Relationship between RNA synthesis and the Ca2+-filled state of the nuclear envelope store.
RNA synthesis and ATP-dependent (45)Ca(2+) uptake were measured simultaneously in isolated nuclear fraction of rat liver nuclei. Maximal level of RNA synthesis was obtained under ATP-dependent (45)Ca(2+)-uptake conditions (1 microM free [Ca(2+)] and 1 mM ATP in the bathing solution). This experimental condition was defined as "stimulated nuclei" condition. ATP-dependent (45)Ca(2+) uptake was inhibited using different strategies including: (a) eliminating Ca(2+) (1 mM EGTA); (b) lowering the ATP concentration; (c) modifying nuclear envelope membranes Ca(2+) permeability (Ca(2+) ionophores); or (d) inhibiting the nuclear Ca(2+) pump (thapsigargin and 3',3'',5',5''-tetraiodophenolsulfonephthalein). Under all the above conditions, RNA synthesis was lower than in "stimulated nuclei" condition. In the presence of ionomycin, RNA synthesis was significantly higher at 500 nM free [Ca(2+)], as compared with RNA synthesis in a Ca(2+)-free medium or at 1muM free [Ca(2+)]. However, even in such condition (500 nM free [Ca(2+)]), RNA synthesis was lower than RNA synthesis obtained in "stimulated nuclei" condition. We suggest two components for the effect of Ca(2+) on RNA synthesis: (A) a direct effect of nucleoplasmic [Ca(2+)]; and (B) an effect dependent on the accumulation of Ca(2+) in the nuclear envelope store mediated by the SERCA nuclear Ca(2+) pump.
Benech
Juan Claudio
JC
Laboratorio de Proteínas y Acidos Nucleicos, Instituto de Investigaciones Biológicas Clemente Estable. Av. Italia 3318, Montevideo, Uruguay. benech@iibce.edu.uy
Escande
Carlos
C
Sotelo
José Roberto
JR
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002614:Chelating Agents / Q000494:pharmacology; D004734:Energy Metabolism / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D009685:Nuclear Envelope / Q000378:metabolism*; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000235:genetics; D012313:RNA / Q000096:biosynthesis*; D051381:Rats; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013347:Subcellular Fractions
D002614:Chelating Agents; D004791:Enzyme Inhibitors; D007476:Ionophores; D009687:Nuclear Proteins; D015759:Ionomycin; D012313:RNA; D000255:Adenosine Triphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium