Amino acid analysis and cell cycle dependent phosphorylation of an H1-like, butyrate-enhanced protein (BEP; H1(0); IP25) from Chinese hamster cells

Comparative transcriptional analysis of mouse hybridoma and recombinant Chinese hamster ovary cells undergoing butyrate treatment

DNA microarray based transcriptome analysis has become widely used in biomedical research; however, the lack of DNA sequence information available for Chinese hamster ovary (CHO) cells has hampered the application of microarrays for this cell line widely used for recombinant therapeutic protein production. We have constructed an expressed sequence tag (EST) based CHO DNA microarray and employed it for comparative transcriptome analysis of CHO cells and mouse hybridoma cells treated with sodium butyrate. Cross-species hybridization of CHO transcripts to mouse DNA microarrays was also performed to assess the utility of cross-species microarray. The average identity among probe sequences present on both the CHO and mouse microarray was 89.6%. Although cross-species hybridization yielded non-contradicting results when compared with the same-species arrays, decreased sensitivity was observed and resulted in fewer differentially expressed genes being confidently identified. The comparatively small number of genes probed using the CHO microarray and the low number of genes identified as differentially expressed in the cross-species hybridization limited physiological interpretation of the response of CHO cells to sodium butyrate treatment. Nevertheless, when all results are combined, mouse hybridoma and CHO cells can be seen to respond similarly to butyrate treatment, affecting histone modification, chaperones, lipid metabolism, and protein processing. To further develop the utility of microarray technology in cell culture process development, an expansion of current CHO cell sequencing efforts to increase the coverage of genes on available microarrays is warranted.

Regulation of glyceraldehyde-3-phosphate dehydrogenase in differentiating HD3 cells

Red blood cells usually replenish their ATP pools by glycolysis, fueled by glucose imported via the cell membrane. Mature red cells of some species (e.g. pig, chicken) have, however, been reported to show very low glucose transport. The subject of this study was the possible dependency of the level of a key glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAD) on glucose transporter activity during the maturation of chicken red cells. The chicken pronormoblast cell line, HD3, was used as a model system. These cells contain higher levels of GAD and glucose transporter activities than normal chicken bone marrow cells, but reduce their levels during maturation. In an attempt to assess whether the decrease in GAD activity is regulated by the glucose transport, the chicken GLUT3 expressed under the control of viral promoter was introduced into HD3 cells by retroviral infection (pDOL-cGT3). Upon cell differentiation and maturation, both cells with and without the exogenous transporter decreased GAD activity. Butyric acid did not affect the regulation of GAD activity upon differentiation. These results show that the development of chicken red cells is manifested by reduction of their GAD activity and that this is not affected by their sugar transporter activity. The very low GAD activity in embryonic chicken red cells is thus due to a loss of this activity at an early stage in their development. Because of the very low glucose transport and GAD activities in mature chicken red cells, rates of glycolysis are likely to be low and suggesting an alternative pathway for ATP production in these cells.

The microheterogeneity of the mammalian H1(0) histone. Evidence for an age-dependent deamidation

Histone H1(0) is known to consist of two subfractions named H1(0)a and H1(0)b. The present work was performed with the aim of elucidating the nature of these two subfractions. By using reversed-phase high performance liquid chromatography in combination with hydrophilic interaction liquid chromatography, we fractionated human histone H1(0) into even four subfractions. Hydrophilic interaction liquid chromatographic analysis of the peptide fragments obtained after cleavage with cyanogen bromide and digestion with chymotrypsin suggested that the four H1(0) subfractions differ only in their small N-terminal end of the H1(0) molecule (30 residues). Edman degradation of the N-terminal H1(0) peptide fragments and mass spectra analysis have indicated that human histone H1(0) consists of intact histones H1(0) (named H1(0) Asn-3) and deamidated H1(0) forms (H1(0) Asp-3) having an aspartic acid residue at position 3 instead of asparagine. Moreover, both H1(0) Asn-3 and H1(0) Asp-3 are blocked (H1(0)a Asn-3, H1(0)a Asp-3) and unblocked (H1(0)b Asn-3, H1(0)b Asp-3) on their N terminus. Acid-urea gel electrophoretic analysis has shown that the histone subfraction, in the literature originally named H1(0)a, actually consists of a mixture of H1(0)a Asn-3 and H1(0)a Asp-3, whereas H1(0)b consists of H1(0)b Asn-3 and H1(0)b Asp-3. Furthermore, we found that hydrophilic interaction liquid chromatography separates rat and mouse histone H1(0) just like human H1(0) into four subfractions. Hydrophilic interaction liquid chromatographic analysis of brain and liver histone H1(0) from rats of different ages revealed an age-dependent increase of both the N-terminally acetylated and the deamidated forms of H1(0). In addition, we found that the relative proportions of the four forms of H1(0) histones differ from tissue to tissue.

