Hazel Tye

STAT3 and STAT1 mediate IL-11–dependent and inflammation-associated gastric tumorigenesis in gp130 receptor mutant mice

Deregulated activation of STAT3 is frequently associated with many human hematological and epithelial malignancies, including gastric cancer. While exaggerated STAT3 signaling facilitates an antiapoptotic, proangiogenic, and proproliferative environment for neoplastic cells, the molecular mechanisms leading to STAT3 hyperactivation remain poorly understood. Using the gp130(Y757F/Y757F) mouse model of gastric cancer, which carries a mutated gp130 cytokine receptor signaling subunit that cannot bind the negative regulator of cytokine signaling SOCS3 and is characterized by hyperactivation of the signaling molecules STAT1 and STAT3, we have provided genetic evidence that IL-11 promotes chronic gastric inflammation and associated tumorigenesis. Expression of IL-11 was increased in gastric tumors in gp130(Y757F/Y757F) mice, when compared with unaffected gastric tissue in wild-type mice, while gp130(Y757F/Y757F) mice lacking the IL-11 ligand-binding receptor subunit (IL-11Ralpha) showed normal gastric STAT3 activation and IL-11 expression and failed to develop gastric tumors. Furthermore, reducing STAT3 activity in gp130(Y757F/Y757F) mice, either genetically or by therapeutic administration of STAT3 antisense oligonucleotides, normalized gastric IL-11 expression and alleviated gastric tumor burden. Surprisingly, the genetic reduction of STAT1 expression also reduced gastric tumorigenesis in gp130(Y757F/Y757F) mice and coincided with reduced gastric inflammation and IL-11 expression. Collectively, our data have identified IL-11 as a crucial cytokine promoting chronic gastric inflammation and associated tumorigenesis mediated by excessive activation of STAT3 and STAT1.

STAT3-Driven Upregulation of TLR2 Promotes Gastric Tumorigenesis Independent of Tumor Inflammation

Gastric cancer (GC) is associated with chronic inflammation; however, the molecular mechanisms promoting tumorigenesis remain ill defined. Using a GC mouse model driven by hyperactivation of the signal transducer and activator of transcription (STAT)3 oncogene, we show that STAT3 directly upregulates the epithelial expression of the inflammatory mediator Toll-like receptor (TLR)2 in gastric tumors. Genetic and therapeutic targeting of TLR2 inhibited gastric tumorigenesis, but not inflammation, characterized by reduced proliferation and increased apoptosis of the gastric epithelium. Increased STAT3 pathway activation and TLR2 expression were also associated with poor GC patient survival. Collectively, our data reveal an unexpected role for TLR2 in the oncogenic function of STAT3 that may represent a therapeutic target in GC.

Inflammation modulates the expression of the intestinal mucins MUC2 and MUC4 in gastric tumors.

Infection of gastric mucosa by Helicobacter pylori induces an inflammatory response with increased levels of proinflammatory cytokines. Among them, tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 induce the activation of signaling pathways that regulate genes expression, such as MUC2 and MUC4 intestinal mucins ectopically detected in gastric tumors. This study evaluated if the predominant inflammatory cell type correlates with MUC2 and MUC4 expression in human intestinal gastric tumors (n=78). In addition, we analyzed the regulatory effects of the associated inflammatory signaling pathways on their expression in gastric cancer cell lines, and in a mouse model with hyperactivated STAT3 signaling pathway. Tumors with predominant lymphoplasmocytic infiltrate (chronic inflammation), presented higher levels of MUC2 and were more differentiated than tumors with predominant polymorphonuclear infiltrate (acute inflammation). These differences can be attributed to specific cytokines, because TNF-α and IL-1β induced MUC2 but no MUC4 expression in gastric cancer cell lines. The two groups of tumors expressed similar levels of MUC4 that correlated with the expression of STAT3 transcription factor, implicated in the activation of genes through the IL-6 pathway. In gastric tissues from gp130+/+, gp130Y757F/Y757F and gp130Y757F/Y757F Stat3−/+ mice, Muc2 was not detected, whereas Muc4 was found in the gastric tumors developed in the gp130Y757F/Y757F mice, with hyperactivated STAT3. These data indicate that the signaling pathways associated with the inflammatory response can modulate the expression of MUC2 and MUC4 intestinal mucin genes, in human and mouse gastric tumors.

Differential role of MyD88 and Mal/TIRAP in TLR2-mediated gastric tumourigenesis.

Signalling by the toll-like receptor (TLR) family of pathogen recognition receptors has emerged as a key molecular component in the pathogenesis of an increasing number of inflammatory-related cancers, among which gastric cancer rates as the second most lethal cancer world-wide. The myeloid differentiation factor 88 (MyD88) adapter molecule has a critical role in mediating innate immune signalling by members of the TLR and interleukin (IL)-1 families, and has been associated with either pro- or antitumourigenic responses in various cancer models. However, little is known about the in vivo role of MyD88 adapter-like (Mal)/TIR-domain containing adapter protein (TIRAP), which is restricted to facilitating TLR4 and TLR2 signalling. To interrogate the role of these innate immune signalling components in gastric tumourigenesis, here we have employed the spontaneous gastric cancer gp130F/F mouse model, in which TLR2 promotes the growth of gastric tumours. Genetic ablation of Myd88 in gp130F/F mice suppressed tumourigenesis and was associated with increased apoptosis and reduced proliferation in the gastric tumour epithelium, comparable to that observed previously upon deletion of Tlr2 in gp130F/F mice. By contrast, the tumour burden in gp130F/F:Mal−/− mice was equivalent to their gp130F/F littermates. At the molecular level, suppressed tumourigenesis in gp130F/F:Myd88−/− mice correlated with reduced expression and activation of TLR2-regulated protumourigenic genes and signalling pathways, respectively. Consistent with the previously defined non-essential role for TLR2 in gastric tumour inflammation, the extent of inflammatory cell infiltrates in gastric tumours from gp130F/F:Mal−/− and gp130F/F:Myd88−/− mice remained unaltered compared with gp130F/F mice. Collectively, our data reveal a differential, but inflammation-independent, requirement for Mal and MyD88 during TLR2-promoted gastric tumourigenesis.

