Phosphorylation of glycosyl-phosphatidylinositol by phosphatidylinositol 3-kinase changes its properties as a substrate for phospholipases

Statin treatment of patients with calcific aortic valve disease modulates extracellular adenosine metabolism on the cell surface of the aortic valve

Statins efficiently prevent cardiovascular events by lipid-dependent and independent mechanisms. We hypothesize that part of these protective effects could be associated with an increased extracellular adenosine signaling. We demonstrated previously that aortic valves obtained from patients with calcific aortic valve disease (CAVD) disclosed disturbances in extracellular adenosine metabolism. This study aimed to analyze the impact of statin treatment on extracellular nucleotides and adenosine metabolism in aortic valves originated from CAVD patients and to elucidate potential mechanisms that are involved in the regulation of ecto-enzyme activities by statins. Aortic valves of CAVD patients treated with statins (n = 45) revealed higher adenosine production and its lower degradation than in non-treated patients (n = 28). Statin treatment was also related to the improvement in pre-operative echocardiographic data indicating milder aortic valve stenosis and a better function of the left ventricle. The rates of aortic valve adenosine conversions correlated with plasma lipid profile parameters, within both statin-treated and non-treated groups. Valvular extracellular AMP hydrolysis correlated negatively, while adenosine deamination positively with plasma total and LDL cholesterol. Atorvastatin treatment of murine heart endothelial cells led to the enhanced ecto-5'nucleotidase (CD73) and decreased ecto-adenosine deaminase (eADA) activity. When endothelial cells were stimulated with thrombin that induces endothelial cell exocytosis, activities of both cell-surface CD73 and eADA were increased, while co-treatment with atorvastatin reversed only thrombin-induced eADA activity. In conclusion, early intervention with statins may provide beneficial effects for CAVD therapy. Here, we presented results showing that these protective outcomes could be mediated via the regulation of extracellular adenosine metabolism pathways.

Hepatitis C virus dysregulates glucose homeostasis by a dual mechanism involving induction of PGC1α and dephosphorylation of FoxO1

The maintenance of glucose homeostasis is a complex process in which the insulin signalling pathway plays a major role. Disruption of insulin-regulated glucose homeostasis is frequently observed in chronic hepatitis C (CHC) infection and might potentially contribute to type 2 diabetes mellitus (T2DM) development. Presently, the mechanism that links HCV infection to insulin resistance remains unclear. Previously, we have reported that HCV protein expression in HCV transgenic mice (B6HCV) leads to an overexpression of protein phosphatase 2A (PP2A) through an ER stress response. In the present work, we describe an association of FoxO1 hypophosphorylation and upregulation of both PGC-1α and G6Pase to phenotypic hyperglycaemia and insulin resistance in B6HCV mice. In vitro, we observed that PGC1α is concomitantly induced with PP2A. Moreover, we show that the enhanced PP2A expression is sufficient to inhibit insulin-induced FoxO1 phosphorylation via blockade of insulin-mediated Akt activation or/and through direct association and dephosphorylation of pS-FoxO1. Consequently, we found that the gluconeogenic gene glucose-6-phosphatase is upregulated. These observations were confirmed in liver biopsies obtained from CHC patients. In summary, our results show that HCV-mediated upregulation of PP2A catalytic subunit alters signalling pathways that control hepatic glucose homeostasis by inhibiting Akt and dephosphorylation of FoxO1.

Inactivation of ras and changes of mitochondrial membrane potential contribute to oridonin-induced autophagy in a431 cells

