Subversion of niche-signalling pathways in colorectal cancer: what makes and breaks the intestinal stem cell

The intestinal epithelium fulfils pleiotropic functions in nutrient uptake, waste elimination, and immune surveillance while also forming a barrier against luminal toxins and gut-resident microbiota. Incessantly barraged by extraneous stresses, the intestine must continuously replenish its epithelial lining and regenerate the full gamut of specialized cell types that underpin its functions. Homeostatic remodelling is orchestrated by the intestinal stem cell (ISC) niche: a convergence of epithelial- and stromal-derived cues, which maintains ISCs in a multipotent state. Following demise of homeostatic ISCs post injury, plasticity is pervasive among multiple populations of reserve stem-like cells, lineage-committed progenitors, and/or fully differentiated cell types, all of which can contribute to regeneration and repair. Failure to restore the epithelial barrier risks seepage of toxic luminal contents, resulting in inflammation and likely predisposing to tumour formation. Here, we explore how homeostatic niche-signalling pathways are subverted in tumorigenesis, enabling ISCs to gain autonomy from niche restraints (“ISC emancipation”) and transform into cancer stem cells capable of driving tumour initiation, progression, and therapy resistance. We further consider the implications of the pervasive plasticity of the intestinal epithelium for the trajectory of colorectal cancer, the emergence of distinct molecular subtypes, the propensity to metastasize, and the development of effective therapeutic strategies

Epithelial-mesenchymal transition and cancer stem cells: a dangerously dynamic duo in breast cancer progression

Aberrant activation of a latent embryonic program - known as the epithelial-mesenchymal transition (EMT) - can endow cancer cells with the migratory and invasive capabilities associated with metastatic competence. The induction of EMT entails the loss of epithelial characteristics and the de novo acquisition of a mesenchymal phenotype. In breast cancer, the EMT state has been associated with cancer stem cell properties including expression of the stem cell-associated CD44+/CD24-/low antigenic profile, self-renewal capabilities and resistance to conventional therapies. Intriguingly, EMT features are also associated with stem cells isolated from the normal mouse mammary gland and human breast reduction tissues as well as the highly aggressive metaplastic and claudin-low breast tumor subtypes. This has implications for the origin of these breast tumors as it remains unclear whether they derive from cells that have undergone EMT or whether they represent an expansion of a pre-existing stem cell population that expresses EMT-associated markers to begin with. In the present review, we consider the current evidence connecting EMT and stem cell attributes and discuss the ramifications of these newly recognized links for our understanding of the emergence of distinct breast cancer subtypes and breast cancer progression

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

Glutathione and p53 independently mediate responses against oxidative stress in ES cells

We have investigated the roles of the antioxidant glutathione and p53 in the response of embryonic stem (ES) cells to oxidative stress. ES cells express γGCS, a critical enzyme in glutathione (GSH) biosynthesis. Treatment with the pro-oxidant menadione led to elevation of GSH, a strong apoptotic response and reduced clonogenic survival. Addition of BSO, a specific γGCS inhibitor depleted GSH pools and prevented the menadione-induced increase in GSH, sensitizing cells to oxidative insult. Although p53 status had no bearing on either the basal levels of GSH or the menadione-induced GSH response, the levels of menadione-induced apoptosis were reduced in the absence of p53. We conclude that the pathways involving p53 and GSH act independently to protect against the deleterious effects of oxidative damage. Furthermore, the presence of an intact p53 pathway confers a long-term growth advantage post oxidative stress. Thus, in the absence of p53 ES cells bearing genotoxic damage are less likely to be propagated, suggesting that p53-dependent apoptosis acts to limit the deleterious effects of oxidative stress during early development

Phosphorylation of serine 367 of FOXC2 by p38 regulates ZEB1 and breast cancer metastasis, without impacting primary tumor growth

Metastatic competence is contingent upon the aberrant activation of a latent embryonic program, known as the epithelial – mesenchymal transition (EMT), which bestows stem cell properties as well as migratory and invasive capabilities upon differentiated tumor cells. We recently identified the transcription factor FOXC2 as a downstream effector of multiple EMT programs, independent of the EMT-inducing stimulus, and as a key player linking EMT, stem cell traits and metastatic competence in breast cancer. As such, FOXC2 could serve as a potential therapeutic target to attenuate metastasis. However, as FOXC2 is a transcription factor, it is difficult to target by conventional means such as small-molecule inhibitors. Herein, we identify the serine/threonine-specific kinase p38 as a druggable upstream regulator of FOXC2 stability and function that elicits phosphorylation of FOXC2 at serine 367 (S367). Using an orthotopic syngeneic mouse tumor model, we make the striking observation that inhibition of p38-FOXC2 signaling selectively attenuates metastasis without impacting primary tumor growth. In this model, circulating tumor cell numbers are significantly reduced in mice treated with the p38 inhibitor SB203580, relative to vehicle-treated counterparts. Accordingly, genetic or pharmacological inhibition of p38 decreases FOXC2 protein levels, reverts the EMT phenotype and compromises stem cell attributes in vitro. We also identify the EMT-regulator ZEB1 —known to directly repress E-cadherin/CDH1—as a downstream target of FOXC2, critically dependent on its activation by p38. Consistent with the notion that activation of the p38-FOXC2 signaling axis represents a critical juncture in the acquisition of metastatic competence, the phosphomimetic FOXC2(S367E) mutant is refractory to p38 inhibition both in vitro and in vivo , whereas the non-phosphorylatable FOXC2(S367A) mutant fails to elicit EMT and upregulate ZEB1. Collectively, our data demonstrate that FOXC2 regulates EMT, stem cell traits, ZEB1 expression and metastasis in a p38-dependent manner, and attest to the potential utility of p38 inhibitors as antimetastatic agents

