Control of interferon mRNA levels and interferon yields in butyrate and 5'-bromodeoxyuridine-treated Namalwa cells

5-Bromo-2'-deoxyuridine induces visible morphological alteration in the DNA puffs of the anterior salivary gland region of Bradysia hygida (Diptera, Sciaridae)

5-Bromo-2'-deoxyuridine (BrdUrd) has long been known to interfere with cell differentiation. We found that treatment of Bradysia hygida larvae with BrdUrd during DNA puff anlage formation in the polytene chromosomes of the salivary gland S1 region noticeably affects anlage morphology. However, it does not affect subsequent metamorphosis to the adult stage. The chromatin of the chromosomal sites that would normally form DNA puffs remains very compact and DNA puff expansion does not occur with administration of 4 to 8 mM BrdUrd. Injection of BrdUrd at different ages provoked a gradient of compaction of the DNA puff chromatin, leading to the formation of very small to almost normal puffs. By immunodetection, we show that the analogue is preferentially incorporated into the DNA puff anlages. When BrdUrd is injected in a mixture with thymidine, it is not incorporated into the DNA, and normal DNA puffs form. Therefore, incorporation of this analogue into the amplified DNA seems to be the cause of this extreme compaction. Autoradiographic experiments and silver grains counting showed that this treatment decreases the efficiency of RNA synthesis at DNA puff anlages.

Overexpression of VDUP1 mRNA sensitizes HeLa cells to paraquat

5-Bromodeoxyuridine (BrdU) induces or suppresses senescence-associated genes in any types of mammalian cells. From a cDNA library upregulated by BrdU in HeLa cells, we identified the gene encoding VDUP1 as a senescence-associated gene in normal human fibroblasts. To address a role of VDUP1 in senescence, we established HeLa cell clones, V7 and V27, which express its mRNA in a doxycycline-dependent manner. Although their growth in liquid culture was moderately retarded, colony formation on semi-solid medium was strongly inhibited by overexpression of the mRNA. We also examined susceptibility of these clones to various reagents. Consequently, colony formation in liquid culture was strongly inhibited by paraquat in these clones. Their superoxide dismutase activity was normal.

5-Bromodeoxyuridine suppresses position effect variegation of transgenes in HeLa cells

An ectopic gene integrated in the host genome is occasionally silenced due to a position effect of its adjacent chromatin structure. We found that 5-bromodeoxyuridine clearly activated such a transgene in HeLa cells. The transgene was also activated to various degrees by inhibitors of histone deacetylase, DNA topoisomerases, or DNA methyltransferase. The peptide antibiotic distamycin A potentiated markedly the effect of 5-bromodeoxyuridine. Transient expression of an artificial AT-hook protein termed MATH20 also potentiated its effect although significantly activated the transgene alone. Since distamycin A and MATH20 are able to displace histone H1 and other DNA-binding proteins bound to specific AT-rich sequences by a dominant, mutually exclusive fashion, these results suggest that 5-bromodeoxyuridine targets such an AT-rich sequence located adjacent to the silenced transgene, resulting in chromatin accessibility.

Induction of senescence-associated genes by 5-bromodeoxyuridine in HeLa cells

5-Bromodeoxyuridine (BrdU) universally induces a senescence-like phenomenon in mammalian cells. To assess this phenomenon at the level of gene expression, we constructed a PCR-based subtractive cDNA library enriched for mRNA species that immediately increase by administration of BrdU to HeLa cells. Candidate cDNA clones were isolated by differential colony hybridization, and then positive clones were identified by Northern blot analysis. Sequencing analysis revealed that the identified cDNA species were classified into three groups: widely used senescence-markers, known species whose relevance to senescence is yet to be reported, and known or novel ESTs. As expected, the majority of them showed an increase in expression in senescent human diploid fibroblasts. These results suggest that similar mechanisms operate in the regulation of BrdU-induced genes and senescence-associated genes.

