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pubmed:abstractText |
The role of endothelin (ET)-1-mediated cytosolic calcium ([Ca2+]i) elevation in regulating ET-1-induced prostaglandin endoperoxide synthase, prostaglandin G/H synthase (PGHS)-2 mRNA expression and protein synthesis was investigated in mesangial cells (MC). Ionomycin, a calcium ionophore, and thapsigargin, an inhibitor of calcium ATPase, mimicked the ET-1-stimulated PGHS-2 mRNA and protein induction. Inhibition of [Ca2+]i increases with (2-¿C2-bis-(carboxymethyl)-amino-5 methylphenoxy]methyl¿-6-methoxy-8-bis-(carboxymethyl)-aminoquinoline tetra-(acetoxymethyl)ester (Quin/AM), a calcium chelator, or with the combined presence of [8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate, HCl] (TMB), an inhibitor of intracellular calcium stores release, and ethyleneglycol-bis-(beta-aminoethyl)- N,N,N',N'-tetra-acetic acid (EGTA) suppressed ET-1, as well as ionomycin and thapsigargin-mediated PGHS-2 mRNA and protein formation. Also, the ET-1-, ionomycin-, and thapsigargin-induced PGHS-2 mRNA expression and protein formation was inhibited in MC pretreated with inhibitors of calcium calmodulin kinase. In contrast, these conditions did not inhibit interleukin (IL)-1-induced PGHS-2 mRNA expression and protein synthesis. Pretreatment with tyrosine kinase inhibitors abolished the ET-1-, ionomycin-, thapsigargin-, and IL-1-mediated PGHS-2 mRNA and protein induction. ET-1-, ionomycin-, and thapsigargin- induced protein tyrosine phosphorylation, but not IL-1-induced protein tyrosine phosphorylation, was suppressed by inhibiting either [Ca2+]i elevation or calcium calmodulin kinase activation. It was concluded that elevation of [Ca2+]i and activation of calcium calmodulin kinases are upstream mediators of ET-1-induced PGHS-2 gene expression through activation of non-receptor-linked protein tyrosine kinase in MC.
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