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PubMed1993

Biochemical and morphological characterization of the nuclear matrix during the synchronous cell cycle of Physarum polycephalum.

We have investigated biochemical and ultrastructural aspects of the nuclear matrix during the naturally synchronous cell cycle of Physarum polycephalum. The morphology of the in situ nuclear matrix exhibited significant cell cycle changes as revealed by electron microscopic examination, especially during the progression of nuclei through mitosis and S-phase. In mitosis the interchromatin matrix was found to be retracted to the nuclear periphery; during S-phase this interchromatin matrix gradually resembled, concomitant with the reconstruction of a nucleolar remnant structure. During the G2-period no significant changes in matrix morphology were observed. The pattern of nuclear matrix proteins was invariant during the cell cycle; no cycle phase-specific proteins could be detected. In vivo labelling of plasmodia with [35S]methionine/cysteine showed that only a few proteins are synthesized and assembled into nuclear matrix structures in a cell cycle-dependent way; the majority of proteins were synthesized almost continuously. This was also shown for nuclear lamins homologues. In contrast to bulk nuclear histones, those histones that remain tightly bound to the nuclear matrix were synthesized and assembled into nuclear structures in the very first hour of S-phase; assembly was terminated in mid-S-phase, indicating that nuclear matrix-bound chromatin is replicated early in S-phase. Comparison of the acetylation pattern of matrix-bound histone H4 with bulk nuclear H4 revealed a largely elevated acetate content of matrix H4. The percentage of acetylated subspecies was entirely different from that in bulk nuclear H4, indicating that matrix-associated histones represent a subpopulation of nuclear histones with distinct properties, reflecting specific structural requirements of matrix-attached chromatin.

Acetylation↗
PubMed2002

Changes of nuclear matrix in long-term culture of limbal epithelial cells.

PURPOSE: This study was undertaken to investigate the changes of nuclear matrix in long-term culture of rabbit limbal epithelial cells. METHODS: Epithelial cells outgrown from limbal basal epithelium were serially cultivated. Nuclear matrices of early and late passages were extracted for morphologic study and protein analysis by two-dimensional gel electrophoresis and immunoblotting. RESULTS: Differential growth and changes in morphology were observed in limbal epithelial cells of early and late passages. Cytokeratin type 3 was expressed in cells of later passages, indicating corneal cell differentiation during the long-term culture. These cells also showed reduced density of nuclear matrix fibrils and thinning of nuclear lamina. They were shown by two-dimensional gel electrophoresis to have lost most nuclear matrix proteins, including lamin A/C and proliferating cell nuclear antigen. However, five new protein entities were also expressed. CONCLUSION: The nuclear matrix appeared to change along with limbal epithelial cell differentiation in culture. Whether such changes may affect the growth and viability of limbal cells after transplantation requires in vivo tissue analysis.

Animals↗
PubMed1990

Tissue specificity of the hormonal response in sex accessory tissues is associated with nuclear matrix protein patterns.

The DNA of interphase nuclei have very specific three-dimensional organizations that are different in different cell types, and it is possible that this varying DNA organization is responsible for the tissue specificity of gene expression. The nuclear matrix organizes the three-dimensional structure of the DNA and is believed to be involved in the control of gene expression. This study compares the nuclear structural proteins between two sex accessory tissues in the same animal responding to the same androgen stimulation by the differential expression of major tissue-specific secretory proteins. We demonstrate here that the nuclear matrix is tissue specific in the rat ventral prostate and seminal vesicle, and undergoes characteristic alterations in its protein composition upon androgen withdrawal. Three types of nuclear matrix proteins were observed: 1) nuclear matrix proteins that are different and tissue specific in the rat ventral prostate and seminal vesicle, 2) a set of nuclear matrix proteins that either appear or disappear upon androgen withdrawal, and 3) a set of proteins that are common to both the ventral prostate and seminal vesicle and do not change with the hormonal state of the animal. Since the nuclear matrix is known to bind androgen receptors in a tissue- and steroid-specific manner, we propose that the tissue specificity of the nuclear matrix arranges the DNA in a unique conformation, which may be involved in the specific interaction of transcription factors with DNA sequences, resulting in tissue-specific patterns of secretory protein expression.

Androgen-Binding Protein↗
PubMed1980

The specific binding of estrogens and androgens to the nuclear matrix of sex hormone responsive tissues.