Sodium butyrate inhibits carcinoma development in a 1,2-dimethylhydrazine-induced rat colon cancer

BACKGROUND

Butyric acid is one of the most important by-products of dietary fiber degradation. It is an important trophic agent for the intestinal mucosa under different experimental conditions. Data obtained from several in vitro studies strongly suggest that butyrate can be a potential therapeutic agent in controlling the growth of some cancer cells. However to date in vivo animal studies have failed to show conclusive results.

METHODS

We evaluated the effects of intracecal administration of butyrate in an experimental model of colonic carcinogenesis induced by 1,2-dimethylhydrazine (DMH), administered at the site where it is naturally produced, the cecum. We studied the incidence of colon tumors and their main histologic features.

RESULTS

Direct application of sodium butyrate significantly decreased the total number of tumors and the incidence of malignancies and carcinoma in the colon.

CONCLUSIONS

Butyrate may inhibit the growth of tumors induced by DMH.

Developmental regulation and butyrate-inducible transcription of the Xenopus histone H1(0) promoter

We have isolated genomic clones of the Xenopus laevis histone H1(0) promoter and identified regulatory elements mediating the transcriptional regulation of the H1(0) gene. Expression of H1(0) is associated with the terminal differentiation of many cell types. During X. laevis development, H1(0) mRNA is present in the oocyte and egg, but remains at low levels during embryogenesis until hatching. After this time, mRNA levels accumulate dramatically correlating with the differentiation of many tissue types, e.g., liver and skin. Accumulation of H1(0) mRNA can be induced at earlier development stages by treating embryos with butyrate. The enhanced transcription of H1(0) in adult somatic cells, as well as the butyrate inducibility of the gene, have been investigated using transfection of adult X. laevis A6 somatic cells. We have defined specific protein-nucleic acid interactions with three cis-acting elements. Two previously defined gene regulatory elements: the H1 box, normally involved in the regulation of the H1 gene, and the H4TF2 site, normally involved in the regulation of the H4 gene, appear to have novel roles in determining differentiation-specific H1(0) expression. These two elements act together with a new distal cis-acting element in order to sustain high levels of basal transcription and to potentiate transcription following butyrate treatment.

Changes in the synthesis of histone H1(0) and H1 in rat FRTL-5 thyroid cells exposed to thyrotropin

In absence of thyrotropin (TSH), FRTL-5 rat thyroid cells stop proliferating and lose the functional characteristics of thyroid tissue. FRTL-5 cells regain their differentiated state and their proliferation activity upon addition of TSH. In this study we investigated the synthesis of histone H1 variants and H19(0) in FRTL-5 cells exposed to 10(-8) M TSH, two days after TSH withdrawal. TSH induced the synthesis of some H1 variants and H1. This effect was already evident six hours after TSH addition, thus well before proliferation, DNA or thyroglobulin synthesis was induced. These data indicate that the induction of H1(0) and some H1 variants is an early event after TSH stimulation and may thus be related to the functional differentiation of FRTL-5 cells.

Proliferation and differentiation are not directly related to H1(0) accumulation in cultured glial cells

A basic nuclear chromatin protein with electrophoretic mobility of H1(0) histone is present in C6 rat glial cells and in primary cultures of rat brain astroglial cells. That this protein is identical to H1(0) is further demonstrated by the finding that it accumulates in C6 cells in a time- and dose-dependent manner in response to butyrate, an agent which is known to induce this protein in other cell types. Other short-chain fatty acids were found to influence H1(0) levels similarly although to a lesser extent than butyrate. There was a very close correlation between the induction of H1(0) and the inhibition of growth induced by different concentrations of short-chain fatty acids which supports the idea that the concentration of this protein is higher in non-proliferating cells. However, when cell growth was inhibited by dexamethasone or agents that increase intracellular cyclic adenosine monophosphate levels, H1(0) levels were not affected, even though these compounds also blocked DNA synthesis and induced morphologic changes in C6 cells. These observations suggest that, at least in glial cells, the accumulation of H1(0) is specifically caused by short-chain fatty acids and that suppression of cell division or commitment to differentiation are not sufficient 'per se' for the induction of this protein.

