[Show abstract][Hide abstract] ABSTRACT: Insertion of reporter cassettes into the Lgr5 locus has enabled the characterization of mouse intestinal stem cells (ISCs). However, low cell surface abundance of LGR5 protein and lack of high-affinity anti-LGR5 antibodies represent a roadblock to efficiently isolate human colonic stem cells (hCoSCs). We set out to identify stem cell markers that would allow for purification of hCoSCs. In an unbiased approach, membrane-enriched protein fractions derived from in vitro human colonic organoids were analyzed by quantitative mass spectrometry. Protein tyrosine pseudokinase PTK7 specified a cell population within human colonic organoids characterized by highest self-renewal and re-seeding capacity. Antibodies recognizing the extracellular domain of PTK7 allowed us to isolate and expand hCoSCs directly from patient-derived mucosa samples. Human PTK7+ cells display features of canonical Lgr5+ ISCs and include a fraction of cells that undergo differentiation toward enteroendocrine lineage that resemble crypt label retaining cells (LRCs).
[Show abstract][Hide abstract] ABSTRACT: Recent molecular classifications of colorectal cancer (CRC) based on global gene expression profiles have defined subtypes displaying resistance to therapy and poor prognosis. Upon evaluation of these classification systems, we discovered that their predictive power arises from genes expressed by stromal cells rather than epithelial tumor cells. Bioinformatic and immunohistochemical analyses identify stromal markers that associate robustly with disease relapse across the various classifications. Functional studies indicate that cancer-associated fibroblasts (CAFs) increase the frequency of tumor-initiating cells, an effect that is dramatically enhanced by transforming growth factor (TGF)-β signaling. Likewise, we find that all poor-prognosis CRC subtypes share a gene program induced by TGF-β in tumor stromal cells. Using patient-derived tumor organoids and xenografts, we show that the use of TGF-β signaling inhibitors to block the cross-talk between cancer cells and the microenvironment halts disease progression.
[Show abstract][Hide abstract] ABSTRACT: Aberrant activation of WNT signalling and loss of BMP signals represent the two main alterations leading to the initiation of colorectal cancer (CRC). Here we screen for genes required for maintaining the tumour stem cell phenotype and identify the zinc-finger transcription factor GATA6 as a key regulator of the WNT and BMP pathways in CRC. GATA6 directly drives the expression of LGR5 in adenoma stem cells whereas it restricts BMP signalling to differentiated tumour cells. Genetic deletion of Gata6 from mouse colon adenomas increases the levels of BMP factors, which signal to block self-renewal of tumour stem cells. In human tumours, GATA6 competes with β-catenin/TCF4 for binding to a distal regulatory region of the BMP4 locus that has been linked to increased susceptibility to development of CRC. Hence, GATA6 creates an environment permissive for CRC initiation by lowering the threshold of BMP signalling required for tumour stem cell expansion.
No preview · Article · Jun 2014 · Nature Cell Biology
[Show abstract][Hide abstract] ABSTRACT: A large proportion of colorectal cancers (CRCs) display mutational inactivation of the TGF-β pathway, yet, paradoxically, they are characterized by elevated TGF-β production. Here, we unveil a prometastatic program induced by TGF-β in the microenvironment that associates with a high risk of CRC relapse upon treatment. The activity of TGF-β on stromal cells increases the efficiency of organ colonization by CRC cells, whereas mice treated with a pharmacological inhibitor of TGFBR1 are resilient to metastasis formation. Secretion of IL11 by TGF-β-stimulated cancer-associated fibroblasts (CAFs) triggers GP130/STAT3 signaling in tumor cells. This crosstalk confers a survival advantage to metastatic cells. The dependency on the TGF-β stromal program for metastasis initiation could be exploited to improve the diagnosis and treatment of CRC.
[Show abstract][Hide abstract] ABSTRACT: The formation and maintenance of complex organs requires segregation of distinct cell populations into defined territories (that is, cell sorting) and the establishment of boundaries between them. Here we have investigated the mechanism by which Eph/ephrin signalling controls the compartmentalization of cells in epithelial tissues. We show that EphB/ephrin-B signalling in epithelial cells regulates the formation of E-cadherin-based adhesions. EphB receptors interact with E-cadherin and with the metalloproteinase ADAM10 at sites of adhesion and their activation induces shedding of E-cadherin by ADAM10 at interfaces with ephrin-B1-expressing cells. This process results in asymmetric localization of E-cadherin and, as a consequence, in differences in cell affinity between EphB-positive and ephrin-B-positive cells. Furthermore, genetic inhibition of ADAM10 activity in the intestine of mice results in a lack of compartmentalization of Paneth cells within the crypt stem cell niche, a defect that phenocopies that of EphB3-null mice. These results provide important insights into the regulation of cell migration in the intestinal epithelium and may help in the understanding of the nature of the cell sorting process in other epithelial tissues where Eph-ephrin interactions play a central role.
[Show abstract][Hide abstract] ABSTRACT: A frequent complication in colorectal cancer (CRC) is regeneration of the tumor after therapy. Here, we report that a gene signature specific for adult intestinal stem cells (ISCs) predicts disease relapse in CRC patients. ISCs are marked by high expression of the EphB2 receptor, which becomes gradually silenced as cells differentiate. Using EphB2 and the ISC marker Lgr5, we have FACS-purified and profiled mouse ISCs, crypt proliferative progenitors, and late transient amplifying cells to define a gene program specific for normal ISCs. Furthermore, we discovered that ISC-specific genes identify a stem-like cell population positioned at the bottom of tumor structures reminiscent of crypts. EphB2 sorted ISC-like tumor cells display robust tumor-initiating capacity in immunodeficient mice as well as long-term self-renewal potential. Taken together, our data suggest that the ISC program defines a cancer stem cell niche within colorectal tumors and plays a central role in CRC relapse.