Hiromasa Morikawa

T Cell Receptor Stimulation-Induced Epigenetic Changes and Foxp3 Expression Are Independent and Complementary Events Required for Treg Cell Development

The transcription factor Foxp3 is essential for the development of regulatory T (Treg) cells, yet its expression is insufficient for establishing the Treg cell lineage. Here we showed that Treg cell development was achieved by the combination of two independent processes, i.e., the expression of Foxp3 and the establishment of Treg cell-specific CpG hypomethylation pattern. Both events were induced by T cell receptor stimulation. The Treg cell-type CpG hypomethylation began in the thymus and continued to proceed in the periphery and could be fully established without Foxp3. The hypomethylation was required for Foxp3(+) T cells to acquire Treg cell-type gene expression, lineage stability, and full suppressive activity. Thus, those T cells in which the two events have concurrently occurred are developmentally set into the Treg cell lineage. This model explains how Treg cell fate and plasticity is controlled and can be exploited to generate functionally stable Treg cells.

Genetic and epigenetic basis of Treg cell development and function: from a FoxP3‐centered view to an epigenome‐defined view of natural Treg cells

Naturally occurring regulatory T (nTreg) cells, which specifically express the transcription factor Forkhead box protein P3 (FoxP3), are indispensable for the maintenance of immunological self‐tolerance and homeostasis. Recent studies have shown that developing nTreg cells in the thymus acquire a Treg‐specific and stable hypomethylation pattern in a limited number of genes, which encode key molecules including FoxP3, essential for Treg cell function. This epigenetic change is acquired via T‐cell receptor (TCR) stimulation, beginning prior to FoxP3 expression. The Treg‐specific DNA hypomethylated regions generally act as gene enhancers in steady state nTreg cells, contributing to the stable expression of Treg function‐associated key genes including Ctla4, Il2ra, and Ikzf4 in addition to Foxp3. Upon TCR stimulation of mature nTreg cells, FoxP3 strongly represses many genes including Il2, contributing to Treg suppressive activity. Thus, the Treg‐specific epigenome alteration can determine the heritable Treg‐specific gene network including Foxp3 regulation. Considering physiological presence of non‐suppressive FoxP3+ T cells in the immune system and loss of FoxP3 in Treg cells under certain immunological conditions, functional nTreg cells can be more accurately defined as a T‐cell subpopulation possessing the Treg‐type epigenome, rather than FoxP3+ T cells. This epigenome‐based definition of Treg cells would enable better understanding of functional stability, plasticity, and heterogeneity of Treg cells.

Differential roles of epigenetic changes and Foxp3 expression in regulatory T cell-specific transcriptional regulation.

Naturally occurring regulatory T (Treg) cells, which specifically express the transcription factor forkhead box P3 (Foxp3), are engaged in the maintenance of immunological self-tolerance and homeostasis. By transcriptional start site cluster analysis, we assessed here how genome-wide patterns of DNA methylation or Foxp3 binding sites were associated with Treg-specific gene expression. We found that Treg-specific DNA hypomethylated regions were closely associated with Treg up-regulated transcriptional start site clusters, whereas Foxp3 binding regions had no significant correlation with either up- or down-regulated clusters in nonactivated Treg cells. However, in activated Treg cells, Foxp3 binding regions showed a strong correlation with down-regulated clusters. In accordance with these findings, the above two features of activation-dependent gene regulation in Treg cells tend to occur at different locations in the genome. The results collectively indicate that Treg-specific DNA hypomethylation is instrumental in gene up-regulation in steady state Treg cells, whereas Foxp3 down-regulates the expression of its target genes in activated Treg cells. Thus, the two events seem to play distinct but complementary roles in Treg-specific gene expression.

Detection of T cell responses to a ubiquitous cellular protein in autoimmune disease

T cells that mediate autoimmune diseases such as rheumatoid arthritis (RA) are difficult to characterize because they are likely to be deleted or inactivated in the thymus if the self antigens they recognize are ubiquitously expressed. One way to obtain and analyze these autoimmune T cells is to alter T cell receptor (TCR) signaling in developing T cells to change their sensitivity to thymic negative selection, thereby allowing their thymic production. From mice thus engineered to generate T cells mediating autoimmune arthritis, we isolated arthritogenic TCRs and characterized the self antigens they recognized. One of them was the ubiquitously expressed 60S ribosomal protein L23a (RPL23A), with which T cells and autoantibodies from RA patients reacted. This strategy may improve our understanding of the underlying drivers of autoimmunity. In a mouse model of rheumatoid arthritis, autoimmune T cells recognize a protein from the ribosome. Finding the targets of T cells gone bad Autoimmune diseases such as rheumatoid arthritis can result when the immune system attacks its own body. If we could identify the specific proteins targeted by autoimmune T cells, we might then be able to block this interaction, which might be useful therapeutically. Ito et al. identified one such target in mice that develop a disease similar to rheumatoid arthritis. Disease-causing T cells recognized a protein that is part of the ribosome, a large protein complex that catalyzes protein synthesis. They also found T cells specific for this protein in people with rheumatoid arthritis. Science, this issue p. 363