Butyrate-induced changes in nuclease sensitivity of chromatin cannot be correlated with transcriptional activation

We examined in the H4IIE rat hepatoma cell line the relationship between butyrate-induced changes in the nuclease sensitivity of chromatin and changes in transcriptional activity of specific genes. The butyrate-inducible metallothionein I (MT-I) gene underwent a dramatic increase in DNase I sensitivity after 3 h of butyrate treatment. However, genes not transcribed in H4IIE cells underwent the same changes in DNase I sensitivity. Thus, butyrate-induced increases in DNase I sensitivity are not sufficient for the transcriptional activation of a gene. Butyrate treatment has also been reported to alter the sensitivity of sequences to micrococcal nuclease (MNase) in a manner reflecting their tissue-specific expression. Butyrate exposure caused increased digestion of the MT-I gene by MNase. However, butyrate-induced MNase sensitivity also occurred for genes which are neither transcribed in untreated cells nor butyrate inducible. Moreover, cadmium, a potent transcriptional activator of the MT-I gene, does not alter the sensitivity of the MT-I gene to MNase. Thus, the butyrate-induced alterations in MNase sensitivity are neither sufficient for, necessary for, nor indicative of transcriptional activation.

Butyrate effect on nuclear proteins of two Chinese hamster cell lines

The effect of sodium butyrate on the nuclear proteins of two Chinese hamster cell lines (V79 and CHO) was studied. Butyrate treatment induces hyperacetylation of core histones in both cell lines, while H1 histone shows a different behavior. In CHO cells H1 is dephosphorylated following butyrate incubation; V79 do not show any change of H1 subtypes. It seems that H1 response to butyrate treatment is cell type dependent. Using silver staining a group of proteins that could be present in vivo in the nucleo-protein complex was also detected.

Butyrate-induced changes in nuclease sensitivity of chromatin cannot be correlated with transcriptional activation

We examined in the H4IIE rat hepatoma cell line the relationship between butyrate-induced changes in the nuclease sensitivity of chromatin and changes in transcriptional activity of specific genes. The butyrate-inducible metallothionein I (MT-I) gene underwent a dramatic increase in DNase I sensitivity after 3 h of butyrate treatment. However, genes not transcribed in H4IIE cells underwent the same changes in DNase I sensitivity. Thus, butyrate-induced increases in DNase I sensitivity are not sufficient for the transcriptional activation of a gene. Butyrate treatment has also been reported to alter the sensitivity of sequences to micrococcal nuclease (MNase) in a manner reflecting their tissue-specific expression. Butyrate exposure caused increased digestion of the MT-I gene by MNase. However, butyrate-induced MNase sensitivity also occurred for genes which are neither transcribed in untreated cells nor butyrate inducible. Moreover, cadmium, a potent transcriptional activator of the MT-I gene, does not alter the sensitivity of the MT-I gene to MNase. Thus, the butyrate-induced alterations in MNase sensitivity are neither sufficient for, necessary for, nor indicative of transcriptional activation.

Biphasic effects of dibutyryl cyclic adenosine 3',5'-monophosphate on synergistic stimulation of DNA synthesis by diacylglycerol, and the ionophore A23187 in guinea pig lymphocytes

When guinea pig lymphocytes were cultured with 1-oleoyl-2-acetylglycerol (OAG) and the ionophore A23187 for 8 h, [3H]-thymidine incorporation into the acid-insoluble fraction of the cells was stimulated synergistically. Further addition of dibutyryl cAMP caused a biphasic effect on the synergistic stimulation. Dibutyryl cAMP augmented the synergistic stimulation when A23187 was at the concentration of 0.075 micrograms/ml, but inhibited it when the ionophore was at 0.25 micrograms/ml. At the higher concentration of A23187, dibutyryl cAMP stimulated the [3H]thymidine incorporation when culture was for 4 h, but inhibited it when culture was for 8 h. The results were the same when 12-0-tetradecanoylphorbol-13-acetate (TPA) was used instead of OAG. Butyrate could replace dibutyryl cAMP for stimulation of [3H]thymidine incorporation in combination with TPA and A23187, but not with OAG and A23187 at the lower ionophore concentration. Dibutyryl cAMP but not butyrate stimulated ornithine decarboxylase induction caused by TPA and A23187. These results suggest that the effect of dibutyryl cAMP on DNA synthesis induced by OAG and A23187 was biphasic and depended on the concentration of A23187 and on the time of culture, and that the stimulation mechanism of butyrate is different from that of dibutyryl cAMP.

