腹膜乳斑缺氧激活胃癌干细胞Notch-1通路促进腹膜转移的机制研究

Growth of specific gastric cancer cell clone in appropriate peritoneal microenvironment results in peritoneal metastasis, which is a most life-threatening incidence in gastric cancer patients. Previous researches mainly concentrated on the characteristics of cancer cells, but payed little attention to the important role of the change of microenvironment of peritoneum in metastatic process. In previous trials, we discovered at the early stage of peritoneal metastasis of gastric cancer, the circumambience milky spots of hypoxic area, and the gastric cancer cells colonization located on the edge of hypoxic area. Previous researches revealed hypoxia induced EMT of cancer cells, leading to enrichment of cancer stem cells and maintenance of their self-renew ability. But the connection of hypoxic condition of peritoneal milky spots and peritoneal metastasis of gastric cancer is indistinct. Our previous trials revealed hypoxic microenvironment up-regulated hypoxia induced protein HIF-1α, which is an independent risk factor of gastric cancer mortality and distant metastasis. Furthermore, hypoxia induced activation of Notch-1 signaling pathway, leading to acquisition of stem cell-like properties of gastric cancer cells such as self-renew and anti-apoptosis abilities. In view of the previous trials, we hypothesized: the interaction of hypoxic microenvironment of peritoneal milky spots and gastric cancer stem cells is possible the key mechanism of gastric cancer peritoneal metastasis. The study is aimed to confirm that hypoxic microenvironment of peritoneal is favorable to the gastric cancer stem cells colonization and maintenance of self-renew ability; furthermore, to investigate the influence of hypoxia to the biological characteristics of gastric cancer stem cells; moreover, to explore the molecular mechanism of influence of biological characteristics of gastric cancer cell stem cells through activation of Nothch-1 signaling pathway, which is regulated by hypoxia.

胃癌腹膜转移是特殊癌细胞克隆在适宜的腹膜微环境中生长的结果。既往研究主要围绕癌细胞开展，针对腹膜微环境改变在腹膜转移中作用的研究甚少。前期实验我们发现在胃癌腹膜转移的早期，缺氧区域环形包绕乳斑，胃癌细胞定植在缺氧区域边缘。文献报道缺氧可以诱导肿瘤细胞EMT，使群体富含肿瘤干细胞并维持其自我更新能力，但是关于腹膜乳斑缺氧对胃癌腹膜转移影响的研究尚无报道。前期实验我们发现肿瘤缺氧微环境一方面可以上调缺氧相关蛋白HIF-1α明显降低患者预后、增加肿瘤远处转移风险；还可以通过激活Notch-1通路赋予胃癌细胞自我更新、抗凋亡等肿瘤干细胞特性。由此推测，腹膜乳斑缺氧微环境与胃癌干细胞相互作用可能是胃癌腹膜转移核心机制之一。本研究拟通过证实腹膜缺氧微环境适合胃癌干细胞定植并维持其自我更新能力，明确缺氧对胃癌干细胞生物学行为的影响，并探讨缺氧调控的Notch-1通路激活影响干细胞生物学行为的分子机制。

本研究的总体思路以腹膜乳斑是胃癌细胞入侵腹膜的门户这一临床现象为切入点，以乳斑缺氧微环境对GCSC 生物学行为的调控及Notch-1 通路激活对GCSC 自我更新和分化能力的影响为核心研究内容，以新的视角解释胃癌腹膜转移的成因，以期能够完善胃癌腹膜转移的分子机制。本研究发现HIF-1α广泛表达于胃癌原发灶及转移灶中，对胃癌生物学行为产生重要影响。HIF-1α阳性表达是影响胃癌预后的独立危险因素。HIF-1α阳性表达与某些肿瘤干细胞标志物OCT4及Nestin的表达呈正相关，参与了缺氧微环境对胃癌干细胞样细胞生物学行为的调控。缺氧微环境下HIF-1α调控胃癌干细胞样细胞，增强其自我更新能力，减弱其多向分化能力。腹膜乳斑是适合胃癌干细胞样细胞定植的理想干细胞龛，其内部缺氧微环境调控胃癌干细胞样细胞使其维持未分化状态，处于休眠状态。破坏乳斑缺氧微环境或者破坏乳斑内缺氧信号传递可以减轻裸鼠腹膜转移的程度。胃癌间断性和持续性缺氧模型均可以诱导胃癌细胞缺氧，增强其侵袭转移能力，增加胃癌细胞群体中干细胞样细胞比率。间断性缺氧是比持续性缺氧更有效的缺氧刺激。上述研究成果证明了乳斑缺氧微环境调控胃癌干细胞样细胞自我更新能力促进腹膜转移的发生发展，丰富了胃癌腹膜转移发生的理论研究，为胃癌的早期诊断或阻断治疗提供新的靶点。