Vascular endothelial growth factor activates the Tie family of receptor tyrosine kinases

The ability of cells to respond appropriately to changes in their environment requires integration and cross-talk between relevant signalling pathways. The vascular endothelial growth factor (VEGF) and angiopoietin families of ligands are key regulators of blood vessel formation. VEGF binds to receptor tyrosine kinases of the VEGF-receptor family to activate signalling pathways leading to endothelial migration, proliferation and survival whereas the angiopoietins interact with the Tie receptor tyrosine kinases to control vessel stability, survival and maturation. Here we show that VEGF can also activate the angiopoietin receptor Tie2. Activation of human endothelial cells with VEGF caused a four-fold stimulation of tyrosine phosphorylation of Tie2. This stimulation was not due to VEGF-induction of Tie2 ligands as soluble ligand binding domain of Tie2 failed to inhibit VEGF activation of the receptor. Immunoprecipitation analysis demonstrated no physical interaction between VEGF receptors and Tie2. However Tie2 does interact with the related receptor tyrosine kinase Tie1 and this receptor was found to be essential for VEGF activation of Tie2. VEGF stimulated proteolytic cleavage of Tie1 generating a truncated Tie1 intracellular domain. Similarly, phorbol ester also both stimulated Tie1 truncation and activated Tie2 phosphorylation. Inhibition of Tie1 cleavage with the metalloprotease inhibitor TAPI-2 suppressed VEGF- and phorbol ester-induced phosphorylation of Tie2. Truncated Tie1 formed in response to VEGF was also found to be tyrosine phosphorylated and this was independent of Tie2, though Tie2 could enhance Tie1 intracellular domain phosphorylation. Together these data demonstrate that VEGF activates Tie2 via a mechanism involving proteolytic cleavage of the associated tyrosine kinase Tie1 leading to trans-phosphorylation of Tie2. This novel mechanism of receptor tyrosine kinase activation is likely to be important in integrating signalling between two of the key receptor groups regulating angiogenesis.     

Exploring the Chemical and Biological Potential of Jamun (Syzygium cumini (L.) Skeels) Leaves: A Comprehensive Review

Leaves of jamun collected as agro by-produce during the cultivation of jamun is traditionally used as ayurvedic medicine to treat diabetes, gall bladder stones and other ailments. Most of the beneficial effects of jamun leaves are associated with phytochemicals found in jamun leaves such as gallic acid, tannins, mallic acid, flavonoids, essential oils, jambolin, ellagic acid, jambosine, antimellin and betulinic acid. Jamun possess curative activities like anticancer, antidiabetic, antifertility, anti-inflammatory, antidiarrheal, antimicrobial, antinociceptive, antioxidant, antiradiation, chemotherapeutic, and gastroprotective. The main goal of this review article is to provide information on the nutritional content, phytochemical composition and health promoting properties of jamun leaves. The review of literature based on the phytochemical composition and health promoting benefits of the jamun leaves, suggests that leaves can be used as potential constituent in the formulation of pharmacological drugs. From the review literature it is found that clinical, in-vivo, in-vitro studies are still required to check the health promoting effects of jamun leaves extracts on humans.     

Effect of Nitrate on Bradyrhizobium — Mungbean (Vigna radiata) Symbiosis in presence of Syringaldehyde

Bradyrhizoblum — mungbean (Vigna radiata) symbiosis was influenced by the application of nitrate in combination with.yrlngaldehyde. Application of nitrate alone at lower concentrations (2, 5 mM) caused a reduction at initial stage (10 DAS) while at later stage (35 DAS–45 DAS) enhanced the nodulation status (nodule number, nodule weight) and nodule efficiency (acetylene reduction activity). Higher concentration of nitrate (10 mM) caused a reduction in nodule number, nodule weight and acetylene reduction activity. Syringaldehyde alone improved the nodulation status and nodule efficiency while it acted synergistically when applied in combination with nitrate. These effects were also reflected in the biomass of plants.     

