Crypt base cells are candidates for intestinal epithelial stem cells (ISC). But limited progress has been made concerning the modulation of stem cells. DACH1 is upregulated in LGR5+ ISC cells with stemness maintenance. Hence, we postulated that DACH1 may serve as a putative modulator of intestine stem cells leading to carcinogenesis.
We established colon normal, adenomas and cancers organoids, which supported stem cell proliferation and undifferentiation in vitro. A stable and efficient culture system for colon epithelial crypts and tumor organoids was use to facilitate investigation of the dynamics and factors affecting colon stem cell niche and carcinogenesis.
We showed that in the mouse and human intestine, DACH1 was expressed in discrete crypt base. In colorectal cancer, DACH1 expression became widespread, with increased expression and nuclear localization at all stages. ShRNA-mediated inhibition of DACH1 in colon cancer cells inhibited colony formation in vitro and tumor growth in vivo through affecting cancer stem cell signatures. What is more, DACH1 stimulated both colonosphere formation and tumor organoid formation in vitro. Mechanistic characterization indicated that DACH1 recruited and interacts with SMAD4 to suppress BMP signaling pathway. Eventually, DACH1 induced stemness of organoids through BMP-mediated transcriptional increasing of a large number of stem cell signature genes, including Notch1, Msi-2 and Sox9. Here we provided evidence for an essential role of DACH1 in inducing stem cell self-renewal through direct upregulating stem cell signature genes. In detail, DACH1 was shown by microarray analyses to repress BMP induction of Smad signaling, then DACH1 binding to Smad4 was required for repression of Smad signaling
In conclusion, our findings illustrate an essential role of DACH1 signaling in inducing stem cell expansion during intestinal homeostasis and tumor development. This study also provided a mechanistic insight into the function of DACH1 in maintaining stem cell self-renewal via Smad4.
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