A constituent of green tea, epigallocatechin-3-gallate, activates endothelial nitric oxide synthase by a phosphatidylinositol-3-OH-kinase-, cAMP-dependent protein kinase-, and Akt-dependent pathway and leads to endothelial-dependent vasorelaxation

Epidemiological studies suggest that tea catechins may reduce the risk of cardiovascular disease, but the mechanisms of benefit have not been determined. The objective of the present study was to investigate the effects of epigallocatechin-3-gallate (EGCG), the major constituent of green tea, on vasorelaxation and on eNOS expression and activity in endothelial cells. EGCG (1-50 microm) induced dose-dependent vasodilation in rat aortic rings. Vasodilation was abolished by pretreatment with Ng-nitro L-arginine methyl ester. In bovine aortic endothelial cells, EGCG increased endothelial nitric oxide (eNOS) activity dose-dependently after 15 min. Treatment with EGCG induced a sustained activation of Akt, ERK1/2, and eNOS Ser1179 phosphorylation. Inhibition of extracellular signal-regulated kinase (ERK)1/2 had no influence on eNOS activity or Ser1179 phosphorylation. Simultaneous treatment of cells with selective inhibitors for cAMP-dependent protein kinase (PKA) and Akt completely prevented the increase in eNOS activity by EGCG after 15 min, indicating that both kinases act in concert. Specific phosphatidylinositol-3-OH-kinase inhibitors yielded identical results. Akt inhibition prevented eNOS Ser1179 phosphorylation, whereas inhibition of PKA did not influence Akt and eNOS Ser1179 phosphorylation. Pretreatment of endothelial cells with EGCG for 4 h markedly enhanced the increase in eNOS activity stimulated by Ca-ionomycin, suggesting that Akt accounts for prolonged eNOS activation. Treatment of cells for 72 h with EGCG did not change eNOS protein levels. Our results indicate that EGCG-induced endothelium-dependent vasodilation is primarily based on rapid activation of eNOS by a phosphatidylinositol 3-kinase-, PKA-, and Akt-dependent increase in eNOS activity, independently of an altered eNOS protein content.     

Dynamic Polar Sequestration of Excess MurG May Regulate Enzymatic Function

Advances in bacterial cell biology have demonstrated the importance of protein localization for protein function. In general, proteins are thought to localize to the sites where they are active. Here we demonstrate that in Escherichia coli, MurG, the enzyme that mediates the last step in peptidoglycan subunit biosynthesis, becomes polarly localized when expressed at high cellular concentrations. MurG only becomes polarly localized at levels that saturate MurG''s cellular requirement for growth, and E. coli cells do not insert peptidoglycan at the cell poles, indicating that the polar MurG is not active. Fluorescence recovery after photobleaching (FRAP) and single-cell biochemistry experiments demonstrate that polar MurG is dynamic. Polar MurG foci are distinct from inclusion body aggregates, and polar MurG can be remobilized when MurG levels drop. These results suggest that polar MurG represents a temporary storage mechanism for excess protein that can later be remobilized into the active pool. We investigated and ruled out several candidate pathways for polar MurG localization, including peptidoglycan biosynthesis, the MreB cytoskeleton, and polar cardiolipin, as well as MurG enzymatic activity and lipid binding, suggesting that polar MurG is localized by a novel mechanism. Together, our results imply that inactive MurG is dynamically sequestered at the cell poles and that prokaryotes can thus utilize subcellular localization as a mechanism for negatively regulating enzymatic activity.Cells need ways to deal with having more of a specific protein than they need. Left unchecked, excess protein can be toxic to the cell and interfere with essential processes. In prokaryotes, a common mechanism for dealing with excess protein is degradation (30). Bacterial proteases can break down proteins, salvaging amino acids to produce new protein. This process costs time and energy, especially if the protein being degraded is essential and will need to be resynthesized later. Excess protein can also aggregate into insoluble inclusion bodies. In inclusion bodies, proteins are generally misfolded, and though in some cases these proteins can be refolded (24, 35), inclusion body proteins are not readily accessible for use by the cell (11). A potential alternative strategy for dealing with excess protein is to temporarily store the protein in an inactive form that can later be dynamically remobilized when needed. Here we propose that Escherichia coli uses subcellular localization of MurG to accomplish such dynamic storage.MurG is an essential, membrane-associated N-acetylglucosaminyl transferase involved in catalyzing the final step of peptidoglycan subunit biosynthesis (4, 21). In E. coli, the peptidoglycan cell wall determines both cell shape and growth rate (17). During growth and division, E. coli cells add new peptidoglycan both along the lateral cylindrical portion of the cell and at the division plane, but no new peptidoglycan is added at the cell poles (10). Previous efforts to study the localization of MurG have found that MurG localizes to the cell periphery and division plane in E. coli (25). In this study, we demonstrate that E. coli MurG also localizes to the cell poles in a concentration-dependent manner. We find that the polar MurG represents a dynamic pool of excess protein, suggesting that polar accumulation represents an accessible form of temporary storage.     