Mitochondrial generation of reactive oxygen species is enhanced at the Q<Subscript>o</Subscript> site of the complex III in the myocardium of <Emphasis Type="Italic">Trypanosoma cruzi-</Emphasis>infected mice: beneficial effects of an antioxidant

In this study, we have characterized the cellular source and mechanism for the enhanced generation of reactive oxygen species (ROS) in the myocardium during Trypanosoma cruzi infection. Cardiac mitochondria of infected mice, as compared to normal controls, exhibited 63.3% and 30.8% increase in ROS-specific fluorescence of dihydroethidium (detects O₂ ^•−) and amplex red (detects H₂O₂), respectively. This increase in ROS level in cardiac mitochondria of infected mice was associated with a 59% and 114% increase in the rate of glutamate/malate- (complex I substrates) and succinate- (complex II substrate) supported ROS release, respectively, and up to a 74.9% increase in the rate of electron leakage from the respiratory chain when compared to normal controls. Inhibition studies with normal cardiac mitochondria showed that rotenone induced ROS generation at the Q_Nf-ubisemiquinone site in complex I. In complex III, myxothiazol induced ROS generation from a site located at the Q_o center that was different from the Q_i center of O₂ ^•− generation by antimycin. In cardiac mitochondria of infected mice, the rate of electron leakage at complex I during forward (complex I-to-complex III) and reverse (complex II-to-complex I) electron flow was not enhanced, and complex I was not the main site of increased ROS production in infected myocardium. Instead, defects of complex III proximal to the Q_o site resulted in enhanced electron leakage and ROS formation in cardiac mitochondria of infected mice. Treatment of infected mice with phenyl-α-tert-butyl-nitrone (PBN) improved the respiratory chain function, and, subsequently, decreased the extent of electron leakage and ROS release. In conclusion, we show that impairment of the Q_o site of complex III resulted in increased electron leakage and O₂ ^•− formation in infected myocardium, and was controlled by PBN.     

IL-7 activates the phosphatidylinositol 3-kinase/AKT pathway in normal human thymocytes but not normal human B cell precursors

IL-7 signaling culminates in different biological outcomes in distinct lymphoid populations, but knowledge of the biochemical signaling pathways in normal lymphoid populations is incomplete. We analyzed CD127/IL-7Ralpha expression and function in normal (nontransformed) human thymocytes, and human CD19(+) B-lineage cells purified from xenogeneic cord blood stem cell/MS-5 murine stromal cell cultures, to further clarify the role of IL-7 in human B cell development. IL-7 stimulation of CD34(+) immature thymocytes led to phosphorylation (p-) of STAT5, ERK1/2, AKT, and glycogen synthase kinase-3 beta, and increased AKT enzymatic activity. In contrast, IL-7 stimulation of CD34(-) thymocytes (that included CD4(+)/CD8(+) double-positive, and CD4(+) and CD8(+) single-positive cells) only induced p-STAT5. IL-7 stimulation of CD19(+) cells led to robust induction of p-STAT5, but minimal induction of p-ERK1/2 and p-glycogen synthase kinase-3 beta. However, CD19(+) cells expressed endogenous p-ERK1/2, and when rested for several hours following removal from MS-5 underwent de-phosphorylation of ERK1/2. IL-7 stimulation of rested CD19(+) cells resulted in robust induction of p-ERK1/2, but no induction of AKT enzymatic activity. The use of a specific JAK3 antagonist demonstrated that all IL-7 signaling pathways in CD34(+) thymocytes and CD19(+) B-lineage cells were JAK3-dependent. We conclude that human CD34(+) thymocytes and CD19(+) B-lineage cells exhibit similarities in activation of STAT5 and ERK1/2, but differences in activation of the PI3K/AKT pathway. The different induction of PI3K/AKT may at least partially explain the different requirements for IL-7 during human T and B cell development.     

