The N-terminal region of acyl-CoA synthetase 3 is essential for both the localization on lipid droplets and the function in fatty acid uptake

Abstract

This article is available online at http://www.jlr.org developed very early during evolution. Cytosolic lipid droplets (LDs) are the main reservoir of lipids and are common to many if not all eukaryotic cells ( 1 ). LDs have gained much recent interest because of their regulatory role in lipid homeostasis and their implication in metabolic diseases such as obesity and type 2 diabetes ( 2-4 ). They have a unique structure composed of a hydrophobic core surrounded by a phospholipid monolayer containing a specifi c protein composition. Perilipin family proteins and lipid metabolizing enzymes are the most abundant proteins ( 5, 6 ), and proteomic studies have identifi ed many additional constituents ( 7 ). Little is known how proteins are specifi cally targeted to lipid droplets ( 8, 9 ). The biogenesis of LDs likely involves the endoplasmic reticulum, but the mechanism has not been solved and is debated intensely ( 2,3,10 ).Triglycerides are the main species of neutral lipids stored within the LDs of most cell types. The predominant biosynthetic pathway requires three activated fatty acids for each triglyceride molecule. The fatty acids are taken up from the extracellular medium or are derived from endogenous metabolism by fatty acid synthase. In fact, addition of fatty acids is a very effi cient way to induce the formation of LDs ( 4 ). However, fatty acids are chemically quite inert and need to be activated by esterifi cation with CoA ( 11 ). This activation is catalyzed by the family of acylCoA synthetases ( 12 ); physiologically highly relevant are the long chain (ACSL1, -3, -4, -5, -6) and very long chain (ACSVL1, -2, -3, -4, -5, and -6) fatty acyl-CoA synthetase subfamilies ( 13 ). Apart from their obvious enzymatic role, additional functions have been suggested for ACS(V)L family proteins: metabolic channeling of fatty acids toward specifi c metabolic fates [e.g., phospholipid synthesis vs.Abstract Cytosolic lipid droplets (LDs) are storage organelles for neutral lipids derived from endogenous metabolism. Acyl-CoA synthetase family proteins are essential enzymes in this biosynthetic pathway, contributing activated fatty acids. Fluorescence microscopy showed that ACSL3 is localized to the endoplasmic reticulum (ER) and LDs, with the distribution dependent on the cell type and the supply of fatty acids. The N-terminus of ACSL3 was necessary and sufficient for targeting reporter proteins correctly, as demonstrated by subcellular fractionation and confocal microscopy. The N-terminal region of ACSL3 was also found to be functionally required for the enzyme activity. Selective permeabilization and in silico analysis suggest that ACSL3 assumes a hairpin membrane topology, with the N-terminal hydrophobic amino acids forming an amphipathic helix restricted to the cytosolic leafl et of the ER membrane. ACSL3 was effectively translocated from the ER to nascent LDs when neutral lipid synthesis was stimulated by the external addition of fatty acids. Cellular fatty acid uptake was increased by overexpression and reduced b...

Fibrates Reduce Triacylglycerol Content by Upregulating Adipose Triglyceride Lipase in the Liver of Rats

“…The current study showed that ACSL3 was significantly upregulated by fibrates. Interestingly, a recent study using lined cells showed that ACSL3 is localized to the endoplasmic reticulum and cytosolic lipid droplets and that ACSL3 not only esterifies fatty acids with CoA but also is involved in the cellular uptake of fatty acids, presumably by indirect metabolic trapping, despite the fact that ACSL3 is not a fatty acid transporter (33). Therefore, it is likely that ACSL3 upregulated by fibrates activates and channels fatty acids toward the TAG synthesis pathway in the liver.…”

Epigenetic Alterations by DNA Methylation in House Dust Mite–Induced Airway Hyperresponsiveness

“…Acsl3 is located in 2q36.1, which is a region associated with the asthma susceptibility loci in specific human populations (29). Moreover, acsl3 belongs to the ACSL family of genes, which encode key enzymes in fatty acid metabolism (30). Silencing of acsl3 in lung tissue is expected to influence membrane phospholipid composition and generation Figure 4.…”

Identification of acyl-CoA synthetases involved in the mammalian sphingosine 1-phosphate metabolic pathway

“…ACSL3 expression exhibited the reticular ER structure as well as some ring-like structures. Since ACSL3 is reportedly localized to intracellular lipid droplets [15], we visualized these lipid droplets using nile red dye. We found that ACSL3 surrounded the nile red-stained lipid droplets, while the negative control ACSL1 did not (Fig.…”