Oncogenic BRAF, unrestrained by TGFβ-receptor signalling, drives right-sided colonic tumorigenesis

Right-sided (proximal) colorectal cancer (CRC) has a poor prognosis and a distinct mutational profile, characterized by oncogenic BRAF mutations and aberrations in mismatch repair and TGFβ signalling. Here, we describe a mouse model of right-sided colon cancer driven by oncogenic BRAF and loss of epithelial TGFβ-receptor signalling. The proximal colonic tumours that develop in this model exhibit a foetal-like progenitor phenotype (Ly6a/Sca1+) and, importantly, lack expression of Lgr5 and its associated intestinal stem cell signature. These features are recapitulated in human BRAF-mutant, right-sided CRCs and represent fundamental differences between left- and right-sided disease. Microbial-driven inflammation supports the initiation and progression of these tumours with foetal-like characteristics, consistent with their predilection for the microbe-rich right colon and their antibiotic sensitivity. While MAPK-pathway activating mutations drive this foetal-like signature via ERK-dependent activation of the transcriptional coactivator YAP, the same foetal-like transcriptional programs are also initiated by inflammation in a MAPK-independent manner. Importantly, in both contexts, epithelial TGFβ-receptor signalling is instrumental in suppressing the tumorigenic potential of these foetal-like progenitor cells

Control of translation elongation in health and disease.

Regulation of protein synthesis makes a major contribution to post-transcriptional control pathways. During disease, or under stress, cells initiate processes to reprogramme protein synthesis and thus orchestrate the appropriate cellular response. Recent data show that the elongation stage of protein synthesis is a key regulatory node for translational control in health and disease. There is a complex set of factors that individually affect the overall rate of elongation and, for the most part, these influence either transfer RNA (tRNA)- and eukaryotic elongation factor 1A (eEF1A)-dependent codon decoding, and/or elongation factor 2 (eEF2)-dependent ribosome translocation along the mRNA. Decoding speeds depend on the relative abundance of each tRNA, the cognate:near-cognate tRNA ratios and the degree of tRNA modification, whereas eEF2-dependent ribosome translocation is negatively regulated by phosphorylation on threonine-56 by eEF2 kinase. Additional factors that contribute to the control of the elongation rate include epigenetic modification of the mRNA, coding sequence variation and the expression of eIF5A, which stimulates peptide bond formation between proline residues. Importantly, dysregulation of elongation control is central to disease mechanisms in both tumorigenesis and neurodegeneration, making the individual key steps in this process attractive therapeutic targets. Here, we discuss the relative contribution of individual components of the translational apparatus (e.g. tRNAs, elongation factors and their modifiers) to the overall control of translation elongation and how their dysregulation contributes towards disease processes

RASSF1A uncouples Wnt from Hippo signalling and promotes YAP mediated differentiation via p73

Transition from pluripotency to differentiation is a pivotal yet poorly understood developmental step. Here, we show that the tumour suppressor RASSF1A is a key player driving the early specification of cell fate. RASSF1A acts as a natural barrier to stem cell self-renewal and iPS cell generation, by switching YAP from an integral component in the β-catenin-TCF pluripotency network to a key factor that promotes differentiation. We demonstrate that epigenetic regulation of the Rassf1A promoter maintains stemness by allowing a quaternary association of YAP–TEAD and β-catenin–TCF3 complexes on the Oct4 distal enhancer. However, during differentiation, promoter demethylation allows GATA1-mediated RASSF1A expression which prevents YAP from contributing to the TEAD/β-catenin–TCF3 complex. Simultaneously, we find that RASSF1A promotes a YAP–p73 transcriptional programme that enables differentiation. Together, our findings demonstrate that RASSF1A mediates transcription factor selection of YAP in stem cells, thereby acting as a functional “switch” between pluripotency and initiation of differentiation

Oncogenic BRAF, unrestrained by TGFβ-receptor signalling, drives right-sided colonic tumorigenesis

Right-sided (proximal) colorectal cancer (CRC) has a poor prognosis and a distinct mutational profile, characterized by oncogenic BRAF mutations and aberrations in mismatch repair and TGFβ signalling. Here, we describe a mouse model of right-sided colon cancer driven by oncogenic BRAF and loss of epithelial TGFβ-receptor signalling. The proximal colonic tumours that develop in this model exhibit a foetal-like progenitor phenotype (Ly6a/Sca1+) and, importantly, lack expression of Lgr5 and its associated intestinal stem cell signature. These features are recapitulated in human BRAF-mutant, right-sided CRCs and represent fundamental differences between left- and right-sided disease. Microbial-driven inflammation supports the initiation and progression of these tumours with foetal-like characteristics, consistent with their predilection for the microbe-rich right colon and their antibiotic sensitivity. While MAPK-pathway activating mutations drive this foetal-like signature via ERK-dependent activation of the transcriptional coactivator YAP, the same foetal-like transcriptional programs are also initiated by inflammation in a MAPK-independent manner. Importantly, in both contexts, epithelial TGFβ-receptor signalling is instrumental in suppressing the tumorigenic potential of these foetal-like progenitor cells