NOTUM from Apc-mutant cells biases clonal competition to initiate cancer

Funding Information: Acknowledgements We thank the Core Services and Advanced Technologies at the Cancer Research UK Beatson Institute (C596/A17196 and A31287), and particularly the Biological Services Unit, Histology Service and Molecular Technologies; members of the Sansom and Katajisto laboratories for discussions of the data and manuscript; and BRC Oxford for supplying patient material. O.J.S. and his laboratory members were supported by Cancer Research UK (A28223, A21139, A12481 and A17196). D.J.F. and M.C.H. were supported by the UK Medical Research Council (MR/R017247/1 and MR/J50032X/1, respectively). SpecifiCancer CRUK Grand Challenge (C7932/A29055) is funded by Cancer Research UK and the Mark Foundation for Cancer Research. P.K. and his laboratory members were supported by the Academy of Finland Centre of Excellence MetaStem (266869, 304591 and 320185), the ERC Starting Grant 677809, the Swedish Research Council 2018-03078, the Cancerfonden 190634, the Jane and Aatos Erkko Foundation and the Cancer Foundation Finland. N.P. was supported by the Finnish Cultural Foundation, the Biomedicum Helsinki Foundation, the Orion Research Foundation sr and The Paulo Foundation. P.V.F. was supported by Alzheimer’s Research UK and The Francis Crick Institute. The ARUK UCL Drug Discovery Institute receives its core funding from Alzheimer’s Research UK (520909). The Francis Crick Institute receives its core funding from Cancer Research UK (FC001002), the UK Medical Research Council (FC001002) and the Wellcome Trust (FC001002). Publisher Copyright: © 2021, The Author(s), under exclusive licence to Springer Nature Limited.The tumour suppressor APC is the most commonly mutated gene in colorectal cancer. Loss of Apc in intestinal stem cells drives the formation of adenomas in mice via increased WNT signalling(1), but reduced secretion of WNT ligands increases the ability of Apc-mutant intestinal stem cells to colonize a crypt (known as fixation)(2). Here we investigated how Apc-mutant cells gain a clonal advantage over wild-type counterparts to achieve fixation. We found that Apc-mutant cells are enriched for transcripts that encode several secreted WNT antagonists, with Notum being the most highly expressed. Conditioned medium from Apc-mutant cells suppressed the growth of wild-type organoids in a NOTUM-dependent manner. Furthermore, NOTUM-secreting Apc-mutant clones actively inhibited the proliferation of surrounding wild-type crypt cells and drove their differentiation, thereby outcompeting crypt cells from the niche. Genetic or pharmacological inhibition of NOTUM abrogated the ability of Apc-mutant cells to expand and form intestinal adenomas. We identify NOTUM as a key mediator during the early stages of mutation fixation that can be targeted to restore wild-type cell competitiveness and provide preventative strategies for people at a high risk of developing colorectal cancer.Peer reviewe

FOXC2 expression links epithelial-mesenchymal transition and stem cell properties in breast cancer

* Free to read full-text published version on publisher\ud \ud ABSTRACT: \ud \ud Resistance to chemotherapy and metastases are the major causes of breast cancer-related mortality. Moreover, cancer stem cells (CSC) play critical roles in cancer progression and treatment resistance. Previously, it was found that CSC-like cells can be generated by aberrant activation of epithelial–mesenchymal transition (EMT), thereby making anti-EMT strategies a novel therapeutic option for treatment of aggressive breast cancers. Here, we report that the transcription factor FOXC2 induced in response to multiple EMT signaling pathways as well as elevated in stem cell-enriched factions is a critical determinant of mesenchymal and stem cell properties, in cells induced to undergo EMT- and CSC-enriched breast cancer cell lines. More specifically, attenuation of FOXC2 expression using lentiviral short hairpin RNA led to inhibition of the mesenchymal phenotype and associated invasive and stem cell properties, which included reduced mammosphere-forming ability and tumor initiation. Whereas, overexpression of FOXC2 was sufficient to induce CSC properties and spontaneous metastasis in transformed human mammary epithelial cells. Furthermore, a FOXC2-induced gene expression signature was enriched in the claudin-low/basal B breast tumor subtype that contains EMT and CSC features. Having identified PDGFR-β to be regulated by FOXC2, we show that the U.S. Food and Drug Administration-approved PDGFR inhibitor, sunitinib, targets FOXC2-expressing tumor cells leading to reduced CSC and metastatic properties. Thus, FOXC2 or its associated gene expression program may provide an effective target for anti-EMT-based therapies for the treatment of claudin-low/basal B breast tumors or other EMT-/CSC-enriched tumors

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

Right-sided colorectal cancer (rCRC) has a different mutational spectrum to the left-sided counterpart. Here the authors develop a mouse model of rCRC that recapitulates human BRAF-mutant rCRC and show that loss of TGFβ-receptor signalling and inflammation induce the development of colonic tumours with a foetal-like phenotype