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.
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.
|Tsukamoto, Kosuke; Wales, Thomas E; Daniels, Kathleen et al. (2013) Noncanonical role of the PDZ4 domain of the adaptor protein PDZK1 in the regulation of the hepatic high density lipoprotein receptor scavenger receptor class B, type I (SR-BI). J Biol Chem 288:19845-60|
|Birrane, Gabriel; Mulvaney, Eamon P; Pal, Rinku et al. (2013) Molecular analysis of the prostacyclin receptor's interaction with the PDZ1 domain of its adaptor protein PDZK1. PLoS One 8:e53819|
|Tsukamoto, Kosuke; Buck, Lorenna; Inman, Walker et al. (2013) Challenges in using cultured primary rodent hepatocytes or cell lines to study hepatic HDL receptor SR-BI regulation by its cytoplasmic adaptor PDZK1. PLoS One 8:e69725|
|Brill, Alexander; Yesilaltay, Ayce; De Meyer, Simon F et al. (2012) Extrahepatic high-density lipoprotein receptor SR-BI and apoA-I protect against deep vein thrombosis in mice. Arterioscler Thromb Vasc Biol 32:1841-7|
|Kocher, Olivier; Birrane, Gabriel; Yesilaltay, Ayce et al. (2011) Identification of the PDZ3 domain of the adaptor protein PDZK1 as a second, physiologically functional binding site for the C terminus of the high density lipoprotein receptor scavenger receptor class B type I. J Biol Chem 286:25171-86|
|Kocher, Olivier; Birrane, Gabriel; Tsukamoto, Kosuke et al. (2010) In vitro and in vivo analysis of the binding of the C terminus of the HDL receptor scavenger receptor class B, type I (SR-BI), to the PDZ1 domain of its adaptor protein PDZK1. J Biol Chem 285:34999-5010|
|Yesilaltay, Ayce; Daniels, Kathleen; Pal, Rinku et al. (2009) Loss of PDZK1 causes coronary artery occlusion and myocardial infarction in Paigen diet-fed apolipoprotein E deficient mice. PLoS One 4:e8103|
|Fenske, Sara A; Yesilaltay, Ayce; Pal, Rinku et al. (2009) Normal hepatic cell surface localization of the high density lipoprotein receptor, scavenger receptor class B, type I, depends on all four PDZ dmains of PDZK1. J Biol Chem 284:5797-806|
|Kocher, Olivier; Krieger, Monty (2009) Role of the adaptor protein PDZK1 in controlling the HDL receptor SR-BI. Curr Opin Lipidol 20:236-41|
|Fenske, Sara A; Yesilaltay, Ayce; Pal, Rinku et al. (2008) Overexpression of the PDZ1 domain of PDZK1 blocks the activity of hepatic scavenger receptor, class B, type I by altering its abundance and cellular localization. J Biol Chem 283:22097-104|
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