The effects of enteropathogenic Escherichia coli on the classical genetic pathways of colorectal cancer, using in vitro and ex vivo human models

Despite high prevalence and mortality, and an excellent knowledge of the aetiologic genetic changes of sporadic colorectal cancer, the causes of this disease are not well defined. DNA mismatch repair and Wnt signalling (via (3-catenin) are classic genetic pathways altered during colorectal carcinogenesis, currently there is little evidence to suggest how gene-environment interactions could influence these pathways. Recent studies have found that adherent Escherichia coli are associated with colonic adenocarcinomas, leading to speculation that in similarity to gastric cancer, bacterial infection has a central role in colonic tumourigenesis. The attaching and effacing (AE) bacterium enteropathogenic E. coli (EPEC) intimately attaches to the intestinal epithelium and is found in 2.5-10% of healthy children and adults in developed countries. When attaching to host cells, EPEC secretes effector proteins that have wide ranging effects on host molecular biology. The aim of this study was to test the hypothesis that EPEC infection causes molecular changes in host epithelial cells that predispose to neoplastic transformation. Model systems for EPEC infection were successfully established using in vitro co-culture with human colorectal cancer cell lines and co-culture with ex vivo human colonic mucosa; human adenocarcinomas were also probed for the presence of AE E. coli. Immunofluorescence identified mucosa associated AE E. coli in 5/20 (25%) adenocarcinomas. When co-cultured with normal human colonic mucosa, EPEC entered 10.6% of crypts, and closely associated with cells in the proliferative progenitor compartment. Mass spectrometry and microarray analysis validated the in vitro model and revealed a range of proteomic and transcriptomic effects in EPEC infected cells. Western blots and quantitative immunofluorescence demonstrated that EPEC downregulated the expression of key DNA mismatch repair proteins MSH2 and MLH1 and the Wnt signalling / adhesion protein (3-catenin in vitro. Disruption of DNA mismatch repair is a causative factor in the development of many hereditary and sporadic colorectal cancers, and disruption of cell-cell adhesion has the potential to subvert normal colonic crypt homeostasis. These novel findings therefore suggest that chronic EPEC infection can predispose to cancer development by increasing the susceptibility of colonic epithelial cells to mutation by dietary or other carcinogens, and by altering expression of cytoskeletal and cell attachment protein

An Escherichia coli effector protein promotes host mutation via depletion of DNA mismatch repair proteins.

Enteropathogenic Escherichia coli (EPEC) is an attaching and effacing (A/E) human pathogen that causes diarrhea during acute infection, and it can also sustain asymptomatic colonization. A/E E. coli depletes host cell DNA mismatch repair (MMR) proteins in colonic cell lines and has been detected in colorectal cancer (CRC) patients. However, until now, a direct link between infection and host mutagenesis has not been fully demonstrated. Here we show that the EPEC-secreted effector protein EspF is critical for complete EPEC-induced depletion of MMR proteins. The mechanism of EspF activity on MMR protein was posttranscriptional and dependent on EspF mitochondrial targeting. EPEC infection also induced EspF-independent elevation of host reactive oxygen species levels. Moreover, EPEC infection significantly increased spontaneous mutation frequency in host cells, and this effect was dependent on mitochondrially targeted EspF. Taken together, these results support the hypothesis that A/E E. coli can promote colorectal carcinogenesis in humans

Metabolic regulation by p53 family members

The function of p53 is best understood in response to genotoxic stress, but increasing evidence suggests that p53 also plays a key role in the regulation of metabolic homeostasis. p53 and its family members directly influence various metabolic pathways, enabling cells to respond to metabolic stress. These functions are likely to be important for restraining the development of cancer but could also have a profound effect on the development of metabolic diseases, including diabetes. A better understanding of the metabolic functions of p53 family members may aid in the identification of therapeutic targets and reveal novel uses for p53-modulating drugs

Serine, but not glycine, supports one-carbon metabolism and proliferation of cancer cells

Previous work has shown that some cancer cells are highly dependent on serine/glycine uptake for proliferation. Although serine and glycine can be interconverted and either might be used for nucleotide synthesis and one-carbon metabolism, we show that exogenous glycine cannot replace serine to support cancer cell proliferation. Cancer cells selectively consumed exogenous serine, which was converted to intracellular glycine and one-carbon units for building nucleotides. Restriction of exogenous glycine or depletion of the glycine cleavage system did not impede proliferation. In the absence of serine, uptake of exogenous glycine was unable to support nucleotide synthesis. Indeed, higher concentrations of glycine inhibited proliferation. Under these conditions, glycine was converted to serine, a reaction that would deplete the one-carbon pool. Providing one-carbon units by adding formate rescued nucleotide synthesis and growth of glycine-fed cells. We conclude that nucleotide synthesis and cancer cell proliferation are supported by serine—rather than glycine—consumption

