Tyrosine protein kinase from cattle cerebral cortex: purification, characteristics, protein substrates for phosphorylation and inhibitors of activity]

Tyrosine protein kinase present in the membrane fraction of bovine cerebral cortex were extracted and chromatographically fractionated. The activity associated with tyrosine protein kinases was fully extracted from the membranes by 1% sodium cholate and eluted in two peaks (I and II) during chromatography of protein extracts on DEAE-Toyopearl in the presence of sodium cholate. The predominant in cerebral cortex membrane tyrosine protein kinase of peak I (about 75% of the total activity) was purified 1930-fold by gel filtration on Sephacryl S-300, chromatography on hexyl- and phenyl-Sepharose and by rechromatography on DEAE-Toyopearl. The amount of the enzyme prepared from 250 g of bovine brain was 20 micrograms, the enzyme yield and specific activity being 3.8% and 3.9 nmol/mg protein/min, respectively. The purified protein kinase of peak I represents a protein with Mr of 62-63,000 (p62) capable of being autophosphorylated in the presence of [gamma-32P]. Protein kinase p62 phosphorylates enolase, tubulin and calpactin I as well as model substrates in the series: histone H5 greater than poly(G, T)n greater than or equal to histone H2A greater than poly(G, A, T)n, histone H4 greater than caseins, histones H1 and H2B, poly(G, A, L, T)n. The enzyme is specific for Mn2+ at the optimal concentration about 1 mM. The KmMn-ATP is 0.3 microM; Km for histone H5 and poly(G, T)n are 0.45 mg/ml and 0.06 mg/ml, respectively. The protein kinase p62 activity is inhibited by NaCl (IC50 approximately 75-100 mM) as well as by quercetin, adriamycin and lasalocid (IC50 approximately 14-34, 23 and 90 microM, respectively). It is concluded that protein kinase p62 is analogous to the c-src gene protein kinase.     

The Rab-GTPase-activating protein TBC1D1 regulates skeletal muscle glucose metabolism

The Rab-GTPase-activating protein TBC1D1 has emerged as a novel candidate involved in metabolic regulation. Our aim was to determine whether TBC1D1 is involved in insulin as well as energy-sensing signals controlling skeletal muscle metabolism. TBC1D1-deficient congenic B6.SJL-Nob1.10 (Nob1.10(SJL)) and wild-type littermates were studied. Glucose and insulin tolerance, glucose utilization, hepatic glucose production, and tissue-specific insulin-mediated glucose uptake were determined. The effect of insulin, AICAR, or contraction on glucose transport was studied in isolated skeletal muscle. Glucose and insulin tolerance tests were normal in TBC1D1-deficient Nob1.10(SJL) mice, yet the 4-h-fasted insulin concentration was increased. Insulin-stimulated peripheral glucose utilization during a euglycemic hyperinsulinemic clamp was similar between genotypes, whereas the suppression of hepatic glucose production was increased in TBC1D1-deficient mice. In isolated extensor digitorum longus (EDL) but not soleus muscle, glucose transport in response to insulin, AICAR, or contraction was impaired by TBC1D1 deficiency. The reduction in glucose transport in EDL muscle from TBC1D1-deficient Nob1.10(SJL) mice may be explained partly by a 50% reduction in GLUT4 protein, since proximal signaling at the level of Akt, AMPK, and acetyl-CoA carboxylase (ACC) was unaltered. Paradoxically, in vivo insulin-stimulated 2-deoxyglucose uptake was increased in EDL and tibialis anterior muscle from TBC1D1-deficient mice. In conclusion, TBC1D1 plays a role in regulation of glucose metabolism in skeletal muscle. Moreover, functional TBC1D1 is required for AICAR- or contraction-induced metabolic responses, implicating a role in energy-sensing signals.     

Exercise-associated differences in an array of proteins involved in signal transduction and glucose transport

Vastus lateralismuscle biopsies were obtained from endurance-trained (running ~50km/wk) and untrained (no regular physical exercise) men, and theexpression of an array of insulin-signaling intermediates wasdetermined. Expression of insulin receptor and insulin receptorsubstrate-1 and -2 was decreased 44% (P < 0.05), 57%(P < 0.001), and 77% (P < 0.001),respectively, in trained vs. untrained muscle. The downstream signalingtarget, Akt kinase, was not altered in trained subjects. Components ofthe mitogenic signaling cascade were also assessed. Extracellularsignal-regulated kinase 1/2 mitogen-activated protein kinase expressionwas 190% greater (P < 0.05), whereas p38 mitogen-activatedprotein kinase expression was 32% lower (P < 0.05), intrained vs. untrained muscle. GLUT-4 protein expression was twofoldhigher (P < 0.05), and the GLUT-4 vesicle-associatedprotein, the insulin-regulated aminopeptidase, was increased 4.7-fold(P < 0.05) in trained muscle. In conclusion, the expressionof proteins involved in signal transduction is altered in skeletalmuscle from well-trained athletes. Downregulation of early componentsof the insulin-signaling cascade may occur in response to increasedinsulin sensitivity associated with endurance training.