Comparisons of histones in retinal and brain nuclei from newborn and adult mice

Histone proteins from purified nuclei of neonatal and adult mouse retinas were analyzed and compared utilizing SDS-polyacrylamide gel electrophoresis. Identical procedures were applied to examine the histones extracted from the brains of the same animals. In the newborn and mature retina and brain, 8 histone fractions have been separated, identified and quantified by scanning densitometry. These are the linker histone (H1), consisting of 3 subfractions (H1a, H1b, H1(0); the semi-histone uH2A (A24); and the 4 nucleosome core histones (H2A, H2B, H3, H4). Developmental differences are exhibited by the linker histone in both brain and retinal cells. The greatest differences between the histone patterns of retina and brain are also in the H1 group. Because the linker histone is subject to the greatest variability. H1 was selectively extracted with 5% perchloric acid from both neonatal and adult brain. This procedure established that the observed differences are a developmental phenomenon and are not due to interactions of the linker histones with other nuclear proteins. The ratio of the non-histone chromosomal proteins to total histone was found to be significantly greater in both adult and neonatal brain compared to retina at either age.

H1(0) histones of normal and cancer human cells. Amino acid composition of H1 purified by polyacrylamide gel electrophoresis

H1 histones were purified by preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis from human lung carcinoma (line DMS79), human hepatoblastoma (HepG2), human adult lung and human adult and fetal liver. The purified human H1 histones were analyzed for their amino acid composition and terminal residues. The comparative analysis of the amino acid compositions of the different human H1 histones showed that: all the H1 preparations have the characteristically high lysine content associated with a low arginine content, which distinguishes outer histones from core histones; H1 is distinguishable from other H1 histones by the presence of methionine and histidine; H1 histones from human adult, fetal and cancer cells are very similar in amino acid composition, and in cancer cells the level of the H1 histone is not inversely related with cell growth rate nor with the expression of the alpha-fetoprotein gene.

Butyrate converts rat 3T3 fibroblasts into giant cells

Butyrate inhibits proliferation of rat 3T3 cells by blocking the cell cycle in late G1. In these cells, DNA synthesis is completely arrested 24 h after butyrate addition, whereas RNA and protein synthesis proceed unaffected. This partial inhibition of proliferation progressively converts normal cells into giant ones. Transcription and protein synthesis are both more intense in the giant cells than in normal cells. Cell enlargement is inhibited by cell-to-cell contact and the conversion of a normal into a giant cell is reversible. Giant cells may be of use when designing new approaches to the study of cell structure and motility as well as differentiation and proliferation.

Modulation in proportions of H1 histone subfractions by differential changes in synthesis and turnover during butyrate treatment of neuroblastoma cells

Mouse neuroblastoma cells treated with millimolar concentrations of butyrate adjusted their recipe of histone H1 subfractions over the course of several days, eventually attaining an enrichment of about 5-fold in H1(0). This adjustment in the proportions of the H1's, which was essentially complete by 4 days, was brought about by changes in synthesis and turnover that were different for each of the three H1 subfractions. As the cells stopped dividing, the synthesis of all histones slowed substantially, but core histones were affected more than the H1's. Transiently, therefore, there was an overproduction of H1's relative to core histones, but the excess H1 was eventually removed by turnover. The very slow turnover of H1(0) and the rapid turnover of H1c were not substantially affected by butyrate treatment, but the turnover of H1ab was greatly accelerated by butyrate. Acetylation of the core histones was not necessary for maintenance of elevated H1(0) levels in the nondividing cells, although we did not rule out its involvement in the initial accumulation of H1(0).

