Anti-histone H1 Research Articles

The High Mobility Group I/Y Protein Is Hypophosphorylated in Endoreduplicating Maize Endosperm Cells and Is Involved in Alleviating Histone H1-mediated Transcriptional Repression

The High Mobility Group I/Y Protein Is Hypophosphorylated in Endoreduplicating Maize Endosperm Cells and Is Involved in Alleviating Histone H1-mediated Transcriptional Repression

Identification of Histone H1 as a Cognate Antigen of the Ulcerative Colitis-associated Marker Antibody pANCA

Perinuclear anti-neutrophil cytoplasmic antibody (pANCA)4is a predominant serum marker of ulcerative colitis (UC), and a familial trait associated with disease susceptibility and disease associated MHC haplotypes. This study characterizes the pANCA antigen defined by representative UC-pANCA human monoclonal antibodies, Fab 5–3 and 5–2. Western blot analysis probed with Fab 5–3 revealed specific binding to a nuclear protein doublet (apparent MW=32–33kDa) expressed in several cell types. Purification and tryptic peptide sequencing identified the protein as histone H1, and this specificity was confirmed by Fab 5–3 binding to purified H1. Rabbit anti-histone H1 immunostaining and Western blot analysis confirmed that the pANCA epitope is preferentially immunoaccessible in polymorphonuclear neutrophils (PMN). The epitope was localized to the COOH-terminal region by site-specific proteolysis, and recombinant deletants further localized binding activity for both Fab 5–2 and 5–3 to two non-overlapping segments (AA 69–171 and 172–226) associated with a recurring PKKAK motif. Serum IgG binding was detectable to these segments, but was not significantly correlated with pANCA titer or disease status. These findings indicate that histone H1 bears a recurring COOH-terminal epitope recognized by monoclonal ulcerative colitis-associated pANCA marker antibodies, but this epitope is not a predominant specificity of serum pANCA.

Identification and characterization of a calreticulin-binding nuclear protein as histone (H1), an autoantigen in systemic lupus erythematosus.

Our objective was to identify nuclear calreticulin-binding protein(s) and investigate whether there is a correlation between presence of autoantibodies against calreticulin and calreticulin-binding protein(s) in the sera of patients suffering from systemic lupus erythematosus (SLE). The ligand overlay procedure using digoxigenin-labelled calreticulin was used to identify a calreticulin-binding protein in the nuclear fraction of bovine brain. Fractionation of the nuclear components was used to localize the major positive calreticulin-binding protein. The protein was partially purified using hydroxylapatitie chromatography and subjected to NH2-amino acid sequence analysis. Immunoblots using the sera of SLE patients were then carried out on calreticulin and the calreticulin-binding protein. The calreticulin-binding protein present in the nucleoplasm was identified as histone H1. Approximately 62% (26/42) patients with SLE had IgG antibodies directed against H1 whereas the sera of healthy individuals did not react with the antigen; 36% of patients with SLE had both anti-calreticulin and anti-histone H1 antibodies. Phosphorylation of the latter protein did not alter its immunoreactivity. These findings demonstrate that the concomitant presence of autoantibodies directed against both calreticulin and histone H1 occurs frequently in patients with SLE and may help shed some light on the mechanisms which bring about the autoimmune response.

Nuclear antigen histone H1 is primarily involved in lupus erythematosus cell formation.

To elucidate the nature of the antigen reactive with the "lupus erythematosus (LE) cell factor," the autoantibody involved in the LE cell phenomenon. Serum samples from systemic lupus erythematosus (SLE) patients who were positive for the LE cell phenomenon (LEc+) and SLE patients who were negative for the LE cell phenomenon (LEc-) were used to characterize the nuclear antigen bound by the LE cell factor, by immunoblotting and immunoprecipitation techniques. All LEc+ sera, but none of the LEc- sera, uniformly reacted with a double band of MW approximately 30 kd in nuclear extracts. Depletion of nuclear protein extracts of antigens bound by pooled LEc- serum allowed precipitation of a low molecular weight protein by pooled LEc+ serum. This protein was able to block LE cell formation by LEc+ serum. Based on its reactivity with antihistone antibody and an electrophoretic mobility identical with that of precipitated and purified histone H1, this protein was identified as histone H1. Moreover, all LEc+ sera, but none of the LEc- sera, reacted with purified histone H1 by immunoblotting, whereas other histones were reactive with both types of sera. In addition, purified histone H1, but none of the other histones, strongly inhibited the induction of LE cells by LEc+ serum. Histone H1 represents the major antigenic component recognized by the LE cell factor. Thus, the LE cell phenomenon appears to be due primarily to anti-histone H1 reactivity.

