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.

Intestinal-specific activatable Myb initiates colon tumorigenesis in mice.

Transcription factor Myb is overexpressed in most colorectal cancers (CRC). Patients with CRC expressing the highest Myb are more likely to relapse. We previously showed that mono-allelic loss of Myb in an Adenomatous polyposis coli (APC)-driven CRC mouse model (Apc(Min/+)) significantly improves survival. Here we directly investigated the association of Myb with poor prognosis and how Myb co-operates with tumor suppressor genes (TSGs) (Apc) and cell cycle regulator, p27. Here we generated the first intestinal-specific, inducible transgenic model; a MybER transgene encoding a tamoxifen-inducible fusion protein between Myb and the estrogen receptor-α ligand-binding domain driven by the intestinal-specific promoter, Gpa33. This was to mimic human CRC with constitutive Myb activity in a highly tractable mouse model. We confirmed that the transgene was faithfully expressed and inducible in intestinal stem cells (ISCs) before embarking on carcinogenesis studies. Activation of the MybER did not change colon homeostasis unless one p27 allele was lost. We then established that MybER activation during CRC initiation using a pro-carcinogen treatment, azoxymethane (AOM), augmented most measured aspects of ISC gene expression and function and accelerated tumorigenesis in mice. CRC-associated symptoms of patients including intestinal bleeding and anaemia were faithfully mimicked in AOM-treated MybER transgenic mice and implicated hypoxia and vessel leakage identifying an additional pathogenic role for Myb. Collectively, the results suggest that Myb expands the ISC pool within which CRC is initiated while co-operating with TSG loss. Myb further exacerbates CRC pathology partly explaining why high MYB is a predictor of worse patient outcome.

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 gp130(F/F) mouse model, in which TLR2 promotes the growth of gastric tumours. Genetic ablation of Myd88 in gp130(F/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 gp130(F/F) mice. By contrast, the tumour burden in gp130(F/F):Mal(-/-) mice was equivalent to their gp130(F/F) littermates. At the molecular level, suppressed tumourigenesis in gp130(F/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 gp130(F/F):Mal(-/-) and gp130(F/F):Myd88(-/-) mice remained unaltered compared with gp130(F/F) mice. Collectively, our data reveal a differential, but inflammation-independent, requirement for Mal and MyD88 during TLR2-promoted gastric tumourigenesis.