Essential role of a ThPOK autoregulatory loop in the maintenance of mature CD4+ T cell identity and function.

The transcription factor ThPOK (encoded by the Zbtb7b gene) controls homeostasis and differentiation of mature helper T cells, while opposing their differentiation to CD4+ intraepithelial lymphocytes (IELs) in the intestinal mucosa. Thus CD4 IEL differentiation requires ThPOK transcriptional repression via reactivation of the ThPOK transcriptional silencer element (SilThPOK). In the present study, we describe a new autoregulatory loop whereby ThPOK binds to the SilThPOK to maintain its own long-term expression in CD4 T cells. Disruption of this loop in vivo prevents persistent ThPOK expression, leads to genome-wide changes in chromatin accessibility and derepresses the colonic regulatory T (Treg) cell gene expression signature. This promotes selective differentiation of naive CD4 T cells into GITRloPD-1loCD25lo (Triplelo) Treg cells and conversion to CD4+ IELs in the gut, thereby providing dominant protection from colitis. Hence, the ThPOK autoregulatory loop represents a key mechanism to physiologically control ThPOK expression and T cell differentiation in the gut, with potential therapeutic relevance.

KLF5 governs sphingolipid metabolism and barrier function of the skin.

Stem cells are fundamental units of tissue remodeling whose functions are dictated by lineage-specific transcription factors. Home to epidermal stem cells and their upward-stratifying progenies, skin relies on its secretory functions to form the outermost protective barrier, of which a transcriptional orchestrator has been elusive. KLF5 is a Krüppel-like transcription factor broadly involved in development and regeneration whose lineage specificity, if any, remains unclear. Here we report KLF5 specifically marks the epidermis, and its deletion leads to skin barrier dysfunction in vivo. Lipid envelopes and secretory lamellar bodies are defective in KLF5-deficient skin, accompanied by preferential loss of complex sphingolipids. KLF5 binds to and transcriptionally regulates genes encoding rate-limiting sphingolipid metabolism enzymes. Remarkably, skin barrier defects elicited by KLF5 ablation can be rescued by dietary interventions. Finally, we found that KLF5 is widely suppressed in human diseases with disrupted epidermal secretion, and its regulation of sphingolipid metabolism is conserved in human skin. Altogether, we established KLF5 as a disease-relevant transcription factor governing sphingolipid metabolism and barrier function in the skin, likely representing a long-sought secretory lineage-defining factor across tissue types.

Inflammation and Cancer: Triggers, Mechanisms, and Consequences.

Inflammation predisposes to the development of cancer and promotes all stages of tumorigenesis. Cancer cells, as well as surrounding stromal and inflammatory cells, engage in well-orchestrated reciprocal interactions to form an inflammatory tumor microenvironment (TME). Cells within the TME are highly plastic, continuously changing their phenotypic and functional characteristics. Here, we review the origins of inflammation in tumors, and the mechanisms whereby inflammation drives tumor initiation, growth, progression, and metastasis. We discuss how tumor-promoting inflammation closely resembles inflammatory processes typically found during development, immunity, maintenance of tissue homeostasis, or tissue repair and illuminate the distinctions between tissue-protective and pro-tumorigenic inflammation, including spatiotemporal considerations. Defining the cornerstone rules of engagement governing molecular and cellular mechanisms of tumor-promoting inflammation will be essential for further development of anti-cancer therapies.

Cell-Type-Specific Responses to Interleukin-1 Control Microbial Invasion and Tumor-Elicited Inflammation in Colorectal Cancer.