Developmental changes in DNA methylation of the two tobacco pollen nuclei during maturation.

Changes in DNA methylation during tobacco pollen development have been studied by confocal fluorescence microscopy using a monoclonal anti-5-methylcytosine (anti-m5C) antibody and a polyclonal anti-histone H1 (anti-histone) antibody as an internal standard. The specificity of the anti-m5C antibody was demonstrated by a titration series against both single-stranded DNA and double-stranded DNA substrates in either the methylated or unmethylated forms. The antibody was found to show similar kinetics against both double- and single-stranded DNA, and the fluorescence was proportional to the amount of DNA used. No signal was observed with unmethylated substrates. The extent of methylation of the two pollen nuclei remained approximately constant after the mitotic division that gave rise to the vegetative and generative nuclei. However, during the subsequent development of the pollen, the staining of the generative nucleus decreased until it reached a normalized value of (1)/(5) of that of the vegetative nucleus. The use of a confocal microscope makes these data independent of possible focusing artefacts. The anti-histone antibody was used as a control to show that, while the antibody staining directed against 5-methylcytosine changed dramatically during pollen maturation, the histone signal did not. We observed the existence of structural dimorphism amongst tobacco pollen grains, the majority having three pollen apertures and the rest with four. However, the methylation changes observed occurred to the same extent in both subclasses.

Antisera Directed against Anti-Histone H4 Antibodies Recognize Linker Histones: NOVEL IMMUNOLOGICAL PROBES TO DETECT HISTONE INTERACTIONS

We introduce a novel immunological approach to detect structural interactions between chromosomal proteins. Antigenically pure core histone H4 was prepared from chicken erythrocytes and used to produce anti-histone H4 antisera. IgG fractions were isolated from purified anti-H4 antibodies and used as antigens to produce "second generation" antisera. Epitopes cross-reacting with the second generation antisera were then identified within chromosomal proteins. These epitopes were presumed to mimic the complementary molecular surface of the original anti-H4 antibodies, and thus proteins containing these epitopes were putatively identified as specific ligands of H4 in chromatin. Surprisingly, we found this immunoreactivity was predominantly directed against H1 compared with H5 from chicken erythrocytes. Further, the immunoreactive epitopes were located within the C-terminal tail domain of the linker histones. These results suggest similar complementary interactions occur between H4 and the C-terminal tail domain of H1s in native chromatin. This could occur either within a single nucleosome as suggested by a previous report (Banères, J.-L., Essalouh, L., Jariel-Encontre, I., Mesnier, D., Garrod, S., and Parello, J. (1994) J. Mol. Biol., 243, 48-59) or between neighboring nucleosomes within the condensed chromatin fiber. The implications of these results with regard to the structure of the chromatin fiber and the future utility of this technique are discussed.

Ontogeny of histone H1 in guinea pig renal cortex. 258

Histone H1 has been implicated in transcriptional regulation, in some instances by inhibiting thyroid receptorDNA interactions. We have shown a postnatal increase in renal cortical Na,KATPase abundance and activity in guinea pig and demonstrated a potential role for thyroid hormones in mediating this increase. Therefore, we wish to understand the ontogeny of H1 histones in the kidney around the time of birth. SDS polyacrylamide gel electrophoresis(SDSPAGE) of renal cortical homogenates revealed a 32 kDa protein band greatly more abundant in renal cortex from nearterm guinea pig fetuses (> 60 days gestation; term is 68 days) than from postnatal cortex. An 11amino acid fragment from this band was sequenced and found to be from a histone H1. Immunoblots of renal cortical homogenates from fetal (F), newborn (NB) and adult guinea pigs (n=6/group) were probed with an antihistone H1 antibody as well as antiserum to guinea pig outer medullary Na,KATPaseαβheterodimer. The abundances of these proteins were inversely related, with histone H1/Na,KATPase declining with maturation (F 1.9±0.5; NB 0.7±0.1; adults 0.02±0.01). This decline was largely accounted for simply by postnatal tubular cell hypertrophy. We isolated nuclei from renal cortex of the 3 groups, measured total histone H1 in silverstained SDSPAGE gels of nuclei and noted, however, that there was still a maturational decline in histone H1 abundance; F had 32±13% greater total histone H1 than NB and 26±12% greater than adults, while the abundance of the nucleosome core histones (H2H4) in these gels did not change with maturation (n=23/group). We also measured histone H1 isoform abundances in nuclei preps from the 3 groups. Similar to prior studies of the postnatal development of the mouse and rat kidneys, we noted a maturational decline in the ratio of histone H1A/histone H1° abundances in guinea pig renal cortical nuclei, (F 4.6±0.2; NB 2.6±0.3; adults 2.1±0.2, n=23/group). We conclude that there are maturational decreases in total H1 histone and shifts in histone H1 isoforms. We speculate that these changes may influence the maturation of renal tubular function. Glucocorticoid and thyroid receptors and response elements are known to interact with histone H1, and so the abundance of histone H1 isoforms may be a critical determinant of how the developing kidney responds to hormonal stimuli.

