结直肠癌是常见的恶性肿瘤，其发生发展可由肿瘤干细胞调控，但目前对调控结直肠癌肿瘤干细胞干性的分子及机制尚未阐明。本项目通过分析临床标本及构建多种细胞模型发现：负性共刺激分子B7-H3高表达于结直肠癌肿瘤干样细胞中，且干扰B7-H3后，肿瘤干细胞干性特征显著下降。在机制方面，利用免疫共沉淀及蛋白质谱分析发现，B7-H3通过结合癌基因编码蛋白c-Met，引起下游Stat3磷酸化水平下调，进而通过Twist1蛋白引起干性基因Bmi1表达改变，从而导致干性特征改变。本项目以肿瘤干细胞干性调控为切入点，根据B7-H3与结直肠癌肿瘤干细胞干性的相关性研究，利用临床标本、细胞株及模型动物进行体内外实验论证B7-H3通过c-Met/p-Stat3/Twist1/Bmi1信号维持肿瘤干细胞干性。本项目将从肿瘤干性这个新视点阐明B7-H3在结直肠癌细胞中异常表达的生物学作用及机制，为结直肠癌的治疗提供新思路。

Colorectal cancer is one of the most lethal cancers of the gastrointestinal system. The concept of tumor development driven by a unique subpopulation of cancer stem cells (CSCs) may help to explain the high mortality, low response to treatment and tendency of developing multiple tumors in cancer. However, the molecular mecshanim regulated the cancer stem cells are remain to be elucidated. The B7-H3, a kind of B7 family negative costimulatory molecular, mediates tumor evasion of immunosurveillance. Our previous study has found that B7-H3 was abnormally expressed in colorectal cancer (CRC) tissues, correlating to CRC stages and tumor progression; B7-H3 is highly expressed in CD133 positive fractions by flow cytometry; Blocking B7-H3 by siRNAs in CRC cell lines reduced formation of spheroids, expression of stem cell associated genes and surface marker of cancer stem cell; Mechanismly, B7-H3 could bind to c-Met which is an important oncogene by Co-IP and mass spectrometry assay. Knockdown B7-H3 reduced phosphorylation level of Stat3 which was considered as downstream of c-Met signal pathway. Furthermore, Bmi1, which regulated by Stat3 signal and Twist1, is considered as effector gene to maintain stemness of CRC. On this basis, we have analyzed the correlation between B7-H3 and Bmi1 in clinical samples. Tissue IHC analysis of CRC specimens from 197 patients revealed a close correlation between B7-H3 expression and Bmi1 levels. We will further confirm the feature and mechanism of cancer stemness regulation by B7-H3/c-Met/Stat3/Twist1/Bmi1 signal pathway via in vitro and in vivo experiments. In general, the achievement of this program will improve the stemness regulation mechanism research of B7-H3 and provide the new target for clinical tumor immunotherapy.