Effect of butyrate on the expression of microinjected or transfected genes

We have studied the effect of sodium n-butyrate on the expression of specific genes. For this purpose, tk-ts13 cells (a thymidine kinase-deficient mutant originating from Syrian hamster cells) were microinjected or transfected with pC2, a plasmid containing the entire SV40 genome and the herpes simplex virus thymidine kinase gene (HSV-TK), cloned in pBR322. As a measure of the expression of these two genes, one of which is spliced (SV40) and the other one (HSV-TK) which is not, we have taken the protein levels (amount of T antigen for SV40 and incorporation of [3H]thymidine for HSV-TK) and the levels of RNA (by dot blot hybridization). The expression of the microinjected genes was inhibited when tk-ts13 cells were exposed to butyrate, actinomycin D, cycloheximide, and mitomycin C, but not when the cells were treated with insulin or dexamethasone. Further studies showed that a decrease in the percentage of T-positive cells occurs at lower concentrations of butyrate than a decrease in the levels of specific mRNA. In tk-ts13 cells transfected with pC2 and treated with butyrate at a concentration of 3 mM, SV40 mRNA levels are not decreased but the percentage of T-positive cells is decreased 50%. At 5 mM, the amount of T antigen/cell is decreased a further 40%. These results indicate that butyrate may have at least two sites of action, one at the level of mRNA amount and a second at the level of protein amount. In addition, our studies show that the use of microinjected or transfected genes offers certain unique possibilities for studies on the effects of environmental manipulations on gene expression.