Rabbit anti-chromatin antibodies recognize similar epitopes on a histone H1 molecule as lupus autoantibodies

Autoantibodies in systemic lupus erythematosus (SLE) are believed to be produced through an antigen-driven mechanism, i.e., autosensitization with autoantigens. If this is the case, it is conceivable that antigenic determinants reactive with SLE autoantibodies and induced antibodies raised by immunization are quite similar. To examine this issue, rabbits were immunized with purified histone H1 or chromatin. Although immunization with purified histone H1 did not produce detectable amounts of anti-histone H1 antibodies, immunization with chromatin mounted relatively good antibody responses against not only all histone subunits but also ssDNA. Epitopes on a histone H1 molecule reactive with SLE autoantibodies and rabbit antisera were determined using deletion mutants of a histone Hl molecule. At least two epitopes reactive with induced antibodies were found on a histone H1 and these were closely related to or the same as major autoepitopes in SLE. These data might indicate that B cells producing anti-histone Hl autoantibodies are quite similar to those induced by immunization and provide additional evidence that autosensitization with an autoantigen might be operative and a particulate antigen chromatin could be one of the immunogens for the production of anti-nuclear antibodies of various kinds in SLE.

Molecular mimicry: histone H3 and mycobacterial protein epitopes.

A 15-kDa protein detected initially in amyloidotic ileum from a transgenic mouse and subsequently in control (nontransgenic) ileum by various polyclonal rabbit antiserums applied to electroblots of extracts derived from these tissues was identified by partial sequence analysis as histone H3. Antiserums were made against immunogens unrelated to the histone, but they recognized calf thymus histone H3 (14.7 kDa) on Western blots. The bacterial component of the Freund's medium used as an adjuvant for the immunogens was either Mycobacterium butyricum or Mycobacterium smegmatis. Absorption tests with histone H3 and sonicated M. butyricum substantiated the presence of anti-histone H3 activity in the antiserums. These findings indicate that the two mycobacterium species make a protein with epitopes perceived as nonself by recipient rabbits but sufficiently similar to epitopes of mammalian histone H3 that the rabbits produced antibodies cross-reactive with the histone.

Interrelationship between Autoepitope, DNA-Binding Domain, and CRP-Binding Domain on a Histone H1 Molecule

The interrelationship between autoepitopes, DNA-binding domains, and C-reactive protein (CRP)-binding domains on a histone H1 molecule was examined using fusion proteins of β-galactosidase and truncated histone H1 molecules. At least two CRP-binding sites were detected on a histone H1 molecule. Site 1 was composed of ∼25 amino acids and calcium ion was required for the binding of CRP. Site 2, composed of ∼20 amino acids and not requiring calcium ion, was identical or located very close to a DNA-binding domain and an epitope of anti-histone H1 autoantibodies in SLE sera. These data suggest that, at physiological ionic strength, histone H1 of either free or immune-complexed form could bind to CRP via site 1. These data are discussed with respect to the possible role of CRP in the handling and clearance of immune complexes in patients with systemic lupus erythematosus.

The repressor MDBP-2 is a member of the histone H1 family that binds preferentially in vitro and in vivo to methylated nonspecific DNA sequences.

