Acyl-CoA:Lysophosphatidylcholine Acyltransferase I (Lpcat1) Catalyzes Histone Protein O-Palmitoylation to Regulate mRNA Synthesis

Abstract

The enzyme acyl-CoA:lysophosphatidylcholine acyltransferase (Lpcat1) is a critical cytosolic enzyme needed for lung surfactant synthesis that catalyzes an acyltransferase reaction by adding a palmitate to the sn-2 position of lysophospholipids. Here we report that histone H4 protein is subject to palmitoylation catalyzed by Lpcat1 in a calcium-regulated manner. The enzyme acyl-CoA:lysophosphatidylcholine acyltransferase (Lpcat1) was recently cloned from lung epithelia and is indispensable for generation of pulmonary surfactant. Lpcat1 catalyzes an O-acyltransferase reaction by covalently adding saturated acyl-CoAs (palmitoyl groups, 16:0) to its acceptor lysophospholipids. Specifically, in the lung, it catalyzes an oxyester linkage between palmitate and lysophosphatidylcholine to generate dipalmitoylphosphatidylcholine, the major surface tension-lowering component of pulmonary surfactant in the remodeling pathway (1, 2). However, Lpcat1 appears to be somewhat promiscuous and acts on substrates that include lysophosphatidylcholine, lysoplasmanylcholine, and lysophosphatidylglycercol (1-3). Notably, in addition to lipid substrates, O-acyltransferases can also lipidate some protein substrates (4 -7). These enzymes share a highly conserved histidine residue within a catalytic core that is essential for their functionality.Protein palmitoylation, a prototypical form of lipidation, is an important post-translational modification that occurs ubiquitously in eukaryotes. Protein palmitoylation is generally categorized as S-palmitoylation, N-palmitoylation, and O-palmitoylation based on the chemical linkage between donor and acceptor substrates. Among these, S-palmitoylation is best characterized and involves generation of a reversible thioester bond between a cysteine residue and a palmitate group (8). As many as 250 proteins were found to be modified by S-palmitoylation in mammalian neurons, and these reactions are largely catalyzed by aspartate-histidine-histidine-cysteine (DHHC) palmitoyl acyltransferase family members (8, 9). The biochemistry of N-palmitoylation and O-palmitoylation, however, is less studied. One known substrate for N-palmitoylation is the Sonic Hedgehog protein because its NH 2 -terminal cysteine is palmitoylated via an amide linkage by Hedgehog acyltransferase (Hhat) (5). O-Palmitoylation is exemplified by Wnt/Wg proteins that harbor an oxyester linkage between monounsaturated palmitate and a serine residue. Another recently described O-palmitoylation target, the peptide hormone preghrelin, is modified by octanoylation at a serine residue. The enzymes that catalyze the oxyester linkages within Wnt/Wg proteins and preghrelin are porcupine (6) and ghrelin O-acyltransferase (7), respectively. The physiological consequences of palmitoylation are diverse; by increasing substrate hydrophobicity, these lipidation reactions appear to modulate interactions of substrates with other biomolecules, often affecting signal transduction, protein stability, intracellular trafficking, and localization (10 -12).Histo...

Ubiquitination and Proteolysis in Acute Lung Injury

“…In a recent study it has been demonstrated that lipopolysaccharide causes polyubiquitination and subsequent degradation of acyl-CoA:lysophosphatidylcholine acyltransferase, an enzyme critically involved in the synthesis of the bioactive surfactant phospholipid, dipalmitoylphosphatidylcholine, using the Skp1-Cullin-F-box ubiquitin E3 ligase component, b -transducin repeat-containing protein. 33 Furthermore, in a murine model of Pseudomonas aeruginosa -induced surfactant deficiency, which was characterized by the loss of CTP: phosphocholine cytidylyltransferase a , a nuclear enzyme that catalyzes the rate-limiting step in phosphatidylcholine synthesis, lung injury could be prevented by inhibition of the Skp1-Cullin-F-box E3 ligase, which was shown to monoubiquitinate CTP:phosphocholine cytidylyltransferase a leading to its degradation. Thus, ubiquitination may be critically important in surfactant homeostasis and ALI.…”

LPS impairs oxygen utilization in epithelia by triggering degradation of the mitochondrial enzyme Alcat1

“…Fluorescent immunostaining was conducted as previously described (Zou et al, 2011b). Briefly, cells (2×10 5 ) were plated at 70% confluence onto 35-mm MatTek glass-bottomed culture dishes.…”

“…Murine lung epithelial (MLE) cells were cultured in HITES medium (500 ml of DMEM/F12, 2.5 mg of insulin, transferrin, sodium selenite, 2.5 mg of transferrin, 10 μM hydrocortisone, 10 μM β-estradiol, 10 mM Hepes, and 2 mM L-glutamine) and supplemented with 10% fetal bovine serum, as described previously (Zou et al, 2011b). MG132 (20 µM final concentration), leupeptin (20 µM final) and cycloheximide (10 µM) were purchased from Calbiochem.…”

Does Epigenetic Regulation Plays a Critical Role in Acute Lung Injury?

“…Interestingly, LPS treatment and bacterial infection triggers Lpcat1 to migrate into the nucleus. Nuclear Lpcat1 catalyzes a novel histone modification referred to as histone O-palmitoylation that regulates pro-inflammatory gene transcription [6,15]. LPS treatment also results in Histone acetyltransferases binding to origin recognition complex (HBO1) degradation [18].…”

“…Some of these chemical groups are well studied small chemicals that include the acetyl, methyl, or phosphorus groups. Some of them are small proteins such as ubiquitin, or even long chain fatty acid palmitoyl group [6].…”