Metabolic profiling stratifies colorectal cancer and reveals adenosylhomocysteinase as a therapeutic target

The genomic landscape of colorectal cancer (CRC) is shaped by inactivating mutations in tumour suppressors such as APC, and oncogenic mutations such as mutant KRAS. Here we used genetically engineered mouse models, and multimodal mass spectrometry-based metabolomics to study the impact of common genetic drivers of CRC on the metabolic landscape of the intestine. We show that untargeted metabolic profiling can be applied to stratify intestinal tissues according to underlying genetic alterations, and use mass spectrometry imaging to identify tumour, stromal and normal adjacent tissues. By identifying ions that drive variation between normal and transformed tissues, we found dysregulation of the methionine cycle to be a hallmark of APC-deficient CRC. Loss of Apc in the mouse intestine was found to be sufficient to drive expression of one of its enzymes, adenosylhomocysteinase (AHCY), which was also found to be transcriptionally upregulated in human CRC. Targeting of AHCY function impaired growth of APC-deficient organoids in vitro, and prevented the characteristic hyperproliferative/crypt progenitor phenotype driven by acute deletion of Apc in vivo, even in the context of mutant Kras. Finally, pharmacological inhibition of AHCY reduced intestinal tumour burden in ApcMin/+ mice indicating its potential as a metabolic drug target in CRC

Epigenetic silencing of RASSF1A promotes tumourigenesis via alternative transcript expression, SFK activation and exosome secretion

Loss of the tumour-suppressor gene RASSF1A upon promoter methylation is one of the most frequent events in sporadic human malignancies. Loss of RASSF1A is associated with progression and pathogenesis of solid tumours; and more aggressive clinical phenotype, leading to poor prognosis in breast, lung and colon cancers, amongst others. RASSF1A functions in a number of cellular processes, inducing apoptosis in response to DNA damage, cell cycle arrest and growth control. In tumours with RASSF1 promoter methylation, an alternative isoform, RASSF1C, is expressed and we find is able to bind and activate SRC. We also identify a novel tumour-suppressor role for RASSF1A, associating with the kinase inactivation of SRC. RASSF1C expression promotes SRC-dependent phosphorylation and internalisation of adherens junctions, leading to loss of cell-cell contacts and subsequent increase in cell motility, growth and invasiveness, both in vitro and in vivo. RASSF1C, via active SRC, mediates the phosphorylation of β-catenin and YAP1, promoting their nuclear localisation and association with the transcription factors TEAD1 and TBX3, resulting in the upregulation of anti-apoptotic and pro-survival genes. We show that RASSF1C expression leads to differential packaging and secretion of exosomes, modulating the communication between cancer cells and increasing their tumourigenicity. Finally, we find that cells expressing RASSF1C undergo phenotypic and transcriptional changes associated with the generation of cancer stem cells. We conclude that RASSF1C is an oncogene that plays a variety of roles in cell adhesion, invasion, survival and extracellular communication, resulting in increased tumourigenesis. These functions are inhibited by the tumour suppressor RASSF1A. This work highlights the association of the epigenetic inactivation of the RASSF1A gene with the more aggressive, metastatic tumours, and its relation to increased cancer outcome and risk.</p

Epigenetic silencing of RASSF1A promotes tumourigenesis via alternative transcript expression, SFK activation and exosome secretion

Loss of the tumour-suppressor gene RASSF1A upon promoter methylation is one of the most frequent events in sporadic human malignancies. Loss of RASSF1A is associated with progression and pathogenesis of solid tumours; and more aggressive clinical phenotype, leading to poor prognosis in breast, lung and colon cancers, amongst others. RASSF1A functions in a number of cellular processes, inducing apoptosis in response to DNA damage, cell cycle arrest and growth control. In tumours with RASSF1 promoter methylation, an alternative isoform, RASSF1C, is expressed and we find is able to bind and activate SRC. We also identify a novel tumour-suppressor role for RASSF1A, associating with the kinase inactivation of SRC. RASSF1C expression promotes SRC-dependent phosphorylation and internalisation of adherens junctions, leading to loss of cell-cell contacts and subsequent increase in cell motility, growth and invasiveness, both in vitro and in vivo. RASSF1C, via active SRC, mediates the phosphorylation of &beta;-catenin and YAP1, promoting their nuclear localisation and association with the transcription factors TEAD1 and TBX3, resulting in the upregulation of anti-apoptotic and pro-survival genes. We show that RASSF1C expression leads to differential packaging and secretion of exosomes, modulating the communication between cancer cells and increasing their tumourigenicity. Finally, we find that cells expressing RASSF1C undergo phenotypic and transcriptional changes associated with the generation of cancer stem cells. We conclude that RASSF1C is an oncogene that plays a variety of roles in cell adhesion, invasion, survival and extracellular communication, resulting in increased tumourigenesis. These functions are inhibited by the tumour suppressor RASSF1A. This work highlights the association of the epigenetic inactivation of the RASSF1A gene with the more aggressive, metastatic tumours, and its relation to increased cancer outcome and risk.</p