Expression of DNA topoisomerases in chronic proliferative kidney disease

BACKGROUND

Circulating autoantibodies to human topoisomerases have been reported in glomerular kidney disease associated with scleroderma and systemic lupus erythematosus. However, limited information is available about the expression of topoisomerases in the kidney under normal and pathological conditions.

METHODS

The expression of DNA topoisomerases I and IIalpha was studied by immunohistochemistry on archival biopsies from 70 patients with chronic renal diseases. Normal kidney tissue was examined for comparison. Topoisomerase I was detected by means of monoclonal antibody (mAb) C21, and topoisomerase IIalpha was detected by means of mAb Ki-S4. In addition, mAb Ki-M1p was used to assess the density of monocytic infiltrates. All parameters were assessed in a semiquantitative manner.

RESULTS

Glomerular topoisomerase IIalpha levels were increased in mesangial proliferative glomerulonephritis (MPGN), rapidly progressive glomerulonephritis (RPGN), and lupus nephritis (LN) and were reduced in membranous glomerulonephritis (MGN), chronic transplant nephropathy (CTN), and tubulointerstitial nephritis (TIN). Tubular epithelia displayed high topoisomerase IIalpha levels in mesangiocapillary glomerulonephritis (MCGN), RPGN, TIN, miscellaneous entities (MISC) and LN, and displayed low levels in MPGN and CTN. Topoisomerase I expression was high in the glomeruli of focal segmental glomerulosclerosis (FSGS), MCGN, and RPGN and was extreme in LN, whereas it was strikingly diminished in the glomeruli of MGN, CTN, and TIN. Almost all conditions displayed lower tubular topoisomerase I levels than normal kidney, except for LN, in which the enzyme content was markedly increased. Increased glomerular monocytic infiltrates were found in FSGS, MCGN, RPGN, TIN, and LN, and tubulointerstitial Ki-M1p+ cells were seen at high numbers in MCGN, RPGN, TIN, MISC, and LN. The expression of the topoisomerases I and IIalpha was significantly correlated; also, topoisomerases showed a positive association with the density of monocytic infiltrates. The parameter profiles exhibited significant differences between distinct types of chronic renal disease.

CONCLUSION

Topoisomerase IIalpha expression is tightly linked to cell cycling, and topoisomerase I is likely a reflection of gene transcription. Rapidly progressing glomerular disease therefore appears to be accompanied by active mesangial cell proliferation and increased metabolic activity in glomerular cells. The correlation with inflammatory infiltrates is likely to reflect a positive feedback mechanism involving cytokines, growth factors, and adhesion molecules. Assessment of topoisomerases may therefore be of diagnostic help and might allow prognostic predictions. Provided that our observations are supported by clinicopathological follow-up studies, one might envisage the use of topoisomerase inhibitors in the therapy of chronic proliferative renal disease refractory to current treatment protocols.

Anti-topoisomerase II alpha autoantibodies in systemic sclerosis-association with pulmonary hypertension and HLA-B35

We have previously detected autoantibodies against topoisomerase II alpha (anti-topo II alpha) in sera from patients with idiopathic pulmonary fibrosis. To determine whether anti-topo II alpha is also present in systemic sclerosis (SSc) patients with pulmonary involvement, we screened sera from 92 patients and 34 healthy controls. Presence of anti-topo II alpha was investigated with respect to clinical and serological features, including the frequencies of HLA class I and II alleles. Anti-topo II alpha was detected in 20/92 (21.7%) patients. No association was found with either anti-topoisomerase I (Scl-70 or anti-topo I) or anti-centromere antibodies. However, anti-topo II alpha was associated with the presence of pulmonary hypertension (PHT) (as opposed to pulmonary fibrosis), and with a decrease of carbon monoxide diffusing capacity. Anti-topo II alpha was strongly associated with the presence of the class I antigen HLA-B35. No significant association was found with HLA class II antigens. HLA-B35 also turned out to be associated with the presence of PHT. These results indicate that in SSc patients, the presence of anti-topo II alpha is associated with PHT, and that the simultaneous presence of HLA-B35 seems to add to the risk of developing PHT.

Relationship between autoantibodies against glutamic acid decarboxylase, thyroglobulin/thyroid microsome and DNA topoisomerase II in the clinical manifestation of patients with type 1 diabetes mellitus in Taiwan

OBJECTIVE

In a preliminary cross-sectional study, we discovered that DNA topoisomerase II autoantibodies (anti-TopII) were detected in 49.2% of 195 Chinese type 1 diabetes mellitus (type 1 DM) patients with a mean age of 14.5 years and a mean duration of disease of 4.6 years. In order to demonstrate the relationship between anti-TopII and other immunological characteristics in Chinese type 1 DM patients, and to evaluate its putative prediction efficacy in Chinese patients, we simultaneously examined the frequency of anti-glutamic acid decarboxylase autoantibodies (anti-GAD), anti-TopII, antithyroglobulin/antimicrosomal autoantibodies (ATA/AMiA) and C-peptide concentrations in our patients in the present study.