Chronic inflammation drives the progression of colorectal cancer (CRC). Increased expression of interleukin (IL)-17A is associated with poor prognosis, and IL-17A blockade curbs tumor progression in preclinical models of CRC. Here we examined the impact of IL-1 signaling, a key regulator of the IL-17 pathway, in different cell types within the CRC microenvironment. Genetic deletion of the IL-1 receptor (IL-1R1) in epithelial cells alleviated tumorigenesis in the APC model of CRC, demonstrating a cell-autonomous role for IL-1 signaling in early tumor seed outgrowth. T cell specific ablation of IL-1R1 decreased tumor-elicited inflammation dependent on IL-17 and IL-22, thereby reducing CRC progression. The pro-tumorigenic roles of IL-1 were counteracted by its effects on myeloid cells, particularly neutrophils, where IL-1R1 ablation resulted in bacterial invasion into tumors, heightened inflammation and aggressive CRC progression. Thus, IL-1 signaling elicits cell-type-specific responses, which, in aggregate, set the inflammatory tone of the tumor microenvironment and determine the propensity for disease progression.

ß-Hydroxybutyrate suppresses colorectal cancer.

Colorectal cancer (CRC) is among the most frequent forms of cancer, and new strategies for its prevention and therapy are urgently needed1. Here we identify a metabolite signalling pathway that provides actionable insights towards this goal. We perform a dietary screen in autochthonous animal models of CRC and find that ketogenic diets exhibit a strong tumour-inhibitory effect. These properties of ketogenic diets are recapitulated by the ketone body ß-hydroxybutyrate (BHB), which reduces the proliferation of colonic crypt cells and potently suppresses intestinal tumour growth. We find that BHB acts through the surface receptor Hcar2 and induces the transcriptional regulator Hopx, thereby altering gene expression and inhibiting cell proliferation. Cancer organoid assays and single-cell RNA sequencing of biopsies from patients with CRC provide evidence that elevated BHB levels and active HOPX are associated with reduced intestinal epithelial proliferation in humans. This study thus identifies a BHB-triggered pathway regulating intestinal tumorigenesis and indicates that oral or systemic interventions with a single metabolite may complement current prevention and treatment strategies for CRC.

An Interleukin-23-Interleukin-22 Axis Regulates Intestinal Microbial Homeostasis to Protect from Diet-Induced Atherosclerosis.

Although commensal flora is involved in the regulation of immunity, the interplay between cytokine signaling and microbiota in atherosclerosis remains unknown. We found that interleukin (IL)-23 and its downstream target IL-22 restricted atherosclerosis by repressing pro-atherogenic microbiota. Inactivation of IL-23-IL-22 signaling led to deterioration of the intestinal barrier, dysbiosis, and expansion of pathogenic bacteria with distinct biosynthetic and metabolic properties, causing systemic increase in pro-atherogenic metabolites such as lipopolysaccharide (LPS) and trimethylamine N-oxide (TMAO). Augmented disease in the absence of the IL-23-IL-22 pathway was mediated in part by pro-atherogenic osteopontin, controlled by microbial metabolites. Microbiota transfer from IL-23-deficient mice accelerated atherosclerosis, whereas microbial depletion or IL-22 supplementation reduced inflammation and ameliorated disease. Our work uncovers the IL-23-IL-22 signaling as a regulator of atherosclerosis that restrains expansion of pro-atherogenic microbiota and argues for informed use of cytokine blockers to avoid cardiovascular side effects driven by microbiota and inflammation.

Immunity, inflammation, and cancer.

Inflammatory responses play decisive roles at different stages of tumor development, including initiation, promotion, malignant conversion, invasion, and metastasis. Inflammation also affects immune surveillance and responses to therapy. Immune cells that infiltrate tumors engage in an extensive and dynamic crosstalk with cancer cells, and some of the molecular events that mediate this dialog have been revealed. This review outlines the principal mechanisms that govern the effects of inflammation and immunity on tumor development and discusses attractive new targets for cancer therapy and prevention.

N-glycosylation Regulates Intrinsic IFN-γ Resistance in Colorectal Cancer: Implications for Immunotherapy.

