子宫内膜癌Leptin抑制IGFBP7表达机制的研究

Hyperinsulinemia, the hallmarker of metabolic syndrome, is closely associated with endometrial carcinoma. The insulin/insulin-like growth factor 1 (IGF1)-insulin-like growth factor binding proteins (IGFBPs) axis and adipokines are two major pathways that play essential roles in the pathogenesis of hyperinsulinemia-related endometrial carcinoma.Insulin-like growth factor binding protein 7 (IGFBP7) is the most important IGFBPs that regulates the bioavailability of insulin while leptin is the most important adipokine in metabolic syndrome related cancer. IGFBP7 is proved to be a tumor suppressor gene in colorectal cancers in our previous studies. Our recent epidemiological study indicated that Chinese women with high serum IGFBP7 have lower endometrial cancer risks while those with high serum insulin or leptin have increased cancer risks. Leptin can suppress IGFBP7 expression and upregulate SOX9 expression in endometrial cancer cells. SOX9 is the dowanstream transcript factor of Wnt pathway. Bioinformatics analysis indicates the presence of SOX9 regulatory elements in the 5'-region of IGFBP7.However,there is no regulatory elements of the trasncript factors in ERK1/2 MAPK pathway, which is closely associated with leptin function in endometrial carcinoma. Thus, we hypothesize that leptin might regulate IGFBP7 expression via a possible crosstalk between ERK1/2 MAPK pathway and Wnt pathway.SOX9 will be the potential target gene that directly interacts with the 5'-region of IGFBP7. Our ongoing work will try to confirm this hypothesis by using common molecular and cellular biological methods. This work will be of great significance in the prevention and intervention of metabolic syndrome-related endometrial carcinoma.

高胰岛素血症主要通过调节胰岛素/IGF1-IGFBPs轴功能、脂肪因子分泌来促进子宫内膜癌的发展。IGFBP7是调节胰岛素生物可利用度最重要的IGFBPs，是一个肿瘤抑制基因。Leptin则是最重要的脂肪因子。申请人流行病学研究发现，血清IGFBP7升高是子宫内膜癌发生的保护因素，Leptin升高是一个促癌因素。Leptin可抑制子宫内膜癌细胞表达IGFBP7，并上调Wnt信号通路转录因子SOX9的表达。生物信息学分析发现在IGFBP7的5'-区存在SOX9的作用元件，但无Letpin下游ERK1/2 MAPK信号通路相关转录因子的作用元件。基于前述工作，我们推测Leptn可能通过ERK1/2 MAPK和Wnt信号通路（SOX9）之间的Crosstalk来调控IGFBP7的表达。本项目将通过经典的细胞与分子生物学手段来验证这一假说，为子宫内膜癌的预防、干预提供新的作用靶点。

高胰岛素血症是代谢综合征的标志，它主要通过调节胰岛素/IGF1-IGFBPs轴功能、脂肪因子分泌来促进子宫内膜癌的发展。IGFBP7是调节胰岛素生物可利用度最重要的IGFBPs，Leptin则是代谢综合征及相关肿瘤发生中最重要的脂肪因子。本项目检测IGFBP7、Leptin等蛋白在子宫内膜癌组织及癌旁组织中的表达，观察Leptin对子宫内膜癌细胞IGFBP7表达的影响；结合MAPK信号通路抑制剂PD98059、β-Catenin 和SOX9基因沉默，明确ERK1/2 MAPK信号通路、Wnt信号通路在Leptin调控子宫内膜癌细胞IGFBP7表达中的作用；报告基因、染色质免疫共沉淀、凝胶阻滞实验等鉴定转录因子SOX9和IGFBP7的5’-调控区SOX9作用元件的结合和表达调控能力。通过上述研究，我们发现：IGFBP7在I型子宫内膜癌组织中高表达，但发现它在体外细胞系促进细胞凋亡、抑制细胞增殖，发挥肿瘤抑制基因的功能。Leptin抑制子宫内膜癌细胞表达IGFBP7，同时使p-Ob-R、p-ERK和p-GSK3β水平升高，β-Catenin蛋白胞浆蓄积增加，表明Leptin通过激活MAPK/ERK信号通路和Wnt信号通路抑制子宫内膜癌细胞表达IGFBP7。但是，PD98059处理对Leptin所致的β-Catenin胞浆蓄积影响并不明显。Leptin诱导的子宫内膜癌细胞IGFBP7表达抑制作用受β-Catenin沉默和SOX9沉默影响。β-Catenin沉默阻断Leptin对子宫内膜癌细胞IGFBP7表达的抑制作用，SOX9沉默则增强Leptin对IGFBP7表达的抑制效应。PD98059处理也不影响前述β-Catenin和SOX9的沉默效应。因此，在Leptin抑制子宫内膜癌细胞表达IGFBP7的作用机制中，推测MAPK/ERK信号通路和Wnt信号通路之间可能不存在crosstalk。Wnt信号通路转录因子SOX9通过与IGFBP7 5’-启动子区域的相互作用从转录水平实现对IGFBP7的表达调控。项目明确Leptin-β-Catenin -SOX9-IGFBP7轴的表达调控机制，该轴作为“高胰岛素血症-子宫内膜癌”作用途径的主要联系节点，将为代谢综合征相关子宫内膜癌的预防、干预提供新的作用靶点。