SERIneALanine Killer: SPT promiscuity inhibits tumour growth via intra-tumoral deoxysphingolipid production

No abstract available

A neuronal relay mediates a nutrient responsive gut/fat body axis regulating energy homeostasis in adult Drosophila

The control of systemic metabolic homeostasis involves complex inter-tissue programs that coordinate energy production, storage, and consumption, to maintain organismal fitness upon environmental challenges. The mechanisms driving such programs are largely unknown. Here, we show that enteroendocrine cells in the adult Drosophila intestine respond to nutrients by secreting the hormone Bursicon α, which signals via its neuronal receptor DLgr2. Bursicon α/DLgr2 regulate energy metabolism through a neuronal relay leading to the restriction of glucagon-like, adipokinetic hormone (AKH) production by the corpora cardiaca and subsequent modulation of AKH receptor signaling within the adipose tissue. Impaired Bursicon α/DLgr2 signaling leads to exacerbated glucose oxidation and depletion of energy stores with consequent reduced organismal resistance to nutrient restrictive conditions. Altogether, our work reveals an intestinal/neuronal/adipose tissue inter-organ communication network that is essential to restrict the use of energy and that may provide insights into the physiopathology of endocrine-regulated metabolic homeostasis

The KRAS-BCAA-BCAT2 axis in PDAC development

Understanding the metabolic rewiring of pancreatic ductal adenocarcinoma is an emerging strategy for identifying cancer-associated liabilities and improving treatment. A new study now elucidates the function of the transaminase BCAT2 in the early stages of tumor development, providing insights that could stimulate novel therapeutic strategies

Serine one-carbon catabolism with formate overflow

Serine catabolism to glycine and a one-carbon unit has been linked to the anabolic requirements of proliferating mammalian cells. However, genome-scale modeling predicts a catabolic role with one-carbon release as formate. We experimentally prove that in cultured cancer cells and nontransformed fibroblasts, most of the serine-derived one-carbon units are released from cells as formate, and that formate release is dependent on mitochondrial reverse 10-CHO-THF synthetase activity. We also show that in cancer cells, formate release is coupled to mitochondrial complex I activity, whereas in nontransformed fibroblasts, it is partially insensitive to inhibition of complex I activity. We demonstrate that in mice, about 50% of plasma formate is derived from serine and that serine starvation or complex I inhibition reduces formate synthesis in vivo. These observations transform our understanding of one-carbon metabolism and have implications for the treatment of diabetes and cancer with complex I inhibitors

One-carbon metabolism in cancer

Cells require one-carbon units for nucleotide synthesis, methylation and reductive metabolism, and these pathways support the high proliferative rate of cancer cells. As such, anti-folates, drugs that target one-carbon metabolism, have long been used in the treatment of cancer. Amino acids, such as serine are a major one-carbon source, and cancer cells are particularly susceptible to deprivation of one-carbon units by serine restriction or inhibition of de novo serine synthesis. Recent work has also begun to decipher the specific pathways and sub-cellular compartments that are important for one-carbon metabolism in cancer cells. In this review we summarise the historical understanding of one-carbon metabolism in cancer, describe the recent findings regarding the generation and usage of one-carbon units and explore possible future therapeutics that could exploit the dependency of cancer cells on one-carbon metabolism

Colon cancer cells evade drug action by enhancing drug metabolism [pre-print]

Colorectal cancer (CRC) is the second most deadly cancer worldwide. One key reason is the failure of therapies that target RAS proteins, which represent approximately 40% of CRC cases. Despite the recent discovery of multiple alternative signalling pathways that contribute to resistance, durable therapies remain an unmet need. Here, we use liquid chromatography/mass spectrometry (LC/MS) analyses on CRC tumour models to identify multiple metabolites in the glucuronidation pathway-a toxin clearance pathway-as upregulated in trametinib-resistant (" ") tumours compared to trametinib-sensitive tumours. Elevating glucuronidation was sufficient to direct trametinib resistance in animals while, conversely, inhibiting different steps along the glucuronidation pathway strongly reversed resistance to trametinib. For example, blocking an initial HDAC1-mediated deacetylation step with the FDA-approved drug vorinostat strongly suppressed trametinib resistance in tumours. We provide functional evidence that pairing oncogenic RAS with hyperactive WNT activity strongly elevates PI3K/AKT/GLUT signalling, which in turn directs elevated glucose and subsequent glucuronidation. Finally, we show that this mechanism of trametinib resistance is conserved in an mouse CRC tumour organoid model. Our observations demonstrate a key mechanism by which oncogenic RAS/WNT activity promotes increased drug clearance in CRC. The majority of targeted therapies are glucuronidated, and our results provide a specific path towards abrogating this resistance in clinical trials