BACKGROUND & AIMS: Advanced colorectal carcinoma (CRC) is characterized by a high frequency of primary immune evasion and refractoriness to immunotherapy. Given the importance of interferon (IFN)-γ in CRC immunosurveillance, we investigated whether and how acquired IFN-γ resistance in tumor cells would promote tumor growth, and whether IFN-γ sensitivity could be restored. METHODS: Spontaneous and colitis-associated CRC development was induced in mice with a specific IFN-γ pathway inhibition in intestinal epithelial cells. The influence of IFN-γ pathway gene status and expression on survival was assessed in patients with CRC. The mechanisms underlying IFN-γ resistance were investigated in CRC cell lines. RESULTS: The conditional knockout of the IFN-γ receptor in intestinal epithelial cells enhanced spontaneous and colitis-associated colon tumorigenesis in mice, and the loss of IFN-γ receptor α (IFNγRα) expression by tumor cells predicted poor prognosis in patients with CRC. IFNγRα expression was repressed in human CRC cells through changes in N-glycosylation, which decreased protein stability via proteasome-dependent degradation, inhibiting IFNγR-signaling. Downregulation of the bisecting N-acetylglucosaminyltransferase III (MGAT3) expression was associated with IFN-γ resistance in all IFN-γ-resistant cells, and highly correlated with low IFNγRα expression in CRC tissues. Both ectopic and pharmacological reconstitution of MGAT3 expression with all-trans retinoic acid increased bisecting N-glycosylation, as well as IFNγRα protein stability and signaling. CONCLUSIONS: Together, our results demonstrated that tumor-associated changes in N-glycosylation destabilize IFNγRα, causing IFN-γ resistance in CRC. IFN-γ sensitivity could be reestablished through the increase in MGAT3 expression, notably via all-trans retinoic acid treatment, providing new prospects for the treatment of immune-resistant CRC.

TET1 and TDG Suppress Inflammatory Response in Intestinal Tumorigenesis: Implications for Colorectal Tumors With the CpG Island Methylator Phenotype.

BACKGROUND & AIMS: Aberrant DNA methylation is frequent in colorectal cancer (CRC), but underlying mechanisms and pathologic consequences are poorly understood. METHODS: We disrupted active DNA demethylation genes Tet1 and/or Tdg from ApcMin mice and characterized the methylome and transcriptome of colonic adenomas. Data were compared to human colonic adenocarcinomas (COAD) in The Cancer Genome Atlas. RESULTS: There were increased numbers of small intestinal adenomas in ApcMin mice expressing the TdgN151A allele, whereas Tet1-deficient and Tet1/TdgN151A-double heterozygous ApcMin colonic adenomas were larger with features of erosion and invasion. We detected reduction in global DNA hypomethylation in colonic adenomas from Tet1- and Tdg-mutant ApcMin mice and hypermethylation of CpG islands in Tet1-mutant ApcMin adenomas. Up-regulation of inflammatory, immune, and interferon response genes was present in Tet1- and Tdg-mutant colonic adenomas compared to control ApcMin adenomas. This up-regulation was also seen in murine colonic organoids and human CRC lines infected with lentiviruses expressing TET1 or TDG short hairpin RNA. A 127-gene inflammatory signature separated colonic adenocarcinomas into 4 groups, closely aligned with their microsatellite or chromosomal instability and characterized by different levels of DNA methylation and DNMT1 expression that anticorrelated with TET1 expression. Tumors with the CpG island methylator phenotype (CIMP) had concerted high DNMT1/low TET1 expression. TET1 or TDG knockdown in CRC lines enhanced killing by natural killer cells. CONCLUSIONS: Our findings reveal a novel epigenetic regulation, linked to the type of genomic instability, by which TET1/TDG-mediated DNA demethylation decreases methylation levels and inflammatory/interferon/immune responses. CIMP in CRC is triggered by an imbalance of methylating activities over demethylating activities. These mice represent a model of CIMP CRC.

IL-22 gets to the stem of colorectal cancer.

Cytokines can provide survival and proliferation signals to cancer cells, thus promoting tumor progression. In this issue of Immunity, Kryczek et al. (2014) reveal that interleukin-22 can also promote "stemness" in human colorectal cancer via transcription factor STAT3-mediated epigenetic regulation of stem cell genes.

