Changes in either cytosolic or nucleoplasmic inositol 1,4,5-trisphosphate levels can control nuclear Ca2+ concentration.
The free nucleoplasmic Ca2+ concentration ([Ca2+]n) may regulate many nuclear events, such as gene transcription. Since the nucleus may possess the enzymes necessary to generate the second messenger inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), and because the nuclear envelope may enclose an Ins(1,4,5)P3-releasable Ca2+ store, we tested the hypothesis that nuclear and/or cytosolic levels of Ins(1,4,5)P3 can control [Ca2+]n. To assay [Ca2+]n, we measured the fluorescence of the Ca2+ indicator fluo 3 in the nucleus of Xenopus oocytes by confocal microscopy. When we injected Ins(1,4,5)P3 into the cytosol, [Ca2+]n increased. This increase in [Ca2]n still occurred when heparin was present in the nucleus, but was abolished when heparin was present in the cytosol, indicating that cytosolic Ins(1,4,5)P3 levels could control [Ca2+]n. When we injected Ins(1,4,5)P3 directly into the nucleus, [Ca2+]n increased, even when heparin was present in the cytosol, indicating that Ins(1,4,5)P3 could control [Ca2+]n from within the nucleus. These results provide functional evidence for Ins(1,4,5)P3 receptors facing the nucleoplasm and raise the possibility that a phosphoinositide cycle situated at the nuclear membranes can control Ca(2+)-dependent nuclear functions.
Hennager
D J
DJ
Veterans Administration Medical Center, Iowa City, Iowa.
Welsh
M J
MJ
DeLisle
S
S
D000814:Aniline Compounds; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005260:Female; D005456:Fluorescent Dyes; D006493:Heparin / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007700:Kinetics; D018613:Microscopy, Confocal / Q000379:methods; D009865:Oocytes / Q000378:metabolism*; D014966:Xanthenes; D014981:Xenopus
D000814:Aniline Compounds; D005456:Fluorescent Dyes; D014966:Xanthenes; C059715:Fluo-3; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D002118:Calcium