Identification and Characterization of a Lysophosphatidylcholine Acyltransferase That is Primarily Expressed in Metabolic Tissues

Phosphatidylcholine (PC) is synthesized through the Kennedy pathway but more than 50% of PC is remodeled through Lands cycle, i.e. the deacylation and reacylation of PC to attain the final and proper fatty acids within PC. The reacylation step is catalyzed by lysophosphatidylcholine (LPC) acyltransferase (LPCAT) and we report here the identification of a novel LPCAT, which we named LPCAT3. LPCAT3 belongs to the membrane bound Oacyltransferase (MBOAT) family and encodes a protein of 487 amino acids with a calculated molecular weight of 56 kD. Membranes from HEK293 cells overexpressing LPCAT3 showed significantly increased LPCAT activity as assessed by thin layer chromatography analysis with substrate preference towards unsaturated fatty acids. LPCAT3 is localized within endoplasmic reticulum (ER) and is primarily expressed in metabolic tissues including liver, adipose and pancreas. In a human hepatoma cell line Huh7 cells, RNA interference (RNAi) mediated knockdown of LPCAT3 resulted in virtually complete loss of membrane LPCAT activity suggesting that LPCAT3 is primarily responsible for hepatic LPCAT activity. Furthermore, peroxisome proliferator-activator receptor α (PPARα) agonists dose-dependently regulated LPCAT3 in liver in a PPARα-dependent fashion, implicating a role of LPCAT3 in lipid homeostasis. Our studies identify a long-sought enzyme that plays a critical role in PC remodeling in metabolic tissues and provide an invaluable tool for future investigations on how PC remodeling may potentially impact glucose and lipid homeostasis. Introduction The biomembrane lipid bilayer serves as an important structure that compartmentalizes living cells and also forms organized intracellular membrane organelles for various physiological functions. The major and essential structural components of membrane lipid bilayers are phospholipids (PLs) including phosphatidylcholine (PC), phosphatidylserine (PS) and phosphatidylethanolamine (PE), among which PC is the most abundant in mammals. Besides the fundamental role in maintaining the membrane structure, some PLs such as phosphatidylinositol (PI) and diacylglycerol (DG) play important roles in signal transduction. The pathway of P http://www.jbc.org/cgi/doi/10.1074/jbc.M710422200 The latest version is at JBC Papers in Press. Published on January 14, 2008 as Manuscript M710422200 Copyright 2008 by The American Society for Biochemistry and Molecular Biology, Inc. by gest on Sptem er 6, 2017 hp://w w w .jb.org/ D ow nladed from