DESIGN AND METHODS

The frequency of anti-GAD and C-peptide levels, anti-TopII, and ATA/AMiA were examined in our patients by radioimmunoassay, enzyme-linked immunosorbant assay and hemagglutination respectively. Univariate comparisons were performed using Student's t-test for normal distributed data and Chi-square test for diclomatous data. Multivariate analysis was used for interpreting the independent risk factors which increased the incidence of anti-TopII.

RESULTS AND CONCLUSIONS

The positivities for anti-GAD, anti-TopII, ATA/AMiA and C-peptide were 45.8%, 50.2%, 13.4% and 11.4% respectively. Anti-GAD and anti-TopII frequencies in our patients were similar when we stratified the patients by age, age at onset and duration. These observations imply that anti-GAD and anti-TopII remain persistent in Chinese patients with long-term type 1 DM duration. The most interesting finding is that anti-TopII frequency is more persistent than anti-GAD in our patients, especially when the diabetic duration is longer than 11 years. This indicates that anti-TopII, rather than anti-GAD, might act as a better indicator for monitoring the pathogenesis of Chinese type 1 DM patients especially in patients with a long-standing duration of disease. The late age of onset (>18 years) is a risk factor which increased the incidence of anti-TopII according to multivariate analysis. We further analyzed different manifestations between the youth- and adult-onset type 1 DM and found that adult-onset type 1 DM is characterized by better preservation of residual beta-cell function and higher frequencies of autoantibodies.

DNA topoisomerase II-alpha immunoreactivity as a marker of tumor aggressiveness in invasive breast cancer

OBJECTIVE

The nuclear enzyme DNA topoisomerase (topo) II breaks and rejoins DNA strands; its isoform topo IIalpha is associated with active cell proliferation of mammalian cells. The aim of this study was to examine the relationship between the expression of topo IIalpha and biological behavior markers in breast cancer.

METHODS

Formalin-fixed, paraffin-embedded tissue from 88 samples of infiltrating breast cancer was immunohistochemically stained for topo IIalpha. For each case, a topo IIalpha index was determined by image analysis. Similar indexes were available for Ki-67 protein, a known cell proliferation marker, and p53, bcl-2 and c-erbB-2 oncoproteins. Each case had been staged and graded and the patients had been followed up for a mean period of 61.62 months.

RESULTS

Elevated topo IIalpha immunopositivity (in >10% of malignant nuclei) was detected in 22 tumors, and this immunostatus was statistically associated with poor nuclear differentiation, absence of steroid hormone receptors, high Ki-67 immunoexpression, p53 protein accumulation and c-erbB-2 protein overexpression. Topo IIalpha expression was not linked with disease extent (stage or lymph node status). Neither proliferation marker (topo IIalpha or Ki-67) had any significant influence on the patients' recurrence-free survival.

CONCLUSION

From the above results, we conclude that topo IIalpha overexpression appears to be linked with cellular dedifferentiation and potentially aggressive tumor phenotype in invasive breast cancer.

Serologic responses in patients with malignant mesothelioma: evidence for both public and private specificities

Malignant mesothelioma (MM) is a pulmonary malignancy that appears to be immunogenic based on a large number of studies in both animals and humans. This notion is supported by our recent demonstration using Western blot analysis of immunoglobulin G antibodies reactive with a variety of autoantigens in many patients with MM. In view of the enormous potential of such antigens in early diagnosis, immunotherapy, and vaccination of at-risk individuals, it was essential to identify these antigens. We therefore applied the SEREX technique (serologic identification by recombinant expression cloning), using a serum pool from six patients as the probe against an expressed complementary DNA library derived from a cloned MM cell line. We screened over one million recombinants and obtained sequence information on eight antigens that had provoked immunoglobulin heavy chain class switching, presumably as a consequence of T-cell recognition. Six of these antigens were identifiable (U2AF[65], Siah binding protein, topoisomerase IIbeta, ZFM1, mIre1, and pendulin), and of the others, one was found as a single EST from a myotube library (Jemm-1); the other (Jemm-2) was not represented in any EST database even as a weak homolog. Consistent with our previous findings, each of the characterizable antigens would be expected to be associated with the cell nucleus. Each of the autoantibody specificities was uniquely associated with a single patient with the exception of antibodies to TOPIIbeta and U2AF(65). We found 13 of 14 (93%) patients with MM had antibodies to TOPIIbeta and two of 14 (14%) patients had antibodies to U2AF(65). The number of serum reactivities, taken as a measure of the complexity of the immune response, correlates with patient survival and with an index of systemic inflammation. These data suggest that a broader range of serologic reactivities reflects a more active host response to the presence of tumor.

