Transcriptional repression of TFF1 in gastric epithelial cells by CCAAT/enhancer binding protein-beta

IFNγ-dependent silencing of TFF1 during Helicobacter pylori infection

Chronic Helicobacter pylori infection is the leading cause of intestinal-type adenocarcinoma, as prolonged Helicobacter colonization triggers chronic active gastritis, which may evolve into adenocarcinoma of the intestinal type. In this environment, cytokines play a significant role in determining the evolution of the infection. In combination with other factors (genetic, environmental and nutritional), the pro-inflammatory response may trigger pro-oncogenic mechanisms that lead to the silencing of tumour-suppressor genes, such as trefoil factor 1 (TFF1). The latter is known to play a protective role by maintaining the gastric mucosa integrity and retaining H. pylori in the mucus layer, preventing the progression of infection and, consequently, the development of gastric cancer (GC). Since TFF1 expression is reduced during chronic Helicobacter infection with a loss of gastric mucosa protection, we investigated the molecular pathways involved in this reduction. Specifically, we evaluated the effect of some pro-inflammatory cytokines on TFF1 regulation in GC and primary gastric cells by RT-qPCR and luciferase reporter assay analyses and the repressor role of the transcription factor C/EBPβ, overexpressed in gastric-intestinal cancer. Our results show that, among several cytokines, IFNγ stimulates C/EBPβ expression, which acts as a negative regulator of TFF1 by binding its promoter at three different sites.

C/EBPβ regulates homeostatic and oncogenic gastric cell proliferation

Abstract

Cancer of the stomach is among the leading causes of death from cancer worldwide. The transcription factor C/EBPβ is frequently overexpressed in gastric cancer and associated with the suppression of the differentiation marker TFF1. We show that the murine C/EBPβ knockout stomach displays unbalanced homeostasis and reduced cell proliferation and that tumorigenesis of human gastric cancer xenograft is inhibited by knockdown of C/EBPβ. Cross-species comparison of gene expression profiles between C/EBPβ-deficient murine stomach and human gastric cancer revealed a subset of tumors with a C/EBPβ signature. Within this signature, the RUNX1t1 tumor suppressor transcript was down-regulated in 38 % of gastric tumor samples. The RUNX1t1 promoter was frequently hypermethylated and ectopic expression of RUNX1t1 in gastric cancer cells inhibited proliferation and enhanced TFF1 expression. These data suggest that the tumor suppressor activity of both RUNX1t1 and TFF1 are mechanistically connected to C/EBPβ and that cross-regulation between C/EBPβ-RUNX1t1-TFF1 plays an important role in gastric carcinogenesis.

Key message

C/EBPβ controls proliferation and differentiation balance in the stomach.

Homeostatic differentiation/proliferation balance is altered in gastric cancer.

RUNX1t1 is a C/EBPβ-associated tumor suppressor.

RUNX1t1 negatively regulates C/EBPβ pro-oncogenic functions.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-016-1447-7) contains supplementary material, which is available to authorized users.

Interleukin-1B signalling leads to increased survival of gastric carcinoma cells through a CREB-C/EBPβ-associated mechanism

BACKGROUND

Polymorphisms in inflammation-related genes have been associated with a risk of gastric carcinoma (GC). However, the biological mechanisms underlying these associations are still elusive. Our objective was to determine whether chronic inflammation-associated IL1Β signalling, as seen in the context of Helicobacter pylori infection, could be linked to gastric carcinogenesis by modulating the behaviour of gastric epithelial cells.

METHODS

The effect of IL1B was assessed by studying the expression and activation status of the IL1Β-activated transcription factors C/EBPβ and CREB in GC cell lines. Interaction between CREB and C/EBPβ was explored through interference RNA, chromatin immunoprecipitation and chemical inhibition. CREB and C/EBPβ expression was analysed in 66 samples of primary GC and in normal gastric mucosa. GC cell growth was analysed in vitro by BrdU incorporation and in vivo employing a chicken embryo chorioallantoic membrane model.

RESULTS

We found that IL1B regulates the expression/activation status of both C/EBPβ and CREB in GC cells through an ERK1/2-dependent mechanism. Our results show that CREB is a direct transactivator of CEBPB, acting as an upstream effector in this regulatory mechanism. Furthermore, we found CREB to be overexpressed in 94 % of GC samples and significantly associated with C/EBPβ expression (P < 0.05). Finally, we demonstrated both in vitro and in vivo that CREB can mediate IL1B-induced GC cell proliferation.