Transcription factor T-bet regulates intraepithelial lymphocyte functional maturation.

The intestinal epithelium harbors large populations of activated and memory lymphocytes, yet these cells do not cause tissue damage in the steady state. We investigated how intestinal T cell effector differentiation is regulated upon migration to the intestinal epithelium. Using gene loss- and gain-of-function strategies, as well as reporter approaches, we showed that cooperation between the transcription factors T-bet and Runx3 resulted in suppression of conventional CD4(+) T helper functions and induction of an intraepithelial lymphocyte (IEL) program that included expression of IEL markers such as CD8αα homodimers. Interferon-γ sensing and T-bet expression by CD4(+) T cells were both required for this program, which was distinct from conventional T helper differentiation but shared by other IEL populations, including TCRαß(+)CD8αα(+) IELs. We conclude that the gut environment provides cues for IEL maturation through the interplay between T-bet and Runx3, allowing tissue-specific adaptation of mature T lymphocytes.

Interleukin-17 receptor a signaling in transformed enterocytes promotes early colorectal tumorigenesis.

Interleukin-17A (IL-17A) is a pro-inflammatory cytokine linked to rapid malignant progression of colorectal cancer (CRC) and therapy resistance. IL-17A exerts its pro-tumorigenic activity through its type A receptor (IL-17RA). However, IL-17RA is expressed in many cell types, including hematopoietic, fibroblastoid, and epithelial cells, in the tumor microenvironment, and how IL-17RA engagement promotes colonic tumorigenesis is unknown. Here we show that IL-17RA signals directly within transformed colonic epithelial cells (enterocytes) to promote early tumor development. IL-17RA engagement activates ERK, p38 MAPK, and NF-κB signaling and promotes the proliferation of tumorigenic enterocytes that just lost expression of the APC tumor suppressor. Although IL-17RA signaling also controls the production of IL-6, this mechanism makes only a partial contribution to colonic tumorigenesis. Combined treatment with chemotherapy, which induces IL-17A expression, and an IL-17A neutralizing antibody enhanced the therapeutic responsiveness of established colon tumors. These findings establish IL-17A and IL-17RA as therapeutic targets in colorectal cancer.

Keratinocyte-derived S100A9 modulates neutrophil infiltration and affects psoriasis-like skin and joint disease.

OBJECTIVES: S100A9, an alarmin that can form calprotectin (CP) heterodimers with S100A8, is mainly produced by keratinocytes and innate immune cells. The contribution of keratinocyte-derived S100A9 to psoriasis (Ps) and psoriatic arthritis (PsA) was evaluated using mouse models, and the potential usefulness of S100A9 as a Ps/PsA biomarker was assessed in patient samples. METHODS: Conditional S100A9 mice were crossed with DKO* mice, an established psoriasis-like mouse model based on inducible epidermal deletion of c-Jun and JunB to achieve additional epidermal deletion of S100A9 (TKO* mice). Psoriatic skin and joint disease were evaluated in DKO* and TKO* by histology, microCT, RNA and proteomic analyses. Furthermore, S100A9 expression was analysed in skin, serum and synovial fluid samples of patients with Ps and PsA. RESULTS: Compared with DKO* littermates, TKO* mice displayed enhanced skin disease severity, PsA incidence and neutrophil infiltration. Altered epidermal expression of selective pro-inflammatory genes and pathways, increased epidermal phosphorylation of STAT3 and higher circulating TNFα were observed in TKO* mice. In humans, synovial S100A9 levels were higher than the respective serum levels. Importantly, patients with PsA had significantly higher serum concentrations of S100A9, CP, VEGF, IL-6 and TNFα compared with patients with only Ps, but only S100A9 and CP could efficiently discriminate healthy individuals, patients with Ps and patients with PsA. CONCLUSIONS: Keratinocyte-derived S100A9 plays a regulatory role in psoriatic skin and joint disease. In humans, S100A9/CP is a promising marker that could help in identifying patients with Ps at risk of developing PsA.

