REGULATIONS OF BETA CATENIN BY PROTEIN PHOSPHATASE 2A

蛋白质磷酸酶 2A 对 β 连环蛋白的调节

• 批准号: 6362698
• 负责人: DAVID M VIRSHUP
• 金额: $ 23.6万
• 依托单位: UNIVERSITY OF UTAH
• 依托单位国家: 美国
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-03-01 至 2005-02-28
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6362698
• 关键词: Xenopus; biological signal transduction; cadherins; carcinogenesis; cell proliferation; clinical research; colon neoplasms; enzyme activity; gene induction /repression; genetically modified animals; human subject; laboratory mouse; oncoproteins; phosphoprotein phosphatase

The analysis of colorectal carcinomas suggests that deregulation of the Wnt pathway is an essential step in their malignant transformation. Understanding the regulation of this pathway may therefore lead to improved prevention and treatment of human carcinomas. One crucial function of the Wnt pathway in the colon is to regulate beta-catenin-dependent transcription via a phosphorylation-regulated signal transduction pathway. Although several kinases have been shown to regulate the Wnt pathway, no phosphatase has previously been clearly identified as a component of this pathway. Our data show that the B56 regulatory subunits of protein phosphatase 2A (PP2A) interact with the adenomatous polyposis coli (APC) protein, and that B56 overexpression causes decreased beta-catenin abundance, leading to decreased beta-catenin-dependent gene expression in mammalian tissue culture cells and Xenopus embryo explants. The overexpression of B56 appears to activate the phosphorylation-dependent, proteasome-mediated, degradation of beta-catenin. In addition, the phosphatase inhibitor okadaic acid causes increased levels of beta-catenin, as would be expected if PP2A inhibited Wnt signaling. Our results suggest, therefore, that the B56-containing PP2A holoenzyme is a key regulator of a Wnt signal transduction pathway. The objective of this proposal is to define the precise role of B56 and PP2A in the Wnt signal transduction pathway and the development of intestinal cancers. We propose to (1) identify critical Wnt pathway components that are PP2A:B56 substrates, (2) determine with which additional components of the pathway B56 interacts, (3) test if Wnt propagates its signal in part by regulating PP2A:B56 activity, and (4) use transgenic mice to test the hypothesis that overexpression of B56 suppresses colon carcinogenesis, while dominant-negative B56 alleles promote it.

对结直肠癌的分析表明，Wnt 通路的失调是其恶性转化的重要步骤。 因此，了解该途径的调节可能会改善人类癌症的预防和治疗。 结肠中 Wnt 通路的一项重要功能是通过磷酸化调节的信号转导通路来调节 β-连环蛋白依赖性转录。 尽管多种激酶已被证明可以调节 Wnt 通路，但此前尚未明确确定磷酸酶是该通路的组成部分。我们的数据表明，蛋白磷酸酶 2A (PP2A) 的 B56 调节亚基与腺瘤性结肠息肉病 (APC) 蛋白相互作用，并且 B56 过度表达会导致 β-连环蛋白丰度降低，从而导致哺乳动物组织中 β-连环蛋白依赖性基因表达降低培养细胞和非洲爪蟾胚胎外植体。 B56 的过度表达似乎会激活磷酸化依赖性、蛋白酶体介导的 β-连环蛋白降解。 此外，磷酸酶抑制剂冈田酸会导致 β-连环蛋白水平升高，正如 PP2A 抑制 Wnt 信号传导所预期的那样。因此，我们的结果表明，含有 B56 的 PP2A 全酶是 Wnt 信号转导途径的关键调节因子。 该提案的目的是明确 B56 和 PP2A 在 Wnt 信号转导途径和肠癌发展中的精确作用。 我们建议 (1) 确定作为 PP2A:B56 底物的关键 Wnt 通路成分，(2) 确定 B56 通路的哪些其他成分相互作用，(3) 测试 Wnt 是否部分通过调节 PP2A:B56 活性来传播其信号， (4)使用转基因小鼠来检验B56过度表达抑制结肠癌发生，而显性失活B56等位基因促进结肠癌发生的假设。