and Foxo1, which are inhibitors of NF-κB, was observed in PPARγ-deficient T cells that were prone to produce all the signature cytokines under Th1, Th2, Th17, and Th9 skewing condition. Interestingly, 1-year-old CD4-PPARγKO mice spontaneously developed moderate autoimmune phenotype by increased activated T cells, follicular helper T cells (TFH cells) and germinal center B cells with glomerular inflammation and enhanced autoantibody production. Sheep red blood cell immunization more induced TFH cells and germinal centers in CD4-PPARγKO mice and the T cells showed increased of Bcl-6 and IL-21 expression suggesting its regulatory role in germinal center reaction. Collectively, these results suggest that PPARγ has a regulatory role for TFH cells and germinal center reaction to prevent autoimmunity.

Regulatory T (Treg) cells are essential for maintenance of immune homeostasis. Foxp3 is the key transcription factor for Treg-cell differentiation and function; however, molecular mechanisms for its negative regulation are poorly understood. Here we show that YY1 expression is lower in Treg cells than Tconv cells, and its overexpression causes a marked reduction of Foxp3 expression and abrogation of suppressive function of Treg cells. YY1 is increased in Treg cells under inflammatory conditions with concomitant decrease of suppressor activity in dextran sulfate-induced colitis model. YY1 inhibits Smad3/4 binding to and chromatin remodelling of the Foxp3 locus. In addition, YY1 interrupts Foxp3-dependent target gene expression by physically interacting with Foxp3 and by directly binding to the Foxp3 target genes. Thus, YY1 inhibits differentiation and function of Treg cells by blocking Foxp3.