Specific sex steroid hormone binding sites have been identified in a discrete nuclear subfraction that is chromatin-depleted and salt-insoluble. This structure, referred to as the nuclear matrix, contains a residual pore complex-lamina, remnants of an internal network, and a residual nucleolus. The nuclear matrix of an estrogen-responsive tissue (chicken liver) and of an androgen target tissue (rat ventral prostate) contains binding sites for estradiol and dihydrotestosterone, respectively. The binding of steroids to these sites is saturable, high affinity (Kd approximately 10(-9) M), steroid-specific (liver binds estrogens, prostate binds androgens), and heat- and pronase-sensitive. The levels of these matrix-associated steroid binding sites change in response to manipulation of the hormonal status of the animal. Thus, the liver nuclear matrix of laying hens contains a significant number of estradiol binding sites, whereas that of untreated chicks or roosters contains very few sites. Treatment of chicks or roosters with a dose of estrogen that stimulates the liver to synthesize vitellogenin leads to a marked increase in the number of estradiol binding sites associated with the liver nuclear matrix. In the rat ventral prostate, the nuclear matrix-associated binding sites for dihydrotestosterone that are present in intact adults essentially disappear within 24 h after castration. Androgen replacement therapy restores, within 1 h, the number of matrix binding sites for dihydrotestosterone to normal levels. Inhibitors of proteolysis (phenylmethylsulfonyl fluoride) are essential for the protection of these androgen binding sites. Conditions that lead to the solubilization of the internal network material of the nuclear matrix also result in the extraction of 70 to 85% of the specific dihydrotestosterone binding sites from the matrix; a limited number of binding sites still remain associated with the peripheral lamina.

Animals↗
PubMed1987

Pre-mRNA splicing and the nuclear matrix.

We examined the relationship between pre-mRNA splicing and the nuclear matrix by using an in vivo system that we have developed. Plasmids containing the inducible herpesvirus tk gene promoter linked to an intron-containing segment of the rabbit beta-globin gene were transfected into HeLa cells, and then the promoter was transactivated by infection with a TK- virus. Northern analysis revealed that the globin pre-mRNA and all its splicing intermediates and products are associated with the nuclear matrix prepared from such transfected cells. When the nuclear matrix was incubated with a HeLa cell in vitro splicing extract in the presence of ATP, the amount of matrix-associated precursor progressively decreased without a temporal lag in the reaction, with a corresponding increase in free intron lariat. Thus, most of the events of the splicing process (endonucleolytic cuts and branching) occur in this in vitro complementation reaction. However, ligation of exons cannot be monitored in this system because of the abundance of preexisting mature mRNA. Since the matrix is not a self-splicing entity, whereas the in vitro splicing system cannot process efficiently deproteinized matrix RNA, we conclude from our in vitro complementation results (which can be reproduced by using micrococcal nuclease-treated splicing extract) that the nuclear matrix preparation retains parts of preassembled ribonucleoprotein complexes that have the potential to function when supplemented with soluble factors (presumably other than most of the small nuclear ribonucleoproteins known to participate in splicing) present in the HeLa cell extract.

Animals↗
PubMed2000

NP/NMP4 transcription factors have distinct osteoblast nuclear matrix subdomains.

The mechanisms underlying the coupling of type I collagen and matrix metalloproteinase (MMP) expression to cell structure and adhesion are poorly understood. We propose that nuclear matrix architectural transcription factors link cell structure and transcription via their association with nuclear matrix subdomains and by their capacity for altering promoter geometry. NP/NMP4 are nuclear matrix proteins that contain from five to eight Cys(2)His(2) zinc fingers. Some NP/NMP4 isoforms bind to the rat type I collagen alpha1(I) polypeptide chain promoter in the manner of architectural transcription factors and alter basal transcription in osteoblast-like cells (Thunyakitpisal et al. in review). Certain isoforms of NP/NMP4 are identical to CIZ, Cas-interacting zinc finger protein, a nucleocytoplasmic shuttling protein that associates with focal adhesions and regulates MMP expression [Nakamoto et al. (2000): Mol Cell Biol 20:1649-1658]. To better understand the role of subnuclear architecture in collagen and MMP expression, we mapped the osteoblast nuclear distribution of NP/NMP4 proteins and identified the functional motifs necessary for nuclear localization and nuclear matrix targeting. Immunofluorescence microscopy was used to determine the cellular and subnuclear distribution of native NP/NMP4 proteins and green fluorescent protein (GFP)-NP/NMP4 fusion proteins in osteoblast-like cells. All GFP-NP/NMP4 fusion proteins localized to the nucleus, but accumulated in distinct nuclear matrix subdomains. The zinc finger domain was necessary and sufficient for nuclear import and matrix targeting. We conclude that the arrangement of the NP/NMP4 zinc fingers largely determines the subnuclear location of these isoforms.