Construction of self-recognizing regulatory T cells from conventional T cells by controlling CTLA-4 and IL-2 expression

Significance Naturally occurring regulatory T (Treg) cells suppress aberrant or excessive immune responses, thereby maintaining immune self-tolerance and homeostasis. This study shows that a combination of IL-2 repression, CTLA-4 expression, and antigenic stimulation is able to convert conventional T cells to potently immunosuppressive Treg-like cells, which are able to deprive IL-2 and CD28 signal from other T cells. Like natural Treg cells, they acquire a self-skewed T-cell receptor repertoire in the course of their thymic development, enabling them to control autoimmune responses effectively. This Treg construction by targeting IL-2 and CTLA-4 in conventional T cells is a novel way of immune suppression. Thymus-produced CD4+ regulatory T (Treg) cells, which specifically express the transcription factor forkhead box p3, are potently immunosuppressive and characteristically possess a self-reactive T-cell receptor (TCR) repertoire. To determine the molecular basis of Treg suppressive activity and their self-skewed TCR repertoire formation, we attempted to reconstruct these Treg-specific properties in conventional T (Tconv) cells by genetic manipulation. We show that Tconv cells rendered IL-2 deficient and constitutively expressing transgenic cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) were potently suppressive in vitro when they were preactivated by antigenic stimulation. They also suppressed in vivo inflammatory bowel disease and systemic autoimmunity/inflammation produced by Treg deficiency. In addition, in the thymus, transgenic CTLA-4 expression in developing Tconv cells skewed their TCR repertoire toward higher self-reactivity, whereas CTLA-4 deficiency specifically in developing thymic Treg cells cancelled their physiological TCR self-skewing. The extracellular portion of CTLA-4 was sufficient for the suppression and repertoire shifting. It interfered with CD28 signaling to responder Tconv cells via outcompeting CD28 for binding to CD80 and CD86,or modulating CD80/CD86 expression on antigen-presenting cells. Thus, a triad of IL-2 repression, CTLA-4 expression, and antigenic stimulation is a minimalistic requirement for conferring Treg-like suppressive activity on Tconv cells, in accordance with the function of forkhead box p3 to strongly repress IL-2 and maintain CTLA-4 expression in natural Treg cells. Moreover, CTLA-4 expression is a key element for the formation of a self-reactive TCR repertoire in natural Treg cells. These findings can be exploited to control immune responses by targeting IL-2 and CTLA-4 in Treg and Tconv cells.

VEGF-B promotes cancer metastasis through a VEGF-A–independent mechanism and serves as a marker of poor prognosis for cancer patients

Significance Cancer metastasis is responsible for a majority of the mortality in cancer patients and involves complex interactions, modulated by various factors and cytokines, between malignant and host cells. Vascular structures in solid tumors are crucial for cancer cell intravasation into the circulation. Our present work shows that VEGF-B produced by tumor cells significantly remodels tumor microvasculature, leading to leaky vascular networks that are highly permissive for tumor cell invasion. VEGF-B–promoted cancer metastasis occurs through a VEGF-A–independent mechanism. Thus, inhibition of VEGF-B should be considered an independent approach for the development of new drugs for the treatment of cancer invasion and metastasis. VEGF-B also may be considered as an independent prognostic marker for cancer metastasis. The biological functions of VEGF-B in cancer progression remain poorly understood. Here, we report that VEGF-B promotes cancer metastasis through the remodeling of tumor microvasculature. Knockdown of VEGF-B in tumors resulted in increased perivascular cell coverage and impaired pulmonary metastasis of human melanomas. In contrast, the gain of VEGF-B function in tumors led to pseudonormalized tumor vasculatures that were highly leaky and poorly perfused. Tumors expressing high levels of VEGF-B were more metastatic, although primary tumor growth was largely impaired. Similarly, VEGF-B in a VEGF-A–null tumor resulted in attenuated primary tumor growth but substantial pulmonary metastases. VEGF-B also led to highly metastatic phenotypes in Vegfr1 tk−/− mice and mice treated with anti–VEGF-A. These data indicate that VEGF-B promotes cancer metastasis through a VEGF-A–independent mechanism. High expression levels of VEGF-B in two large-cohort studies of human patients with lung squamous cell carcinoma and melanoma correlated with poor survival. Taken together, our findings demonstrate that VEGF-B is a vascular remodeling factor promoting cancer metastasis and that targeting VEGF-B may be an important therapeutic approach for cancer metastasis.

The PDGF-BB-SOX7 axis-modulated IL-33 in pericytes and stromal cells promotes metastasis through tumour-associated macrophages

Signalling molecules and pathways that mediate crosstalk between various tumour cellular compartments in cancer metastasis remain largely unknown. We report a mechanism of the interaction between perivascular cells and tumour-associated macrophages (TAMs) in promoting metastasis through the IL-33–ST2-dependent pathway in xenograft mouse models of cancer. IL-33 is the highest upregulated gene through activation of SOX7 transcription factor in PDGF-BB-stimulated pericytes. Gain- and loss-of-function experiments validate that IL-33 promotes metastasis through recruitment of TAMs. Pharmacological inhibition of the IL-33–ST2 signalling by a soluble ST2 significantly inhibits TAMs and metastasis. Genetic deletion of host IL-33 in mice also blocks PDGF-BB-induced TAM recruitment and metastasis. These findings shed light on the role of tumour stroma in promoting metastasis and have therapeutic implications for cancer therapy.

