Browsing by Subject "Tyrosine"

Now showing 1 - 5 of 5
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    Antagonists of the system L neutral amino acid transporter (LAT) promote endothelial adhesivity of human red blood cells.
    (Thrombosis and haemostasis, 2017-06) Dosier, Laura Beth Mann; Premkumar, Vikram J; Zhu, Hongmei; Akosman, Izzet; Wempe, Michael F; McMahon, Timothy J
    The system L neutral amino acid transporter (LAT; LAT1, LAT2, LAT3, or LAT4) has multiple functions in human biology, including the cellular import of S-nitrosothiols (SNOs), biologically active derivatives of nitric oxide (NO). SNO formation by haemoglobin within red blood cells (RBC) has been studied, but the conduit whereby a SNO leaves the RBC remains unidentified. Here we hypothesised that SNO export by RBCs may also depend on LAT activity, and investigated the role of RBC LAT in modulating SNO-sensitive RBC-endothelial cell (EC) adhesion. We used multiple pharmacologic inhibitors of LAT in vitro and in vivo to test the role of LAT in SNO export from RBCs and in thereby modulating RBC-EC adhesion. Inhibition of human RBC LAT by type-1-specific or nonspecific LAT antagonists increased RBC-endothelial adhesivity in vitro, and LAT inhibitors tended to increase post-transfusion RBC sequestration in the lung and decreased oxygenation in vivo. A LAT1-specific inhibitor attenuated SNO export from RBCs, and we demonstrated LAT1 in RBC membranes and LAT1 mRNA in reticulocytes. The proadhesive effects of inhibiting LAT1 could be overcome by supplemental L-CSNO (S-nitroso-L-cysteine), but not D-CSNO or L-Cys, and suggest a basal anti-adhesive role for stereospecific intercellular SNO transport. This study reveals for the first time a novel role of LAT1 in the export of SNOs from RBCs to prevent their adhesion to ECs. The findings have implications for the mechanisms of intercellular SNO signalling, and for thrombosis, sickle cell disease, and post-storage RBC transfusion, when RBC adhesivity is increased.
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    Dual enzymatic formation of hybrid hydrogels with supramolecular-polymeric networks.
    (Chemical communications (Cambridge, England), 2014-11) Mao, Yanjie; Su, Teng; Wu, Qing; Liao, Chuanan; Wang, Qigang
    This communication describes a mild construction of hybrid hydrogels with supramolecular-polymeric networks via a dual enzymatic reaction.
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    Involvement of tyrosine residues located in the carboxyl tail of the human beta 2-adrenergic receptor in agonist-induced down-regulation of the receptor.
    (Proc Natl Acad Sci U S A, 1990-07) Valiquette, M; Bonin, H; Hnatowich, M; Caron, MG; Lefkowitz, RJ; Bouvier, M
    Chronic exposure of various cell types to adrenergic agonists leads to a decrease in cell surface beta 2-adrenergic receptor (beta 2AR) number. Sequestration of the receptor away from the cell surface as well as a down-regulation of the total number of cellular receptors are believed to contribute to this agonist-mediated regulation of receptor number. However, the molecular mechanisms underlying these phenomena are not well characterized. Recently, tyrosine residues located in the cytoplasmic tails of several membrane receptors, such as the low density lipoprotein and mannose-6-phosphate receptors, have been suggested as playing an important role in the agonist-induced internalization of these receptors. Accordingly, we assessed the potential role of two tyrosine residues in the carboxyl tail of the human beta 2AR in agonist-induced sequestration and down-regulation of the receptor. Tyr-350 and Tyr-354 of the human beta 2AR were replaced with alanine residues by site-directed mutagenesis and both wild-type and mutant beta 2AR were stably expressed in transformed Chinese hamster fibroblasts. The mutation dramatically decreased the ability of the beta 2AR to undergo isoproterenol-induced down-regulation. However, the substitution of Tyr-350 and Tyr-354 did not affect agonist-induced sequestration of the receptor. These results suggest that tyrosine residues in the cytoplasmic tail of human beta 2AR are crucial determinants involved in its down-regulation.
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    Phosphorylation at tyrosine 262 promotes GADD34 protein turnover.
    (The Journal of biological chemistry, 2013-11) Zhou, Wei; Jeyaraman, Krishna; Yusoff, Permeen; Shenolikar, Shirish
    In mammalian cells, metabolic and environmental stress increases the phosphorylation of the eukaryotic translational initiation factor, eIF2α, and attenuates global protein synthesis. Subsequent transcriptional activation of GADD34 assembles an eIF2α phosphatase that feeds back to restore mRNA translation. Active proteasomal degradation of GADD34 protein then reestablishes the sensitivity of cells to subsequent bouts of stress. Mass spectrometry established GADD34 phosphorylation on multiple serines, threonines, and tyrosines. Phosphorylation at tyrosine 262 enhanced the rate of the GADD34 protein turnover. Substrate-trapping studies identified TC-PTP (PTPN2) as a potential GADD34 phosphatase, recognizing phosphotyrosine 262. Reduced GADD34 protein levels in TC-PTP-null MEFs following ER stress emphasized the importance of TC-PTP in determining the cellular levels of GADD34 protein. The susceptibility of TC-PTP-null MEFs to ER stress-induced apoptosis was significantly ameliorated by ectopic expression of GADD34. The data suggested that GADD34 phosphorylation on tyrosine 262 modulates endoplasmic reticulum stress signaling and cell fate.
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    Tyrosine phosphorylation of G protein alpha subunits by pp60c-src.
    (Proc Natl Acad Sci U S A, 1992-07-01) Hausdorff, WP; Pitcher, JA; Luttrell, DK; Linder, ME; Kurose, H; Parsons, SJ; Caron, MG; Lefkowitz, RJ
    A number of lines of evidence suggest that cross-talk exists between the cellular signal transduction pathways involving tyrosine phosphorylation catalyzed by members of the pp60c-src kinase family and those mediated by guanine nucleotide regulatory proteins (G proteins). In this study, we explore the possibility that direct interactions between pp60c-src and G proteins may occur with functional consequences. Preparations of pp60c-src isolated by immunoprecipitation phosphorylate on tyrosine residues the purified G-protein alpha subunits (G alpha) of several heterotrimeric G proteins. Phosphorylation is highly dependent on G-protein conformation, and G alpha(GDP) uncomplexed by beta gamma subunits appears to be the preferred substrate. In functional studies, phosphorylation of stimulatory G alpha (G alpha s) modestly increases the rate of binding of guanosine 5'-[gamma-[35S]thio]triphosphate to Gs as well as the receptor-stimulated steady-state rate of GTP hydrolysis by Gs. Heterotrimeric G proteins may represent a previously unappreciated class of potential substrates for pp60c-src.