Overexpression of regucalcin suppresses cell death and apoptosis in cloned rat hepatoma H4-II-E cells induced by lipopolysaccharide, PD 98059, dibucaine, or Bay K 8644

The effect of regucalcin, a regulatory protein in intracellular signaling pathway, on cell death was investigated by using the cloned rat hepatoma H4-II-E cells overexpressing regucalcin. The hepatoma cells (wild-type) and stable regucalcin (RC)/pCXN2 transfectants were cultured for 72 h in medium containing 10% fetal bovine serum (FBS) to obtain subconfluent monolayers. After culture for 72 h, cells were further cultured for 12-72 h in medium without FBS containing either vehicle or lipopolysaccharide (LPS; 0.1 or 1.0 microg/ml). The number of wild-type cells was significantly decreased by culture for 24 or 48 h in the presence of LPS (0.1 or 1.0 microg/ml). The effect of LPS (0.1 or 1.0 microg/ml) in decreasing the number of hepatoma cells was significantly prevented in transfectants overexpressing regucalcin. However, the culture with LPS (0.1 or 1.0 microg/ml) for 72 h caused a significant decrease in cell number of transfectants. Ca(2+)/calmodulin-dependent nitric oxide (NO) synthase activity was significantly decreased by culture with LPS (1.0 microg/ml) for 24-72 h of wild-type cells. This decrease was significantly prevented in transfectants. LPS (0.1 or 1.0 microg/ml)-induced decrease in the number of wild-type cells was significantly prevented by culture with caspase-3 inhibitor (10(-8) M). Moreover, the number of wild-type cells was significantly decreased by culture with PD 98059 (10(-6) M), dibucaine (10(-6) M), or staurosporine (10(-6) M), which is an inhibitor of various protein kinases. The effect of PD 98059 or dibucaine on the number of wild-type cells was not observed in transfectants, although the effect of staurosporine was seen in transfectants. Culture with Bay K 8644 (2.5 x 10(-6) M), an agonist of Ca(2+) entry in cells, caused a significant decrease in the number of wild-type cells. Such an effect was not seen in transfectants. The presence of LPS did not significantly decrease the number of wild-type cells in the presence of Bay K 8644. Agarose gel electrophoresis showed the presence of low-molecular-weight deoxyribonucleic acid (DNA) fragments of adherent wild-type cells cultured with Bay K 8644, and this DNA fragmentation was significantly prevented in transfectants. This study demonstrates that overexpression of regucalcin has a suppressive effect on cell death induced by LPS or various intracellular signaling-related factors.