Chaoran Li

miR-126 and miR-126 * repress recruitment of mesenchymal stem cells and inflammatory monocytes to inhibit breast cancer metastasis

The tumour stroma is an active participant during cancer progression. Stromal cells promote tumour progression and metastasis through multiple mechanisms including enhancing tumour invasiveness and angiogenesis, and suppressing immune surveillance. We report here that miR-126/miR-126*, a microRNA pair derived from a single precursor, independently suppress the sequential recruitment of mesenchymal stem cells and inflammatory monocytes into the tumour stroma to inhibit lung metastasis by breast tumour cells in a mouse xenograft model. miR-126/miR-126* directly inhibit stromal cell-derived factor-1 alpha (SDF-1α) expression, and indirectly suppress the expression of chemokine (C–C motif) ligand 2 (Ccl2) by cancer cells in an SDF-1α-dependent manner. miR-126/miR-126* expression is downregulated in cancer cells by promoter methylation of their host gene Egfl7. These findings determine how this microRNA pair alters the composition of the primary tumour microenvironment to favour breast cancer metastasis, and demonstrate a correlation between miR-126/126* downregulation and poor metastasis-free survival of breast cancer patients.

Molecular dissection of the miR-17-92 cluster's critical dual roles in promoting Th1 responses and preventing inducible Treg differentiation

Mir-17-92 encodes 6 miRNAs inside a single polycistronic transcript, the proper expression of which is critical for early B-cell development and lymphocyte homeostasis. However, during the T-cell antigen response, the physiologic function of endogenous miR-17-92 and the roles of the individual miRNAs remain elusive. In the present study, we functionally dissected the miR-17-92 cluster and revealed that miR-17 and miR-19b are the key players controlling Th1 responses through multiple coordinated biologic processes. These include: promoting proliferation, protecting cells from activation-induced cell death, supporting IFN-γ production, and suppressing inducible regulatory T-cell differentiation. Mechanistically, we identified Pten (phosphatase and tensin homolog) as the functionally important target of miR-19b, whereas the function of miR-17 is mediated by TGFβRII and the novel target CREB1. Because of its vigorous control over the Th1 cell-inducible regulatory T cell balance, the loss of miR-17-92 in CD4 T cells results in tumor evasion. Our results suggest that miR-19b and miR-17 could be harnessed to enhance the efficacy of T cell-based tumor therapy.

miR-17-92 Cluster Targets Phosphatase and Tensin Homology and Ikaros Family Zinc Finger 4 to Promote TH17-mediated Inflammation

Background: miRNA is a key component of post-transcriptional network governing the fate of T cells. Results: By targeting PTEN and IKZF4, miR-17-92 cluster promotes TH17 differentiation and TH17-related inflammation. Conclusion: miR-19b and miR-17 within the cluster additively promote TH17 responses through distinct regulatory networks. Significance: Our study provides novel regulatory mechanisms and potential therapeutic candidates against autoimmunity. The miR-17-92 cluster regulates a broad spectrum of biological processes of T cell immunity. This cluster was found to facilitate T cell proliferation, enhance antitumor activities and promote T cell-dependent antibody responses. However, little is known about the role of this miRNA cluster in the development of autoimmune diseases. Multiple sclerosis is a neuro-destructive autoimmune disease caused by the pathogenicity of TH17 cells, whose differentiation is tightly controlled by a variety of transcriptional and post-transcriptional regulators. Our study unveils the critical role of miR-17-92 in TH17 differentiation: T cell-specific miR-17-92 deficiency reduced TH17 differentiation and ameliorated experimental autoimmune encephalomyelitis (EAE) symptoms. We demonstrated that miR-17 and miR-19b are the two miRNAs in this cluster responsible for promoting TH17 responses. MiR-19b represses the expression of Phosphatase and Tensin Homology (PTEN), thereby augmenting the PI3K-AKT-mTOR axis essential for proper TH17 differentiation. Meanwhile, miR-17 enhances TH17 polarization by inhibiting a novel target, Ikaros Family Zinc Finger 4 (IKZF4). By establishing the miR-17-92 cluster as a key driver of TH17 responses, our data identify this miRNA cluster as a potential therapeutic target for the clinical intervention of multiple sclerosis.