Translational blockade imposed by cytokine-derived UA-rich sequences

The messenger RNAs specifying certain proteins involved in the inflammatory response and certain oncoproteins contain a conserved UA-rich sequence in the 3' untranslated region. This sequence, which is composed of several interspersed repeats of the octanucleotide UUAUUUAU, has been shown to destabilize mRNA in some eukaryotes. However, this effect is not seen when mRNAs are transferred to Xenopus oocytes, which made it possible to separate stability from translational regulation. For interferon, granulocyte-macrophage colony-stimulating factor, and c-fos RNAs, the UA-rich sequence was observed to preclude mRNA translation.

Identification of a translation inhibitory element (TIE) in the 3' untranslated region of the human interferon-beta mRNA

We have previously reported that the 3' untranslated region (UTR) of the human interferon-beta mRNA has an inhibitory effect on the mRNA translation both in vitro, in a rabbit reticulocyte lysate, and in vivo, in the Xenopus oocyte. In the present study, we identify the sequence in the 3' UTR which is responsible for this translation inhibition. We show that this sequence is located between the 100th and 161st nucleotides downstream from the translation stop codon. It contains several repeats of the A + U-rich consensus octanucleotide UUAUUUAU, which is also present in the 3' UTR of several mRNAs involved in the inflammatory response. We also demonstrate here that the inhibitory effect of the sequence on the mRNA translation does not depend on its position in relation to the termination codon. However, no inhibition of translation is observed when this sequence is inserted in the 5' UTR of the mRNA. The removal of the translation inhibitory sequence not only improves the mRNA translation in Xenopus oocytes but it also strongly decreases the IFN-beta mRNA stability in those cells. This suggests that, in this system at least, the mRNA degradation is linked to its translational efficiency.

Differential regulation of interferon synthesis in lymphoblastoid cells

We have examined the molecular mechanisms involved in the induction and regulation of expression of alpha and beta 1 human interferons (HuIFN) in Namalva cells. Cloned IFN-alpha and -beta 1 cDNAs, and antisera to purified IFN-alpha and -beta 1 were used as specific probes to determine the expression of HuIFN genes both on the RNA and protein levels. The rates of gene transcription were correlated with the relative levels of HuIFN mRNA present in induced cells and with the amounts of HuIFN peptides synthesized by these cells. The comparative rate of transcription of HuIFN-alpha and -beta 1 genes was measured in nuclei isolated from Namalva cells before and after induction. No transcription of HuIFN-alpha and -beta 1 genes was detected in nuclei isolated from the uninduced cells. The correspondence in the rate of HuIFN-alpha and -beta 1 genes transcription after virus infection with the relative levels of HuIFN mRNA in the induced cells indicates that the stimulation of HuIFN synthesis by viral infection results from the activation of the transcription of HuIFN genes. The relative levels of alpha and beta 1 induced transcripts were the same in spite of the differences in the number of copies of HuIFN-alpha and -beta 1 genes indicating that the beta 1 gene is transcribed more efficiently than the alpha genes. The steady-state levels of HuIFN-alpha and -beta 1 mRNAs in induced Namalva cells are comparable, however, the overall amount of HuIFN-beta 1 synthesized (as determined by radioimmunoassay and biological activity) is approximately 10-fold lower than that of IFN-alpha. No evidence has been found that would indicate that HuIFN-beta 1 mRNA induced in Namalva cells is different from that induced in human fibroblasts. The data indicate, however, that in Namalva cells, the IFN-beta 1 polypeptide has a higher turnover rate and slower rate of release into medium than the HuIFN-alpha polypeptides, indicating that the observed difference in the overall amounts of these two types of interferons present in the medium is due to regulation on posttranslational level.