Pericyte–fibroblast transition promotes tumor growth and metastasis

Significance We show that vascular pericytes significantly contribute to cancer invasion and metastasis by the mechanism of the pericyte–fibroblast transition (PFT). This study proposes this concept and indicates the vascular pericyte’s role. Vascular pericytes were considered to remodel tumor vessels toward a mature phenotype. However, once dissociated from tumor vessels their functions within the tumor tissue are not known. In the present study, we show that pericytes, once detached from tumor microvasculatures, underwent differentiation to become stromal fibroblasts, which are known to contribute to tumor invasion and metastasis. Our results show that vascular pericytes are the important source of stromal fibroblasts and targeting PFT may offer a new treatment option in cancer metastasis. Vascular pericytes, an important cellular component in the tumor microenvironment, are often associated with tumor vasculatures, and their functions in cancer invasion and metastasis are poorly understood. Here we show that PDGF-BB induces pericyte–fibroblast transition (PFT), which significantly contributes to tumor invasion and metastasis. Gain- and loss-of-function experiments demonstrate that PDGF-BB-PDGFRβ signaling promotes PFT both in vitro and in in vivo tumors. Genome-wide expression analysis indicates that PDGF-BB–activated pericytes acquire mesenchymal progenitor features. Pharmacological inhibition and genetic deletion of PDGFRβ ablate the PDGF-BB–induced PFT. Genetic tracing of pericytes with two independent mouse strains, TN-AP-CreERT2:R26R-tdTomato and NG2-CreERT2:R26R-tdTomato, shows that PFT cells gain stromal fibroblast and myofibroblast markers in tumors. Importantly, coimplantation of PFT cells with less-invasive tumor cells in mice markedly promotes tumor dissemination and invasion, leading to an increased number of circulating tumor cells and metastasis. Our findings reveal a mechanism of vascular pericytes in PDGF-BB–promoted cancer invasion and metastasis by inducing PFT, and thus targeting PFT may offer a new treatment option of cancer metastasis.

A Case of Primary Synovial Sarcoma of the Thorax With a Variant SYT-SSX1 Fusion Transcript

With synovial sarcoma (SS) of the thorax, being exceptionally rare, its definite diagnosis is difficult, and the optimal therapy has not yet been established. An examination of our patient, a 64-year-old man with SS using a chest roentgenogram showed a large mass with homogeneous density in the lower two-thirds of the left hemithorax. A computed tomographic image of the chest revealed a large, heterogeneous, enhanced mass in the left hemithorax. Histologic examination of the resected tumor tissues suggested monophasic fibrous SS. A fragment of the SYT-SSX1 fusion transcript, which was smaller than the control, was amplified with reverse transcriptase polymerase chain reaction. Direct sequence analyses revealed the fusion between exon 9 of SYT and exon 5 of SSX1 instead of fusion between exon 10 of SYT and exon 6 of SSX1, which is found in most cases. Although the biological and clinical significance of this rare variant is not yet known, our data present another example of the usefulness of molecular analyses for making a definite diagnosis of SS in unusual sites.

Impact of genetic risk loci for multiple sclerosis on expression of proximal genes in patients

Despite advancements in genetic studies, it is difficult to understand and characterize the functional relevance of disease-associated genetic variants, especially in the context of a complex multifactorial disease such as multiple sclerosis (MS). As a large proportion of expression quantitative trait loci (eQTLs) are context-specific, we performed RNA-Seq in peripheral blood mononuclear cells from MS patients (n = 145) to identify eQTLs in regions centered on 109 MS risk single nucleotide polymorphisms and 7 associated human leukocyte antigen variants. We identified 77 statistically significant eQTL associations, including pseudogenes and non-coding RNAs. Thirty-eight out of 40 testable eQTL effects were colocalized with the disease association signal. As many eQTLs are tissue specific, we aimed to detail their significance in different cell types. Approximately 70% of the eQTLs were replicated and characterized in at least one major peripheral blood mononuclear cell-derived cell type. Furthermore, 40% of eQTLs were found to be more pronounced in MS patients compared with non-inflammatory neurological diseases patients. In addition, we found two single nucleotide polymorphisms to be significantly associated with the proportions of three different cell types. Mapping to enhancer histone marks and predicted transcription factor binding sites added additional functional evidence for eight eQTL regions. As an example, we found that rs71624119, shared with three other autoimmune diseases and located in a primed enhancer (H3K4me1) with potential binding for STAT transcription factors, significantly associates with ANKRD55 expression. This study provides many novel and validated targets for future functional characterization of MS and other diseases.