L1CAM defines the regenerative origin of metastasis-initiating cells in colorectal cancer.

Metastasis-initiating cells with stem-like properties drive cancer lethality, yet their origins and relationship to primary-tumor-initiating stem cells are not known. We show that L1CAM+ cells in human colorectal cancer (CRC) have metastasis-initiating capacity, and we define their relationship to tissue regeneration. L1CAM is not expressed in the homeostatic intestinal epithelium, but is induced and required for epithelial regeneration following colitis and in CRC organoid growth. By using human tissues and mouse models, we show that L1CAM is dispensable for adenoma initiation but required for orthotopic carcinoma propagation, liver metastatic colonization and chemoresistance. L1CAMhigh cells partially overlap with LGR5high stem-like cells in human CRC organoids. Disruption of intercellular epithelial contacts causes E-cadherin-REST transcriptional derepression of L1CAM, switching chemoresistant CRC progenitors from an L1CAMlow to an L1CAMhigh state. Thus, L1CAM dependency emerges in regenerative intestinal cells when epithelial integrity is lost, a phenotype of wound healing deployed in metastasis-initiating cells.

Stable inhibitory activity of regulatory T cells requires the transcription factor Helios.

The maintenance of immune homeostasis requires regulatory T cells (T(regs)). Given their intrinsic self-reactivity, T(regs) must stably maintain a suppressive phenotype to avoid autoimmunity. We report that impaired expression of the transcription factor (TF) Helios by FoxP3(+) CD4 and Qa-1-restricted CD8 T(regs) results in defective regulatory activity and autoimmunity in mice. Helios-deficient T(regs) develop an unstable phenotype during inflammatory responses characterized by reduced FoxP3 expression and increased effector cytokine expression secondary to diminished activation of the STAT5 pathway. CD8 T(regs) also require Helios-dependent STAT5 activation for survival and to prevent terminal T cell differentiation. The definition of Helios as a key transcription factor that stabilizes T(regs) in the face of inflammatory responses provides a genetic explanation for a core property of T(regs).

Distinct EMT programs control normal mammary stem cells and tumour-initiating cells.

Tumour-initiating cells (TICs) are responsible for metastatic dissemination and clinical relapse in a variety of cancers. Analogies between TICs and normal tissue stem cells have led to the proposal that activation of the normal stem-cell program within a tissue serves as the major mechanism for generating TICs. Supporting this notion, we and others previously established that the Slug epithelial-to-mesenchymal transition-inducing transcription factor (EMT-TF), a member of the Snail family, serves as a master regulator of the gland-reconstituting activity of normal mammary stem cells, and that forced expression of Slug in collaboration with Sox9 in breast cancer cells can efficiently induce entrance into the TIC state. However, these earlier studies focused on xenograft models with cultured cell lines and involved ectopic expression of EMT-TFs, often at non-physiological levels. Using genetically engineered knock-in reporter mouse lines, here we show that normal gland-reconstituting mammary stem cells residing in the basal layer of the mammary epithelium and breast TICs originating in the luminal layer exploit the paralogous EMT-TFs Slug and Snail, respectively, which induce distinct EMT programs. Broadly, our findings suggest that the seemingly similar stem-cell programs operating in TICs and normal stem cells of the corresponding normal tissue are likely to differ significantly in their details.

Epigenetic mechanisms underlying the dynamic expression of cancer-testis genes, PAGE2, -2B and SPANX-B, during mesenchymal-to-epithelial transition.

Cancer-testis (CT) genes are expressed in various cancers but not in normal tissues other than in cells of the germline. Although DNA demethylation of promoter-proximal CpGs of CT genes is linked to their expression in cancer, the mechanisms leading to demethylation are unknown. To elucidate such mechanisms we chose to study the Caco-2 colorectal cancer cell line during the course of its spontaneous differentiation in vitro, as we found CT genes, in particular PAGE2, -2B and SPANX-B, to be up-regulated during this process. Differentiation of these cells resulted in a mesenchymal-to-epithelial transition (MET) as evidenced by the gain of epithelial markers CDX2, Claudin-4 and E-cadherin, and a concomitant loss of mesenchymal markers Vimentin, Fibronectin-1 and Transgelin. PAGE2 and SPAN-X up-regulation was accompanied by an increase in Ten-eleven translocation-2 (TET2) expression and cytosine 5-hydroxymethylation as well as the disassociation of heterochromatin protein 1 and the polycomb repressive complex 2 protein EZH2 from promoter-proximal regions of these genes. Reversal of differentiation resulted in down-regulation of PAGE2, -2B and SPANX-B, and induction of epithelial-to-mesenchymal transition (EMT) markers, demonstrating the dynamic nature of CT gene regulation in this model.