In vivo regulation of rRNA transcription occurs rapidly in nondividing and dividing Drosophila cells in response to a phorbol ester and serum.

Abstract

The synthesis of ribosomes is an essential cellular process which requires the transcription of the rRNA genes by RNA polymerase I (Pol I). The regulation of rRNA synthesis is known to be coupled to growth regulation.In nongrowing, slowly growing, and rapidly growing Drosophila cells, exposure to the tumor-promoting phorbol ester 12-0-tetradecanoylphorbol-13-acetate (TPA) increases the synthesis of precursor and mature rRNAs. Using nuclear run-on assays, we show that TPA enhances transcription of the rRNA genes. These results suggest that TPA regulates expression of rRNA genes transcribed by Pol I, irrespective of the growth state of the cells. In slowly dividing Drosophila cells, increasing the serum concentration rapidly alters the accumulation of rRNA by enhancing rDNA transcription within 1 h. Thus, TPA and serum are each able to rapidly regulate rRNA gene expression in Drosophila cells. These results indicate that the RNA Pol I transcription system can be regulated by agents which have previously been shown to effect specific genes transcribed by the RNA Pol II system.It is now widely accepted that tumor-promoting phorbol esters, which mimic the action of diacylglycerol, can activate a calcium-and phospholipid-dependent protein kinase, protein kinase C (reviewed in references 4, 17, and 20). We have previously observed that protein synthesis can be stimulated within minutes in nondividing Drosophila cells by reagents that act through a pathway involving calcium and the activation of protein kinase C (32). We found that phorbol esters stimulated protein synthesis and that this stimulation was dependent on the presence of calcium, suggesting a common signaling pathway. Since in most systems, the cellular processes of protein and rRNA synthesis are closely coupled (reviewed in reference 21), we have investigated whether in nondividing cells, activation of protein kinase C by 12-O-tetradecanoylphorbol-13-acetate (TPA) can bring about changes in rRNA synthesis parallel to its affects on protein synthesis.Since TPA is known to affect growth-related events in dividing cells, we also chose to investigate the effects of this reagent on rRNA synthesis in dividing Drosophila cultured cells which were either growing slowly, i.e., under serumreduced conditions, or growing rapidly, in the presence of a high concentration of serum.There are several levels at which stimulation or inhibition of RNA synthesis could potentially be controlled. We have investigated the changes in rDNA transcription which take place in Drosophila cells treated with TPA and serum by using nuclear run-on assays to examine the number of active polymerase I (Pol I) complexes present on the 18S and 28S rRNA genes. MATERIALS AND METHODS Drosophila culture and male accessory gland isolation.Wild-type Drosophila melanogaster (Oregon-R) was grown at 25°C on a standard cornmeal-Karo-yeast agar medium supplemented with live yeast cells. After eclosion, the flies were separated according to sex. Accessory glands from 10 virgin males (7 to 10 days old) were ...

Regulation of RNA Polymerase I-Dependent Promoters by the Hepatitis B Virus X Protein via Activated Ras and TATA-Binding Protein

“…To examine the mechanism for the X-mediated induction of the RNA Pol I-dependent promoters observed, we considered the possibility that this regulatory event was dependent on the activation of cellular signaling pathways. Previous studies have shown that rRNA transcription is upregulated in both mammalian (1,51) and Drosophila (54,64) cells by the phorbol ester tetradecanoyl phorbol acetate (TPA), a potent activator of protein kinase C (PKC). X has been shown to activate both PKC (30) and Ras (3), and activation of these signaling proteins is required for X transactivation of certain RNA Pol II (3, 5, 13, 30, 42)-and RNA Pol III (61, 62)-dependent promoters.…”

Induction of Drosophila RNA polymerase III gene expression by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) is mediated by transcription factor IIIB.

“…However, in the Drosophila system, the TPA response did not produce a detectable increase in the expression of several RNA pol II genes examined (21). The TPA response has also been shown to induce the transcription of RNA pol I genes (7,67). Whether the activity of the TBP-containing RNA pol I factor, SL1, is enhanced in this regulatory event remains to be determined.…”

“…The analysis of the transcriptional response of many of the genes to phorbol esters revealed that a common DNA sequence element, TPA-responsive element, was required (1) and that this element was the recognition sequence for the transcription factor, AP-1, composed of fos and jun polypeptides (51). Examination of TPAinducible genes in the Drosophila system has revealed that both RNA pol III (21) and RNA pol l (7,67) gene expression is activated by TPA. Under the conditions used, the Drosophila fos-and jun-related antigen genes, however, were not found to be inducible (21) Extracts and transcription factor preparation.…”

Coordinate Regulation of Ribosomal Component Synthesis in Acanthamoeba castellanii: 5S RNA Transcription Is Down Regulated during Encystment by Alteration of TFIIIA Activity

“…Therefore, the rate of biosynthesis of ribosomes varies with the cellular proliferation rate, in response to cellular growth without cell division (e.g., cardiac hypertrophy [1]), and with significant changes in protein synthesis rates in secretory tissues (e.g., the Drosophila paragonial gland [29] [reviewed in reference 22]). The synthesis of the 80 to 90 components of the ribosome must be coordinately up or down regulated to correspond to changes in ribosome elaboration rate.…”