High-fat-diet-mediated dysbiosis promotes intestinal carcinogenesis independently of obesity.

Several features common to a Western lifestyle, including obesity and low levels of physical activity, are known risk factors for gastrointestinal cancers. There is substantial evidence suggesting that diet markedly affects the composition of the intestinal microbiota. Moreover, there is now unequivocal evidence linking dysbiosis to cancer development. However, the mechanisms by which high-fat diet (HFD)-mediated changes in the microbial community affect the severity of tumorigenesis in the gut remain to be determined. Here we demonstrate that an HFD promotes tumour progression in the small intestine of genetically susceptible, K-ras(G12Dint), mice independently of obesity. HFD consumption, in conjunction with K-ras mutation, mediated a shift in the composition of the gut microbiota, and this shift was associated with a decrease in Paneth-cell-mediated antimicrobial host defence that compromised dendritic cell recruitment and MHC class II molecule presentation in the gut-associated lymphoid tissues. When butyrate was administered to HFD-fed K-ras(G12Dint) mice, dendritic cell recruitment in the gut-associated lymphoid tissues was normalized, and tumour progression was attenuated. Importantly, deficiency in MYD88, a signalling adaptor for pattern recognition receptors and Toll-like receptors, blocked tumour progression. The transfer of faecal samples from HFD-fed mice with intestinal tumours to healthy adult K-ras(G12Dint) mice was sufficient to transmit disease in the absence of an HFD. Furthermore, treatment with antibiotics completely blocked HFD-induced tumour progression, suggesting that distinct shifts in the microbiota have a pivotal role in aggravating disease. Collectively, these data underscore the importance of the reciprocal interaction between host and environmental factors in selecting a microbiota that favours carcinogenesis, and they suggest that tumorigenesis is transmissible among genetically predisposed individuals.

IkappaBbeta is an essential co-activator for LPS-induced IL-1beta transcription in vivo.

Inhibitor of κB (IκB) ß (IκBß) represents one of the major primary regulators of NF-κB in mammals. In contrast to the defined regulatory interplay between NF-κB and IκBα, much less is known about the biological function of IκBß. To elucidate the physiological role of IκBß in NF-κB signaling in vivo, we generated IκBß-deficient mice. These animals proved to be highly refractory to LPS-induced lethality, accompanied by a strong reduction in sepsis-associated cytokine production. In response to LPS, IκBß is recruited to the IL-1ß promoter forming a complex with the NF-κB subunits RelA/c-Rel required for IL-1ß transcription. Further transcriptome analysis of LPS-stimulated wild-type and IκBß-deficient BM-derived macrophages revealed several other genes with known regulatory functions in innate immunity arguing that a subset of NF-κB target genes is under control of IκBß. Collectively, these findings provide an essential proinflammatory role for IκBß in vivo, and establish a critical function for IκBß as a transcriptional coactivator under inflammatory conditions.