大肠癌SM22表达下调的机制及在NF-κB激活中的意义

Smooth muscle (SM) 22 (namely transgelin) is recently identified as a novel biomarker which is closely associated with poor prognosis in colorectal cancer patients. SM22 inhibits inflammation and cell proliferation. The disruption of SM22 has been reported in a variety of cell types on transformation. We hypothesized that the disruption of SM22 may be the novel molecular mechanisms which results in the development and poor prognosis in colorectal cancer via activation of NF-κB pathway. To address this issue, we will identify the characteristics of SM22 expression and investigate the relationship among downregulation of SM22, NF-κB activation and inflammatory factor expression in patients with colorectal cancer. The project is going to determine the mechanisms of SM22 disruption in colorectal cancer based on the perspective of epigenetics, signaling transduction and protein modification, respectively, and to clarify the signaling pathways of SM22 disruption activating NF-κB, as well as the relationship with tumor cell growth and invasion. The project will confirm the antiinflammation and antineoplasmic activity of SM22 in vivo using colorectal cancer model in Sm22?/? mice. Our research will find new molecular therapeutic target, provide insight for understanding the molecular mechanisms governing colorectal cancer development as well as predicting the prognosis of colorectal cancer patients.

平滑肌（SM）22是新近发现的一种与细胞转化和肿瘤不良预后有关的细胞骨架相关蛋白，具有抗炎和抗增殖活性。在肿瘤和转化的细胞中，SM22表达下调。我们假设，SM22缺失介导的NF-κB活化是大肠癌慢性炎症新的信号调节机制。本项目拟探讨临床大肠癌组织SM22下调与肿瘤炎症标志物表达活性的关系及其与大肠癌进展的临床病理相关性；分析大肠癌组织的sm22启动子甲基化水平、TGFβ-Smad3途径活性和SM22泛素化降解速率，在细胞水平上，分别从表观遗传学、信号转导和蛋白质修饰角度，阐明大肠癌SM22表达缺失的分子机制；通过考察SM22对大肠癌细胞IκBα-NF-κB、CK-II- NF-κB和Sirt1- NF-κB相互作用的影响，揭示SM22缺失激活NF-κB的信号途径和干预靶点。利用sm-/-小鼠建立大肠癌模型，证实体内SM22的抗炎和抗肿瘤活性。以期为大肠癌炎症学说提供新的理论依据及药物靶标。

基于SM22α是一种新的肿瘤抑制因子，在肿瘤转化过程中表达下降，启动子甲基化是基因转录沉默的一种表观遗传学机制，本项目用MS-qPCR分析52例患者肿瘤组织中的SM22α基因启动子区甲基化水平，其中，53.85%(28/52)肿瘤组织中SM22α启动子甲基化水平较癌旁正常组织升高（P<0.05）。Western blot分析，发现67.31%的患者（35/52）SM22α在肿瘤组织中的表达水平明显低于癌旁正常组织（P<0.05）。24例肿瘤组织中SM22α启动子甲基化水平增高而蛋白表达水平降低，启动子甲基化水平降低而蛋白表达增高者13例，两者均高者为4例，均低者为11例。此外，采用人大肠癌细胞株HT29细胞条件培养基(TCM)孵育VSMC，观察其对VSMC增殖的影响。研究表明，肿瘤条件培养基通过激活Caspase3和提高Bax/Bcl2比值，进而诱导血管平滑肌细胞凋亡。第三，首次证实血小板表达的DR5可介导TRAIL诱导的肿瘤细胞侵袭。本项目分别揭示了大肠癌SM22α转录沉默、血小板诱导肿瘤细胞侵袭及肿瘤血管结构缺陷的新机制及其在大肠癌发生发展中的意义，为大肠癌的临床干预提供了研究证据和靶点。