The biology of gastrin-ferric ion complexes

描述(由申请人提供)：该项目的长期目标是了解铁离子和非酰胺化胃泌素(NAG)之间的络合物的生物学意义。这个实验室已经证明，NAG选择性地结合2个铁离子，铁离子结合对于体外生物活性是必不可少的，胃泌素与转铁蛋白相互作用。该项目的具体目标是：(1)确定铁离子是否在体内对NAG刺激结直肠癌(CRC)的发展是必需的；(2)开发NAG拮抗剂；(3)确定NAG在铁稳态中的作用；(4)确定NAG-转铁蛋白复合体在细胞离子摄取中的作用并确定其结构。该项目的健康意义在于，NAG作为正常胃和结肠粘膜的生长因子，加速胃和结直肠癌的发展，并可能参与铁稳态的紊乱。研究设计反映了特定的目标，并利用了主要调查人员独特的技能组合。首先，已知可以阻止铁离子与NAG结合的试剂将作为NAG抑制剂在四种结直肠癌发展的动物模型中进行测试。其次，交换惰性金属离子-NAG络合物和结构修饰的胃泌素片段将作为NAG抑制剂在结直肠癌细胞系和动物模型中进行测试。第三，在饮食铁摄取改变的小鼠和血色沉着症患者中，将通过放射免疫测定来测量孕激素的表达和加工模式。高胃泌素血症和胃泌素缺乏的转基因小鼠饮食中铁摄取改变，以及高胃泌素血症患者的铁状况也将被测量。第四，将研究胃泌素/转铁蛋白复合体在细胞铁转运中的作用，并将使用共价交联和一组NAG和转铁蛋白突变体的X射线结晶学来确定形成复合体的结构要求。这些研究有望证明铁离子在体内胃泌素生物活性中的意想不到的作用，以及胃泌素在铁离子动态平衡中的作用。认识到金属离子对NAG的生物活性是必不可少的，这可能会促进结肠癌新疗法的发展。

DESCRIPTION (provided by applicant): The long-term objective of this project is to understand the biological significance of the complex between ferric ions and non-amidated gastrins (NAGs). This laboratory has shown that NAGs selectively bind 2 ferric ions that ferric ion binding is essential for biological activity in vitro, and that gastrin interacts with transferrin. The specific aims of the project are: (1) to determine whether or not ferric ions are essential for the stimulation of colorectal carcinoma (CRC) development by NAGs in vivo, (2) to develop NAG antagonists, (3) to establish the role of NAGs in iron homeostasis, and (4) to define the role of the NAG-transferrin complex in cellular ion uptake and determine its structure. The health significance of the project lies in the facts that NAGs act as growth factors for the normal gastric and colonic mucosa, accelerate the development of both gastric and colorectal cancer, and may be involved in disorders of iron homeostasis. The research design mirrors the specific aims, and utilizes the unique combination of skills of the principal investigators. Firstly, agents known to block the binding of ferric ions to NAGs will be tested as NAG inhibitors in four animal models of CRC development. Secondly, exchange inert metal ion-NAG complexes and structurally modified gastrin fragments will be tested as NAG inhibitors in CRC cell lines and in animal CRC models. Thirdly, patterns of progastrin expression and processing will be measured by radioimmunoassy in mice with altered dietary iron uptake, and in patients with hemochromatosis. Iron status will also be measured in hypergastrinemic and gastrin-deficient transgenic mice with altered dietary iron uptake, and in patients with hypergastrinemia. Fourthly, the role of the gastrin/transferrin complex in cellular iron trafficking will be investigated, and covalent cross-linking and X-ray crystallography with a panel of NAG and transferrin mutants will be used to define the structural requirements for formation of the complex. These studies are expected to demonstrate an unexpected role for ferric ions in gastrin bioactivity in vivo, and for gastrins in ferric ion homeostasis. Recognition that metal ions are essential for the biological activity of NAGs may permit the development of novel therapies for colon cancer.