Challenging the dominant model for ATP regulation of KATP channels

挑战 KATP 通道 ATP 调节的主导模型

• 批准号: 8630333
• 负责人: Joseph Bryan
• 金额: $ 36.12万
• 依托单位: PACIFIC NORTHWEST RESEARCH INSTITUTE
• 依托单位国家: 美国
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8630333
• 关键词: ATP Hydrolysis; ATP phosphohydrolase; Address; Adenine Nucleotides; Adenylyl Imidodiphosphate; Affect; Affinity; Agonist; Binding; Biological Assay; Blood Glucose; CRSP3 gene; Cells; Consensus; Coupling; Data; Diabetes Mellitus; Diazoxide; Dimerization; Disease; Dose; Drug usage; Equilibrium; Genes; Genetic Polymorphism; Goals; Health; Hormones; Hydrolysis; Hyperactive behavior; Hyperinsulinism; Hypoglycemic Agents; Islets of Langerhans; Kir6.2 channel; Laboratories; Membrane Potentials; Metabolic Control; Metabolism; MgADP; Modeling; Molecular Conformation; Mutation; Neonatal; Neurons; Neurosecretory Systems; Non-Insulin-Dependent Diabetes Mellitus; Nucleotides; Pancreas; Pathologic; Patients; Persistent Hyperinsulinemia Hypoglycemia of Infancy; Physiological; Play; Potassium Channel; Potassium Channel Binding; Predictive Value; Property; Proteins; Regulation; Reporting; Research; Risk; S cerevisiae SWI3 protein; Secondary to; Structural Models; Sulfonylurea Compounds; Testing; Time; Vanadates; Variant; Work; analog; base; blood glucose regulation; clinical phenotype; cofactor; diabetes risk; enzyme substrate; glucose metabolism; inorganic phosphate; insight; insulin secretion; mutant; neonatal diabetes mellitus; novel; patch clamp; prevent; programs; receptor

DESCRIPTION (provided by applicant): The long-term objective of this program is to understand the regulation of ATP-sensitive K+, KATP, channels by adenine nucleotides; the short-term goal is to challenge the prevailing regulatory model. The levels of adenine nucleotides, ATP and ADP, in pancreatic ß-cells vary with the rate of glucose metabolism. KATP channels respond to these variations and are key players in the normal control of insulin secretion by blood glucose. These channels are the targets for sulfonylureas, hypoglycemic drugs used to treat type 2 diabetes. Mutations in the ABCC8/SUR1 or KCNJ11/Kir6.2 channel components are causes of neonatal diabetes (ND) and neonatal hyperinsulinism (HI) while polymorphisms in both subunits confer increased risk for type 2 diabetes. The prevailing regulatory hypothesis, used to interpret how mutations and polymorphisms alter channel activity, is that ATP hydrolysis at SUR1 is required to counteract or antagonize the inhibitory action of ATP on the Kir6.2 pore. Thus an overactive SUR1 produces ND by 'hyperactivating' the Kir6.2 pore. Altered SUR1 ATPase activity is proposed to underlie hyperactivation and the increased risk posed by ABCC8 polymorphisms. A recent study from our laboratory challenges the prevailing model (Ortiz et al, JBC, 2012). This study used two ND mutant SURs, without an associated Kir6.2, to define the allosteric relations between ATP and sulfonylurea binding with changes in SUR1 conformation. We established that ATP hydrolysis is not essential to switch SUR1 into a stimulatory conformation and proposed that an increased affinity for ATP is the underlying cause of the disorder. This study has now been extended to show there is a direct relation between the affinity of SUR1 for ATP and clinical phenotype; SURs with greater than normal affinity for ATP correlate with neonatal diabetes, those with lower affinity correlate with congenital hyperinsulinism. The negative allosteric relation between ATP and sulfonylurea interactions with SUR1 underlies the known need for higher doses of sulfonylureas to achieve metabolic control in ND patients. The proposed work will extend the analysis to full channels using pharmacologic and electrophysiologic studies on additional ND SUR1 mutants, polymorphisms, and on SURs with substitutions that inhibit ATPase activity. Previous studies on the action of ATP analogs on KATP channel function are used to support the prevailing model, thus additional work is proposed to define their action on conformational switching of SUR1. The overall objective of the project is to develop the data required to modify the prevailing model so that it can adequately explain regulation of KATP channels under normal physiologic conditions and has predictive value for understanding how mutations, particularly ABCC8 mutations, affect channel function.

描述（由申请人提供）：该项目的长期目标是了解腺嘌呤核苷酸对 ATP 敏感的 K+、KATP 通道的调节；短期目标是挑战现行的腺嘌呤调节模式。胰腺β细胞中的核苷酸、ATP 和 ADP 随葡萄糖代谢速率的变化而变化，KATP 通道对这些变化做出反应，并且是正常控制血液胰岛素分泌的关键因素。这些通道是用于治疗 2 型糖尿病的降血糖药物磺酰脲类药物的靶标。ABCC8/SUR1 或 KCNJ11/Kir6.2 通道成分的突变是导致新生儿糖尿病 (ND) 和新生儿高胰岛素血症 (HI) 的原因。两个亚基都会增加 2 型糖尿病的风险，用于解释突变和多态性如何改变通道活性的普遍监管假设是： SUR1 上的 ATP 水解需要抵消或拮抗 ATP 对 Kir6.2 孔的抑制作用，因此过度活跃的 SUR1 通过“过度激活”Kir6.2 孔而产生 ND，认为 SUR1 ATP 酶活性的改变是过度激活和增加的基础。 ABCC8 多态性带来的风险。我们实验室最近的一项研究挑战了流行的模型（Ortiz 等人，JBC， 2012)。这项研究使用了两个 ND 突变体 SUR，没有相关的 Kir6.2，来定义 ATP 和磺酰脲结合与 SUR1 构象变化之间的变构关系，我们确定 ATP 水解对于将 SUR1 转变为刺激性构象并不重要。提出对 ATP 的亲和力增加是该疾病的根本原因。这项研究现已扩展，表明 SUR1 对 ATP 的亲和力与临床之间存在直接关系。表型；对 ATP 的亲和力高于正常值的 SUR 与新生儿糖尿病相关，而亲和力较低的 SUR 与先天性高胰岛素血症相关。拟议的工作将利用对其他 ND SUR1 突变体、多态性和 SUR 的药理学和电生理学研究将分析扩展到全通道。先前关于 ATP 类似物对 KATP 通道功能的作用的研究被用来支持流行的模型，因此建议进行额外的工作来定义它们对 SUR1 构象转换的作用。开发修改现行模型所需的数据，使其能够充分解释正常生理条件下 KATP 通道的调节，并对理解突变（特别是 ABCC8 突变）如何影响通道功能具有预测价值。