Meiotic events at the centromeric heterochromatin: histone H3 phosphorylation, topoisomerase II alpha localization and chromosome condensation

Mechanisms of chromosome condensation and segregation during the first meiotic division are not well understood. Resolution of recombination events to form chiasmata is important, for it is chiasmata that hold homologous chromosomes together for their oppositional orientation on the meiotic metaphase spindle, thus ensuring their accurate segregation during anaphase I. Events at the centromere are also important in bringing about proper attachment to the spindle apparatus. This study was designed to correlate the presence and activity of two proteins at the centromeric heterochromatin, topoisomerase II alpha (TOP2A) and histone H3, with the processes of chromosome condensation and individualization of chiasmate bivalents in murine spermatocytes. We tested the hypothesis that phosphorylation of histone H3 is a key event instigating localization of TOP2A to the centromeric heterochromatin and condensation of chromosomes as spermatocytes exit prophase and progress to metaphase. Activity of topoisomerase II is required for condensation of chromatin at the end of meiotic prophase. Histone H3 becomes phosphorylated at the end of prophase, beginning with its phosphorylation at the centromeric heterochromatin in the diplotene stage. However, it cannot be involved in localization of TOP2A, since TOP2A is localized to the centromeric heterochromatin throughout most of meiotic prophase. This observation suggests a meiotic function for TOP2A in addition to its role in chromatin condensation. The use of kinase inhibitors demonstrates that phosphorylation of histone H3 can be uncoupled from meiotic chromosome condensation; therefore other proteins, such as those constituting metaphase-promoting factor, must be involved. These results define the timing of important meiotic events at the centromeric heterochromatin and provide insight into mechanisms of chromosome condensation for meiotic metaphase.

Cloning and characterization of the gene encoding Aspergillus nidulans DNA topoisomerase II

We have determined the complete nucleotide sequence of a 5544bp genomic DNA fragment from Aspergillus nidulans that encodes DNA topoisomerase II (topo II). It contains a single open reading frame of 4740bp that codes for 1579 amino acid residues with a molecular weight of 178kDa; when expressed in Escherichia coli and Saccharomyces cerevisiae the molecular weight was 180kDa. The gene (TOP2) is divided into three exons. Two introns, 54bp and 60bp in length, are located at nucleotide positions 187 and 3214 respectively. Comparison of the deduced amino acid sequence with other eukaryotic topo II sequences showed a higher degree of identity with other fungal enzymes than the human topo IIalpha. One of monoclonal antibodies raised against human topo II, 6H8, can cross-react with Aspergillus topo II.

Mapping of topoisomerase II alpha epitopes recognized by autoantibodies in idiopathic pulmonary fibrosis

Autoantibodies against DNA topoisomerase II alpha have been identified in the sera of patients with idiopathic pulmonary fibrosis (IPF). To map topoisomerase II autoepitopes, we tested by ELISA and immunoblotting the IPF anti-topoisomerase II-positive sera against a series of recombinant proteins which covered the full length of topoisomerase II alpha. Specific patterns of reactivity were observed, indicating the existence of multiple epitopes on topoisomerase II, either highly complex or conformational/discontiguous or conformational/contiguous ones. The latter resided in amino acid residues 854-1147 and 1370-1447. A detailed analysis of these regions was undertaken, but we were not able to pinpoint a sequential peptide-sized epitope, or any significant homology with foreign pathogens. Further, we observed a significant correlation between the progression from a contiguous to a quaternary/tertiary structure-dependent autoepitope and the disease duration but not with the disease severity. Therefore, this result supports the hypothesis that anti-topoisomerase II autoreactivity evolves following an antigen-driven process.

Casein kinase II catalyzes a mitotic phosphorylation on threonine 1342 of human DNA topoisomerase IIalpha, which is recognized by the 3F3/2 phosphoepitope antibody

The 3F3/2 antibody recognizes a phosphoepitope that is implicated in the mitotic checkpoint regulating the metaphase-to-anaphase transition. Immunoprecipitation and Western blotting revealed that the 3F3/2 antibody binds to human DNA topoisomerase II alpha (HsTIIalpha) from mitotic but not interphase HeLa cells. Extracts from mitotic cells efficiently catalyzed the formation of the 3F3/2 phosphoepitope on fragments of HsTIIalpha expressed in bacteria. Expression and site-directed mutagenesis of various HsTIIalpha protein fragments mapped the 3F3/2 phosphoepitope to the region of HsTIIalpha containing phosphorylated threonine 1342. This threonine lies within a consensus sequence for phosphorylation by casein kinase II (CKII). CKII is present in cellular extracts and is associated with isolated mitotic chromosomes. The 3F3/2 phosphoepitope kinase present in mitotic cell extracts was able to create the epitope using GTP and was inhibited by heparin. A kinase associated with the isolated chromosomes also generated the 3F3/2 phosphoepitope on HsTIIalpha. Recombinant CKII catalyzed the formation of the 3F3/2 phosphoepitope on fragments of HsTIIalpha containing threonine 1342. These results indicate that the mitotic 3F3/2 phosphoepitope kinase activity is attributable to CKII. We suggest that the 3F3/2 phosphoepitope reflects a CKII-catalyzed phosphorylation of threonine 1342 that may regulate mitotic functions of HsTIIalpha.

