Effect of cortisol on cell proliferation and the expression of lipoprotein lipase and vascular endothelial growth factor in a human osteosarcoma cell line. The aim of this study is to investigate whether cortisol inhibited cell proliferation and the expressions of lipoprotein lipase (LPL), a key enzyme involved in the energy metabolism in tumor cells, and vascular endothelial growth factor (VEGF), a potent angiogenic factor in the tumor, in cultures of OST cells, a human osteosarcoma cell line.OST cells were treated for 48 h with or without cortisol. To examine the effect of cortisol on cell proliferation, the expression of proliferating cell nuclear antigen (PCNA) was examined by Western blotting, and the amount of (3)H-thymidine incorporated into DNA during the last 30 min of the 48-h treatment period was measured. To examine the effect of cortisol on the expression of LPL, the activity and mass of LPL were measured in the extract of acetone/ether powder of cells, and the amount of (35)S-methionine incorporated into LPL during the last 2 h of the 48-h treatment period was measured by immunoprecipitation. The expression of VEGF was examined by immunohistochemistry and Western blotting.The amount of (3)H-thymidine incorporated into DNA and the level of PCNA were lower in the cortisol-treated cultures than in the untreated cultures, thus indicating that cortisol inhibited the proliferation of OST cells. The synthetic rate and activity of LPL were lower in the cortisol-treated cultures than in the untreated cultures but no difference in the specific activity of LPL between the two cultures was observed, thus indicating that cortisol inhibited LPL synthesis, thereby resulting in a decreased LPL activity. The expression of VEGF was lower in the cortisol-treated cultures than in the untreated cultures.Cortisol not only has the ability to inhibit cell proliferation but also the ability to inhibit the expressions of LPL and VEGF in cultures of OST cells.