Interferon production by human lymphoblastoid cells is stimulated by inducers of Friend cell differentiation

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.

Monoclonal antibodies and enzyme immunoassays specific for human interferon (IFN) omega 1: evidence that IFN-omega 1 is a component of human leukocyte IFN

Four hybridoma cell lines secreting monoclonal IgG antibodies to human interferon (IFN) omega 1 (= IFN-alpha II 1) were developed, using spleen cells of mice immunized with IFN-omega 1 and/or a novel hybrid interferon, IFN-omega 1/alpha 2. All antibodies (OMG-2, -4, -5, and -7) neutralize the antiviral activity of IFN-omega 1 and show distinct patterns of reactivity with the hybrid proteins, IFN-omega 1/alpha 2 and IFN-alpha 2c/omega 1. However, none of the antibodies is able to neutralize human IFN-alpha, confirming earlier observations that IFN-omega 1 and IFN-alpha are antigenically unrelated. The epitope specificities of the antibodies were further characterized in direct and competitive enzyme immunoassays (ELISAs). All binary antibody combinations were tested for their suitability for a two-site ("sandwich") ELISA for IFN-omega 1, using horse radish peroxidase as the marker enzyme. A configuration employing OMG-2 for antigen capture and OMG-7 as the detector antibody resulted in the highest assay sensitivity (approximately 10 pg IFN-omega 1/ml) and was studied further. This one-step assay is highly specific for IFN-omega 1 and does not recognize human IFN-alpha, -beta, and -gamma, thus allowing for determination of IFN-omega 1 levels in natural mixtures of human IFNs. Using this ELISA, it was found that IFN-omega 1 is present in IFN preparations derived from virus-induced human peripheral blood leukocytes and may constitute as much as 15% of the total leukocyte IFN activity. IFN-omega 1 was also detected at somewhat lower levels in preparations of human "lymphoblastoid" IFN.

Increased nuclease sensitivity of the human interferon-alpha 1-related genes and the interferon-beta 1 gene during induction by virus

The chromatin structure of the human interferon (IFN) genes was evaluated during induction of human lymphoblastoid (Namalwa) cells by Sendai virus. Namalwa cells were treated with bromodeoxyuridine (BrdUrd) for 36-48 h and induced with Sendai virus for 7 h; the nuclear fraction was isolated and treated with low levels of either micrococcal nuclease or DNAse I. DNA was extracted from the nuclease-treated chromatin, restricted with Eco RI and analyzed by Southern blotting using IFN-alpha 1 and -beta 1 cDNA probes. An increase in the digestibility of the IFN-alpha 1-related genes and the IFN-beta 1 gene was observed in chromatin prepared from BrdUrd-treated, Sendai virus-induced Namalwa cells as compared with chromatin from uninduced Namalwa cells. Our results indicate that, during IFN induction in Namalwa cells by Sendai virus, the IFN genes assume a more open conformation consistent with increased transcriptional activity across these genes.

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.

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.

Preferential alkaline phosphatase isoenzyme induction by sodium butyrate

SW-620, a continuous cell line derived from a poorly differentiated human colon carcinoma, produces two alkaline phosphatases. Under basal conditions the heat-stable, term-placental is the major isoenzyme and the heat-labile, liver/bone/kidney form represents a minor component. Exposing SW-620 cells to sodium butyrate causes induction of increased levels of activity accompanied by a striking shift in isoenzyme distribution not observed heretofore. The activity increase is accounted for entirely by augmentation of the liver/bone/kidney isoenzyme, with the term-placental form not being affected. Two other known alkaline phosphatase inducers, prednisolone and hyperosmolality, do not influence specific activity and isoenzyme distribution. The preferential induction of the liver/bone/kidney form of alkaline phosphatase in SW-620 cells may reflect a butyrate-elicited expression of a more differentiated state.

Enhancement of polyethylene glycol-mediated cell hybridization by inducers of erythroleukemia cell differentiation

Dimethyl sulfoxide (DMSO) has many biological effects, which include enhancement of polyethylene glycol (PEG) -mediated cell fusion, induction of cell differentiation in erythroleukemia and other cell systems, and cryoprotection of cells from freezing damage. In this study, compounds which induce erythroleukemia cell differentiation were tested for their ability to enhance PEG-mediated cell fusion. It was found that many compounds which induce erythroleukemia cell differentiation also promote cell membrane fusion as well as protect cells against freezing damage. Hence, many inducers of erythroleukemia cell differentiation have direct and similar effects on cell membranes. This study also demonstrates previously unrecognized effects of cryoprotective agents and cell fusogens on the differentiated state of cultured cells.

