Role of PDZK1 in lipid metabolism and atherosclerosis

描述(申请人提供)：接头、锚定和支架蛋白在信号转导中起重要作用。在许多情况下，信号蛋白之间的相互作用是由与特定蛋白结构域结合的小氨基酸序列介导的，如src同源(SH)、pTyr结合(PTB)或PDZ结构域。这些相互作用负责决定受体和转运蛋白的位置、功能和活性等。几年前，我们分离出一种新的蛋白质，我们将其命名为PDZK1。PDZK1含有四个PDZ蛋白相互作用结构域，与许多膜相关蛋白的羧基末端相互作用，包括高密度脂蛋白清道夫受体SR-BI和几个离子通道，其中一个参与多药耐药。因此，PDZK1可能在脂代谢和心血管疾病、离子通道组织和多药耐药等多种生物学过程中发挥重要作用。我们产生了一只PDZK1基因敲除小鼠，其特征是血浆胆固醇水平上升，肝脏SR-BI表达显著减少，导致胆固醇反向运输受损。PDZK1加入了ARH(常染色体隐性遗传性高胆固醇血症缺陷基因的产物)的行列，可能是一个不断壮大的细胞质适配器蛋白家族，控制细胞表面受体的组织特异性活动。最近，我们利用PDZK1 KO小鼠肝脏中截短形式的PDZK1过表达的转基因小鼠模型，确定了PDZK1的所有四个PDZ结构域对于正常的SR-BI表达、定位和功能都是必需的，尽管单个结构域，特别是PDZ2和PDZ4的确切作用尚不清楚。我们已经确定，除了与PDZ1的已知相互作用外，SR-BI还能够与PDZK1中的另一个位点相互作用。此外，我们还解决了PDZK1第一结构域的晶体结构及其与SR-BI的相互作用。我们还确定PDZK1具有动脉粥样硬化保护作用，这表明PDZK1可能是心血管疾病治疗的一个有吸引力的靶点。我们现在的目标是研究PDZK1/SR-BI蛋白质簇的分子组织。我们将定义PDZK1的第二和第四个PDZ结构域(PDZ2和PDZ4)的功能并确定它们的结合伙伴，通过X射线结晶学定义PDZK1的完整结构，以获得分子的三维结构，并了解PDZK1如何与其结合伙伴相互作用。我们将使用转基因小鼠模型将体外获得的结果关联起来，其中改变(突变/截短)的PDZK1转基因将在PDZK1KO小鼠的肝脏中表达。这些研究可能为促进胆固醇反向转运以防止动脉粥样硬化病变和心肌梗死形成的新疗法的开发提供必要的背景。 与公共卫生相关：几年前，我们分离出一种新的蛋白质，我们将其命名为PDZK1。PDZK1包含四个特定的结构域，使其能够与其他蛋白质相互作用，其中大多数与细胞膜有关。其中一种名为高密度脂蛋白(高密度脂蛋白)清道夫受体SR-BI的蛋白质参与了“好胆固醇”的代谢和预防冠心病。SR-BI受PDZK1调控。我们产生了一只PDZK1基因敲除小鼠，其中PDZK1被灭活，并确定PDZK1以组织特异性的方式控制SR-BI的表达。最近，我们确定PDZK1是预防动脉粥样硬化的蛋白质之一，这表明PDZK1可能是心血管疾病治疗的一个有吸引力的靶点。我们的目标是研究PDZK1/SR-BI蛋白簇的分子组织。这样的研究可能会导致新疗法的开发，目的是促进“好胆固醇”的代谢，以防止动脉粥样硬化病变和心肌梗死的形成。

DESCRIPTION (provided by applicant): Adaptor, anchoring and scaffolding proteins play an important role in signal transduction. In many situations, the interaction between signaling proteins is mediated by small amino acid sequences binding to specific protein domains, such as src homology (SH), pTyr-binding (PTB) or PDZ domains. These interactions are responsible for determining location, function and activity of receptor and transporter proteins among others. A few years ago, we isolated a novel protein that we named PDZK1. PDZK1 contains four PDZ protein-interaction domains and interacts with the carboxy-terminal portion of a number of membrane associated proteins including the high density lipoprotein (HDL) scavenger receptor SR-BI and several ion channels, one of them involved in multidrug resistance. As a result, PDZK1 is likely to play an important role in biological processes as diverse as lipid metabolism and cardiovascular disease, ion channel organization and multidrug resistance. We generated a PDZK1 knockout mouse which is characterized by increased plasma cholesterol levels and markedly reduced expression of SR-BI in the liver, resulting in impaired "reverse cholesterol transport". PDZK1 joins ARH (the product of the defective gene in autosomal recessive hypercholesterolemia) in what is likely to be a growing family of cytoplasmic adaptor proteins that control the tissue specific activity of cell surface receptors. More recently, we have determined, using a transgenic mouse model in which truncated forms of PDZK1 were overexpressed in the liver of PDZK1 KO mice, that all four PDZ domains of PDZK1 are necessary for normal SR-BI expression, localization and function, although the precise role of individual domains, PDZ2 and PDZ4 in particular, remains unknown. We have determined that SR-BI is able to interact with another site within PDZK1, in addition to the known interaction with PDZ1. In addition, we have solved the crystal structure of the first domain of PDZK1 and its interaction with SR-BI. We have also determined that PDZK1 is atheroprotective, suggesting that PDZK1 may be an attractive target for therapies in cardiovascular diseases. Our objectives are now to study the molecular organization of the PDZK1/SR-BI protein cluster. We will define the functions of the second and fourth PDZ domains (PDZ2 and PDZ4) of PDZK1 and identify their binding partners, define the complete structure of PDZK1 by X-ray crystallography to obtain a three dimensional structure of the molecule and understand how PDZK1 interacts with its binding partners. We will correlate the results obtained in vitro using a transgenic mouse model, where altered (mutated/truncated) PDZK1 transgenes will be expressed in the liver of PDZK1 KO mice. Such studies may provide the necessary background for the development of new therapies promoting reverse cholesterol transport to prevent the formation of atherosclerotic lesions and myocardial infarction. PUBLIC HEALTH RELEVANCE: A few years ago, we isolated a novel protein that we named PDZK1. PDZK1 contains four specific domains that allow it to interact with other proteins, most of them associated with the cell membrane. One of these proteins called the high density lipoprotein (HDL) scavenger receptor SR-BI participates in metabolizing the "good cholesterol" and preventing coronary heart disease. SR-BI is regulated by PDZK1. We generated a PDZK1 knockout mouse, in which PDZK1 is inactivated, and determined that PDZK1 controls the expression of SR-BI in a tissue specific fashion. More recently, we determined that PDZK1 is among the proteins that prevent atherosclerosis, suggesting that PDZK1 may be an attractive target for therapies in cardiovascular diseases. Our objectives are to study the molecular organization of the PDZK1/SR-BI protein cluster. Such studies may lead to the development of new therapies with the goal of promoting the metabolism of "good cholesterol" to prevent the formation of atherosclerotic lesions and myocardial infarction.