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Ceramide-1-phosphate transfer protein (CPTP) regulation by phosphoinositides.

ABSTRACT: Ceramide-1-phosphate transfer proteins (CPTPs) are members of the glycolipid transfer protein (GLTP) superfamily that shuttle ceramide-1-phosphate (C1P) between membranes. CPTPs regulate cellular sphingolipid homeostasis in ways that impact programmed cell death and inflammation. CPTP downregulation specifically alters C1P levels in the plasma and trans-Golgi membranes, stimulating proinflammatory eicosanoid production and autophagy-dependent inflammasome-mediated cytokine release. However, the mechanisms used by CPTP to target the trans-Golgi and plasma membrane are not well understood. Here, we monitored C1P intervesicular transfer using fluorescence energy transfer (FRET) and showed that certain phosphoinositides (phosphatidylinositol 4,5 bisphosphate (PI-(4,5)P₂) and phosphatidylinositol 4-phosphate (PI-4P)) increased CPTP transfer activity, whereas others (phosphatidylinositol 3-phosphate (PI-3P) and PI) did not. PIPs that stimulated CPTP did not stimulate GLTP, another superfamily member. Short-chain PI-(4,5)P_2, which is soluble and does not remain membrane-embedded, failed to activate CPTP. CPTP stimulation by physiologically relevant PI-(4,5)P₂ levels surpassed that of phosphatidylserine (PS), the only known non-PIP stimulator of CPTP, despite PI-(4,5)P₂ increasing membrane equilibrium binding affinity less effectively than PS. Functional mapping of mutations that led to altered FRET lipid transfer and assessment of CPTP membrane interaction by surface plasmon resonance indicated that di-arginine motifs located in the α-6 helix and the α3-α4 helix regulatory loop of the membrane-interaction region serve as PI-(4,5)P₂ headgroup-specific interaction sites. Haddock modeling revealed specific interactions involving the PI-(4,5)P₂ headgroup that left the acyl chains oriented favorably for membrane embedding. We propose that PI-(4,5)P₂ interaction sites enhance CPTP activity by serving as preferred membrane targeting/docking sites that favorably orient the protein for function.

SUBMITTER: Gao YG

PROVIDER: S-EPMC8091061 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundSeveral attempts to decipher the genetics of hypertension of unknown causes have been made including large-scale genome-wide association analysis (GWA), but only a few genes have been identified. Unsolved heterogeneity of the regulation of blood pressure and the shortcomings of the prevailing monogenic approach to capture genetic effects in a polygenic condition are the main reasons for the modest results. The level of the blood pressure is the consequence of the genotypic state of the presumably vast network of genes involved in regulating the vascular tonus and hence the blood pressure. Recently it has been suggested that components of the sphingolipid metabolism pathways may be of importance in vascular physiology. The basic metabolic network of sphingolipids has been established, but the influence of genetic variations on the blood pressure is not known. In the approach presented here the impact of genetic variations in the sphingolipid metabolism is elucidated by a two-step procedure. First, the physiological heterogeneity of the blood pressure is resolved by a latent class/structural equation modelling to obtain homogenous subpopulations. Second, the genetic effects of the sphingolipid metabolism with focus on de novo synthesis of ceramide are analysed. The model does not assume a particular genetic model, but assumes that genes operate in networks.ResultsThe stratification of the study population revealed that (at least) 14 distinct subpopulations are present with different propensity to develop hypertension. Main effects of genes in the de novo synthesis of ceramides were rare (0.14% of all possible). However, epistasis was highly significant and prevalent amounting to approximately 70% of all possible two-gene interactions. The phenotypic variance explained by the ceramide synthesis network were substantial in 4 of the subpopulations amounting to more than 50% in the subpopulation in which all subjects were hypertensive. Construction of the network using the epistatic values revealed that only 17% of the interactions detected were in the direct metabolic pathway, the remaining jumping one or more intermediates.ConclusionsThis study established the components of the ceramide/sphingosine-1-phosphate rheostat as central to blood pressure regulation. The results in addition confirm that epistasis is of paramount importance and is most conspicuous in the regulation of the rheostat network. Finally, it is shown that applying a simple case-control approach with single gene association analysis is bound to fail, short of identifying a few potential genes with small effects.

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Ceramide-1-phosphate transfer protein (CPTP) regulation by phosphoinositides.

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