DNA topoisomerase II alpha and Ki-67 in human adrenocortical neoplasms: a possible marker of differentiation between adenomas and carcinomas

Cell kinetic information is valuable in evaluating the diagnosis and/or biologic behavior of various human neoplasms. Monoclonal antibody Ki-67 recognizes the cells other than G0 of the cell cycle. A cell cycle-related intranuclear protein, topoisomerase II alpha (topoII alpha), separates chromosomes at the end of mitosis. Its expression is mostly limited to the S to G2/M phases of the cell cycle. We studied cell proliferative activity in adrenocortical adenomas (n = 28), carcinomas (n = 17), and normal adrenal glands (n = 6) by immunohistochemical analysis of Ki-67 and topoII alpha to evaluate their value in the diagnosis of adrenocortical malignancy. We detected Ki-67 and topoII alpha immunohistoreactivity in the nuclei of each case we examined. There was a significant positive correlation (r = 0.927) between the Ki-67 and topoII alpha labeling indexes (LIs), the percentage of positive cells. In normal adrenal cortex and adenoma, the LIs for Ki-67 and topoII alpha were 0.48 +/- 0.16 and 0.44 +/- 0.15 for normal and 0.64 +/- 0.11 and 0.72 +/- 0.12 for adenoma, respectively, with no significant differences in the LIs of adenomas and normal adrenals. The Ki-67 and topoII alpha LIs in the carcinomas were 5.84 +/- 1.33 and 6.13 +/0 1.65, respectively; these LIs were significantly higher than the LIs of adenomas. Eleven of 17 carcinomas demonstrated topoII alpha and Ki-67 LIs of more than 2.5, whereas none of the adenomas did. The topoII alpha and Ki-67 LIs in carcinomas with metastasis (11.21 +/- 3.15 and 9.75 +/- 2.31 respectively; n = 7) were significantly higher than in those without metastasis (2.58 +/- 0.61 and 3.12 +/- 0.90, respectively; n = 10). This indicates that immunohistochemical analysis of Ki-67 and topoII alpha could help to differentiate carcinoma from adenoma in resected adrenocortical neoplasms and might predict aggressive biologic behavior in carcinomas.

MPM-2 antibody-reactive phosphorylations can be created in detergent-extracted cells by kinetochore-bound and soluble kinases

The MPM-2 antibody labels mitosis-specific and cell cycle-regulated phosphoproteins. The major phosphoproteins of mitotic chromosomes recognized by the MPM-2 antibody are DNA topoisomerase II (topoII) alpha and beta. In immunofluorescence studies of PtK1 cytoskeletons, prepared by detergent lysis in the presence of potent phosphatase inhibitors, the MPM-2 antibody labels phosphoproteins found at kinetochores, chromosome arms, midbody and spindle poles of mitotic cells. In cells extracted without phosphatase inhibitors, labeling of the MPM-2 antibodies at kinetochores is greatly diminished. However, in cytoskeletons this epitope can be regenerated through the action of kinases stably bound at the kinetochore. Various kinase inhibitors were tested in order to characterize the endogenous kinase responsible for these phosphorylations. We found that the MPM-2 epitope will not rephosphorylate in the presence of the broad specificity kinase inhibitors K-252a, staurosporine and 2-aminopurine. Several other inhibitors had no effect on the rephosphorylation indicating that the endogenous MPM-2 kinase at kinetochores is not p34cdc2, casein kinase II, MAP kinase, protein kinase A or protein kinase C. The addition of N-ethylmaleimide inactivated the endogenous kinetochore kinase; this allowed testing of several purified kinases in the kinetochore rephosphorylation assay. Active p34cdc2-cyclin B, casein kinase II and MAP kinase could not generate the MPM-2 phosphoepitope. However, bacterially expressed NIMA from Aspergillus and ultracentrifuged mitotic HeLa cell extract were able to catalyze the rephosphorylation of the MPM-2 epitope at kinetochores. Furthermore, fractionation of mitotic HeLa cell extract showed that kinases that create the MPM-2 epitope at kinetochores and chromosome arms are distinct. Our results suggest that multiple kinases (either soluble or kinetochore-bound), including a homolog of mammalian NIMA, can create the MPM-2 phosphoepitope. The kinetochore-bound kinase that catalyzes the formation of the MPM-2 phosphoepitope may play an important role in key events such as mitotic kinetochore assembly and sister chromatid separation at anaphase.