T Cell Receptor (TCR) and Transforming Growth Factor β (TGF-β) Signaling Converge on DNA (Cytosine-5)-methyltransferase to Control forkhead box protein 3 (foxp3) Locus Methylation and Inducible Regulatory T Cell Differentiation

Background: TCR and TGF-β signaling regulate the differentiation of Foxp3+-inducible regulatory T cells. Results: Through posttranscriptional regulation of DNMTs, TCR and TGF-β signaling control foxp3 promoter methylation. Conclusion: During antigen-induced proliferation, TCR and TGF-β signaling program T cells epigenetically to achieve heritage maintenance. Significance: Our results illustrate a single mechanism that can comprehensively underpin the interplay between antigen and environment in guiding iTreg differentiation. Naïve T cells can be induced to differentiate into Foxp3+ regulatory T cells (iTregs) upon suboptimal T cell receptor (TCR) stimulus or TCR stimulus in conjunction with TGF-β signaling; however, we do not fully understand how these signals coordinately control foxp3 expression. Here, we show that strong TCR activation, in terms of both duration and ligand affinity, causes the accumulation of DNA (cytosine-5)-methyltransferase 1 (DNMT1) and DNMT3b and their specific enrichment at the foxp3 locus, which leads to increased CpG methylation and inhibits foxp3 transcription. During this process the augmentation of DNMT1 is regulated through at least two post-transcriptional mechanisms; that is, strong TCR signal inactivates GSK3β to rescue DNMT1 protein from proteasomal degradation, and strong TCR signal suppresses miR-148a to derepress DNMT1 mRNA translation. Meanwhile, TGF-β signaling antagonizes DNMT1 accumulation via activation of p38 MAP kinase. Thus, independent of transcription factor activation, TCR and TGF-β signals converge on DNMT1 to modulate the expression of foxp3 epigenetically, which marks mother cell iTreg lineage choice within the genome of differentiating daughter cells.

MeCP2 Reinforces STAT3 Signaling and the Generation of Effector CD4+ T Cells by Promoting miR-124–Mediated Suppression of SOCS5

A transcriptional regulator implicated in a neurodevelopmental disorder is required for the generation of certain effector T cells. Neurons and T Cells Need MeCP2 Methyl CpG binding protein 2 (MeCP2) is a multifunctional transcriptional regulator involved in chromatin remodeling and the activation of gene expression. Heterozygous loss-of-function mutations in MECP2 are found in patients with the neurodevelopmental disorder Rett syndrome, and polymorphisms in MECP2 are linked to increased susceptibility to autoimmune diseases. Jiang et al. found in naïve CD4+ T cells that MeCP2 was required for the expression of a microRNA without which cytokine-dependent activation of the transcriptional regulators of the STAT family was defective. MeCP2-deficient naïve CD4+ T cells failed to differentiate into specific types of effector T cells in vitro and in mice. Furthermore, neurons and astrocytes deficient in MeCP2 also exhibited defective STAT signaling, which suggests that MeCP2 may regulate similar pathways in both neuronal and immune cell types. Methyl CpG binding protein 2 (MeCP2) is an X-linked, multifunctional epigenetic regulator that is best known for its role in the neurological disorder Rett syndrome; however, it is also linked to multiple autoimmune disorders. We examined a potential role for MeCP2 in regulating the responses of CD4+ T cells to stimulation with antigen. MeCP2 was indispensable for the differentiation of naïve CD4+ T cells into T helper type 1 (TH1) and TH17 cells and for TH1- or TH17-mediated pathologies in vitro and in vivo. Loss of MeCP2 in CD4+ T cells impaired the expression of the microRNA (miR) miR-124 and consequently relieved miR-124–mediated repression of the translation of suppressor of cytokine signaling 5 (Socs5) mRNA. The resulting accumulation of SOCS5 inhibited the cytokine-dependent activation of signal transducer and activator of transcription 1 (STAT1) and STAT3, which are necessary for the differentiation of TH1 and TH17 cells, respectively. Upon silencing of MeCP2, primary neurons and astrocytes also failed to respond properly to STAT3-dependent signaling stimulated by neurotrophic factors. Together, these findings suggest that the regulation of STAT3 signaling may represent a common etiology underpinning the roles of MeCP2 in both the nervous and immune systems.