MDBP-2 is a repressor that binds preferentially to methylated DNA. Peptides derived from MDBP-2 were sequenced. The sequences of the two peptides, KPAGPS-VTELITK and ALAAGGYDVEK, are identical to those found in the chicken histone H1 core protein. In SDS/polyacrylamide gels MDBP-2 has an apparent molecular mass of 21 kDa, and antibodies directed against calf thymus total histone H1 cross-react with MDBP-2. The preferential binding of affinity-purified MDBP-2 to methylated DNA is not sequence-specific but requires a minimum length of 30 base pairs and one pair of symmetrically methylated (i.e., methylated on both strands) CpG dinucleotides. As previously shown, there is a decrease in the binding activity of MDBP-2 to methylated DNA upon estradiol treatment. Immunoblots show that upon estradiol treatment the amount of immunocrossreacting MDBP-2 protein remains unchanged. MDBP-2 enables another protein to bind DNA which by itself does not bind methylated DNA. Ultraviolet crosslinking and selective immunoadsorption assays with anti-histone H1 antibodies show that in vivo MDBP-2 preferentially binds to the methylated repressed vitellogenin gene. It is concluded that MDBP-2 may participate in the long-term silencing of genes (formation of heterochromatin) through selective binding to methylated DNA.

Autoantibodies to nucleolin cross-react with histone H1 in systemic lupus erythematosus.

IgM autoantibodies to nucleolin and histone H1 are strongly associated in the serum of patients with systemic lupus erythematosus. IgM eluted from immobilized nucleolin specifically stained histone H1 blotted to nitrocellulose; conversely, IgM eluates prepared from immobilized histone H1 stained nucleolin blots. We conclude that the linkage of anti-nucleolin and anti-histone H1 autoantibodies in SLE is due, at least in part, to immunologic cross-reactivity between these two autoantigens, which share certain similar structural features.

Relationship between autoepitope and DNA-binding site on a histone H1 molecule.

Autoepitope and DNA-binding domain on a histone H1 molecule were compared using truncated histone H1 peptides as antigens. At least two epitopes (epitope A, N-terminal side; epitope B, C-terminal side) were found both of which were composed of approximately 20 amino acids. IgM from all 17 anti-histone H1-positive SLE sera reacted with epitope A. IgG from 12 sera reacted with epitope A and IgG from 4 sera reacted with epitope B. In one case, no IgG anti-histone H1 reactivities were found while IgM from the same patient reacted with epitope A. Epitope A had the ability to bind DNA. The reactivities against histone H1 of affinity-purified antiepitope A autoantibodies were inhibited by DNA. These data suggest that some anti-histone H1 antibodies are directed against a histone H1 DNA-binding site, raising the possibility that an idiotype/anti-idiotype network, at least in part, is involved in the generation of anti-histone H1 autoantibodies.

Autoantibodies against different histone hi subtypes in systemic lupus erythematosus sera

The H1 histones represent the most heterogenous class of histone proteins. In this study, we analyzed the specificity of human antibodies against 6 H1 subtypes. H1 histones from rat organs were separated by reverse-phase high performance liquid chromatography and used as antigens in immunoblotting experiments. Sera containing anti-histone H1 antibodies were obtained from patients with systemic lupus erythematosus. Of the 9 sera tested, 2 reacted with only 1 H1 subtype. The other sera recognized different combinations of H1 subtypes. Only 1 serum reacted with all 6 H1 subtypes. Histones H1.5 and H1.1 were the subtypes most frequently recognized by the human autoantibodies. Our data indicate that human anti-H1 antibodies represent a heterogenous population, directed mainly against epitopes localized in the variable region of the H1 molecule.

Monoclonal anti-histone H1 autoantibodies from MRL lpr/lpr mice

Hybridomas producing anti-histone monoclonal antibodies were generated from a 2-month old MRL lpr/lpr mouse. Five IgM antibodies showed binding to histone H3 and three of these IgM antibodies also bound histone H1. Two IgG 2a antibodies (MRA3 and MRA12) were specific for histone H1 and their binding was further characterized. Both reacted strongly with mouse and calf thymus histones H1, but showed limited (if any) binding to H1 from non-mammalian species such as duck, trout, or sea urchin sperm. Histone H1 is composed of three domains: N (N-terminal), G (globular) and C (C-terminal). The binding of MRA3 and MRA12 antibodies to the N, G and C domains of the histone H1 molecule was also investigated, using purified H1 fragments. Significant binding was observed only with the GC fragment but not with isolated NG, G or C fragments. Moreover, the integrity of most, if not all, of the G domain (residues 33–122) was necessary for antibody binding, since cleavage of the H1 molecule either at residue 72 or 106 abolished the binding to MRA3 and MRA12. Taken together, these results could indicate that MRA3 and MRA12 antibodies recognize a conformational determinant of the H1 molecule.