CONCLUSIONS

Our results support the hypothesis that the effect of chronic inflammation on gastric carcinogenesis, as seen in the context of genetically susceptible individuals infected with Helicobacter pylori, includes the modulation of signalling pathways that regulate survival mechanisms in epithelial cells. IL1B is able to increase the expression/activation status of CREB and its target gene C/EBPβ, which are mandatory for GC cell survival. Our results may help inform new strategies for the prevention and treatment of GC, including the control of chronic inflammation.

Trefoil factors: Gastrointestinal-specific proteins associated with gastric cancer

Trefoil factor family (TFF), composed of TFF1, TFF2, and TFF3, is a cluster of secreted peptides characterized by trefoil domain (s) and C-terminal dimerization domain. TFF1, a gastric tumor suppressor, is a single trefoil peptide originally detected in breast cancer cell lines but expressed mainly in the stomach; TFF2, a candidate of gastric cancer suppressor with two trefoil domains, is abundant in the stomach and duodenal Brunner's glands; and TFF3 is another single trefoil peptide expressed throughout the intestine which can promote the development of gastric carcinoma. According to multiple studies, TFFs play a regulatory function in the mammals' digestive system, namely in mucosal protection and epithelial cell reconstruction, tumor suppression or promotion, signal transduction and the regulation of proliferation and apoptosis. Action mechanisms of TFFs remain unresolved, but the recent demonstration of a GKN (gastrokine) 2-TFF1 heterodimer implicates structural and functional interplay with gastrokines. This review aims to encapsulate the structural and biological characteristics of TFF.

DNA methylation of trefoil factor 1 (TFF1) is associated with the tumorigenesis of gastric carcinoma

Trefoil factor 1 (TFF1) is a tumor suppressor gene that encodes a peptide belonging to the trefoil factor family of protease‑resistant peptides. Although TFF1 expression is frequently lost in gastric carcinomas (GCs), the tumorigenic pathways that are affected have yet to be determined. The aim of the current study was to identify the mechanism(s) by which the TFF1 gene is regulated in gastric carcinogenesis. In this study, TFF1 was shown to be silenced or downregulated in gastric tumor tissue compared with matched non‑cancerous tissue. In addition, human gastric cells weakly expressed TFF1. The hypermethylation status in the promoter CpG islands appeared to be correlated with TFF1 expression levels in gastric cell lines or specimen tissue. Further molecular analysis indicated that the CpG islands play a role in the promoter activity of the TFF1 gene. The expression of TFF1 and DNA methylation of its promoter affected cell proliferation and apoptosis. The expression of TFF1 in gastric cell lines was restored with a demethylating agent, 5‑azacytidine. Low expression of TFF1 in gastric cell lines and cancer tissue is associated with TP 53. In conclusion, the current study demonstrates that DNA methylation is a key mechanism of silencing TFF1 expression in human gastric cells and TFF1 gene hypermethylation of the CpG islands is a potential biomarker for GC.

Loss of TFF1 is associated with activation of NF-κB-mediated inflammation and gastric neoplasia in mice and humans

Trefoil factor 1 (TFF1) is a tumor suppressor gene that encodes a peptide belonging to the trefoil factor family of protease-resistant peptides. Although TFF1 expression is frequently lost in gastric carcinomas, the tumorigenic pathways this affects have not been determined. Here we show that Tff1-knockout mice exhibit age-dependent carcinogenic histological changes in the pyloric antrum of the gastric mucosa, progressing from gastritis to hyperplasia, low-grade dysplasia, high-grade dysplasia, and ultimately malignant adenocarcinoma. The histology and molecular signatures of gastric lesions in the Tff1-knockout mice were consistent with an inflammatory phenotype. In vivo, ex-vivo, and in vitro studies showed that TFF1 expression suppressed TNF-α-mediated NF-κB activation through the TNF receptor 1 (TNFR1)/IκB kinase (IKK) pathway. Consistent with these mouse data, human gastric tissue samples displayed a progressive decrease in TFF1 expression and an increase in NF-κB activation along the multi-step carcinogenesis cascade. Collectively, these results provide evidence that loss of TFF1 leads to activation of IKK complex-regulated NF-κB transcription factors and is an important event in shaping the NF-κB-mediated inflammatory response during the progression to gastric tumorigenesis.