Interaction of herpes primase with the sugar of a NTP

We analyzed the interaction of nucleoside triphosphates (NTPs) containing modified sugars to develop a better understanding of how DNA primase from herpes simplex virus I catalyzes primer synthesis. During the NTP binding reaction, primase tolerated a large number of modifications to the sugar ring. Altering the 2' and 3' carbons and even converting the furanose sugar into an acyclic sugar did not prevent binding. Whether or not the base on the NTP could form a correct base pair with the template base being replicated also had minimal effect on the binding reaction, indicating that primase does not use this process to discriminate between right and wrong NTPs. Rather, the key feature that primase recognizes to bind a NTP is the 5'-gamma-phosphate since converting a NTP into a NDP greatly compromised binding. During the polymerization reaction, primase tolerated substantial modification of the 2'-carbon, including the presence of either an ara or ribo hydroxyl, two hydrogens, or two fluorines. However, polymerization absolutely required that the NTP contain a 3'-hydroxyl and an intact sugar ring. Modifications at the 2'-carbon of the nucleotide at the primer 3'-terminus significantly impaired further polymerization events. Compared to a ribonucleotide, incorporation of a 2'-deoxyribo- or 2',2'-difluoro-2'-deoxyribonucleotide resulted in strong chain termination, while incorporation of an aranucleotide resulted in very strong chain termination. The implications of these data with respect to the mechanism of primase and the relationship between human and herpes primase are discussed.     

Cardiac high molecular weight calmodulin-binding protein is homologous to calpastatin I and calpastatin II

Calpastatin is an endogenous inhibitor of calpain, which has been implicated in various physiological and pathological processes. In the present study we determined the molecular and inhibitory properties of HMWCaMBP, calpastatin I, and calpastatin II. Western blot analysis with antibodies raised against either full length HMWCaMBP or internal peptides that are common to all isoforms showed that all three homologs have common antigenic epitopes. However, additional Western blot analysis with N-terminal specific antibodies showed that all three proteins are different at the N-terminal end. HMWCaMBP is clearly different from two other homologues, calpastatin I and II, at the N-terminal end. In addition, HMWCaMBP also showed the same affinities for m-calpain as calpastatin I and calpastatin II. Our findings suggest that HMWCaMBP is the homolog of calpastatin and may be a CaM-binding form of calpastatin.     

Effects of glucagon-like peptide-1, yohimbine, and nitrergic modulation on sympathetic and parasympathetic activity in humans

Glucagon-like peptide-1 (GLP-1), an incretin, which is used to treat diabetes mellitus in humans, inhibited vagal activity and activated nitrergic pathways. In rats, GLP-1 also increased sympathetic activity, heart rate, and blood pressure (BP). However, the effects of GLP-1 on sympathetic activity in humans are unknown. Our aims were to assess the effects of a GLP-1 agonist with or without alpha(2)-adrenergic or -nitrergic blockade on autonomic nervous functions in humans. In this double-blind study, 48 healthy volunteers were randomized to GLP-1-(7-36) amide, the nitric oxide synthase (NOS) inhibitor N(G)-monomethyl-l-arginine acetate (l-NMMA), the alpha(2)-adrenergic antagonist yohimbine, or placebo (i.e., saline), alone or in combination. Hemodynamic parameters, plasma catecholamines, and cardiac sympathetic and parasympathetic modulation were measured by spectral analysis of heart rate. Thereafter, the effects of GLP-1-(7-36) amide on muscle sympathetic nerve activity (MSNA) were assessed by microneurography in seven subjects. GLP-1 increased (P = 0.02) MSNA but did not affect cardiac sympathetic or parasympathetic indices, as assessed by spectral analysis. Yohimbine increased plasma catecholamines and the low-frequency (LF) component of heart rate power spectrum, suggesting increased cardiac sympathetic activity. l-NMMA increased the BP and reduced the heart rate but did not affect the balance between sympathetic and parasympathetic activity. GLP-1 increases skeletal muscle sympathetic nerve activity but does not appear to affect cardiac sympathetic or parasympathetic activity in humans.