Modulation of human triosephosphate isomerase gene transcription by serum

We have monitored the level of mRNA encoding the glycolytic and gluconeogenic enzyme triosephosphate isomerase (TPI) during the growth arrest of cells by serum deprivation and the subsequent growth activation of cells by serum addition. This analysis has demonstrated that the steady state level of TPI mRNA changes 5-20-fold, depending upon the cell type, during the traversal of cells from a proliferative to a nonproliferative state and vice versa. These changes are largely attributable to changes in the rate of TPI gene transcription rather than to alterations in post-transcriptional processes as determined by nuclear run-on measurements. Following serum stimulation, the increase in TPI gene expression is maximal at or around the onset of DNA synthesis. We have also quantitated TPI mRNA throughout the cell cycle following cell synchronization with aphidicolin. Our results indicate that the steady state level of TPI mRNA is relatively constant throughout the division cycle of proliferating cells. Thus, while TPI gene expression is modulated during the traversal of cells to and from a nonproliferative state, it is not significantly modulated during the cycle of events that is characteristic of continuously proliferating cells.