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The macrolide antibiotic rapamycin inhibits cellular proliferation by interfering with the highly conserved TOR (for target of rapamycin) signaling pathway. Growth arrest of budding yeast cells treated with rapamycin is followed by the program of molecular events that characterizes entry into G 0 (stationary phase), including the induction of polymerase (Pol) II genes typically expressed only in G 0 . Normally, progression into G 0 is characterized by transcriptional repression of the Pol I and III genes. Here, we show that rapamycin treatment also causes the transcriptional repression of Pol I and III genes. The down-regulation of Pol III transcription is TOR dependent. While it coincides with translational repression by rapamycin, transcriptional repression is due in part to a translation-independent effect that is evident in extracts from a conditional tor2 mutant. Biochemical experiments reveal that RNA Pol III and probably transcription initiation factor TFIIIB are targets of repression by rapamycin. In view of previous evidence that TFIIIB and Pol III are inhibited when protein phosphatase 2A (PP2A) function is impaired, and that PP2A is a component of the TOR pathway, our results suggest that TOR signaling regulates Pol I and Pol III transcription in response to nutrient growth signals.Gradual nutrient depletion in Saccharomyces cerevisiae provokes a broad spectrum of morphological and biochemical changes that result in a terminal cell cycle arrest phenotype called G 0 or stationary phase (reviewed in references 44 and 45). Stationary-phase cells have a 1n DNA content, are uniformly large and unbudded, and display a prominent vacuole. The G 0 state is further characterized by reduced protein synthesis, and the pattern of RNA polymerase (Pol) II transcripts is distinct in cycling and G 0 cells. Thus, more than 95% of Pol II genes are repressed in G 0 , and a subset of Pol II genes whose products promote survival under conditions of nutrient limitation are massively induced at the transcriptional level (8). Induction of the G 0 pattern of Pol II transcription in yeast accompanies the repression of transcription of the large rRNA genes by Pol I and the tRNA and 5S rRNA genes by Pol III (9,26,33,36). Since tRNA and rRNA synthesis accounts for about 70% of nuclear transcription, this regulatory mechanism may enhance survival in G 0 by limiting the energetically costly production of relatively stable RNA products not immediately required for viability.While there is striking repression of translation in G 0 , some critical aspects of the stationary-phase response are not simply downstream consequences of a decreased rate of protein synthesis. For example, treatment of cultures with cycloheximide does not cause the accumulation of large unbudded cells or cells with a 1n DNA content (6), and in some strains there is no inhibition of Pol I or Pol III transcription in extracts from cells treated with cycloheximide (9). Key physiological steps in the differentiation of a stationary-phase cell are therefore likely to...

IL-6 abundance in amniotic fluid and uterine tissues increases in late gestation or with infection-associated preterm labor. A role in regulation of labor onset is suggested by observations that IL-6 increases expression of genes controlling prostaglandin synthesis and signaling in isolated uterine cells, but whether IL-6 is essential for normal parturition is unknown. To evaluate the physiological role of IL-6 in parturition in mice, we investigated the effect of Il6 null mutation on the timing of parturition and expression of genes associated with uterine activation. Il6 null mutant mice delivered 24 h later than wild-type mice, although circulating progesterone fell similarly in both genotypes during the prepartal period. Il6 null mutant mice were also refractory to low doses of lipopolysaccharide sufficient to induce preterm delivery in wild-type mice. The characteristic late-gestation elevation in uterine expression of Oxtr mRNA encoding oxytocin receptor, and peripartal increases in Ptgfr and Ptgs2 mRNAs regulating prostaglandin synthesis and signaling were delayed by 24 h in Il6 null mutant mice. Conversely, Ptger4 mRNA encoding the prostaglandin E receptor-4 was abnormally elevated in late-gestation in Il6 null mutant mice. Administration of recombinant IL-6 from d 11.5 postcoitum until term restored the normal timing of delivery and normalized Ptger4 mRNA expression in late gestation. We conclude that IL-6 has a key role in controlling the progression of events culminating in parturition and that it acts downstream of luteolysis in the uterus to regulate genes involved in the prostaglandin-mediated uterine activation cascade.

The molecular mechanisms that regulate the expression of genes involved in parturition are poorly understood. The mRNA expression of the prostaglandin F(2alpha) receptor (PTGFR), a uterine activating gene, is increased at labor and is required for uterine contractile activity in numerous animal models, although the signaling pathways responsible for this increased expression have not been identified. Proinflammatory cytokines have been proposed to regulate the expression of the uterine activating genes via activation of the nuclear transcription factor, NFkappaB, and initiate labor. However, it is uncertain whether uterine PTGFR is regulated this way. In this report, we demonstrate for the first time that treatment of immortalized human myometrial-derived ULTR cells with the proinflammatory cytokine IL1beta causes an increase in PTGFR mRNA levels. Furthermore, IL1beta treatment increased the nuclear levels of the RELA subunit of NFkappaB and increased binding of RELA to the NFkappaB DNA-binding site. Inhibition of NFkappaB activation with either the proteasome inhibitor MG132 or phenethyl caffeiate reduced PTGFR mRNA levels, which indicates that this transcription factor is important for basal transcription. Furthermore, this inhibition prevented IL1beta induction ofPTGFRmRNA, which confirms that NFkappaB is required for the IL1beta-induced increase inPTGFR. These results are consistent with the proposal that proinflammatory cytokines directly regulate uterine activation genes and that the transcription factor NFkappaB is involved in both basal and IL1beta-stimulated transcription of the PTGFR gene.

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