C/EBPbeta represses p53 to promote cell survival downstream of DNA damage independent of oncogenic Ras and p19(Arf)

CCAAT/enhancer-binding protein-beta (C/EBPbeta) is a mediator of cell survival and tumorigenesis. When C/EBPbeta(-/-) mice are treated with carcinogens that produce oncogenic Ras mutations in keratinocytes, they respond with abnormally elevated keratinocyte apoptosis and a block in skin tumorigenesis. Although this aberrant carcinogen-induced apoptosis results from abnormal upregulation of p53, it is not known whether upregulated p53 results from oncogenic Ras and its ability to induce p19(Arf) and/or activate DNA-damage response pathways or from direct carcinogen-induced DNA damage. We report that p19(Arf) is dramatically elevated in C/EBPbeta(-/-) epidermis and that C/EBPbeta represses a p19(Arf) promoter reporter. To determine whether p19(Arf) is responsible for the proapoptotic phenotype in C/EBPbeta(-/-) mice, C/EBPbeta(-/-);p19(Arf-/-) mice were generated. C/EBPbeta(-/-);p19(Arf-/-) mice responded to carcinogen treatment with increased p53 and apoptosis, indicating p19(Arf) is not essential. To ascertain whether oncogenic Ras activation induces aberrant p53 and apoptosis in C/EBPbeta(-/-) epidermis, we generated K14-ER:Ras;C/EBPbeta(-/-) mice. Oncogenic Ras activation induced by 4-hydroxytamoxifen did not produce increased p53 or apoptosis. Finally, when C/EBPbeta(-/-) mice were treated with differing types of DNA-damaging agents, including alkylating chemotherapeutic agents, they displayed aberrant levels of p53 and apoptosis. These results indicate that C/EBPbeta represses p53 to promote cell survival downstream of DNA damage and suggest that inhibition of C/EBPbeta may be a target for cancer cotherapy to increase the efficacy of alkylating chemotherapeutic agents.

Differentiation of the Gastric Mucosa IV. Role of trefoil peptides and IL-6 cytokine family signaling in gastric homeostasis

Gastric trefoil peptides mediate mucosal repair by stimulating cell migration, inhibiting apoptosis and inflammation, and likely augmenting the barrier function of mucus. One of these, tff1, is a gastric-specific tumor suppressor gene, which when repressed is associated with gastric cancer progression. IL-6 family cytokines play an important role in maintaining gastric homeostasis by regulating tff1 and other mediators of mucosal proliferation, inflammation, angiogenesis, and apoptosis. In this review the signaling cascades downstream of the common IL-6 cytokine family coreceptor gp130 that contribute to control of this homeostasis are described, as are the pathological outcomes of imbalancing these pathways.

Decreased survival of C/EBP beta-deficient keratinocytes is due to aberrant regulation of p53 levels and function

Recent studies have identified roles for C/EBPbeta in cellular survival and tumorigenesis, however, the mechanisms through which C/EBPbeta regulates these processes are not fully understood. Previously, we demonstrated that C/EBPbeta(-/-) mice are resistant to carcinogen-induced skin tumorigenesis and in response to topical carcinogen treatment display a 17-fold increase in keratinocyte apoptosis compared to wild-type mice. Here, we have investigated the mechanisms through which C/EBPbeta regulates apoptosis in response to carcinogenic stress. Analysis of carcinogen-treated C/EBPbeta(-/-) mouse skin revealed a striking increase in the number of p53 immunopositive keratinocytes in the epidermis of C/EBPbeta(-/-) mice compared to wild-type mice and this increase was temporally associated with a concomitant anomalous increase in apoptosis. The increased levels of p53 were functional as Mdm2, Bcl-2, C/EBPalpha and p21 were differentially regulated in the epidermis of carcinogen-treated C/EBPbeta(-/-) mice. The increase in p53 protein was not associated with an increase in p53 mRNA levels. To determine whether p53 is required for the increased apoptosis in C/EBPbeta(-/-) mice, C/EBPbeta/p53 compound knockout mice were generated. Carcinogen-treated C/EBPbeta/p53 compound knockout mice did not display increased apoptosis demonstrating p53 is required for the proapoptotic phenotype in C/EBPbeta(-/-) mice. Our results demonstrate that altered keratinocyte survival in C/EBPbeta(-/-) mice results from aberrant regulation of p53 protein and function and indicate C/EBPbeta has a role in the negative regulation of p53 protein levels in response to carcinogen-induced stress.