     

Combined prime-boost vaccination against tick-borne encephalitis (TBE) using a recombinant vaccinia virus and a bacterial plasmid both expressing TBE virus non-structural NS1 protein

Background  

Heterologous prime-boost immunization protocols using different gene expression systems have proven to be successful tools in protecting against various diseases in experimental animal models. The main reason for using this approach is to exploit the ability of expression cassettes to prime or boost the immune system in different ways during vaccination procedures. The purpose of the project was to study the ability of recombinant vaccinia virus (VV) and bacterial plasmid, both carrying the NS1 gene from tick-borne encephalitis (TBE) virus under the control of different promoters, to protect mice against lethal challenge using a heterologous prime-boost vaccination protocol.     

Receptor-mediated inhibition of renal Na+-K+-ATPase is associated with endocytosis of its alpha - and beta -subunits

The mechanisms involved in receptor-mediated inhibition ofNa⁺-K⁺-ATPaseremain poorly understood. In this study, we evaluate whether inhibitionof proximal tubuleNa⁺-K⁺-ATPaseactivity by dopamine is linked to its removal from the plasma membraneand internalization into defined intracellular compartments.Clathrin-coated vesicles were isolated by sucrose gradientcentrifugation and negative lectin selection, and early and lateendosomes were separated on a flotation gradient. Inhibition ofNa⁺-K⁺-ATPaseactivity by dopamine, in contrast to its inhibition by ouabain, wasaccompanied by a sequential increase in the abundance of the-subunit in clathrin-coated vesicles (1 min), early endosomes (2.5 min), and late endosomes (5 min), suggesting its stepwise translocationbetween these organelles. A similar pattern was found for the-subunit. The increased incorporation of both subunits in allcompartments was blocked by calphostin C. The results demonstrate thatthe dopamine-induced decrease inNa⁺-K⁺-ATPaseactivity in proximal tubules is associated with internalization of its- and -subunits into early and late endosomes via aclathrin-dependent pathway and that this process is protein kinase Cdependent. The presence ofNa⁺-K⁺-ATPasesubunits in endosomes suggests that these compartments may constitutenormal traffic reservoirs during pump degradation and/orsynthesis.

     

Phosphatidylinositol 3-Kinase-mediated Endocytosis of Renal Na+,K+-ATPase α Subunit in Response to Dopamine

Dopamine (DA) inhibition of Na⁺,K⁺-ATPase in proximal tubule cells is associated with increased endocytosis of its α and β subunits into early and late endosomes via a clathrin vesicle-dependent pathway. In this report we evaluated intracellular signals that could trigger this mechanism, specifically the role of phosphatidylinositol 3-kinase (PI 3-K), the activation of which initiates vesicular trafficking and targeting of proteins to specific cell compartments. DA stimulated PI 3-K activity in a time- and dose-dependent manner, and this effect was markedly blunted by wortmannin and LY 294002. Endocytosis of the Na⁺,K⁺-ATPase α subunit in response to DA was also inhibited in dose-dependent manner by wortmannin and LY 294002. Activation of PI 3-K generally occurs by association with tyrosine kinase receptors. However, in this study immunoprecipitation with a phosphotyrosine antibody did not reveal PI 3-K activity. DA-stimulated endocytosis of Na⁺,K⁺-ATPase α subunits required protein kinase C, and the ability of DA to stimulate PI 3-K was blocked by specific protein kinase C inhibitors. Activation of PI 3-K is mediated via the D₁ receptor subtype and the sequential activation of phospholipase A₂, arachidonic acid, and protein kinase C. The results indicate a key role for activation of PI 3-K in the endocytic sequence that leads to internalization of Na⁺,K⁺-ATPase α subunits in response to DA, and suggest a mechanism for the participation of protein kinase C in this process.     

Activation of morphogenesis and proliferation by low specificity chemical effectors

Activation of highly specific biochemical processes by simple chemical agents is demonstrated for morphogenesis (anlage and development of female gametophyte in cereal) and mitosis (in cell cultures and animal and plant tissues). The effects of these agents are tissue-specific. Structure--activity relationship is analyzed in this group of compounds. Thus, the phenomenon reveals the exact pathways of the influence of allelopathic and anthropogenic chemical agents on evolution of plant biocenoses.     

Organization of fusicoccin receptor in higher plant plasma membrane: relationship between affinity and molecular mass

Higher plant plasma membranes carry receptors of different affinity for the phytotoxin fusicoccin. Reception of fusicoccin involves proteins belonging to the highly conserved 14-3-3 family, but the complete structure of the fusicoccin receptor (FCR) is unknown. Using radiation inactivation analysis, we estimated the molecular masses of low-affinity and high-affinity FCR at 63 +/- 7 and 130 +/- 15 kD, respectively. The dose dependences of receptor inactivation indicate that microsomal specimens contain "silent" FCRs of 420 +/- 90 kD in amounts commensurate with that of the active FCRs. Both low- and high-affinity FCRs are inactivated by hydrolytic enzymes from the outer surface of the plasma membrane, and impairment of protoplast integrity causes an irreversible transition of the low-affinity binding site into the high-affinity one. A scheme is proposed for the organization of different types of FCR in the plasma membrane, implying that the membrane affinity for fusicoccin reflects the interaction between proteins in the FCR complex.