Epigenetic Regulation of Cancer Stem Cell Marker Cd133 by Transforming Growth Factor-β

Abstract

Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality worldwide. CD133, a transmembrane glycoprotein, is an important cell surface marker for both stem cells and cancer stem cells in various tissues including liver. CD133 expression has been recently linked to poor prognosis in HCC patients. CD1331 liver cancer cells are characterized by resistance to chemotherapy, self-renewal, multilineage potential, increased colony formation, and in vivo cancer initiation at limited dilution. Recent studies demonstrate that CD133 expression is regulated by DNA methylation. In this study, we explored the role of transforming growth factor b (TGFb), a multifunctional cytokine that plays a critical role in chronic liver injury, in the regulation of CD133 expression. TGFb1 is capable of up-regulating CD133 expression specifically within the Huh7 HCC cell line in a time-and dose-dependent manner. Most important, TGFb1-induced CD1331 Huh7 cells demonstrate increased tumor initiation in vivo. Forced expression of inhibitory Smads, including Smad6 and Smad7, attenuated TGFb1-induced CD133 expression. Within CD1332 Huh7 cells, TGFb1 stimulation inhibited the expression of DNA methyltransferases (DNMT) 1 and DNMT3b, which are critical in the maintenance of regional DNA methylation, and global DNMT activity in CD1332 Huh7 cells was inhibited by TGFb1. DNMT3b inhibition by TGFb1 was partially rescued with overexpression of inhibitory Smads. Lastly, TGFb1 treatment led to significant demethylation in CD133 promoter-1 in CD1332 Huh7 cells. Conclusion: TGFb1 is able to regulate CD133 expression through inhibition of DNMT1 and DNMT3b expression and subsequent demethylation of promoter-1. TGFb1-induced CD1331 Huh7 cells are tumorigenic. The mechanism by which TGFb induces CD133 expression is partially dependent on the Smads pathway. (HEPATOLOGY 2010;51:1635-1644 We have recently demonstrated that CD133 reliably identifies liver cancer stem cells (CSCs) in two independent murine models of chronic injury. [10][11][12] In the human HCC cell line Huh7, CD133þ cells demonstrated many stem cell-like properties including colony formation, self-renewal and differentiation ability, as well as a greater ability to initiate tumors in vivo compared to CD133À cells. 3Despite the high volume of recent publications related to CD133, little is known about the regulation

Hypoxia induces CD133 expression in human lung cancer cells by up-regulation of OCT3/4 and SOX2

“…roles in the regulation of various genes (19,(40)(41)(42), which might be explained by a different cellular context of epigenetic regulation in lung cancer cell lines. Therefore, epigenetic modification may be the final determinant of CD133 expression and stem-like features.…”

Cancer stem cells in the development of liver cancer

“…Signaling of OSM and BMP4 appears to induce hepatocytic differentiation of liver CSCs (66,67), while TGF-β signaling is implicated in the biliary differentiation of hepatoblasts; loss of TGF-β signaling by β2-spectrin knockout resulted in the expansion of progenitor cells in mice (68,69). TGF-β signaling may also regulate the development and maintenance of HCC and liver CSCs, but its role seems paradoxical and is often referred to as a double-edged sword (70)(71)(72)(73). In addition, TGF-β signaling may promote HCC progression by recruiting regulatory T cells to establish a favorable microenvironment for tumor metastasis (74,75).…”

Expression profiling of GIST: CD133 is associated with KIT exon 11 mutations, gastric location and poor prognosis

“…The expression of CD133 in tumors depends on CD133 promoter methylation 37 as well as Notch, TGFb, mTOR and HIF1a signaling. 38,39 However, the functions of CD133 in normal physiology or neoplasia are not well understood. In normal cells, CD133 may function as an organizer of plasma membrane topology.…”