Valproic acid induces extracellular signal-regulated kinase 1/2 activation and inhibits apoptosis in endothelial cells

The histone deacetylase (HDAC) inhibitor valproic acid (VPA) was recently shown to inhibit angiogenesis, but displays no toxicity in endothelial cells. Here, we demonstrate that VPA increases extracellular signal-regulated kinase 1/2 (ERK 1/2) phosphorylation in human umbilical vein endothelial cells (HUVEC). The investigation of structurally modified VPA derivatives revealed that the induction of ERK 1/2 phosphorylation is not correlated to HDAC inhibition. PD98059, a pharmacological inhibitor of the mitogen-activated protein kinase kinase 1/2, prevented the VPA-induced ERK 1/2 phosphorylation. In endothelial cells, ERK 1/2 phosphorylation is known to promote cell survival and angiogenesis. Our results showed that VPA-induced ERK 1/2 phosphorylation in turn causes phosphorylation of the antiapoptotic protein Bcl-2 and inhibits serum starvation-induced HUVEC apoptosis and cytochrome c release from the mitochondria. Moreover, the combination of VPA with PD98059 synergistically inhibited angiogenesis in vitro and in vivo.     

Biosynthesis of hopanoids by sulfate-reducing bacteria (genus Desulfovibrio)

Sulfate reduction accounts for about a half of the remineralization of organic carbon in anoxic marine shelf regions. Moreover, it was already a major microbial process in the very early ocean at least 2.4 billion years before the present. Here we demonstrate for the first time the capability of sulfate-reducing bacteria (SRB) to biosynthesize hopanoids, compounds that are quantitatively important and widely distributed biomarkers in recent and fossil sediments dating back to the late Archean. We found high concentrations (9.8-12.3 mg per gram of dry cells) of non-extended and extended bacteriohopanoids (bacteriohopanetetrol, aminobacteriohopanetriol, aminobacteriohopanetetrol) in pure cultures of SRB belonging to the widely distributed genus Desulfovibrio. Biohopanoids were found--considered as membrane rigidifiers--in more than 50% of bacterial species analysed so far. However, their biosynthesis appeared to be restricted to aerobes or facultative anaerobes with a very few recently described exceptions. Consequently, findings of sedimentary hopanoids are often used as indication for oxygenated settings. Nevertheless, our findings shed new light on the presence of hopanoids in specific anoxic settings and suggests that SRB are substantial sources of this quantitatively important lipid class in recent but also past anoxic environments.     