Tying the knot between cytokine and toll-like receptor signaling in gastrointestinal tract cancers

Inflammation‐associated malignancies of the gastrointestinal tract (GI), including those of the stomach and colon, collectively rank as the highest cause of cancer‐related deaths worldwide. It has been well documented that the deregulated activation of the archetypal pro‐inflammatory and oncogenic transcription factors nuclear factor‐kappa B (NF‐κB) and signal transducer and activator of transcription (STAT)3 is a common feature of GI cancers that invariably correlates with poor prognosis. Signal transducer and activator of transcription 3 and NF‐κB are key downstream signal transducers of the interleukin (IL)‐6 cytokine and toll‐like receptor (TLR) families, respectively, and until recently, the potential involvement of these two families in the pathogenesis of cancer has been investigated in isolation. However, there is now emerging evidence of the complex interplay between the IL‐6 cytokine and TLR families in GI tract cancers, with a surprising twist in the identification of a non‐immune role for specific TLR family members. In this review, we discuss the molecular mechanisms associated with cross‐talk between the IL‐6 cytokine family/STAT3 signaling network and the TLR family/NF‐κB signaling network, and we address the potential benefit of their therapeutic targeting in gastric and colorectal cancers.

Granzyme M has a critical role in providing innate immune protection in ulcerative colitis

Inflammatory bowel disease (IBD) is an immunoregulatory disorder, associated with a chronic and inappropriate mucosal immune response to commensal bacteria, underlying disease states such as ulcerative colitis (UC) and Crohn’s disease (CD) in humans. Granzyme M (GrzM) is a serine protease expressed by cytotoxic lymphocytes, in particular natural killer (NK) cells. Granzymes are thought to be involved in triggering cell death in eukaryotic target cells; however, some evidence supports their role in inflammation. The role of GrzM in the innate immune response to mucosal inflammation has never been examined. Here, we discover that patients with UC, unlike patients with CD, display high levels of GrzM mRNA expression in the inflamed colon. By taking advantage of well-established models of experimental UC, we revealed that GrzM-deficient mice have greater levels of inflammatory indicators during dextran sulfate sodium (DSS)-induced IBD, including increased weight loss, greater colon length reduction and more severe intestinal histopathology. The absence of GrzM expression also had effects on gut permeability, tissue cytokine/chemokine dynamics, and neutrophil infiltration during disease. These findings demonstrate, for the first time, that GrzM has a critical role during early stages of inflammation in UC, and that in its absence colonic inflammation is enhanced.

Inflammasome Adaptor ASC Suppresses Apoptosis of Gastric Cancer Cells by an IL18-Mediated Inflammation-Independent Mechanism

Inflammasomes are key regulators of innate immunity in chronic inflammatory disorders and autoimmune diseases, but their role in inflammation-associated tumorigenesis remains ill-defined. Here we reveal a protumorigenic role in gastric cancer for the key inflammasome adaptor apoptosis-related speck-like protein containing a CARD (ASC) and its effector cytokine IL18. Genetic ablation of ASC in the gp130F/F spontaneous mouse model of intestinal-type gastric cancer suppressed tumorigenesis by augmenting caspase-8-like apoptosis in the gastric epithelium, independently from effects on myeloid cells and mucosal inflammation. This phenotype was characterized by reduced activation of caspase-1 and NF-κB activation and reduced expression of mature IL18, but not IL1β, in gastric tumors. Genetic ablation of IL18 in the same model also suppressed gastric tumorigenesis, whereas blockade of IL1β and IL1α activity upon genetic ablation of the IL1 receptor had no effect. The specific protumorigenic role for IL18 was associated with high IL18 gene expression in the gastric tumor epithelium compared with IL1β, which was preferentially expressed in immune cells. Supporting an epithelial-specific role for IL18, we found it to be highly secreted from human gastric cancer cell lines. Moreover, IL18 blockade either by a neutralizing anti-IL18 antibody or by CRISPR/Cas9-driven deletion of ASC augmented apoptosis in human gastric cancer cells. In clinical specimens of human gastric cancer tumors, we observed a significant positive correlation between elevated mature IL18 protein and ASC mRNA levels. Collectively, our findings reveal the ASC/IL18 signaling axis as a candidate therapeutic target in gastric cancer.Significance: Inflammasome activation that elevates IL18 helps drive gastric cancer by protecting cancer cells against apoptosis, with potential implications for new therapeutic strategies in this setting. Cancer Res; 78(5); 1293-307. ©2017 AACR.