Inhibitory effect of calcium-binding protein regucalcin on ribonucleic acid synthesis in isolated rat liver nuclei

Abstract

The effect of regucalcin, a Ca2+-bindingf protein isolated from rat livercytosol, on ribonucleic acid (RNA) synthesis in the nuclei of normal ratliver and of regenerating rat liver was investigated. The liver weight at 1day after partial hepatectomy was increased about 50% of that ofsham-operated (control) rats. Calcium chloride (1.0-20 µM Ca2+ asfinal concentration) was added into the reaction mixture of nuclear RNAsynthesis. RNA synthesis was established by incorporation of [3H]-uridine5'-triphosphate (UTP) into the nuclear RNA. Addition of Ca2+ (5 and 10µM) caused a significant increase of RNA synthesis in the nuclei fromcontrol rat liver. Such effect of Ca2+ was potentiated in the nuclei ofregenerating liver; nuclear RNA synthesis was increased about 2 fold by the1.0 and 2.5 µM Ca2+ addition. The stimulatory effect of Ca2+ wassignificantly inhibited by the presence of a-amanitin (10-8 M), an inhibitorof RNA polymerase II. The presence of regucalcin (0.25 and 0.5 µM)significantly inhibited RNA synthesis in the nuclei from control rat liverand from regenerating rat liver. The inhibitory effect of regucalcin wasremarkable in the presence of EGTA (0.5 mM), and it was weakened by theaddition of Ca2+ (5 µM). Such regucalcin effect was not seen in thepresence of a-amanitin. The presence of anti-regucalcin IgG in the reactionmixture significantly increased RNA synthesis in the nuclei from control ratliver, indicating that the endogenous regucalcin may be involved in nuclearRNA synthesis. The present resuits demonstrate that regucalcin can inhibitnuclear RNA synthesis in rat liver. Regucalcin may have an inhibitory rolein the regulation of liver nuclear RNA synthesis.