Suppressive effect of endogenous regucalcin on deoxyribonuclic acid synthesis in the nuclei of rat renal cortex

The effect of regucalcin, a regulatory protein of Ca(2+) signaling, on deoxyribonucleic acid (DNA) synthesis activity in the nuclei isolated from rat renal cortex was investigated. The addition of calcium chloride (10-100 muM) in the reaction mixture containing the nuclei caused a significant decrease in DNA synthesis activity. Nuclear DNA synthesis activity was significantly raised in the presence of EGTA (1 mM), a chelator of Ca(2+), indicating that nuclear Ca(2+) has an inhibitory effect. Regucalcin (0.1-0.5 muM) added in the reaction mixture in the presence of either EGTA (1 mM) or calcium chloride (50 muM) had a significant inhibitory effect on nuclear DNA synthesis activity. The presence of anti-regucalcin monoclonal antibody (10-50 ng/ml) in the reaction mixture caused a significant increase in DNA synthesis activity. This increase was completely abolished by the addition of regucalcin (0.5 muM). The effect of anti-regucalcin monoclonal antibody in increasing DNA synthesis was enhanced in the presence of EGTA. Additionally, an inhibitory effect of calcium chloride (10 or 50 muM) was enhanced in the presence of anti-regucalcin monoclonal antibody (25 ng/ml). The present study demonstrates that endogenous regucalcin has a suppressive effect on DNA synthesis in the nuclei of rat renal cortex.