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...

Background: HBO1 is a crucial enzyme needed for DNA replication, yet mechanisms for its disposal are unknown. Results: A ubiquitin E3 ligase subunit, Fbxw15, mediates HBO1 degradation in concert with Mek1 kinase after endotoxin exposure. Conclusion: Fbxw15 targets HBO1 for its site-specific ubiquitination and degradation leading to reduced histone acetylation and cellular proliferation. Significance: The molecular control of HBO1 protein levels may impact fundamental cellular processes during inflammation.

with Arg abrogated LPCAT1 polyubiquitination. LPS profoundly reduced immunoreactive LPCAT1 levels and impaired lung surfactant mechanics, effects that were overcome by siRNA to ␤-TrCP and GSK-3␤ or LPCAT1 gene transfer, respectively. Thus, LPS appears to destabilize the LPCAT1 protein by GSK-3␤-mediated phosphorylation within a canonical phosphodegron for ␤-TrCP docking and site-specific ubiquitination. LPCAT1 is the first lipogenic substrate for ␤-TrCP, and the results suggest that modulation of the GSK-3␤-SCF␤ TrCP E3 ligase effector pathway might be a unique strategy to optimize dipalmitoylphosphatidylcholine levels in sepsis.

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