The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, induces specific transcription by RNA polymerase III in Drosophila Schneider cells.

We have examined the ability of the tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), to regulate RNA polymerase III gene expression in Drosophila. Using nuclear run-on assays, we detected a 3-5-fold increase in tRNA synthesis following treatment of Drosophila Schneider S2 cells with TPA, whereas transcription from the actin 5C, fos-, and jun-related antigen promoters was unaffected. This response is rapid and transient, peaking at about a 45-min exposure of the cells to TPA, and dissipating after 60 min. We have reproduced this stimulation in vitro. Extracts prepared from cells treated with TPA show an approximate 10-fold increase in specific transcription using a 5 S RNA and various tRNA gene templates. The nonspecific transcription by RNA polymerase III in these extracts, however, is essentially unchanged. Mixing the extracts derived from uninduced and induced cells suggests that the TPA stimulation observed may be due to the increase of a positive-acting factor. These results are the first to demonstrate that a phorbol ester can induce RNA polymerase III gene expression. The ability to reproduce this activation in vitro will now allow us to assess the role of the transcription components in this regulatory event, and the biochemical consequence of this signaling pathway.