Ascl2作为Wnt信号通路的靶基因，是控制肠粘膜内隐窝基底干细胞及结肠癌前体细胞自更新的重要转录因子，其独特地过表达在肠道的隐窝干细胞及结肠癌前体细胞。我们前期试验证明Ascl2通过miRNA-302b控制结肠癌前体细胞的干性，阻遏miRNA-200家族的表达调节结肠癌的EMT的可塑性，阻遏CDX2的表达抑制结肠癌细胞的分化。但是结肠癌前体细胞内Ascl2过表达的调控机制不清。本课题拟从Hippo/MST信号与经典的Wnt信号的Crosstalk和从PI3K/AKT/mTOR/Sp1与经典的Wnt信号的Crosstalk来诱导Ascl2的转录调控激活；从Ascl2自转录调节，形成结肠癌前体细胞内Ascl2的正反馈激活环三个分子机制，达到诱导Ascl2在结肠癌前体细胞内的过表达。我们通过上述研究揭示结肠癌前体内细胞Ascl2过表达调控机制，为将来针对结肠癌前体细胞的治疗提供新的靶位和思路。

Achaete scute-like 2 (Ascl2), a basic helix-loop-helix (bHLH) transcription factor, is a downstream target of Wnt signaling that controls the fate of intestinal cryptic stem cells and colon cancer progenitor cells. Ascl2 is exclusively expressed in the intestinal mucosal cryptic stem cells and the colon cancer progenitor cells. Our previous works confirmed that Ascl2 decided the stemness and the self-renewal of conlon cancer progenitor cells via miRNA-302b, Ascl2 posttranscriptionally repressed miRNA-200 family members and further modulated the plasticity of EMT-MET in colon cancer cells and Ascl2 posttranscriptionally repressed CDX2 expression and modulated the differentiation of colon cancer cells towards goblet-cell phenotype (unpublished). However, the reason and the mechanism(s) of Ascl2 overexpression in colon cancer progenitor cells are largely unknown. The present project applying for financial support is to investigate the molecular mechanism(s) in which activates Ascl2 overexpression in colon cancer progenitor cells including (1) Crosstalk between Hippo/MST signaling and canonical WNT signaling leads to the overexpression of Yap1, phosphorylation of Yap1, nuclear translocation of phosphorylated Yap1 and complexed with β-catenin, and further activates Ascl2 overexpression; (2) Crosstalk between PI3K/AKT/mTOR/Sp1 signaling and canonical WNT signaling leads to the phosphorylation ofβ-catenin, and further activates Ascl2 overexpression, Sp1 expression and nuclear translocation of Sp1 and binding the cis-element of Sp1 in the Ascl2 proximal promoter, and further activates Ascl2 overexpression; (3) Ascl2 self-activated its expression in colon cancer progenitor cells through its binding the rich E-box present at its own proximal promoter, and transcriptinally activates its own expression and forms a positive feed-back aitivation loop, and further activates Ascl2 overexpression. These molecular mechanism(s) will help to find a possible target to inhibit Ascl2 expression in colon cancer progenitor cells and finally to inhibit the self-renewal of colon cancer progenitor cells.