Histone expressions in mouse-rat somatic reconstituted cells

A critical analysis of histone expression was performed on the four interspecific and the two intraspecific reconstituted cells formed between karyoplast from mouse B16 cells and the cytoplast from rat cells (L6TG.CAPr) or mouse cells (B82.CAPr). All the reconstituted cells had the same pattern of mouse histones and the same amount of mouse-specific H2B. 2 histone as that of mouse nuclear donor cells. A hybrid between B16 and L6TG.CAPr contained both mouse and rat-specific H1b subtypes, whereas no rat-specific H1b was detected in the interspecific reconstituted cells. In both intra- and interspecific reconstituted cells, the proportion of H1b content was lower than that of B16 cells but that of H1 degree was higher, indicating that the mouse H1 patterns from these cells slightly resembled the pattern of slower growing and differentiated cytoplast donor cells. As an effect of the tumor promoter, the H1 pattern tended to revert to that of the nuclear donor cells in agreement with the phenotypic reversion, without any significant change in cell growth.

G1- and S-phase syntheses of histones H1 and H1o in mitotically selected CHO cells: utilization of high-performance liquid chromatography

We have employed high-performance liquid chromatography (HPLC) to investigate the syntheses of histones H1 and H1o as synchronized cells traverse from mitosis to S phase. Chinese hamster (line CHO) cells were synchronized by mitotic selection, and, at appropriate times, they were pulse labeled for 1 h with [3H]lysine. Histones H1 and H1o were extracted by blending radiolabeled and carrier cells directly in 0.83 M HC1O4; the total HC1O4-soluble, Cl3CCO2H-precipitable proteins were then separated by a modification of an HPLC system employing three mu Bondapak reversed-phase columns [Gurley, L. R., D'Anna, J. A., Blumenfeld, M., Valdez, J. G., Sebring, R. J., Donahue, D. K., Prentice, D. A., & Spall, W. D. (1984) J. Chromatogr. 297, 147-165]. These procedures (1) produce minimally perturbed populations of synchronized proliferating cells and (2) maximize the recovery of radiolabeled histones during isolation and analysis. Measurements of rates of synthesis indicate that the rate of H1 synthesis increases (3.6 +/- 0.5)-fold as cells traverse from early to mid G1; as cells enter S phase, the rate of H1 synthesis increases an additional congruent to 22-fold and is proportional to the number of S-phase cells. In contrast to H1, the rate of H1o synthesis is nearly constant throughout G1. As cells progress into S phase, the rate of H1o synthesis increases (3.1 +/- 0.2)-fold so that it also appears to be proportional to the number of S-phase cells. Except for the first 1-2 h after mitotic selection, these results are similar to those obtained when cells are synchronized in G1 with the isoleucine deprivation procedure.

Histone H1o in developing rat brain cells

Histone H1o was found both in neuronal and oligodendrocyte rat-brain nuclei fractionated by sucrose-gradient isopycnic centrifugation. This histone was absent during the early stages of development when the brain cells were still proliferating, but it appeared in significant amounts in the terminally differentiated cells.

The nonhistone proteins of developing mammalian erythroid cells

Anaemic rabbit bone marrow cells, labelled with [35S]methionine, were separated at unit gravity. Chromatin was isolated from these cells and proteins were separated from DNA, using urea/salt extraction. Two-dimensional gel electrophoresis of the nonhistone proteins showed that these proteins appeared to change quantitatively but not qualitatively, with one important exception, as cell development proceeded. The one protein that did change had a molecular weight of approximately 20,000 and was very basic. This protein was synthesised at low levels in the early cells, but its synthesis was seen to increase at the polychromatic stage of cell development, just prior to nuclear condensation. Treatment of bone marrow cells with sodium butyrate was shown to increase the synthesis of this protein in the early cells.

Presence of histone H1o-related fraction in chicken liver

The lysine-rich histones of chicken liver were studied in order to see whether a protein similar to mammalian histone H1o was present in this lower vertebrate. The following biochemical methods were used: sodium dodecylsulphate and acid-urea electrophoresis, gel exclusion chromatography on BioGel P100, and ion-exchange chromatography on BioRex 70. Specific polyclonal antibodies were elicited against purified mouse liver H1o and chicken erythrocyte H5, and applied for the further characterization of the chicken H1 subfractions obtained chromatographically. The results from microcomplement fixation and enzyme-linked immunosorbent assays showed that the presumptive chicken liver H1o shared common antigenic determinants with the mammalian H1o and the chicken liver H5. Based on the combined biochemical and immunological evidence, we conclude that an H1o-like protein is present in quiescent differentiated avian cells. The data of Smith et al. [34], who did not find this specific lysine-rich histone in resting chicken cells, are discussed.

