Agonist-induced calcium signaling is impaired in fibroblasts overproducing inositol 1,3,4,5-tetrakisphosphate.
The proposed Ca(2+)-signaling actions of inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4), formed by phosphorylation of the primary Ca(2+)-mobilizing messenger, inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), were analyzed in NIH 3T3 and CCL39 fibroblasts transfected with rat brain Ins(1,4,5)P3 3-kinase. In such kinase-transfected cells, the conversion of Ins(1,4,5)P3 to Ins(1,3,4,5)P4 during agonist stimulation was greatly increased, with a concomitant reduction in Ins(1,4,5)P3 levels and attenuation of both the cytoplasmic Ca2+ increase and the Ca2+ influx response. This reduction in Ca2+ signaling was observed during activation of receptors coupled to guanine nucleotide-binding proteins (thrombin and bradykinin), as well as with those possessing tyrosine kinase activity. Single-cell Ca2+ measurements in CCL39 cells revealed that the smaller averaged Ca2+ response of enzyme-transfected cells was due to a marked increase in the number of cells expressing small and slow Ca2+ increases, in contrast to the predominantly large and rapid Ca2+ responses of vector-transfected controls. There was no evidence that high Ins(1,3,4,5)P4 levels promote Ca2+ mobilization, Ca2+ entry, or Ca2+ sequestration. These data indicate that Ins(1,4,5)P3 is the major determinant of the agonist-induced Ca2+ signal in fibroblasts and that Ins(1,3,4,5)P4 does not appear to contribute significantly to this process. Instead, Ins(1,4,5)P3 3-kinase may serve as a negative regulator of the Ca(2+)-phosphoinositide signal transduction mechanism.
Balla
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T
Endocrinology and Reproduction Research Branch, National Institutes of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Sim
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Iida
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Choi
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Catt
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Rhee
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D016475:3T3 Cells; D000818:Animals; D015153:Blotting, Western; D001839:Bombesin / Q000494:pharmacology; D001921:Brain / Q000201:enzymology / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000235:genetics; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D007295:Inositol Phosphates / Q000096:biosynthesis*; D008168:Lung / Q000378:metabolism; D051379:Mice; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D010770:Phosphotransferases / Q000235:genetics / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor); D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D013917:Thrombin / Q000494:pharmacology; D014162:Transfection
D007295:Inositol Phosphates; D010982:Platelet-Derived Growth Factor; C081655:inositol-1,3,4,5-tetrakisphosphate; D004247:DNA; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase; D010727:Phosphoric Diester Hydrolases; D013917:Thrombin; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D001839:Bombesin; D002118:Calcium