Amino Acid Motifs↗
PubMed1993

Nuclear matrix association of multiple sequence-specific DNA binding activities related to SP-1, ATF, CCAAT, C/EBP, OCT-1, and AP-1.

The association of DNA binding proteins with the nuclear matrix may be related to a functional role of this subcellular structure in chromatin organization and gene regulation. In this study, nuclear matrix preparations from human HeLa S3 cervical carcinoma and rat ROS 17/2.8 osteosarcoma cells were assayed for the presence of DNA binding activities using consensus binding sequences of well-characterized transcription factors as probes. Competition analysis shows that each probe interacts with different nuclear matrix proteins in a sequence-specific manner and that DNA binding activities related to or identical with SP-1, ATF, CCAAT, C/EBP, OCT-1, and AP-1 are present in the nuclear matrix fraction of different cell types. Comparison of the relative abundance of these transcription factor binding activities in nuclear matrix and nonmatrix nuclear fractions suggests that the distribution between these two fractions is cell type specific, cell growth dependent, or independent of these biological parameters. These results are consistent with the postulated role of the nuclear matrix in transcriptional regulation of gene expression.

Activating Transcription Factors↗
PubMed2005

Nuclear matrix binding regulates SATB1-mediated transcriptional repression.

Special AT-rich binding protein 1 (SATB1) originally was identified as a protein that bound to the nuclear matrix attachment regions (MARs) of the immunoglobulin heavy chain intronic enhancer. Subsequently, SATB1 was shown to repress many genes expressed in the thymus, including interleukin-2 receptor alpha, c-myc, and those encoded by mouse mammary tumor virus (MMTV), a glucocorticoid-responsive retrovirus. SATB1 binds to MARs within the MMTV provirus to repress transcription. To address the role of the nuclear matrix in SATB1-mediated repression, a series of SATB1 deletion constructs was used to determine protein localization. Wild-type SATB1 localized to the soluble nuclear, chromatin, and nuclear matrix fractions. Mutants lacking amino acids 224-278 had a greatly diminished localization to the nuclear matrix, suggesting the presence of a nuclear matrix targeting sequence (NMTS). Transient transfection experiments showed that NMTS fusions to green fluorescent protein or LexA relocalized these proteins to the nuclear matrix. Difficulties with previous assay systems prompted us to develop retroviral vectors to assess effects of different SATB1 domains on expression of MMTV proviruses or integrated reporter genes. SATB1 overexpression repressed MMTV transcription in the presence and absence of functional glucocorticoid receptor. Repression was alleviated by deletion of the NMTS, which did not affect DNA binding, or by deletion of the MAR-binding domain. Our studies indicate that both nuclear matrix association and DNA binding are required for optimal SATB1-mediated repression of the integrated MMTV promoter and may allow insulation from cellular regulatory elements.

Animals↗
PubMed2001

The nuclear matrix is a thermolabile cellular structure.

Heat shock sensitizes cells to ionizing radiation, cells heated in S phase have increased chromosomal aberrations, and both Hsp27 and Hsp70 translocate to the nucleus following heat shock, suggesting that the nucleus is a site of thermal damage. We show that the nuclear matrix is the most thermolabile nuclear component. The thermal denaturation profile of the nuclear matrix of Chinese hamster lung V79 cells, determined by differential scanning calorimetry (DSC), has at least 2 transitions at Tm = 48 degrees C and 55 degrees C with an onset temperature of approximately 40 degrees C. The heat absorbed during these transitions is 1.5 cal/g protein, which is in the range of enthalpies for protein denaturation. There is a sharp increase in 1-anilinonapthalene-8-sulfonic acid (ANS) fluorescence with Tm = 48 degrees C, indicating increased exposure of hydrophobic residues at this transition. The Tm = 48 degrees C transition has a similar Tm to those predicted for the critical targets for heat-induced clonogenic killing (Tm = 46 degrees C) and thermal radiosensitization (Tm = 47 degrees C), suggesting that denaturation of nuclear matrix proteins with Tm = 48 degrees C contribute to these forms of nuclear damage. Following heating at 43 degrees C for 2 hours, Hsc70 binds to isolated nuclear matrices and isolated nuclei, probably because of the increased exposure of hydrophobic domains. In addition, approximately 25% of exogenous citrate synthase also binds, indicating a general increase in aggregation of proteins onto the nuclear matrix. We propose that this is the mechanism for increased association of nuclear proteins with the nuclear matrix observed in nuclei Isolated from heat-shocked cells and is a form of indirect thermal damage.

