Turnover of bis-diphosphoinositol tetrakisphosphate in a smooth muscle cell line is regulated by beta2-adrenergic receptors through a cAMP-mediated, A-kinase-independent mechanism.
Bis-diphosphoinositol tetrakisphosphate ([PP]2-InsP4 or 'InsP8') is a 'high-energy' inositol phosphate; we report that its metabolism is receptor-regulated in DDT1 MF-2 smooth muscle cells. This conclusion arose by pursuing the mechanism by which F- decreased cellular levels of [PP]2-InsP4 up to 70%. A similar effect was induced by elevating cyclic nucleotide levels, either with IBMX or by application of either Bt2cAMP (EC50 = 14.7 microM), Bt2cGMP (EC50 = 7.9 microM) or isoproterenol (EC50 = 0.4 nM). Isoproterenol (1 microM) decreased [PP]2-InsP4 levels 25% by 5 min, and 71% by 60 min. This novel, agonist-mediated regulation of [PP]2-InsP4 turnover was very specific; isoproterenol did not decrease the cellular levels of either inositol pentakisphosphate, inositol hexakisphosphate or other diphosphorylated inositol polyphosphates. Bradykinin, which activated phospholipase C, did not affect [PP]2-InsP4 levels. Regulation of [PP]2-InsP4 turnover by both isoproterenol and cell-permeant cyclic nucleotides was unaffected by inhibitors of protein kinases A and G. The effectiveness of the kinase inhibitors was confirmed by their ability to block phosphorylation of the cAMP response element-binding protein. Our results indicate a new signaling action of cAMP, and furnish an important focus for future research into the roles of diphosphorylated inositol phosphates in signal transduction.
Safrany
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Inositide Signaling Group, Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, PO Box 12233, NC 27709, USA. Safrany@niehs.nih.gov
Shears
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D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002460:Cell Line; D006224:Cricetinae; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000502:physiology*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D062965:Cyclic GMP-Dependent Protein Kinase Type I; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008647:Mesocricetus; D009130:Muscle, Smooth / Q000201:enzymology / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology*; D012969:Sodium Fluoride / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism; D014649:Vas Deferens
D000318:Adrenergic beta-Agonists; D017362:Cyclic AMP Response Element-Binding Protein; D004791:Enzyme Inhibitors; D007295:Inositol Phosphates; D010726:Phosphodiesterase Inhibitors; D018343:Receptors, Adrenergic, beta-2; C079848:bis(1,4)-diphosphoinositol tetrakisphosphate; D000255:Adenosine Triphosphate; D012969:Sodium Fluoride; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D062965:Cyclic GMP-Dependent Protein Kinase Type I; D017869:Cyclic GMP-Dependent Protein Kinases; D010738:Type C Phospholipases; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D001920:Bradykinin; D015056:1-Methyl-3-isobutylxanthine