Regulation of intestinal stem cell proliferation by human methyl-CpG-binding protein-2 in Drosophila

An miRNA Expression Signature for the Human Colonic Stem Cell Niche Distinguishes Malignant from Normal Epithelia

Malignant transformation of tissue stem cells (SC) may be the root of most cancer. Accordingly, we identified miRNA expression patterns in the normal human colonic SC niche to understand how cancer stem cells (CSC) may arise. In profiling miRNA expression in SC-enriched crypt subsections isolated from fresh, normal surgical specimens, we identified 16 miRNAs that were differentially expressed in the crypt bottom, creating an SC signature for normal colonic epithelia (NCE). A parallel analysis of colorectal cancer tissues showed differential expression of 83 miRNAs relative to NCE. Within the 16 miRNA signature for the normal SC niche, we found that miR-206, miR-007-3, and miR-23b individually could distinguish colorectal cancer from NCE. Notably, miR-23b, which was increased in colorectal cancer, was predicted to target the SC-expressed G protein-coupled receptor LGR5. Cell biology investigations showed that miR-23b regulated CSC phenotypes globally at the level of proliferation, cell cycle, self-renewal, epithelial-mesenchymal transition, invasion, and resistance to the colorectal cancer chemotherapeutic agent 5-fluorouracil. In mechanistic experiments, we found that miR-23b decreased LGR5 expression and increased ALDH⁺ CSCs. CSC analyses confirmed that levels of LGR5 and miR-23b are inversely correlated in ALDH⁺ CSCs and that distinct subpopulations of LGR5⁺ and ALDH⁺ CSCs exist. Overall, our results define a critical function for miR-23b, which, by targeting LGR5, contributes to overpopulation of ALDH⁺ CSCs and colorectal cancer. Cancer Res; 77(14); 3778-90. ©2017 AACR.

Association of TGFβ signaling with the maintenance of a quiescent stem cell niche in human oral mucosa

A dogma in squamous epithelial biology is that proliferation occurs in the basal cell layer. Notable exceptions are squamous epithelia of the human oral cavity, esophagus, ectocervix, and vagina. In these human epithelia, proliferation is rare in the basal cell layer, and the vast majority of cells positive for Ki67 and other proliferation markers are found in para- and suprabasal cell layers. This unique human feature of a generally quiescent basal cell layer overlaid by highly proliferative cells offers the rare opportunity to study the molecular features of undifferentiated, quiescent, putative stem cells in their natural context. Here, we show that the quiescent human oral mucosa basal cell layer expresses putative markers of stemness, while para- and suprabasal cells are characterized by cell cycle genes. We identified a TGFβ signature in this quiescent basal cell layer. In in vitro organotypic cultures, human keratinocytes could be induced to express markers of these quiescent basal cells when TGFβ signaling is activated. The study suggests that the separation of basal cell layer and proliferation in human oral mucosa may function to accommodate high proliferation rates and the protection of a quiescent reserve stem cell pool. Psoriasis, an epidermal inflammatory hyperproliferative disease, exhibits features of a quiescent basal cell layer mimicking normal oral mucosa. Our data indicate that structural changes in the organization of epithelial proliferation could contribute to longevity and carcinogenesis.

Gene expression profiling identifies the zinc-finger protein Charlatan as a regulator of intestinal stem cells in Drosophila

Intestinal stem cells (ISCs) in the adult Drosophila midgut can respond to tissue damage and support repair. We used genetic manipulation to increase the number of ISC-like cells in the adult midgut and performed gene expression profiling to identify potential ISC regulators. A detailed analysis of one of these potential regulators, the zinc-finger protein Charlatan, was carried out. MARCM clonal analysis and RNAi in precursor cells showed that loss of Chn function caused severe ISC division defects, including loss of EdU incorporation, phosphorylated histone 3 staining and expression of the mitotic protein Cdc2. Loss of Charlatan also led to a much reduced histone acetylation staining in precursor cells. Both the histone acetylation and ISC division defects could be rescued by the simultaneous decrease of the Histone Deacetylase 2. The overexpression of Charlatan blocked differentiation reversibly, but loss of Charlatan did not lead to automatic differentiation. The results together suggest that Charlatan does not simply act as an anti-differentiation factor but instead functions to maintain a chromatin structure that is compatible with stem cell properties, including proliferation.

Epigenetic regulation in adult stem cells and cancers

Adult stem cells maintain tissue homeostasis by their ability to both self-renew and differentiate to distinct cell types. Multiple signaling pathways have been shown to play essential roles as extrinsic cues in maintaining adult stem cell identity and activity. Recent studies also show dynamic regulation by epigenetic mechanisms as intrinsic factors in multiple adult stem cell lineages. Emerging evidence demonstrates intimate crosstalk between these two mechanisms. Misregulation of adult stem cell activity could lead to tumorigenesis, and it has been proposed that cancer stem cells may be responsible for tumor growth and metastasis. However, it is unclear whether cancer stem cells share commonalities with normal adult stem cells. In this review, we will focus on recent discoveries of epigenetic regulation in multiple adult stem cell lineages. We will also discuss how epigenetic mechanisms regulate cancer stem cell activity and probe the common and different features between cancer stem cells and normal adult stem cells.