Modulation of glucocorticoid effects and steroid receptor binding in butyrate-treated HeLa S 3 cells

Abstract

Two synergistic actions of glucocorticoid hormones and sodium butyrate in HeLa S 3 cells are reported. Growth of HeLa S 3 cells in dexamethasone and sodium butyrate leads to synergistic effects on both increases in alkaline phosphatase activity and inhibition of [ 3H]thymidine incorporation into DNA. A 7- to 10-fold increase in alkaline phosphatase activity is seen in cells treated for 96 h with either 1 × 10 −7, m dexamethasone or 5 m m sodium butyrate. Simultaneous administration of the two compounds, however, elevates alkaline phosphatase activity in a synergistic manner, reaching levels 7-fold higher than those obtained with either compound alone. In addition, both agents inhibit [ 3H]thymidine incorporation into DNA, and combined administration leads to a synergistic suppression of nucleoside incorporation. These effects are dependent on the steroid hormone concentration employed, being half-maximal at 2 × 10 −8, m dexamethasone. In addition, only active glucocorticoid hormones act synergistically with sodium butyrate suggesting mediation through high affinity glucocorticoid receptors. Unexpectedly, exposure of cells to 5 m m butyrate for 20–24 h results in a significant reduction in the levels of both nuclear and cytoplasmic dexamethasone receptors (33 and 49% reduction, respectively), without altering binding site affinity. Despite decreases in total cellular receptor binding, butyrate treatment of HeLa S 3 cells does not alter absolute levels of 0.4 m KCl residual nuclear binding sites. Our results show that glucocorticoid effects on alkaline phosphatase activity and [ 3H]thymidine incorporation are augmented with butyrate treatment, despite reduced cellular binding of the hormone.