| Abstrakt: |
We have found that butyrate selectively inhibits hormonal induction of a few specific proteins and messenger RNAs in hepatoma cells. The fatty acid salt reversibly abolishes induction of tyrosine aminotransferase by dexamethasone and dibutyryl cyclic AMP in HTC cells by inhibiting the production of tyrosine aminotransferase messenger RNA. Half-maximal inhibition of enzyme induction occurred in 0.9 mM butyrate. This effect is highly specific, since 4 h after the addition of butyrate to induced HTC cells, the relative abundance of only five messenger RNA species out of several hundred observable on two-dimensional gels of translational products is changed. Upon removal of the butyrate from cell cultures pretreated with dexamethasone, tyrosine aminotransferase activity begins to increase more rapidly than if dexamethasone is added to control cultures, indicating that part of the induction process occurs in the presence of butyrate. A dose-dependent reduction of fast histone acetylation by butyrate was demonstrated by treating cells with butyrate followed by a short pulse with [3H]acetate and chase in a high concentration of butyrate. The butyrate concentration test range over which rapid histone acetylation is inhibited is similar to that which inhibits enzyme induction to the same extent. In contrast, the slow form of histone acetylation is unaffected in the concentration range examined. The induction of tyrosine aminotransferase by dexamethasone is delayed in hypoacetylated cells. This lag is consistent with the time required to initiate the recovery of the fast form of histone acetylation after its transient disappearance (Covault, J., Perry, M., and Chalkley, R. (1982) J. Biol. Chem. 257, 13433-13440). We conclude that sodium butyrate interferes with the ability of dexamethasone and dibutyryl cyclic AMP to increase production of several specific species of messenger RNA in hepatoma cells. This effect correlates well with its ability to reduce rapid acetylation of histones in HTC cells; we discuss potential roles of rapid histone acetylation in modulating hormonal stimulation of transcription. |