Early-onset gastric cancers have a different molecular expression profile than conventional gastric cancers

Many studies examine the molecular genetics of gastric cancer, but few look at young patients in particular and there is no comparison of molecular expression between early-onset gastric cancer (< or = 45 years old) and conventional gastric cancers. Expression of cycloxygenase-2 (COX-2) is elevated in gastric adenocarcinomas compared to non-neoplastic mucosa, and in light of studies showing reduced risk of gastric cancer in nonsteroidal anti-inflammatory drug users, we have chosen to investigate the expression of COX-2 and related molecules in 113 early-onset gastric cancers and compare it with 91 conventional gastric cancers, using tissue microarrays. These markers include molecules known to be important in conventional gastric carcinogenesis, such as E-Cadherin, p53, COX-2, Trefoil Factor-1 (TFF1), beta-catenin, p16 and c-myc; as well as molecules not yet described as being important in gastric cancer, such as the transcription factor c-jun, the COX-2 mRNA stabilizer HuR, and C/EBP-beta, a transcription factor for COX-2. All markers showed a statistically significant difference between early-onset gastric cancers and conventional gastric cancers, using a chi2 test. In particular, early-onset gastric cancers displayed a COX-2 Low, TFF1-expressing phenotype, whereas COX-2 overexpression and loss of TFF1 was found in conventional cancers, and this difference between early-onset gastric cancers and conventional cancers remained statistically significant when adjusted for location and histology (P<0.0001 and P = 0.002 respectively). We found that COX-2 overexpression correlates significantly with loss of TFF1 (P = 0.001), overexpression of C/EBP-beta (P<0.001) and cytoplasmic HuR (P = 0.016). COX-2 was significantly associated with p53 positivity (P = 0.003). Abnormalities in E-Cadherin correlated significantly with diffuse phenotype, whereas high expression of COX-2, loss of TFF1 and overexpression of C/EBP-beta correlated with the intestinal phenotype. Our results provide further evidence that early-onset gastric cancer exhibits a distinctive expression profile that may have practical implications.

Overexpression of CEBPbeta correlates with decreased TFF1 in gastric cancer

CCAAT element binding protein beta (C/EBPbeta) is an important regulator of cell growth, differentiation and in promoting tumor invasiveness. C/EBPbeta is located on chromosome 20q, which is amplified in many solid tumors including gastric cancers (GC). We sought to characterize the status of C/EBPbeta expression in GCs, which was recently found to repres TFF1 gene. Microarray analysis revealed overexpression of C/EBPbeta in 25 of 27 (93%) GC when compared to 12 normal gastric tissue samples. RT-PCR analysis confirmed the overexpression of C/EBPbeta transcripts in 54 of 59 (91%) GC. In total, 15 of 18 gastric tumors exhibited at least fivefold higher C/EBPbeta transcript levels compared to their corresponding adjacent normal gastric tissue samples. Moreover, immunohistochemistry analysis demonstrated increased nuclear staining of C/EBPbeta in 10 of 13 GC and at least fourfold overexpression of C/EBPbeta in three primary GC compared to adjacent normal gastric tissue. Furthermore, a striking correlation of decreased TFF1 expression with increased C/EBPbeta was observed in the gastric tumors studied. Microarray analysis demonstrated a loss of TFF1 expression in all 27 GC cases examined, of which 25 exhibited high C/EBPbeta expression compared to normal gastric tissue. RT-PCR analysis revealed loss of TFF1 expression in 56 of 59 gastric tumors in which 54 of these tumors exhibited overexpression of C/EBPbeta. Immunohistochemical analysis revealed overexpression of C/EBPbeta in 10 of 13 gastric tumors that exhibited low expression of TFF1 at the protein level. Thus, overexpression of the transcription factor C/EBPbeta in the majority of GCs is a novel finding.

Transcriptional repression of peroxisome proliferator-activated receptor beta/delta in murine keratinocytes by CCAAT/enhancer-binding proteins

The roles of peroxisome proliferator-activated receptors (PPARs) and CCAAT/enhancer-binding proteins (C/EBPs) in keratinocyte and sebocyte differentiation suggest that both families of transcription factors closely interact in the skin. Initial characterization of the mouse PPARbeta promoter revealed an AP-1 site that is crucial for the regulation of PPARbeta expression in response to inflammatory cytokines in the skin. We now present evidence for a novel regulatory mechanism of the expression of the PPARbeta gene by which two members of the C/EBP family of transcription factors inhibit its basal promoter activity in mouse keratinocytes. We first demonstrate that C/EBPalpha and C/EBPbeta, but not C/EBPdelta, inhibit the expression of PPARbeta through the recruitment of a transcriptional repressor complex containing HDAC-1 to a specific C/EBP binding site on the PPARbeta promoter. Consistent with this repression, the expression patterns of PPARbeta and C/EBPs are mutually exclusive in keratinocytes of the interfollicular epidermis and hair follicles in mouse developing skin. This work reveals the importance of the regulatory interplay between PPARbeta and C/EBP transcription factors in the control of proliferation and differentiation in this organ. Such insights are crucial for the understanding of the molecular control regulating the balance between proliferation and differentiation in many cell types including keratinocytes.