Abstract
The role of endogenous regucalcin in the regulation of ribonucleic acid (RNA) synthesis activity in the nucleus of normal and regenerating rat livers was investigated. Nuclear RNA synthesis was measured by the incorporation of [^3^H]‐uridine 5′‐triphosphate into the nuclear RNA in vitro. The presence of regucalcin (0.25 or 0.5 μM) in the reaction mixture caused a significant decrease in nuclear RNA synthesis of normal rat liver. α‐Amanitin (10^−8^–10^−6^ M), an inhibitor of RNA polymerase II and III, decreased significantly nuclear RNA synthesis activity. The effect of regucalcin (0.25 μM) in decreasing nuclear RNA synthesis activity was not seen in the presence of α‐amanitin (10^−6^ M). The calcium chloride (10 μM)‐increased nuclear RNA synthesis activity was significantly suppressed by the addition of regucalcin (0.25 μM). RNA synthesis activity was significantly enhanced in the nuclei of regenating rat liver obtained at 24, 48, or 72 h after partial hepatectomy. This enhancement was significantly inhibited in the presence of PD98059 (10^−5^ M), staurosporine (10^−6^ M), or vanadate (10^−3^ M). Western analysis of the nuclei of regenerating liver obtained at 24, 48, or 72 h after partial hepatectomy showed a significant increase in regucalcin protein as compared with that of sham‐operated rats. The presence of anti‐regucalcin monoclonal antibody (25 or 50 ng/ml) in the reaction mixture caused a significant increase in nuclear RNA synthesis activity of normal rat liver. This increase was completely blocked by the addition of regucalcin (1.0 μM). The effect of anti‐regucalcin monoclonal antibody (50 ng/ml) in increasing nuclear RNA synthesis activity was significantly enhanced in the nuclei of regenerating liver obtained at 24, 48, or 72 h after partial hepatectomy. This enhancement was significantly suppressed by the addition of α‐amanitin (10^−6^ M), PD98059 (10^−5^ M), staurosporine (10^−6^ M), or vanadate (10^−3^ M) in the reaction mixture. The present study demonstrates that endogenous regucalcin has a suppressive effect on the enhancement of RNA synthesis activity in the nucleus of regenerating rat liver with proliferative cells. J. Cell. Biochem. 87: 450–457, 2002. © 2002 Wiley‐Liss, Inc.