Sodium butyrate induces alkaline phosphatase gene expression in human hepatoma cells

Abstract

Butyrate, a natural product of colonic bacterial flora, has been reported to increase the activities of a number of enzymes, including alkaline phosphatase, (ALP) in several cancer cell lines. However, butyrate-induced ALP gene expression in human hepatoma cells has not been previously demonstrated. In the present study, the effects of sodium butyrate on cell growth and proliferation, cellular activity and expression of ALP gene in human hepatoblastoma-derived HepG2 cells were investigated. The HepG2 cells were treated with sodium butyrate (0-1 mmol/L) and the number of viable cells were counted at 24, 48 and 72 h after treatment. A [3H]-thymidine incorporation study was performed at different concentrations of sodium butyrate for 48 h. The cellular activity of ALP in HepG2 cells by sodium butyrate was measured by a substrate-specific enzymatic assay. To elucidate the effects of sodium butyrate on ALP gene expression, a northern blotting experiment employing hybridization with mouse placental ALP cDNA was performed. Cell growth and proliferation were dose-dependently inhibited by sodium butyrate. Cellular ALP activity was significantly increased in HepG2 cells in a time- and dose-dependent fashion by treatment with sodium butyrate and a maximum activity was observed at 48 h. These effects were reversible when sodium butyrate was removed from the culture medium. By northern blot analysis, the level of ALP messenger RNA was dose-dependently elevated by sodium butyrate. Butyrate, at a concentration relevant to the normal physiology of the liver, causes augmented expression of ALP mRNA in HepG2 cells. We assume that increased ALP synthesis in HepG2 cells by sodium butyrate results from an enhanced rate of transcription rather than translation of mRNA.