Regulation of TGFBeta-induced apoptosis in liver cells

TGFβ诱导的肝细胞凋亡的调节

• 批准号: 7119199
• 负责人: KUNXIN LUO
• 金额: $ 26.73万
• 依托单位: UNIVERSITY OF CALIFORNIA BERKELEY
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-21 至 2009-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7119199
• 关键词: apoptosis; biological signal transduction; cell growth regulation; cell line; cell proliferation; genetic regulation; immunoprecipitation; liver cells; phosphorylation; polymerase chain reaction; protein protein interaction; protein sequence; protein structure function; transfection; transforming growth factors

DESCRIPTION (provided by applicant): The tightly regulated homeostatic mechanisms between hepatocyte proliferation and apoptosis that exist in normal liver tissue are disrupted in many liver diseases and during hepatocarcinogenesis. The transforming growth factor beta (TGFbeta) signaling pathway is a central component of the mechanisms by which cell growth and apoptosis are regulated in the liver. The long-term objective of this project is to understand the molecular mechanism by which TGFbetaa regulates hepatocyte proliferation and apoptosis. TGFbeta is a potent inducer of hepatocyte apoptosis both in vivo and in vitro. The apoptotic activity of TGFbeta can be antagonized by the action of insulin and its downstream signaling molecules. This proposal is designed to understand how TGFbeta pathway and insulin pathway cross talk to regulate the sensitivity of hepatocytes to TGFbeta-induced apoptosis. Smad proteins are critical mediators of TGFbeta signaling. In the absence of ligand, Smad2 and Smad3 are located in the cytoplasm. Upon binding of TGFbeta to its receptors and the subsequent activation of the receptor serine/threonine kinases, Smad2 and Smad3 become phosphorylated by the receptor kinases and then translocate to the nucleus, where they can form heteromeric complexes with Smad4 and activate transcription of TGFbeta responsive genes. Among these Smad proteins, Smad3 has been shown to mediate TGFbeta-induced apoptosis. In a search for molecules that interact with Smad3, the P.I. identified Akt, a critical molecule functioning in the cell survival pathway downstream of insulin. Akt can directly interact with Smad3, and this interaction is regulated by TGFbeta and insulin. Because expression of an activated Akt results in protection of cells from TGFbeta-induced apoptosis, we hypothesized that Akt may protect cells from TGFbeta-induced apoptosis by interacting with Smad3 and preventing it from mediating the apoptotic signals of TGFbeta. The following specific aims are designed to further characterize the interaction between Akt and Smad3 and uncover the physiological significance of this interaction. The specific aims are: 1) Mapping the amino acid residues in Akt and Smad3 required for their interaction. 2) Analysis of the role of the Smad3- Akt interaction in protection from TGFbeta-induced apoptosis. 3) Analysis of the molecular mechanism by which Akt inhibits TGFbeta-induced apoptosis. In particular, we will investigate whether Akt inhibits Smad3 through affecting its phosphorylation or through physical sequestration. These studies will allow us to have a better understanding of how TGFa and insulin signaling pathways cross talk to regulate the sensitivity to TGFbeta-induced apoptosis. Since this cross talk plays an important role in the control of liver size and disruption of this highly regulated process can result in liver diseases and hepatocarcinogenesis, these studies may contribute to a better understanding of the maintenance of normal liver homeostasis and the cause of liver diseases.

描述（由申请人提供）：正常肝组织中存在的肝细胞增殖和凋亡中存在的严格调节的稳态机制在许多肝病中和肝癌发生期间都受到破坏。转化的生长因子β（TGFBETA）信号通路是细胞生长和凋亡在肝脏中调节的机制的核心组成部分。该项目的长期目标是了解TGFBETAA调节肝细胞增殖和凋亡的分子机制。 TGFBETA是体内和体外的肝细胞凋亡的有效诱导剂。 TGFBETA的凋亡活性可以通过胰岛素及其下游信号分子的作用来拮抗。该提案旨在了解TGFBETA途径和胰岛素途径如何交流以调节肝细胞对TGFBETA诱导的凋亡的敏感性。 SMAD蛋白是TGFBETA信号传导的关键介体。在没有配体的情况下，Smad2和Smad3位于细胞质中。 TGFBETA与其受体结合，并随后激活受体丝氨酸/苏氨酸激酶，SMAD2和SMAD3被受体激酶磷酸化，然后转移到细胞核中，在那里它们可以与Smad4形成异晶复合物，并激活TGFBBETA响应基因。在这些SMAD蛋白中，SMAD3已被证明可以介导TGFBETA诱导的凋亡。在寻找与p.i. Smad3相互作用的分子时鉴定出AKT，一种在胰岛素下游的细胞存活途径中起作用的临界分子。 AKT可以直接与SMAD3相互作用，并且这种相互作用受TGFBETA和胰岛素的调节。由于激活的AKT的表达会导致细胞免受TGFBETA诱导的凋亡的保护，因此我们假设AKT可以通过与SMAD3相互作用并防止其介导TGFBETA的凋亡信号来保护细胞免受TGFBETA诱导的凋亡。以下特定目标旨在进一步表征Akt和Smad3之间的相互作用，并揭示了这种相互作用的生理意义。具体目的是：1）映射AKT中的氨基酸残基和SMAD3的相互作用所需的SMAD3。 2）分析SMAD3-AKT相互作用在保护TGFBETA诱导的细胞凋亡中的作用。 3）分析AKT抑制TGFBETA诱导凋亡的分子机制。特别是，我们将研究AKT是通过影响SMAD3的磷酸化还是通过物理隔离来抑制SMAD3。这些研究将使我们能够更好地了解TGFA和胰岛素信号通路如何交流以调节对TGFBETA诱导的凋亡的敏感性。由于此杂音在控制肝脏大小和这种高度调节过程的破坏中起着重要作用，可能会导致肝病和肝癌发生，因此这些研究可能有助于更好地理解对正常肝稳态的维持以及肝病的原因。