Induction of mineralocorticoid receptor by sodium butyrate in small intestinal (IEC6) and colonic (T84) epithelial cell lines

Mineralocorticoid action is essential for colonic sodium and water absorption and is mediated via mineralocorticoid receptors in the upper half of colonic crypts. On the other hand, it has been established that sodium butyrate induces differentiation-like phenomenon in vitro. The aim of this study is to investigate whether this bacterial product participates in the regulation of gene and protein expression of mineralocorticoid receptor in vitro. IEC6 and T84 cells were stimulated by sodium butyrate and RNAs extracted. Gene expression of mineralocorticoid receptor was evaluated by northern blotting or semiquantitative RT-PCR. Protein expression was determined in T84 cells using immunohistochemistry. To investigate whether MR induction was associated with cellular differentiation, we also measured alkaline phosphatase in situ. The mineralocorticoid receptor gene was induced by sodium butyrate in both IEC6 and T84 cells. Immunoreactivity increased in butyrate-treated T84 cells, but receptor-containing cells were not uniformly distributed and often formed clusters. Induction of alkaline phosphate activity was also demonstrated in both IEC6 and T84 cells. Double staining by immunoreactivity and alkaline phosphatase activity clearly demonstrated the colocalization of both after butyrate treatment. In conclusion, sodium butyrate up-regulates gene and protein expression of the functionally important mineralocorticoid receptor in epithelial cells, after induction by differentiation-like condition in vitro.