Decreases in plasma membrane Ca2+‐ATPase in brain synaptic membrane rafts from aged rats

Precise regulation of free intracellular Ca²⁺ concentrations [Ca²⁺]_i is critical for normal neuronal function, and alterations in Ca²⁺ homeostasis are associated with brain aging and neurodegenerative diseases. One of the most important proteins controlling [Ca²⁺]_i is the plasma membrane Ca²⁺‐ATPase (PMCA), the high‐affinity transporter that fine tunes the cytosolic nanomolar levels of Ca²⁺. We previously found that PMCA protein in synaptic plasma membranes (SPMs) is decreased with advancing age and the decrease in enzyme activity is much greater than that in protein levels. In this study, we isolated raft and non‐raft fractions from rat brain SPMs and used quantitative mass spectrometry to show that the specialized lipid microdomains in SPMs, the rafts, contain 60% of total PMCA, comprised all four isoforms. The raft PMCA pool had the highest specific activity and this decreased progressively with age. The reduction in PMCA protein could not account for the dramatic activity loss. Addition of excess calmodulin to the assay did not restore PMCA activity to that in young brains. Analysis of the major raft lipids revealed a slight age‐related increase in cholesterol levels and such increases might enhance membrane lipid order and prevent further loss of PMCA activity.     

Sex-specific effects of spironolactone on blood pressure in gonadectomized male and female Wistar rats

A low-salt diet is known to decrease and salt excess to increase blood pressure in humans and rodents. Sex steroids seem to play a role in salt dependent hypertension. However, little is known about sex differences in mineralocorticoid receptor blockade between male and female rats. The objective of the work was at first to investigate the effects of a low-salt vs. a high-salt diet on blood pressure without the influence of gonadal steroids in male and female rats. Second, to determine the sex-specific effects of mineralocorticoid receptor blockade by spironolactone in high-salt and low-salt fed gonadectomized male and female animals. Normotensive male and female Wistar rats were gonadectomized and put on a low (NaCl<0.03%) or high (NaCl=4%) salt diet. On each diet animals received spironolactone or placebo. Blood pressure was measured by tail-cuff-method; 24-h urine samples were collected in metabolic cages and blood was collected for hormonal measurements. High-salt diet significantly increased systolic blood pressure in both sexes. This effect could be blocked effectively by spironolactone only in male rats. Spironolactone treatment significantly increased aldosterone levels in males and females independent of the sodium content of the diet. High sodium diet significantly increased relative kidney weight, which was not altered by spironolactone treatment. Independently of gonadal steroids a high-salt diet increased blood pressure in gonadectomized male and female rats. Spironolactone lowered blood pressure only in male not in female rats on a high-salt diet clearly indicating sex-specific effects of the mineralo-corticoid antagonist spironolactone.     

Degradation of a cytosolic protein requires endoplasmic reticulum-associated degradation machinery

Protein misfolding is monitored by a variety of cellular "quality control" systems. Endoplasmic reticulum (ER) quality control handles misfolded secretory and membrane proteins and is well characterized. However, less is known about the quality control of misfolded cytosolic proteins (CytoQC). To study CytoQC, we have employed a genetic system in Saccharomyces cerevisiae using a transplantable degron, CL1 (1). Attachment of CL1 to the cytosolic protein Ura3p destabilizes Ura3p, targeting it for rapid proteasomal degradation. We have performed a comprehensive analysis of Ura3p-CL1 degradation requirements. As shown previously, we observe that the ER-localized ubiquitin E2 (Ubc6p, Ubc7p, and Cue1p) and E3 (Doa10p) machinery involved in ER-associated degradation (ERAD) are also responsible for the degradation of the cytosolic substrate Ura3p-CL1. Importantly, we find that the cytosol/ER membrane-localized chaperones Ydj1p and Ssa1p, known to be necessary for the ERAD of membrane proteins with misfolded cytosolic domains, are also required for the ubiquitination and degradation of Ura3p-CL1. In addition, we show a role for the Cdc48p-Npl4p-Ufd1p complex in the degradation of Ura3p-CL1. When ubiquitination is blocked, a portion of Ura3p-CL1 is ER membrane-localized. Furthermore, access to the cytosolic face of the ER is required for the degradation of CL1 degron-containing proteins. The ER is distributed throughout the cytosol, and our data, together with previous studies, suggest that the cytosolic face of the ER membrane serves as a "platform" for the degradation of Ura3p-CL1, which may also be the case for other CytoQC substrates.