Differential expression of human interferon genes

We developed a method for quantitating closely related mRNAs by S1 mapping and used it to determine the levels of mRNAs for IFN-beta, IFN-gamma and various alpha IFNs (IFN-alpha 1, -alpha 2, -alpha 4, -alpha 5, -alpha 6, -alpha 7, -alpha 8 and -alpha 14) in human peripheral blood leukocytes, lymphoblastoid (Namalwa), HeLa and human fibroblastic cells, induced in different fashions. The ratio of alpha to beta IFN transcripts varied greatly, depending on the cell type. The levels of the individual IFN-alpha RNAs were very different: IFN-alpha 1, -alpha 2 and -alpha 4 RNAs constituted the major fraction of the IFN-alpha transcripts measured. Moreover, there was a striking difference in the proportion of individual IFN-alpha mRNA species in different cell types. Use of different induction protocols did not significantly affect the proportion of IFN mRNAs. IFN production was not proportional to mRNA level in all cases, as lymphoblastoid cells induced by incubation at high density and virus-induced HeLa cells contained high levels of IFN-beta but produced little antiviral activity.

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.

Two levels of regulation of beta-interferon gene expression in human cells

We cloned alpha- and beta-interferon cDNA and used them as specific probes to determine the relative levels of interferon mRNA in human fibroblasts cells induced with poly(rI).poly(rC) or Newcastle disease virus to synthesize interferon. Both inducers activated only the beta-interferon gene; however, the half life of beta-interferon mRNA in cells induced with virus was substantially longer than in poly(rI).poly(rC)-induced cells. The transcription rate of beta-interferon RNA sequences was examined in nuclei isolated from poly(rI).poly(rC)-induced cells; it was found that the induction leads to transcriptional activation of the beta-interferon gene and that the shutoff period when no interferon synthesis or cytoplasmic betamRNA are detected. Thus, the synthesis of beta interferon in poly(rI).poly-(rC)-induced human fibroblasts is controlled both by activation of transcription of the beta-interferon gene and by alteration of the beta-interferon mRNA stability.

Expression of interferon-alpha and interferon-beta genes in human lymphoblastoid (Namalwa) cells

Treatment of human lymphoblastoid (Namalwa) cells with Sendai virus induced the coordinate synthesis of both IFN-alpha and IFN-beta interferon mRNAs. One sub-line of Namalwa cells (WRL) produced no IFN-beta activity, although IFN-beta mRNA was induced and was associated with polysomes. The IFN-alpha mRNA was heterogeneous, ranging in size over 1.20-1.35 X 10(3) bases, probably because of variation in the size of the transcribale DNA in the alpha-gene family. The IFN-beta mRNA was monodisperse with a size of 1.05 X 10(3) bases. The kinetics of accumulation and decay of both IFN-alpha and IFN-beta mRNAs, as assessed by hybridization with cDNA probes, were very similar to those of translatable interferon mRNA, as assessed by translation in Xenopus oocytes. Treatment of the cells with butyrate or 5'-bromodeoxyuridine increased the amount of hybridizable IFN-alpha and IFN-beta mRNA about 15-fold and 4-fold respectively, again demonstrating coordinate control of IFN-alpha and IFN-beta production.

Protein synthesis in human lymphoblastoid cells (Namalwa) after treatment with butyrate and 5'-bromodeoxyuridine

The pattern of protein synthesis has been compared in Namalwa cells following treatment with butyrate and 5'-bromodeoxyuridine (BrdUrd). Although these treatments cause a substantial increase in Sendai virus-induced interferon synthesis (up to 300-fold) we observed no comparable effect on the synthesis of other cellular proteins. Using two-dimensional gel electrophoresis we have investigated the proteins synthesised before and 8 h after Sendai virus infection of treated cells. Only 2 of the 300 most abundant cellular proteins were reproducibly affected, these always showed increased rates of synthesis in butyrate-treated cells. The most significant was a 3-4-fold enhancement in synthesis of a 35,000 molecular weight protein which we have called BEP35. On individual occasions treatment caused changes in the rates of synthesis of other proteins, these were not reproducible and involved less than 4% of the proteins investigated. None of the Sendai virus structural proteins or virus-induced cellular proteins were affected by the treatment. We conclude that butyrate and BrdUrd treatments have a relatively specific effect on the synthesis of interferon in Namalwa cells, as the majority of protein synthesis remains unaffected.