A gp130-Src-YAP module links inflammation to epithelial regeneration.

Inflammation promotes regeneration of injured tissues through poorly understood mechanisms, some of which involve interleukin (IL)-6 family members, the expression of which is elevated in many diseases including inflammatory bowel diseases and colorectal cancer. Here we show in mice and human cells that gp130, a co-receptor for IL-6 cytokines, triggers activation of YAP and Notch, transcriptional regulators that control tissue growth and regeneration, independently of the gp130 effector STAT3. Through YAP and Notch, intestinal gp130 signalling stimulates epithelial cell proliferation, causes aberrant differentiation and confers resistance to mucosal erosion. gp130 associates with the related tyrosine kinases Src and Yes, which are activated on receptor engagement to phosphorylate YAP and induce its stabilization and nuclear translocation. This signalling module is strongly activated upon mucosal injury to promote healing and maintain barrier function.

Tumor promotion via injury- and death-induced inflammation.

Inhibition of programmed cell death is considered to be a major aspect of tumorigenesis. Indeed, several key oncogenic transcription factors, such as NF-κB and STAT3, exert their tumor-promoting activity at least in part through upregulation of survival genes. However, many cancers develop in response to chronic tissue injury, in which the resulting cell death increases the tumorigenic potential of the neighboring cells. In this review, we discuss a resolution to this paradox based on cell death-mediated induction of tumor promoting inflammatory cytokines, which enhance cell survival and trigger compensatory proliferation in response to tissue injury.

A Nonpyroptotic IFN-γ-Triggered Cell Death Mechanism in Nonphagocytic Cells Promotes Salmonella Clearance In Vivo.

The cytokine IFN-γ has well-established antibacterial properties against the bacterium Salmonella enterica in phagocytes, but less is known about the effects of IFN-γ on Salmonella-infected nonphagocytic cells, such as intestinal epithelial cells (IECs) and fibroblasts. In this article, we show that exposing human and murine IECs and fibroblasts to IFN-γ following infection with Salmonella triggers a novel form of cell death that is neither pyroptosis nor any of the major known forms of programmed cell death. Cell death required IFN-γ-signaling via STAT1-IRF1-mediated induction of guanylate binding proteins and the presence of live Salmonella in the cytosol. In vivo, ablating IFN-γ signaling selectively in murine IECs led to higher bacterial burden in colon contents and increased inflammation in the intestine of infected mice. Together, these results demonstrate that IFN-γ signaling triggers release of Salmonella from the Salmonella-containing vacuole into the cytosol of infected nonphagocytic cells, resulting in a form of nonpyroptotic cell death that prevents bacterial spread in the gut.

Hepatic expression of HCV RNA-dependent RNA polymerase triggers innate immune signaling and cytokine production.

Innate immunity controls pathogen replication and spread. Yet, certain pathogens, such as Hepatitis C Virus (HCV), escape immune elimination and establish persistent infections that promote chronic inflammation and related diseases. Whereas HCV regulatory proteins that attenuate antiviral responses are known, those that promote inflammation and liver injury remain to be identified. Here, we show that transient expression of HCV RNA-dependent RNA polymerase (RdRp), NS5B, in mouse liver and human hepatocytes results in production of small RNA species that activate innate immune signaling via TBK1-IRF3 and NF-κB and induce cytokine production, including type I interferons (IFN) and IL-6. NS5B-expression also results in liver damage.

Adenoma-linked barrier defects and microbial products drive IL-23/IL-17-mediated tumour growth.