Synergistic induction of alkaline phosphatase in colonic carcinoma cells by sodium butyrate and hyperosmolality

Exposing HT-29 cells to the combination of two inducers of intestinal alkaline phosphatase, sodium butyrate and hyperosmolality, causes a synergistic (over 1000-fold) increase in specific activity. Evidence is presented showing that enzyme induction is reversible; the half-life of the induced activity is approximately 30 h. Preinduction by butyrate or by hyperosmolality does not prime the cells so as to respond synergistically when subsequently exposed to hyperosmolality or butyrate, respectively. This study demonstrates that when applied in combination, the effect on gene expression by one alkaline phosphatase inducer is amplified by the other.

An indirect radioimmunoassay for interferon

An indirect radioimmunoassay for testing the antiviral activity of interferon (IFN) is described. Vero cells are seeded in microtitre plates, treated with appropriate dilutions of interferon and challenged with Sindbis virus. Viral yield is measured using specific antibody and radiolabelled protein A. The assay is able to detect IFN levels of 5 international units (I.U.)/ml, has a high degree of reproducibility, and could be easily adapted to various cell and virus combinations. This microsystem is technically simple, allows testing of small volumes of test material, and eliminates subjectivity in reading of end-points.

Spontaneous production of alpha- and beta-interferon in human lymphoblastoid and lymphoma cell lines

A large number of human haematopoietic cell lines was examined for spontaneous production of interferon. Unconcentrated culture supernatants from 70 out of 71 B-lymphoblastoid cell lines contained considerable amounts of interferon (median titer 22 units per ml); a few lines produced more than 100 units/ml with peak values up to 500 units/ml. In contrast, only one B-lymphoma line out of 18 genuine lymphoma, myeloma, and leukaemia cell lines tested spontaneously produced small amounts of interferon. Following treatment with 5-bromodeoxyuridine (BrdUrd), interferon was produced without further induction in most B-lymphoid cell lines, but not in any of the non-B, non-T, T-lymphoid or myeloid lines examined. Modulation of spontaneous interferon production by chemicals (sodium butyrate, dexamethasone, dimethylsulfoxide, a phorbol ester, and BrdUrd) was studied in more detail in three B-lymphoblastoid and four B-lymphoma cell lines. The patterns of responses observed were different for the action of different chemicals on a given cell line as well as between lymphoblastoid and lymphoma lines in general; furthermore, several lines of evidence suggest that chemicals can differentially influence spontaneous and virus-induced interferon production in an given cell line. The composition of spontaneously produced interferon was analysed using antisera specific for HuIFN-alpha and HuIFN-beta. Interferons produced by untreated as well as BrdUrd-treated lymphoblastoid cells contained more than 95 per cent IFN-alpha, whereas BrdUrd-treated lymphoma cells produced IFN-alpha as well as minor amounts (cell lines Namalwa and NC-37) or even over 90 per cent of IFN-beta (Daudi).

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.

Effects of sodium butyrate, a new pharmacological agent, on cells in culture

Sodium butyrate, at millimolar concentrations, when added to cell cultures produces many morphological and biochemical modifications in a reversible manner. Some of them occur in all cell lines. They concern regulatory mechanisms of gene expression and cell growth: an hyperacetylation of histone resulting from an inhibition of histone deacetylase and an arrest of cell proliferation are almost constantly observed. Some other modifications vary from one cell type to another: induction of proteins, including enzymes, hormones, hemoglobin, inhibition of cell differentiation, reversion of transformed characteristics of cells to normal morphological and biochemical pattern, increase in interferon antiviral efficiency and induction of integrated viruses. Most if not all these effects of butyrate could result from histone hyperacetylation, from changes in chromatin structures as measured by accessibility to DNases and from modifications in cytoskeleton assembly. We do not know at the present time whether butyrate acts on a very specific target site in cell or if it acts on several cell components.

Interferon production in human hematopoietic cell lines: response to chemicals and characterization of interferons