MeCP2 enforces Foxp3 expression to promote regulatory T cells’ resilience to inflammation

Significance Forkhead box P3+ (Foxp3+) regulatory T cells (Tregs) are important for maintaining immune homeostasis and tolerance. The pivotal role of Tregs in immune tolerance demands that they possess a dedicated molecular machinery to maintain stable Foxp3 expression when challenged by an inflammatory environment. Whereas epigenetic mechanisms acting on the foxp3 locus have been extensively implicated in Tregs’ stable expression of Foxp3, the detailed molecular machinery remains elusive. In this study, we show that methyl-CpG binding protein 2 (MeCP2), an X-linked multifunctional epigenetic regulator, is a crucial player in the epigenetic machinery that confers Tregs with resilience against inflammation. Our study provides, to our knowledge, the first mechanistic description by which MeCP2, a molecule best known for its function in the central nervous system, regulates Treg function and immune tolerance. Forkhead box P3+ (Foxp3+) regulatory T cells (Tregs) are crucial for peripheral tolerance. During inflammation, steady Foxp3 expression in Tregs is essential for maintaining their lineage identity and suppressive function. However, the molecular machinery governing Tregs’ resilience to inflammation-induced Foxp3 destabilization remains elusive. Here, we demonstrate that methyl-CpG binding protein 2 (MeCP2), an eminent epigenetic regulator known primarily as the etiological factor of Rett syndrome, is critical to sustain Foxp3 expression in Tregs during inflammation. In response to inflammatory stimuli, MeCP2 is specifically recruited to the Conserved Non-Coding sequence 2 region of the foxp3 locus, where it collaborates with cAMP responsive element binding protein 1 to promote local histone H3 acetylation, thereby counteracting inflammation-induced epigenetic silencing of foxp3. Consequently, Treg-specific deletion of MeCP2 causes spontaneous immune activation in mice and failure in protection against autoimmunity. Furthermore, we demonstrate that Foxp3 expression in MeCP2-deficient Tregs diminishes with time, resulting in their failure to suppress effector T-cell–mediated colitis. Thus, MeCP2 serves as a critical safeguard that confers Tregs with resilience against inflammation.

MicroRNA-23a Curbs Necrosis during Early T Cell Activation by Enforcing Intracellular Reactive Oxygen Species Equilibrium

Upon antigen engagement, augmented cytosolic reactive oxygen species (ROS) are needed to achieve optimal T cell receptor (TCR) signaling. However, uncontrolled ROS production is a prominent cause of necrosis, which elicits hyper-inflammation and tissue damage. Hence, it is critical to program activated T cells to achieve ROS equilibrium. Here, we determined that miR-23a is indispensable for effector CD4(+) T cell expansion, particularly by providing early protection from excessive necrosis. Mechanistically, miR-23a targeted PPIF, gatekeeper of the mitochondria permeability transition pore, thereby restricting ROS flux and maintaining mitochondrial integrity. Upon acute Listeria monocytogenes infection, deleting miR-23a in T cells resulted in excessive inflammation, massive liver damage, and a marked mortality increase, which highlights the essential role of miR-23a in maintaining immune homeostasis.