Partial characterization of the MPM-2 phosphoepitope

The MPM-2 monoclonal antibody recognizes a distinctive group of proteins that are associated with structural components of the mitotic apparatus. These proteins become phosphorylated and MPM-2 reactive during M-phase and appear to be required for both the onset and completion of M-phase. Based upon the analysis of reported MPM-2 reactive sequences, we have developed a model for the essential elements that comprise the MPM-2 epitope. This model was tested by employing a series of synthetic phosphopeptides. We show here that a 14 amino acid synthetic phosphopeptide, derived from a potential MPM-2 site on human DNA topoisomerase II, is recognized by the MPM-2 antibody. This phosphopeptide was sufficient to compete for MPM-2 antibody recognition of (1) an isolated native mitotic MPM-2 antigen on dot blots, (2) proteins on immunoblots of mitotic cell lysates, and (3) specific immunostaining of mitotic cells. These results indicated that the topoisomerase peptide contained all of the essential elements of the MPM-2 epitope. By substituting selected amino acids with alanine, we were able to examine the contribution of different amino acids to the binding between the MPM-2 antibody and the epitope. Changing the amino acid that was adjacent to the phosphorylated threonine residue on the C-terminal side (the +1 position) had no effect on MPM-2 antibody binding. However, substitution of aromatic amino acids at either the -2 or +2 positions reduced antibody recognition. The aromatic amino acid at the -2 position appeared to be the most critical residue of those tested that influenced antibody binding. These results provide information required for the molecular definition of the MPM-2 epitope and should aid in the identification of potential MPM-2 reactive sites on other mitotic phosphoproteins.

Cell cycle-coupled relocation of types I and II topoisomerases and modulation of catalytic enzyme activities

We visualized DNA topoisomerases in A431 cells and isolated chromosomes by isoenzyme-selective immunofluorescence microscopy. In interphase, topoisomerase I mainly had a homogeneous nuclear distribution. 10-15% of the cells exhibited granular patterns, 30% showed bright intranucleolar patches. Topoisomerase II isoenzymes showed spotted (alpha) or reticular (beta) nuclear patterns throughout interphase. In contrast to topoisomerase IIalpha, topoisomerase IIbeta was completely excluded from nucleoli. In mitosis, topoisomerase IIbeta diffused completely into the cytosol, whereas topoisomerases I and IIalpha remained chromosome bound. Chromosomal staining of topoisomerase I was homogeneous, whereas topoisomerase IIalpha accumulated in the long axes of the chromosome arms and in the centriols. Topoisomerase antigens were 2-3-fold higher in mitosis than in interphase, but specific activities of topoisomerase I and II were reduced 5- and 2.4-fold, respectively. These changes were associated with mitotic enzyme hyperphosphorylation. In interphase, topoisomerases could be completely linked to DNA by etoposide or camptothecin, whereas in mitosis, 50% of topoisomerase IIalpha escaped poisoning. Refractoriness to etoposide could be assigned to the salt-stable scaffold fraction of topoisomerase IIalpha, which increased from <2% in G1 phase to 48% in mitosis. Topoisomerases I and IIbeta remained completely extractable throughout the cell cycle. In summary, expression of topoisomerases increases towards mitosis, but specific activities decrease. Topoisomerase IIbeta is released from the heterochromatin, whereas topoisomerase I and IIalpha remain chromosome bound. Scaffold-associated topoisomerase IIalpha appears not to be involved in catalytic DNA turnover, though it may play a role in the replicational cycle of centriols, where it accumulates during M phase.

Redistribution of DNA topoisomerase II beta after in vitro stabilization of human erythroleukemic nuclei by heat or Cu++ revealed by confocal microscopy

Using confocal laser scanning microscope and a monoclonal antibody we have examined by means of indirect immunofluorescence techniques the distribution of DNA topoisomerase II beta (the 180-kDa nucleolar isoform of topoisomerase II) following stabilization of isolated nuclei by exposure to moderate heat (37 degrees or 42 degrees C) or Cu++. In intact cells the antibody specifically decorated the nucleoli. The same pattern was maintained if nuclei were incubated at 0 degree C in a buffer containing spermine/spermidine/KCl or stabilized by means of 0.5 mM Cu++ for 10 minutes at 0 degree C in the same buffer. On the contrary, if stabilization was performed by incubating the nuclei either at 37 degrees or 42 degrees C, the immunoreactivity dispersed all over the nucleus, forming numerous speckles. This phenomenon was not detected if, in addition to spermine/spermidine/KCl, the incubation buffer also contained 5 mM Mg++ and the temperature was 37 degrees C. If the stabilization was performed at 42 degrees C, Mg++ failed to maintain the original distribution of DNA topoisomerase II beta, as seen in intact cells. The analysis on 2-D optical section showed the alteration of the nucleolar profile, particularly at 37 degrees C, even when the samples were treated with Mg++. The 3-D reconstruction figured out the irregularity of the surface at 37 degrees C and the variations of the volume occupied by the fluorescent figures. These were in close proximity to each other both in intact cells and in 0 degree C incubated nuclei; they showed a certain degree of shrinkage in 0 degree C plus Cu++ exposed samples (-20% of the volume), and, on the contrary, the labeled structures were scattered in a volume increased two- or threefold when exposed to 37 degrees or 42 degrees C, respectively. The addition of Mg++ restored the original spatial relationship and volume at 37 degrees C, but not at 42 degrees C, where the volumetric analysis showed an increase of about 50%. Our results demonstrate that heat stabilization of isolated nuclei in a buffer without Mg++ (i.e., a technique often employed to prepare the nuclear matrix or scaffold) cannot be considered an optimal procedure to maintain the original distribution of protein within the nucleus.

