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Regulation of sphingosine-activated protein kinases: selectivity of activation by sphingoid bases and inhibition by non-esterified fatty acids.

ABSTRACT: Sphingosine has been shown to activate protein kinases in Jurkat T cell cytosol [Pushkareva, Khan, Alessenko, Sahyoun and Hannun (1992) J. Biol. Chem. 267, 15246-15251]. In this study, two sphingosine-activated protein kinases were distinguished by their substrate specificity, their dose-response to sphingosine and the specificity of their activation by sphingosine and dihydrosphingosine stereoisomers. A p32-sphingosine-activated protein kinase responded to low concentrations of D-erythrosphingosine with an initial activation observed at 2.5 microM and a peak activity at 10-20 microM. This kinase showed a modest specificity for D-erythro-sphingosine over other sphingosine stereoisomers, and a preference for sphingosines over dihydrosphingosines. Phosphorylation of a p18 substrate required higher concentrations of sphingosine (20-100 microM) and showed a significant preference for the erythro isomers of sphingosine and dihydrosphingosine over the threo isomers. The ability of other lipids to modulate sphingosine activation of these kinases was also examined. Oleic acid, but not oleic alcohol or the methyl ester, induced the phosphorylation of a distinct set of substrates (probably through the activation of protein kinase C), and inhibited sphingosine-induced phosphorylation with an IC50 of approximately 20 microM. Oleic anhydride failed to induce changes in basal protein phosphorylation but inhibited sphingosine-activated protein kinases, thus distinguishing the effects of fatty acids on protein kinase C from the inhibition of sphingosine-induced phosphorylation. These studies define two distinct sphingosine-activated protein kinases and reveal an important interaction between two classes of putative lipid second messengers.

SUBMITTER: Pushkareva MYu

PROVIDER: S-EPMC1134519 | biostudies-other | 1993 Sep

REPOSITORIES: biostudies-other

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Project description:BackgroundIn dairy cows circulating non-esterified fatty acids (NEFA) increase early post-partum while liver and other tissues undergo adaptation to greater lipid metabolism, mainly regulated by peroxisome proliferator-activated receptors (PPAR). PPAR are activated by fatty acids (FA), but it remains to be demonstrated that circulating NEFA or dietary FA activate bovine PPAR. We hypothesized that circulating NEFA and dietary FA activate PPAR in dairy cows.MethodsThe dose-response activation of PPAR by NEFA or dietary FA was assessed using HP300e digital dispenser and luciferase reporter in several bovine cell types. Cells were treated with blood plasma isolated from Jersey cows before and after parturition, NEFA isolated from the blood plasma, FA released from lipoproteins using milk lipoprotein lipase (LPL), and palmitic acid (C16:0). Effect on each PPAR isotype was assessed using specific synthetic inhibitors.ResultsNEFA isolated from blood serum activate PPAR linearly up to ~ 4-fold at 400 μmol/L in MAC-T cells but had cytotoxic effect. Addition of albumin to the culture media decreases cytotoxic effects of NEFA but also PPAR activation by ~ 2-fold. Treating cells with serum from peripartum cows reveals that much of the PPAR activation can be explained by the amount of NEFA in the serum (R2 = 0.91) and that the response to serum NEFA follows a quadratic tendency, with peak activation around 1.4 mmol/L. Analysis of PPAR activation by serum in MAC-T, BFH-12 and BPAEC cells revealed that most of the activation is explained by the activity of PPARδ and PPARγ, but not PPARα. Palmitic acid activated PPAR when added in culture media or blood serum but the activation was limited to PPARδ and PPARα and the response was nil in serum from post-partum cows. The addition of LPL to the serum increased > 1.5-fold PPAR activation.ConclusionOur results support dose-dependent activation of PPAR by circulating NEFA in bovine, specifically δ and γ isotypes. Data also support the possibility of increasing PPAR activation by dietary FA; however, this nutrigenomics approach maybe only effective in pre-partum but not post-partum cows.

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Regulation of sphingosine-activated protein kinases: selectivity of activation by sphingoid bases and inhibition by non-esterified fatty acids.

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