linoleic-acid and benzyloxycarbonylleucyl-leucyl-leucine-aldehyde

Dietary ω-6 lipids such as linoleic acid and its oxidized forms (13-HPODE OxLA) interact with peroxisome proliferator-activated receptors (PPARs) and elicit pro and anti-atherogenic effects in vascular cells. Ligand-dependent PPAR protein turnover is promoted by ubiquitination, but attenuated by binding to its co-activator, peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1α). The objective of our study was to investigate if the dual atherogenic effects of ω-6 lipids are due to its regulation of PPAR turnover.. In rat aortic smooth muscle cells (RASMCs), oxidized linoleic acid (OxLA) at 10-50 μM induced and stabilized PPARα protein at earlier time points (0-4 h) but suppressed it at 12 h. Conversely, it activated PPARγ protein turnover at a later time point (12 h). Pre-treatment with the proteasome inhibitor (MG132) prevented OxLA mediated loss of PPAR stability and transactivity. Co-immunoprecipitation studies indicated a ligand mediated time-dependent reciprocal exchange of PPAR interaction between ubiquitination and PGC-1α. This ω-6 lipid mediated time-dependent switch between PPAR degradation versus stability helped modulate the pro and anti-atherogenic effects of these dietary lipids.. Our findings provide insights into the dual pro and anti-atherogenic effects of dietary ω-6 lipids on vascular cells by the regulation of PPAR turnover.

Topics: Animals; Aorta; Cells, Cultured; Cysteine Proteinase Inhibitors; Gene Expression Regulation; Immunoprecipitation; Leupeptins; Ligands; Linoleic Acid; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Oxidation-Reduction; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; PPAR alpha; PPAR gamma; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Protein Binding; Protein Stability; Proteolysis; Rats; RNA-Binding Proteins; RNA, Messenger; Time Factors; Transcription Factors; Transcriptional Activation; Transfection; Ubiquitination

Proteasomes are multicatalytic proteinase complexes within cells that selectively degrade ubiquitinated proteins. We have recently demonstrated that fatty acids, major components of cell membranes, are able to regulate the proteasomal degradation of tyrosinase, a critical enzyme required for melanin biosynthesis, in contrasting manners by relative increases or decreases in the ubiquitinated tyrosinase. In the present study, we show that altering the intracellular composition of fatty acids affects the post-Golgi degradation of tyrosinase. Incubation with linoleic acid (C18:2) dramatically changed the fatty acid composition of cultured B16 melanoma cells, i.e. the remarkable increase in polyunsaturated fatty acids such as linoleic acid and arachidonic acid (C20:4) was compensated by the decrease in monounsaturated fatty acids such as oleic acid (C18:1) and palmitoleic acid (C16:1), with little effect on the proportion of saturated to unsaturated fatty acid. When the composition of intracellular fatty acids was altered, tyrosinase was rapidly processed to the Golgi apparatus from the ER (endoplasmic reticulum) and the degradation of tyrosinase was increased after its maturation in the Golgi. Retention of tyrosinase in the ER was observed when cells were treated with linoleic acid in the presence of proteasome inhibitors, explaining why melanin synthesis was decreased in cells treated with linoleic acid and a proteasome inhibitor despite the abrogation of tyrosinase degradation. These results suggest that the intracellular composition of fatty acid affects the processing and function of tyrosinase in connection with the ubiquitin-proteasome pathway and suggest that this might be a common physiological approach to regulate protein degradation.

Topics: Animals; Cell Line; Endoplasmic Reticulum; Golgi Apparatus; Leupeptins; Linoleic Acid; Mice; Monophenol Monooxygenase; Palmitic Acid; Proteasome Endopeptidase Complex; Protein Transport; Ubiquitin