Threonine 1342 in human topoisomerase IIalpha is phosphorylated throughout the cell cycle

To investigate the relationship between the modulation of topoisomerase II activity and its phosphorylation state during the cell cycle, a monoclonal antibody against C-terminal peptide (residues 1335-1350) of topoisomerase IIalpha containing a consensus sequence of casein kinase II, TDDE and its phosphorylated threonine were prepared. In an enzyme-linked immunosorbent assay, the antibody, named PT1342, recognized the immunogenic phosphopeptide but not the non-phosphorylated form of the peptide. The PT1342 antibody reacted only with a 170-kDa protein from HeLa cells and recognized anti-topoisomerase IIalpha immunoprecipitants. Furthermore, the antibody did not react with the human topoisomerase IIalpha mutated at codon 1342 from threonine to alanine, showing that PT1342 was directed against the phosphorylated threonine 1342. To examine the level of phosphorylation of threonine 1342 of topoisomerase IIalpha through the cell cycle, HeLa cells were stained simultaneously for phosphorylated topoisomerase IIalpha and DNA and analyzed by flow cytometry. Cells in the G2-M phase contained about double the PT1341-reacted topoisomerase IIalpha than did cells in G1 or S phases. The antibody stained the nuclei in interphase and mitotic chromosomes and its periphery, as seen with anti-topoisomerase IIalpha antibody. Thus, threonine 1342 in topoisomerase IIalpha is phosphorylated throughout the cell cycle.

Immunohistochemical study of DNA topoisomerase II in human gastric disorders

Topoisomerase II (topo II) separates chromosomes at the end of mitosis and is also the target for various chemotherapeutic agents. Expression of this enzyme has been demonstrated to increase rapidly at the end of the S to G2/M phase and decrease after the completion of mitosis. We immunolocalized topo II in specimens of both normal and neoplastic human gastric mucosas to evaluate expression of this enzyme. Three different antibodies were used for the immunostaining of topo II (anti-topo II alpha isoform, anti-topo II beta isoform and anti-topo II alpha and -beta isoforms). There were no significant differences in topo II labeling index (LI) between frozen and paraffin-embedded tissue sections obtained from the same cases. Topo II LI was significantly correlated with Ki67 LI in all of the specimens examined. The area of cells positive for Topo II was much narrower than that of Ki67 in the normal gastric glands, and the pattern of Topo II immunolocalization in both adenomas and adenocarcinomas was also essentially the same as that of Ki67. The topo II LI values (positive cells/1000 cells) for normal gastric gland, adenoma, intestinal-type adenocarcinoma, and diffuse-type adenocarcinoma were 114.7 +/- 2.2, 266.7 +/- 18.8, 277.6 +/- 19.2, and 324.5 +/- 5.3, respectively. Significant differences in topo II LI and topo II/Ki67 index were observed between normal and neoplastic mucosas (P < 0.0001) and between adenomas or intestinal-type adenocarcinoma and diffuse-type adenocarcinoma (P < 0.001 and P < 0.01, respectively). Simultaneous measurement of topo II alpha and nuclear DNA content by two-parameter flow cytometry revealed that the Jurkat cell line established from acute lymphocytic leukemia cells expressed the enzyme in cells at other than S and G2/M phases of the cell cycle whereas topo-II alpha-positive cells were predominantly observed in S and G2/M phases of the cell cycle in the cells from normal lymph nodes. These findings suggest that dys-regulation or qualitative changes of topo II alpha expression are associated with malignancy. Topo II immunostaining can thus detect proliferating cells in routinely processed tissue sections and can indicate the altered topo II alpha expression in human cancers, which may be related to the sensitivity to topo-II-targeted chemotherapeutic agents.

Purification and functional characterization of type II DNA topoisomerase from rat testis and comparison with topoisomerase II from liver