Patterns of Autoimmunity to Nucleoproteins in Patients with Systemic Lupus Erythematosus

The ANAs described above can be accounted for on the basis of an immune response to just three nucleoprotein structures--the nucleosome, the U1 snRNP, and the Ro particle. When these nucleoproteins are looked at in turn, the following picture emerges. The nucleosome is identified by both anti-histone and anti-DNA antibodies. Anti-histone H1 and anti-histone H2B antibodies predominate and tend to occur together. They, as well as the anti-DNA antibodies with which they appear to be linked, recognize external features of the intact nucleosome. The U1 snRNP is recognized by both anti-U1 RNP and anti-Sm antibodies. Most so-called anti-U1 RNP antisera actually contain several linked sets of different antibodies that are directed against various polypeptides (68K, A, and C) found on the U1 snRNP. Anti-Sm antibodies are linked to the occurrence of anti-U1 RNP antibodies. The Ro particle is recognized by both anti-La and anti-Ro antibodies, and almost all sera that contain anti-La antibodies also contain anti-Ro antibodies. Thus, it appears that these three nucleoprotein particles become direct focal points for autoimmune responses in SLE. It is difficult to explain such focused responses on the basis of a general defect in immune regulation or spontaneous B-lymphocyte hyperactivity. Rather it appears that these nucleoproteins themselves are directly involved in determining which B-lymphocyte clones become activated. Thus, the simplest rationalization for the patterns with which these autoantibodies occur is to invoke the possibility that the particles themselves are directly triggering autoimmune responses.

Specificity studies on anti-histone H1 antibodies obtained by different immunization methods

Antibodies were elicited against chromatographically purified histone H l subfractions or against their complexes with RNA and their specificity studied by enzyme-linked immunosorbent assay. The results show that complexing of the pure protein with RNA (i) does not lead to any significant increase in the antibody titer and (ii) results in obtaining antibodies predominantly against the common antigenic determinants present in the HI histone class. On the other hand, using pure histone fractions for immunization gives rise to antibody populations reacting mainly with the subfraction-specific determinants on the histone molecule. In view of these results the literature data should be interpreted with caution.

Antibody to poly(adenosine diphosphate-ribose) polymerase and its use in chromatin analysis.

To facilitate investigations on the organization of poly (ADP-Rib) polymerase in chromatin, and to elucidate its biological function, polymerase purified from HeLa nuclei was used to elicit antibodies in mice. The anti-polymerase sera was found to be specific by multiple criteria. The association of polymerase with oligonucleosomes of differing chain size was determined by the specific binding of polymerase antibody (and as control, anti-histone H3) to nitrocellulose transfers of native electrophoretic gels of these particles. By this technique, polymerase appears to be associated with a select subclass of nucleosomes. Further resolution of the polymerase binding sites within nucleosome classes was achieved with the antibody by two-dimensional native polyacrylamide gel electrophoresis and nitrocellulose transfer.

Molecular homogeneity of the histone content of HeLa chromatin subunits.

Interaction of affinity chromatographically purified antihistone H3 and antihistone H4 with isolated HeLa core particles, followed by separation of unreacted and reacted particles by sedimentation, demonstrates that every core particle contains these histones. Taken together with our previous data indicating the presence of H2B in every nucleosome (Simpson, R. T., and Bustin, M. (1976), Biochemistry 15, 4305), these data lead to the conclusion that each core particle contains two each of the four smaller histones. In contrast to the lack of interference in binding of more than one molecule of antibody to a single species of histone to the core particle, steric hindrance exists when attempts are made to bind both anti-H3 and anti-H4 to core particles.

Purification of anti-histone-H1 antibodies and their use in measuring histone determinants in chromatin by radioimmunoadsorbance

Anti-histone H1 antibodies belonging to the IgG class were purified by affinity chromatography on H1-Sepharose columns. Such antibodies can be labeled with 125I and used to measure the availability of H1 determinants in chromatin.