Suppressive effect of endogenous regucalcin on the enhancement of protein synthesis and aminoacyl-tRNA synthetase activity in regenerating rat liver

The effect of regucalcin, which is a regulatory protein in Ca2+ signaling, on protein synthesis in regenerating rat liver was investigated. Protein sy nthesis was assayed in a reaction mixture containing the 5500 g supernatant fraction in the presence of [H-3]leucine. The presence of anti-regucalcin monoclonal antibody (100 and 150 ng/ml) in the reaction mixture caused a si gnificant elevation of in vitro protein synthesis. This elevation was compl etely prevented by the addition of regucalcin (1.0 mu M). Regenerating live r after partial hepatectomy (HPX) induced a significant increase in protein synthesis. This increase was significantly enhanced by the presence of ant i-regucalcin monoclonal antibody (100 ng/ml). This enhancement was remarkab le at 24 and 48 h after HPX. [H-3]Leucyl-tRNA synthetase activity in the 10 5000 g supernatant fraction (cytosol) of the liver homogenate from normal r ats was significantly raised by the presence of antibody (100 and 150 ng/ml ) in the enzyme reaction mixture. Regenerating liver caused a significant e levation of the enzyme activity at 24, 48, and 72 h after HPX. This elevati ng was significantly enhanced in the presence of antibody (100 ng/ml). The present study suggests that endogenous regucalcin has a suppressive effect on the enhancement of protein synthesis in regenerating rat liver with a pr oliferative cells.