Abstract 3055: Potential role of cyclin D1 in regulation of liver cancer stem cells

Abstract

Abstract Cancer stem cells (CSCs) are capable of self-renewal, multipotency, in vivo tumorigenicity, and driving metastasis. CSCs are more resistant to conventional therapy, allowing recurrence of tumor. Thus, novel therapies capable of eliminating CSCs are needed. Cyclin D1 is deregulated in many types of cancers. Beyond being a cell cycle regulator and oncogene, cyclin D1 also enhances stem cell (SC) self-renewal and promotes induced pluripotent stem cells (iPSCs) reprogramming efficiency. Yet, the role of cyclin D1 in regulation of CSC is not well defined. Here we investigated whether and how cyclin D1 could regulate liver cancer CSC properties. We overexpressed cyclin D1 in two lines of HCC cells, Huh7 and 97H and found that the sphere formation capacity was enriched in Huh7 cyclin D1-expressing cells than Huh7 cells. From dissected single spherical cells, the secondary sphere formation capacity was significantly higher in cyclin D1-expressing cells than both parental Huh7 (p=0.00) and 97H (p=0.02) cells. Anchorage-independent spherical colonies (spheres) are composed of a small number of cancer cells with stem-like properties. Thus, the results suggest that overexpression of cyclin D1 enhanced self-renewal capacity of liver CSCs. The cyclin D1-expressing spheres displayed an increased expression of stem cell-associated genes Nanog, Oct4, and Nordal/Activin. Smad2/3, a TGF-β signaling effector, was highly phosphorylated in cyclin D1-expressing spheres compared to monolayer or spheres without cyclin D1 expression. More importantly, TGF-β/Smad inhibitor (SB431542) inhibited cyclin D1-expressing CSC self-renewal shown by significantly reduction of sphere formation in two lines of cyclin D1-expressing HCC lines, whereas it had no effects on sphere formation in parental cells without cyclin D1 overexpression. In addition, Erk inhibitor (UO126) showed no inhibiting effects, a further proof of the role of cyclin D1 mediated activation of Smad2/3. These results indicate that TGF-β/Smad inhibitor might have therapeutic potential for targeting liver CSCs. HCC cells are highly resistance chemotherapy resulting in enriched CSC population. We further investigated the sphere formation capacity of D1-expressing cells under the treatment of chemotherapeutic agents in combination with Smad inhibitor. We found that SB431542 could inhibit cyclin-D1 expressing spherical cancer cell proliferation therefore sensitized the cells to chemo drug cisplatin. In summary, our results suggest that cyclin D1 might promote liver CSC proliferation and self-renewal via activation of TGF-β/Smad signaling, with underlining mechanism is under investigation. Citation Format: Wei Xia, Xiao Qi Wang. Potential role of cyclin D1 in regulation of liver cancer stem cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3055. doi:10.1158/1538-7445.AM2014-3055