Approximately 2% of colorectal cancer is linked to pre-existing inflammation known as colitis-associated cancer, but most develops in patients without underlying inflammatory bowel disease. Colorectal cancer often follows a genetic pathway whereby loss of the adenomatous polyposis coli (APC) tumour suppressor and activation of ß-catenin are followed by mutations in K-Ras, PIK3CA and TP53, as the tumour emerges and progresses. Curiously, however, 'inflammatory signature' genes characteristic of colitis-associated cancer are also upregulated in colorectal cancer. Further, like most solid tumours, colorectal cancer exhibits immune/inflammatory infiltrates, referred to as 'tumour-elicited inflammation'. Although infiltrating CD4(+) T(H)1 cells and CD8(+) cytotoxic T cells constitute a positive prognostic sign in colorectal cancer, myeloid cells and T-helper interleukin (IL)-17-producing (T(H)17) cells promote tumorigenesis, and a 'T(H)17 expression signature' in stage I/II colorectal cancer is associated with a drastic decrease in disease-free survival. Despite its pathogenic importance, the mechanisms responsible for the appearance of tumour-elicited inflammation are poorly understood. Many epithelial cancers develop proximally to microbial communities, which are physically separated from immune cells by an epithelial barrier. We investigated mechanisms responsible for tumour-elicited inflammation in a mouse model of colorectal tumorigenesis, which, like human colorectal cancer, exhibits upregulation of IL-23 and IL-17. Here we show that IL-23 signalling promotes tumour growth and progression, and development of a tumoural IL-17 response. IL-23 is mainly produced by tumour-associated myeloid cells that are likely to be activated by microbial products, which penetrate the tumours but not adjacent tissue. Both early and late colorectal neoplasms exhibit defective expression of several barrier proteins. We propose that barrier deterioration induced by colorectal-cancer-initiating genetic lesions results in adenoma invasion by microbial products that trigger tumour-elicited inflammation, which in turn drives tumour growth.

Anti-inflammatory natural product goniothalamin reduces colitis-associated and sporadic colorectal tumorigenesis.

The tumor microenvironment offers multiple targets for cancer therapy, including pro-tumorigenic inflammation. Natural compounds represent an enormous source of new anti-inflammatory and anticancer agents. We previously showed that the styryl lactone goniothalamin (GTN) has promising antiproliferative and anti-inflammatory activities. Because inflammation is a major driver of colorectal cancer (CRC), we therefore evaluated the therapeutic and preventive potentials of GTN in colitis, colitis-associated cancer (CAC) and spontaneous CRC. First, in a simplistic model of inflammation in vitro, GTN was able to inhibit cytokine production in bone marrow-derived macrophages induced by lipopolysaccharide. Next, in dextran sulfate sodium (DSS) induced-colitis model, mice treated with GTN displayed restored tissue architecture, increased cell proliferation in the colonic crypts and reduced epithelial damage. Moreover, colon tissue from GTN-treated mice had significantly less expression of the inflammatory genes interleukin 1ß (IL-1ß), tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), S100A9, interleukin 23A (IL-23A), IL-22 and IL-17A In the azoxymethane/DSS model of CAC, GTN reduced tumor multiplicity, load and size. Additionally, GTN suppressed production of IL-6, IL-17 and TNF-α in tumor tissue, as well as abrogated stromal immune cell activation and nuclear translocation of NF-κB. Finally, in a tamoxifen inducible model of sporadic CRC, GTN-treated mice had significantly fewer tumors and decreased levels of IL-17A, IL-6, S100A9 and TNF-α protein within the tumors. These results suggest that GTN possesses anti-inflammatory and antitumor activities and represents a preventive and therapeutic agent modulating the inflammatory environment in the colon during colitis as well as CAC and CRC development.

TLR-signaling and proinflammatory cytokines as drivers of tumorigenesis.

The link between inflammation and cancer was first proposed by R. Virchow. It was later realized that it is chronic inflammation that may promote cancer, whereas acute inflammation can actually block tumor development or even result in cure. Many molecular mediators of these diverse processes have been characterized only during the past 3 decades thanks to the advances in molecular and cellular techniques, as well as due to technologies of reverse genetics. In this chapter we discuss the role of Toll-like receptor (TLR) 4 signaling in cancer and contributions of proinflammatory cytokine signaling (whose expression may be driven by TLR-mediated signals) to tumor-promoting microenvironment. We also discuss recent clinical advances to target these pro-tumorigenic pathways at distinct stages of tumorigenesis.