Rb+ influxes differentiate between growth arrest of cells by different agents

The effect of cell cycle on Rb+ (K+) fluxes was studied in NIH 3T3 mouse fibroblasts. Serum starvation or isoleucine deprivation resulted in cell arrest at an early G1/G0 phase, accompanied by a marked decrease in both ouabain-sensitive and ouabain-resistant Rb+ influx. On the other hand, cells arrested at late G1/G0 phase by hydroxyurea treatment have high ouabain-sensitive and ouabain-resistant Rb+ influx. Butyric acid treatment resulted in cell arrest at an early G1/G0 phase, but in contrast to serum or isoleucine starvation did not decrease Rb+ influxes. It is thus shown that quiescent cells may have Rb+ influx rates as high as that of logarithmically growing cells. The results are consistent with the hypothesis that an increased ion permeability of the cell is initiated at a critical stage in G1/G0 phase, and that butyric acid may arrest the cell beyond that stage.

A qualitative and quantitative study of subfractions of the histone H10 in various mammalian tissues

The histone H10 was examined from seven mammalian species. All tissues were shown to contain two subfractions of H10, except for those of rabbit, in which little or no H10 was found. The subfraction composition was compared quantitatively in different mouse and hamster tissues, with the conclusion that this composition is tissue-specific. It is proposed that the wide occurrence of H10, together with the evidence of no more or less than two subfractions wherever it occurs, and the tissue-specific nature of the ratio of subfractions, signify that these two subfractions have specific individual functions.

Composition and synthesis during G1 and S phase of a high mobility group-E/G component from Chinese hamster ovary cells

A perchloric acid soluble protein from the sedimented chromatin of blended Chinese hamster ovary (line CHO) cells has been isolated by guanidine hydrochloride gradient chromatography on Bio . Rex-70 ion exchange resin. The amino acid composition of the protein (designated as CHO HMG-E/G) is similar to that of mouse HMG-E, but it differs from that of bovine HMG-14 and HMG-17 or any possible mixture of the two. CHO HMG-E/G incorporates [32P]phosphate like HMG-14 and HMG-17 class proteins from other species, but all resolvable molecular species incorporate phosphate, and the more highly-phosphorylated band migrates faster, rather than slower, than the other in acid-urea gel systems. Incorporation of [3H]lysine into HMG-E/G following release from isoleucine deprivation G1 block indicates that the protein is extensively synthesized during both the G1 and S phases of the cell cycle.

Thermal denaturation studies of acetylated nucleosomes and oligonucleosomes

The thermal melting behaviors of control and acetylated mononucleosomes, dinucleosomes and trinucleosomes have been studied. Along each series of oligonucleosomes, the melting profiles change in a manner consistent with the increasing number of nucleosomes. For the control mononucleosome, the melting profile exhibits a premelting region at about 61-64 degrees C and a major cooperative transition at 75-77 degrees C. The melting profiles of the control dinucleosomes and trinucleosomes show a premelt at 61-62 degrees C (similar to that of the nucleosome core); an intermediate transition at 73-74 degrees C for the dinucleosome and at 76-77 degrees C for the trinucleosome and a major cooperative transition at 79-80 degrees C for the dinucleosome and at 81-82 degrees C for the trinucleosome. The major cooperative transition at the highest melting temperatures in the melting profiles of the mononucleosome, dinucleosome and trinucleosome comes from the melting of the central region of DNA in the nucleosome which complexed with the core histones; the premelt region is attributed to two DNA segments per nucleosome which flank this central DNA region and are free or weakly complexed with histones. The origin of the intermediate transition found for the dinucleosomes and trinucleosomes is not fully understood but probably results from the melting of DNA at the entry to and exit from the nucleosome and the linker DNA which are complexed with histones. A very similar pattern of behavior is observed for the acetylated oligonucleosomes. Direct comparison of the melting profiles of acetylated and control mononucleosomes, dinucleosomes and trinucleosomes show that the premelt region is unaffected by histone acetylation whereas the intermediate and major cooperative transitions for the acetylated oligonucleosomes are broader and occur consistently at lower temperatures than for the controls. These differences support proposals that the N-terminal regions of core histones interact within the nucleosome and on linker DNA.