A number of studies in yeast have shown that DNA topoisomerase II is essential for chromosome condensation and disjunction during mitosis at the metaphase/anaphase transition and meiosis I. Accordingly, kinetic and mechanistic studies have implied a role for topoisomerase II in chromosome disjunction. As a step toward understanding the nature and role of topoisomerase II in a mammalian germline in vivo, we have purified topoisomerase II from rat testis to homogeneity and ascertained several of its catalytic activities in conjunction with that of the purified enzyme from liver. The purified enzymes appeared to be monomers under denaturing conditions; however, they differed in their relative molecular mass. Topoisomerase II from testis and liver have apparent molecular masses of 150 +/- 10 kDa and 160 +/- 10 kDa, respectively. The native molecular mass of testis topoisomerase II as assayed by immunoblot analysis of cell-free extracts, prepared in the presence of SDS and a number of protease inhibitors, corroborated with the size of the purified enzyme. Both enzymes are able to promote decatenation and relax supercoiled DNA substrates in an ATP and Mg(2+)-dependent manner. However, quantitative comparison of catalytic properties of topoisomerase II from testis with that of the enzyme from liver displayed significant differences in their efficiencies. Optimal pH values for testis enzyme are 6.5 to 8.5 while they are 6 to 7.5 for the liver enzyme. Intriguingly, the relaxation activity of liver topoisomerase II was inhibited by potassium glutamate at 1 M, whereas testis enzyme required about half its concentration. These findings argue that topoisomerase II from rat testis is structurally distinct from that of its somatic form and the functional differences between the two enzymes parallels with the physiological environment that is unique to these two tissues.

A monoclonal antibody against DNA topoisomerase II labels the axial granules of Pleurodeles lampbrush chromosomes

By immunizing Balb/c mice with oocyte nuclei of Pleurodeles waltl we obtained a monoclonal antibody, mAb 4A6, that labels distinct globular domains of the lampbrush chromosomal axes of Pleurodeles. These domains are found at corresponding sites of homologous chromosomes, often at telomeric and putative centromeric regions, and appear to be devoid of DNA. Because of these characteristic features it is most likely that the mAb 4A6-positive domains correspond to the central part of the "axial granules" of urodelan lampbrush chromosomes. In immunoblotting analyses mAb 4A6 reacts with a nuclear antigen of approximately Mr 180000 and a structurally nonrelated cytoplasmic protein of Mr 98000, which was not characterized any further. Comparative immunofluorescence and immunoblotting studies with mAb 4A6 and an antiserum against DNA topoisomerase II (topo II) as well as immunodepletion experiments demonstrated that the nuclear 4A6 antigen is topo II. Our results indicate that topo II is not a constituent of a continuous, loop-anchoring scaffold in lampbrush chromosomes of Pleurodeles but, rather, is restricted to the axial granules.

Behavior of nuclear matrix proteins during camptothecin-induced apoptosis in HL-60 human leukemia cells

In this study we focused our attention on the behavior of four nuclear matrix proteins during the various stages of apoptosis in the HL-60 cell line exposed to the DNA topoisomerase I inhibitor, camptothecin. We have examined the following antigens by immunocytochemical techniques: (i) the 180-kDa nucleolar isoform of DNA topoisomerase II; (ii) a 126-kDa polypeptide of nuclear bodies; (iii) a 125-kDa protein; and (iv) a 160-kDa polypeptide which are known to be components of the matrix inner network. Indirect immunofluorescence experiments were performed to follow these nuclear matrix antigens during apoptosis. Moreover, the ultrastructural localization of both 125- and 160-kDa proteins was investigated by electron microscope immunocytochemistry with gold-conjugated secondary antibodies. While the antibody to the nucleolar isoform of DNA topoisomerase II gave a fluorescent pattern that was well-maintained until the late phases of apoptosis, the other three nuclear antigens showed marked modifications in their distribution. A common feature, particularly evident for 125- and 160-kDa proteins, was their absence from cap-shaped chromatin marginations, whereas they were present in the areas of remaining decondensed chromatin. The 126-kDa polypeptide concentrated progressively in an irregular mass at the opposite side of the crescentic caps and then broke up in fine spots. The 125- and 160-kDa proteins localized in the nucleolus and precisely within certain granules which are known to appear in the nucleolar area after camptothecin administration. These results show that, in addition to the well-known chromatin changes, nuclear organization undergoes other rearrangements during the apoptotic process.

Immunohistochemical staining for DNA topoisomerase II in non-Hodgkin's lymphomas

DNA topoisomerase II (topo II) is the target of several clinically useful anticancer drugs. Several of these agents, such as doxorubicin and etoposide (VP-16), are used to treat non-Hodgkin's lymphomas (NHL). To understand the therapeutic selectivity of these drugs, a series of 33 cases of NHL for topo II were analyzed using an immunohistochemical technique that detects the enzyme in formalin-fixed, paraffin-embedded tissue. The average topo II index of high grade (Working Formulation) NHL was 48.6 with a range from 24.4 to 79.7. The average topo II index of low grade (Working Formulation) NHL was 4.4 with a range from 0.9 to 11.2. These two values are statistically different (P < .01). The intermediate grade (Working Formulation) NHL are a heterogeneous group based on topo II staining. The average topo II index value for the intermediate grade neoplasms was 26.7 with a range from 1.4 to 54.9. Because the proliferation marker Ki-67 has been shown to be of prognostic importance when used in the analysis of NHL, 27 cases for also were analyzed for MIB1 (Ki-67). The average MIB1 index of the high grade NHL was 59.8 with a range from 40.7 to 80.3. This average is statistically different (P < .01) than the average MIB1 index of 11.2 (range 1.7-28.3) found in the low grade NHL. Similar to results with topo II, the intermediate grade NHL was a heterogeneous group of tumors with respect to MIBI staining and had an average MIB1 index of 49.1 with a range from 8.9 to 86.7. These results show that high grade NHL have topo II and MIB1 indices that are significantly higher than low grade NHL. Intermediate NHL are more heterogeneous and have topo II and MIB1 indices that range from low to high.

