HMGA2通过MDM2依赖的途径促进p53泛素化降解的分子机制研究

HMGA2 and p53 are both oncoproteins that are involved in colorectal (CRC) carcinogenesis. However, their relationship is still unclear. Our previous studies indicated that HMGA2 bound directly to p53 and MDM2, which were verified by Co-IP assay. Furthermore, the exact binding sites were determined. On the basis of the Hmga2 knock-in mice lines, which conditionally expressed Hmga2 in the intestine, we found that Hmga2 was able to promote the intestinal tumorigenesis. In this study, we hypothesize that HMGA2-mediated p53 ubiquitination plays an important role in tumorigenesis and tumor progression of colorectal cancer, in a MDM2 dependent way. Co-IP, GST pull-down, yeast two-hybrid, ubiquitination assays and genetically modified mice were applied. Taken together, our study provides new insights into the mechanisms of HMGA2’s role in colorectal cancer and new therapeutic targets for the treatment of CRC cancer.

HMGA2、p53均是与结肠癌发生发展密切相关的重要原癌蛋白，但它们的关系尚不明确。我们前期研究高度提示HMGA2与p53、MDM2之间可以直接结合，并利用正反向Co-IP实验进行了验证，进一步通过截断蛋白Co-IP实验明确了它们的结合位点。我们在前期构建的肠道特异性Hmga2 KI小鼠成瘤模型中发现Hmga2能显著促进肠道肿瘤形成。本项目拟在此基础上，通过全长及截短Co-IP、GST pull-down、酵母双杂交、p53泛素化、CHX、MG132处理等实验，揭示HMGA2通过MDM2依赖的途径促进p53泛素化降解的过程及分子机制，阐明HMGA2通过p53依赖的途径调控细胞周期和凋亡，并利用多种基因修饰小鼠揭示Hmga2及p53相互作用对结肠癌发生发展的影响，进而完成HMGA2与p53蛋白之间的交互作用关系及分子机制的系统深入研究，为今后以此为靶点进行临床干预提供实验基础和理论依据。

结直肠癌是最常见的消化道恶性肿瘤，严重危害人类健康。HMGA2 (high mobility group AT-hook 2)，即高迁移率族蛋白A2，作为一个癌蛋白，在多种恶性肿瘤中高表达。在本项目中，首先我们发现在结直肠癌中，HMGA2能够通过MDM2依赖的途径促进p53蛋白的降解，进而促进细胞的增殖并抑制其凋亡而调控其恶性进展。其次，我们发现与正常对照相比，结直肠癌患者中的血清循环HMGA2 mRNA表达升高，并且其表达水平在右半、神经浸润阳性、血管浸润阳性、微卫星不稳定和CA199≥37的结直肠癌患者中较高。另外，我们发现在结直肠癌中，PRMT5和MCM7在促进细胞的增殖、迁移和侵袭过程中发挥重要作用，并且我们发现PRMT5表达与结直肠癌患者的预后呈负相关。除此之外，我们使用体内小鼠皮下成瘤模型、条件性Hmga2敲入小鼠的AOM+DSS成瘤模型以及体外肿瘤细胞/巨噬细胞共培养模型，发现HMGA2能够通过STAT3依赖的途径促进巨噬细胞趋化因子CCL2的表达，由此促进肿瘤相关巨噬细胞的招募和M2型极化。综上所述，本项目揭示了HMGA2在结直肠癌发生和发展过程中的功能和分子机制，我们发现HMGA2除了对肿瘤细胞本身产生促癌作用之外，还参与了微环境中肿瘤相关巨噬细胞的招募过程，这些研究为将来以血清循环HMGA2 mRNA表达作为早期诊断结直肠癌的标记物和以HMGA2为靶点治疗结直肠癌提供了理论依据。