Effect of histone acetylation on the formation and removal of B(a)P chromatin adducts

The modification of core histone proteins in mouse 10T1/2 cells and human lung epitheloid (A549) cells by B(a)PDE in vivo and in vitro was found to be similar. Only histones H2A and H3 were extensively modified. Also other proteins, possibly A24 protein and the minor histone H1 species seem to be binding relatively high levels of this ultimate carcinogen. Butyrate treatment which causes hyperacetylation of the core histones, did not change the specificity of B(a)PDE binding to core histones, nor did it affect the initial level of DNA modification. The acetylated species of histone H3 were all accessible to B(a)PDE, suggesting that these epsilon-amino-groups of the lysine residues are not the targets of the B(a)PDE. The rate of removal of B(a)P-DNA adducts was not affected by butyrate treatment in either normal human or XP fibroblasts. Furthermore the B(a)P-core histones were not preferentially removed from normal human fibroblast chromatin during a 24 h post-treatment incubation.

An alteration in the phosphorylation of vimentin-type intermediate filaments is associated with mitosis in cultured mammalian cells

Analysis of cultured Chinese hamster ovary (CHO) cells has shown that vimentin exists primarily as two 57,000 dalton isoelectric variants, a nonphosphorylated form and a slightly more acidic phosphorylated form. Similar analyses of CHO cells that were treated with colcemid show the presence of at least two to three additional, more acidic, phosphorylated vimentin isoelectric variants. An increasing 32P-specific activity of these variants suggests that this alteration involves increased phosphorylation. Analysis of 32P-labeled vimentin from colcemid-treated cells indicates that the amount of the additional phosphorylated variants correlates with the accumulation of cells in mitosis. CHO cells enriched in mitotic cells without antimitotic drugs demonstrate the same alteration in the isoelectric focusing pattern of phosphorylated vimentin. When mitotic cells are replated, the amount of additional phosphorylated variants is reduced within 30 min. The data suggest that an alteration in phosphorylated vimentin is temporally related to the alteration in the organization of intermediate filaments in mitotic cells.

Developmental and hormonal regulation of protein H1 degrees in rodents

The tissue and cellular distribution and regulation of the chromatin protein H1 degrees has been examined in developing and adult mouse and in rat. The protein appears in specific cell types of solid tissues only when the cells have terminated their maturation. This was found for brain, retina, striated and cardiac muscle, and liver. In tissues that depend on hormones for their function and maintenance, the expression of H1 degrees is dependent on the continued presence of the specific maintenance hormone. In regenerating rat liver the amount of H1 degrees decreases to one-third after the onset of DNA synthesis. The possible role of H1 degrees is discussed in light of these results.

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.

Conformation studies of histone H1(0) in comparison with histones H1 and H5

The class of lysine-rich histones, H1, found in most eukaryotic cells is largely replaced by another class of lysine-rich histones, H5, in avian and other erythrocytes. Erythrocytes are transcriptionally inert and this state has been attributed to the presence of H5. Although there are many sequence differences between H1 and H5 both molecules have very similar structures with three well-defined domains: a flexible basic N-terminal region, an apolar globular central region and a flexible basic C-terminal region. The lengths of the N-terminal regions are different for H1 and H5 whereas the lengths of the central and C-terminal regions are very similar. Considerable interest attaches to the findings that another type of mammalian lysine-rich histone H1(0) has an apolar region exhibiting considerable sequence homology (70%) with the central globular region of H5. The abundance of H1 in cells has been found to correlate inversely with their mitotic activities. Conformational studies using high-resolution nuclear magnetic resonance and optical spectroscopy have been made of H1 and its conformational behaviour has been compared with those of H1 and H5. H1 has been found to contain a central globular region of similar size to those found in H1 and H5. However, the conformation and stability of the globular domain of H1 are very similar to the globular region of H5 rather than H1. H1 appears to be a hybrid containing a major feature of the H5 histone. The globular regions of H1 and H5 are known to bind to a specific site on the nucleosome sealing off two turns of DNA. It is proposed that H1 binds to the same site.

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.