Proliferation-associated nuclear antigen Ki-S1 is identical with topoisomerase II alpha. Delineation of a carboxy-terminal epitope with peptide antibodies

Proliferation-linked expression of the nuclear Ki-S1 antigen is a significant prognostic indicator in mammary carcinomas. Here, we show staining of a protein of 170 kd by Ki-S1 antibody in immunoblots of Saccharomyces cerevisiae expressing human topoisomerase II alpha but not in the parental strain. In HL-60 cells containing both isoforms of human topoisomerase II, Ki-S1 antibody binds selectively to the 170-kd isoenzyme in a similar fashion as peptide-antibodies directed against amino acid residues 1 to 15 or 1512 to 1530 of human topoisomerase II alpha. Conversely, antibodies directed against carboxyl-terminal sequences of human topoisomerase II beta selectively stain a 180-kd protein. The immunoreactive pattern of V8 endoproteinase restriction digests of human topoisomerase II alpha was identical for Ki-S1-antibody and peptide-antibodies directed against residues 1512 to 1530 but different for peptide-antibodies directed against residues 1 to 15. The Rf values of the smallest fragment commonly recognized by Ki-S1 antibody and the carboxy terminus-specific peptide-antibody place the Ki-S1 epitope within the last 495 carboxyl-terminal amino acid residues of topoisomerase II alpha.

Intranuclear distribution of DNA topoisomerase II and chromatin

Domain-specific anti-Drosophila DNA topoisomerase II antibodies were generated, affinity purified and used for confocal laser scanning immunofluorescence microscopy. Except for the nucleolus, DNA topoisomerase II is distributed throughout interphase nuclei. In adult accessory glands as well as third instar larval neural ganglion and imaginal disk nuclei, DNA topoisomerase II shows areas of co-localization with chromatin adjacent to areas of extrachromosomal distribution. These observations made in a variety of tissues under different fixation conditions and with a number of molecular probes support the notion that DNA topoisomerase II is a component of a substantially extrachromosomal network that functions to organize interphase chromatin within nuclei.

IFN-beta inhibition of etoposide resistance acquisition in vitro: studies using a human glioblastoma cell line

The inhibition by IFN-beta of acquired resistance to the epipodophillotoxin etoposide was studied using a human glioblastoma cell line, T98G. T98G cells were exposed to either etoposide alone or both etoposide and IFN-beta, and after subculture, the same two series of drug exposure were repeated. Degree of level of resistance was tested by the response of the cells to etoposide and changes in their DNA histograms. Furthermore, topoisomerase II in each set of cells was subjected to fluorescence staining with monoclonal anti-topoisomerase II antibody, and the amount of fluorescence was measured by flow cytometry. Secondary etoposide exposure showed less cytotoxicity when the first exposure was to etoposide alone. In contrast, the cytotoxicity was almost the same as that after the first exposure when IFN-beta was added. Resistance to etoposide may result from qualitative or quantitative alterations in the target enzyme, topoisomerase II. The present results show that resistant cells have less topoisomerase II than sensitive cells, suggesting that IFN-beta inhibits the acquisition of resistance to etoposide by suppressing the alteration in topoisomerase II. The inhibition of acquired resistance to etoposide by IFN-beta suggests that continuous and repeated chemotherapy for glioblastoma and other malignant tumors may be clinically advantageous.

Immunogold localization of GyrA and GyrB proteins in Escherichia coli

Immunogold preparations of Escherichia coli, using anti-GyrA and anti-GyrB antibodies to the subunits of DNA gyrase, showed clear labelling with both secondary antibody and protein A-gold conjugates. Both proteins were located mainly in the cytoplasm, with typically less than 10% in the nucleoid. This partitioning of gyrase proteins between nucleoid and cytoplasm was nonrandom and was consistently observed for a range of different cell preparations. Total gold particle counts were highly variable but suggested levels of at least 1000-3000 molecules per cell for both GyrA and GyrB. Sequential treatment with both anti-GyrA and anti-GyrB monoclonal antibodies resulted in simultaneous labelling of both proteins and revealed no clear association between the two groups of molecules. Treatment of cells with chloramphenicol caused marked changes in nucleoid conformation, but no reduction in cytoplasmic labelling of gyrase proteins. On the assumption that gyrase complexes within the nucleoid are not differentially masked from the monoclonal antibodies, the results obtained in this study suggest that most of the gyrase proteins are not associated with either central nucleoid DNA or cytoplasmic loops of peripheral single-stranded DNA, but are distributed randomly throughout the cytoplasm.