Overexpression of regucalcin suppresses cell response for tumor necrosis factor-α or transforming growth factor-β1 in cloned normal rat kidney proximal tubular epithelial NRK52E cells

The regulatory role of regucalcin on cell responses for tumor necrosis factor-alpha (TNF-) or transforming growth factor-beta 1 (TGF-beta 1) was investigated using the cloned normal rat kidney proximal tubular epithelial NRK52E cells overexpressing regucalcin. NRK52E cells (wild type) and stable regucalcin (RC)/pCXN2-transfected cells (transfectant) were cultured for 72 h in a medium containing 5% bovine serum (BS) to obtain subconfluent monolayers. After culture, cells were further cultured for 24-72 h in medium without BS containing either vehicle, TNF-alpha (0.1 or 1.0 ng/ml of medium), or TGF-beta 1 (1.0 or 5.0 ng/ml). Culture with TNF-alpha or TGF-beta 1 caused a significant decrease in the number of wild-type cells. The decrease was significantly prevented in transfectants overexpressing regucalcin. Agarose gel electrophoresis showed the presence of low-molecular-weight deoxyribonucleic acid (DNA) fragments of adherent wild-type cells cultured with TNF-alpha (1.0 ng/ml) or TGF-beta 1 (5.0 ng/ml). This DNA fragmentation was significantly suppressed in transfectants. TNF-alpha- or TGF-beta 1-induced cell death was significantly prevented in culture with caspase-3 inhibitor(10(-8) M). Nitric oxide (NO) synthase activity in wild-type cells was significantly increased by addition of calcium chloride (10 mu M) and calmodulin (5 mu g/ml) into the enzyme reaction mixture. This increase was significantly suppressed in transfectants. Culture with TNF-alpha caused a significant increase in NO synthase activity in wild-type cells. The effect of TNF-alpha was not seen in transfectants. Culture with TGF-beta 1 did not cause a significant increase in NO synthase activity in wild-type cells and transfectants. Culture with TNF-alpha or TGF-beta 1 caused a remarkable increase in alpha-smooth muscle actin in wild-type cells. This increase was significantly prevented in transfectants. The expression of Smad 2 or NF-kappa B mRNAs was significantly increased in transfectants as compared with that of wild-type cells. Smad 3 or glyceroaldehyde-3-phosphate dehydrogenase (G3PDH) mRNA expression was not significantly changed in transfectants. NF-kappa B mRNA expression in wild-type cells was significantly increased with culture of TNF-alpha. Smad 2 mRNA expression was significantly enhanced in wild-type cells cultured with TGF-beta 1. These effects of TNF-alpha or TGF-beta 1 were not significantly enhanced in transfectants. This study demonstrates that overexpression of regucalcin has suppressive effects on cell responses which are mediated through intracellular signaling pathways of TNF-alpha or TGF-beta 1 in kidney NRK52E cells.