We have previously shown that oridonin isolated from Rabdosia rubescens augmented apoptosis while inhibiting autophagy within 24 h in HeLa cells. However, the mechanisms between apoptosis and autophagy induced by oridonin in A431 cells are largely unknown. Here, it was found that autophagic level is significantly upregulated when A431 cells are pretreated with manumycin A (Ras specific inhibitor) compared with oridonin alone treatment, whereas cells precultured with GW5074 (Raf inhibitor) or PD98059 (ERK inhibitor) did not exhibit such an effect. Ras, but not Raf or ERK, was engaged in the control of oridonin-induced autophagy. At the same time, manumycin A contributes to oridonin-induced downregulation of Ras protein expression. Treatment with the combination of oridonin and manumycin A downregulated phosphorylation of Akt, downstream of phosphatidylinositol 3-OH kinase (PI3-K). Preincubation with the PI3-K inhibitor wortmannin and Akt inhibitor KP372-1 enhanced oridonin-induced apoptosis, whereas it inhibited oridonin-induced autophagy. However, under oridonin treatment, the expression of Beclin-1, which has autophagy-inducing activity, was reduced, suggesting that Beclin-1 did not participate in the oridonin-induced autophagy. Morphologic observations, DNA fragmentation analysis, and LDH activity-based assay showed that 3-methyladenine (3-MA), an inhibitor of autophagy, increased the apoptotic sensitivity of A431 cells to oridonin. In addition, manumycin A contributed to oridonin-induced decrease of mitochondrial membrane potential (Deltapsim), consistent with the upregulation of Bax/Bcl-2 ratio. In conclusion, Ras negatively regulated autophagy in oridonin-treated A431 cells, which might be associated with activation of class I PI3-K. Downregulation of Deltapsim and increasing of the ratio of Bax/Bcl-2 might also be partially responsible for the initiation of the autophagic process.

Structure and dynamics of the conserved protein GPI anchor core inserted into detergent micelles

A suitable approach which combines nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulations have been used to study the structure and the dynamics of the glycosylphosphatidylinositol (GPI) anchor Manalphal-2Manalpha1-6Manalphal -4GlcNalpha1-6myo-inositol-1-OPO(3)-sn-1,2-dimyristoylglycerol (1) incorporated into dodecylphosphatidylcholine (DPC) micelles. The results have been compared to those previously obtained for the products obtainable from (1) after phospholipase cleavage, in aqueous solution. Relaxation and diffusion NMR experiments were used to establish the formation of stable aggregates and the insertion of (1) into the micelles. MD calculations were performed including explicit water, sodium and chloride ions and using the Particle Mesh Ewald approach for the evaluation of the electrostatic energy term. The MD predicted three dimensional structure and dynamics were substantiated by nuclear overhauser effect (NOE) measurements and relaxation data. The pseudopentasaccharide structure, which was not affected by incorporation of (1) into the micelle, showed a complex dynamic behaviour with a faster relative motion at the terminal mannopyranose unit and decreased mobility close to the micelle. This motion may be better described as an oscillation relative to the membrane rather than a folding event.

Phospholipase cleavage of D- and L-chiro-glycosylphosphoinositides asymmetrically incorporated into liposomal membranes

The nature of chiro-inositol-containing inositolphosphoglycans (IPGs), reported to be putative insulin mediators, was studied by examination of the substrate specificities of the phosphatidylinositol-specific phospholipase C (PI-PLC) and the glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) by using a series of synthetic D- and L-chiro-glycosylphosphoinositides. 3-O-alpha-D-Glucosaminyl- (3) and -galactosaminyl-2-phosphatidyl-L-chiro-inositol (4), which show the maximum stereochemical similarity to the 6-O-alpha-D-glucosaminylphosphatidylinositol pseudodisaccharide motifs of GPI anchors, were synthesized and asymmetrically incorporated into phospholipid bilayers in the form of large unilamellar vesicles (LUVs). Similarly, 2-O-alpha-D-glucosaminyl- (5) and -galactosaminyl-1-phosphatidyl-D-chiro-inositol (6), which differ from the corresponding pseudodisaccharide motif of the GPI anchors only in the axial orientation of the phosphatidyl moiety, were also synthesized and asymmetrically inserted into LUVs. The cleavage of these synthetic molecules in the liposomal constructs by PI-PLC from Bacillus cereus and by GPI-PLD from bovine serum was studied with the use of 6-O-alpha-D-glucosaminylphosphatidylinositol (7) and the conserved GPI anchor structure (8) as positive controls. Although PI-PLC cleaved 3 and 4 with about the same efficiency as 7 and 8, this enzyme did not accept 5 or 6. GPI-PLD accepted both the L-chiro- (3 and 4) and the D-chiro- (5 and 6) glycosylinositolphosphoinositides. Therefore, IPGs containing L-chiro-inositol only are expected to be released from chiro-inositol-containing GPIs if the cleavage is effected by a PI-PLC, whereas GPI-PLD cleavage could result in both L-chiro- and D-chiro-inositol-containing IPGs.