We have surveyed interferon production and its modulation by 5-bromodeoxyuridine, butyrate, dexamethasone, dimethylsulfoxide and tetradecanoylphorbolacetate in 20 human hematopoietic cell lines derived from leukemias, lymphomas, myelomas and normal leukocytes, representing various maturation stages of lymphoid and myeloid cells. Sendai virus-induced interferon production was enhanced by at least one of the chemicals in 13 out of 14 B-type lymphoid cell lines, whereas no enhancement was observed in any of the non-B, non-T-, T-lymphoid, or myeloid cell lines tested. Interferon produced by 11 cell lines was partially characterized using antisera specific for HuIFN-alpha and HuIFN-beta. Six cell lines produced both IFN-alpha and IFN-beta, two lines produced by IFN-alpha and three lines (including both T-cell lines tested) produced only IFN-beta. In all cases examined, enhancement by chemicals of total interferon yields was due to selective stimulation of production of IFN-alpha. Poly (I):(C) induction of interferon was studied in a number of B-cell lines. In general, a similar pattern of IFN-alpha and -beta synthesis was observed as in virus-induced cells, but the proportion of IFN-beta was relatively smaller. Treatment with butyrate enhanced interferon production to a similar extent accompanied by a similar shift in composition as in virus-induced cells. Our results demonstrate that even in closely related cell types, production of IFN-alpha and IFN-beta can be regulated differently in response to the same inducer. In a single cell type in response to a single inducer, expression of IFN-alpha and IFN-beta can be differentially affected by chemicals.

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

The human Namalva lymphoma cell line being an established producer, predominantly of alpha interferon, has been reported to enhance interferon synthesis after a preincubation in butyrate containing media. We have performed the corresponding experiments with FS-4 fibroblast cells and show that the synthesis of human beta interferon is adversely affected by this treatment. Both cell types are hyperacetylated by the fatty acid to a comparable extent. However, after the withdrawal of butyrate, the persistence of highly acetylated forms of histone H4 is insufficient in the case of FS-4 to endure the interferon induction period. Concerning fibroblasts, deacetylation proceeds to a hypoacetylated state which is reversed only slowly. With lymphoid cells on the other hand, acetylated H4 specimens are much more stable and persist for more than eight hours in the absence of butyrate. Moreover, the acetylation reactions are supported by other Friend cell stimulators which by themselves are no inhibitors of deacetylase activities.

Selective inhibition by sodium butyrate of glucocorticoid-induced tyrosine aminotransferase synthesis in hepatoma tissue-cultured cells

Sodium butyrate in a 5 mM concentration prevents the induction of tyrosine aminotransferase in hepatoma culture cells, without affecting the basal level of the enzyme. This effect is reversible immediately after the removal of butyrate, or after a lag, if butyrate was present for more than 2 h. Neither the amount of cellular RNA nor the rate of total RNA synthesis were affected by sodium butyrate. Furthermore, butyrate does not inhibit protein synthesis: [35S]methionine incorporation into proteins, measured in a reticulocyte lysate system, shows no significant difference between the translation capacity of the RNAs from butyrate-treated cells and from dexamethasone-induced or uninduced cells. Nevertheless, when tyrosine aminotransferase was isolated from the translation products by its specific antiserum and analyzed by gel electrophoresis, we observed that the amount of the enzyme synthetized in the presence of RNAs from dexamethasone/butyrate-treated cells was strongly diminished relative to that synthesized in the presence of RNA from dexamethasone-induced cells. These experiments indicate that the treatment of the cells with butyrate decreases the activity of the specific messenger RNA for tyrosine aminotransferase to a level close to the basal level.

The extent of histone acetylation induced by butyrate and the turnover of acetyl groups depend on the nature of the cell line

Cells possessing widely different physiological and morphological features have been treated with substances known to stimulate the differentiation of erythroleukemia cells. Only short fatty acids are capable of causing a hyperacetylation of the core histones and of enhancing the level of an H1-like protein in Chinese hamster ovary cells. While the time courses of a butyrate-mediated acetylation are similar for all cells, the maximum histone acetyl contents are much higher for the transformed cell of a given type. A withdrawal of butyrate rapidly (within 45 min) gives rise to a 'hypoacetylated state' for fibroblasts and transformed fibroblast (epithelial) cells from which there is a slow recovery. Lymphoid cells, on the other hand, display a marked persistance of the highly acetylated forms of histone H4.

Effects of sodium butyrate on a human lymphoblastoid cell line (Namalwa) and its interferon production

Treatment of lymphoblastoid cells with sodium butyrate before infection with Sendai virus increases the subsequent yield of interferon and of its messenger RNA. This treatment caused almost complete inhibition of cellular DNA synthesis and consequently cell division, and some inhibition of cellular RNA and protein synthesis. It also caused increased acetylation of histones and alterations in the plasma membrane. There was no decrease in cell viability or change in cell morphology but the cells were smaller than untreated cells and were all in the G1 phase. Sodium butyrate treatment had no effect on the course of Sendai virus infections. The observed increase in interferon yields after butyrate treatment did not correlate with its effects on DNA synthesis, size, cell division and histone acetylation, but did with its effects on RNA and protein synthesis.