Links between effects of butyrate on histone hyperacetylation and regulation of interferon synthesis in Namalva and FS-4 cell lines

Mechanism for transcriptional synergy between interferon regulatory factor (IRF)-3 and IRF-7 in activation of the interferon-β gene promoter

The interferon-beta promoter has been studied extensively as a model system for combinatorial transcriptional regulation. In virus-infected cells the transcription factors ATF-2, c-Jun, interferon regulatory factor (IRF)-3, IRF-7 and NF-kappaB, and the coactivators p300/CBP play critical roles in the activation of this and other promoters. It remains unclear, however, why most other combinations of AP-1, IRF and Rel proteins fail to activate the interferon-beta gene. Here we have explored how different IRFs may cooperate with other factors to activate transcription. First we showed in undifferentiated embryonic carcinoma cells that ectopic expression of either IRF-3 or IRF-7, but not IRF-1, was sufficient to allow virus-dependent activation of the interferon-beta promoter. Moreover, the activity of IRF-3 and IRF-7 was strongly affected by promoter context, with IRF-7 preferentially being recruited to the natural interferon-beta promoter. We fully reconstituted activation of this promoter in insect cells. Maximal synergy required IRF-3 and IRF-7 but not IRF-1, and was strongly dependent on the presence of p300/CBP, even when these coactivators only modestly affected the activity of each factor by itself. These results suggest that specificity in activation of the interferon-beta gene depends on a unique promoter context and on the role played by coactivators as architectural factors.

Gene expression within a chromatin domain: the role of core histone hyperacetylation

Scaffold-attached regions (SAR elements) increase transcriptional rates for integrated but not episomal templates, and this effect can be potentiated by using an epigenetically active reagent, butyrate. The action of butyrate is a direct one, not involving de novo protein synthesis, and can be mimicked by using a novel and highly specific inhibitor of histone deacetylases, (R)-trichostatin A. This leads to a model in which SAR elements serve to stabilize the chromosomal topology arising as a consequence of hyperacetylation of histone cores. The synergistic effects of histone hyperacetylation and SARs are mediated by promoter upstream elements since, for a simple TATA box, the response to both parameters is an additive one.

Chromatin structure and induction-dependent conformational changes of human interferon-beta genes in a mouse host cell

Multiple copies of a human interferon-beta gene introduced into a mouse host cell line can be activated by induction with double-stranded RNA. Several induction-dependent changes of the chromatin structure could be traced by mapping techniques using four different agents [DNase I, micrococcus nuclease, bromoacetaldehyde and methidiumpropyl-EDTA X iron(II)]. Our data show that all copies of the interferon gene have adopted a very similar conformation in the host cell and respond to the inducing stimulus in a highly synchronous fashion. Detailed induction-specific changes were observed best with the chemical reagents which disclose a specific hypersensitive site within a sequence that has been shown to be required for the induction process (around position -80) and three other regions which, in addition to the transcribed region itself, gain single-strand character by an auxiliary process which can be mimicked by the addition of butyrate to the medium and may therefore involve histone hyperacetylation. Six discrete 'phased' nucleosomes are present upstream from the gene and are modulated by induction. At least four nucleosomes are located downstream. The interferon genes are largely protected from micrococcus nuclease in the inactive state. Gene activation increases access to micrococcus nuclease and DNase I indicating gross conformational changes on a higher level of chromatin structure.

Rat fibroblast-derived interferon: production in serum-free medium and enhancement by theophylline

Incubation of rat fibroblasts (RFA-1) with theophylline after Newcastle disease virus (NDV) induction, increased rat fibroblast interferon (RfIFN) yields 3 to 10-fold. However, incubation with butyric acid for 24 or 48 h before NDV addition resulted in no change or decrease in IFN production. Combined treatment with butyric acid and theophylline did not improve the yields obtained with the methylxanthine alone. Production of IFN by RFA-1 cells was the same in serum-free and in serum-containing media. These findings will facilitate RfIFN production and purification.

Nucleosomal particles open as the histone core becomes hyperacetylated

Lymphoblastoid cells grown in the presence of the deacetylase inhibitor butyrate were used to isolate nucleosomal particles in a hyperacetylated state. During a non-denaturing gel electrophoresis these particles revealed a heterogeneity which is only in part due to the presence of nonhistone proteins. Monomers that are free from histone H1 and high-mobility-group (HMG) proteins 14 and 17 yield a subfractionation according to the degree of core histone acetylation beyond a limiting value of 10 acetyl groups/particle. It is shown that hyperacetylation provides particles with low mobilities and a considerable conformational freedom in contrast to HMG protein 14 which locks them in a conformation that has a similar electrophoretic behaviour but is more defined.