Animals↗
PubMed1980

Two-dimensinal gel electrophoresis of rat liver nuclear washes, nuclear matrix, and hnRNA proteins.

The proteins of rat liver cytoplasm, nuclear washes, matrix, membrane, heterogeneous nuclear (hn)RNA proteins and chromatin were examined by two-dimensional gel electrophoresis. The inclusion in the gels of six common protein standards of carefully selected molecular weight and isoelectric point allowed us to clearly follow the distribution of specific proteins during nuclear extraction. In the nuclear washes and chromatin, we observed five classes of proteins: (a) Exclusively cytoplasmic proteins, present in the first saline-EDTA wash but rapidly disappearing from subsequent washes; (b) ubiquitous proteins of 75,000, 68,000, 57,000, and 43,000 mol wt, the latter being actin, found in the cytoplasm, all nuclear washes and the final chromatin pellet; (c) proteins of 94,000, 25,000, and 20,500 mol wt specific to the nuclear washes; (d) proteins present in the nuclear washes and final chromatin, represented by species at 62,000, 55,000, 54,000, and 48,000 mol wt, primarily derived from the nuclear matrix; and (e) two proteins of 68,000 mol wt present only in the final chromatin. The major 65,000-75,000-mol wt proteins seen by one-dimensional gel electrophoresis of nuclear matrix were very heterogeneous and contained a major acidic, an intermediate, and a basic group. A single 68,000-mol wt polypeptide constituted the majority of the membrane-lamina fraction, consistent with immunological studies indicating that a distinct subset of matrix proteins occurs, associated with heterochromatin, at the periphery of the nucleus. Actin was the second major nuclear membrane-lamina protein. Two polypeptides at 36,000 and 34,000 mol wt constituted 60% of the hnRNP. Approximately 80% of the mass of the nonhistone chromosomal proteins (NHP) from unwashed nuclei is contributed by nuclear matrix and hnRNPs, and essentially the same patterns were seen with chromatin NHP. The concept of NHP being a distinct set of DNA-bound proteins is unnecessarily limiting. Many are derived from the nuclear matrix or hnRNp particles and vary in the degree to which they share different intracellular compartments.

Animals↗
PubMed1987

Cytochalasin B selectively releases ovalbumin mRNA precursors but not the mature ovalbumin mRNA from hen oviduct nuclear matrix.

Hen oviduct nuclear matrix-bound mature ovalbumin mRNA is released from the matrix in the presence of ATP, while the ovalbumin mRNA precursors remain bound to this structure. Detachment of the mature mRNA from the matrix by ATP as well as ATP-dependent efflux of mRNA from isolated nuclei were found to be inhibited by cytochalasin B. On the other hand, in the absence of ATP, cytochalasin B exclusively caused the release (and nucleocytoplasmic efflux) of the ovalbumin messenger precursors, but not of the mature mRNA. After cytochalasin B treatment, actin could be detected in the matrix supernatant. Phalloidin which stabilizes actin filaments did not cause RNA liberation in the absence of ATP, but inhibited the ATP-induced detachment of mature mRNA. RNA release was also achieved with a monoclonal antibody against actin but not with monoclonal antibodies against tubulin and intermediate filaments. These results suggest that actin-containing filaments are involved in the restriction of immature messengers to the cell nucleus.

Adenosine Triphosphate↗
PubMedDate not supplied

[Changes in protein, lipid composition, DNA- and RNA- polymerase activity of the chromatin fraction and the nuclear matrix of the rat liver in hypovitaminosis E].

E-hypovitaminosis-induced antioxidant deficiency in rats causes changes in some properties of nuclear structures of the liver cells, i.e. fractions of transcriptionally active and repressed chromatin and nuclear matrix. Changes are found in the protein spectrum of the fraction of transcriptionally active chromatin and nuclear matrix. Lipids of transcriptionally active and repressed chromatin fractions may be peroxidated when this process is stimulated in the NADPH- and ascorbate-dependent systems. In antioxidant deficiency these processes are intensified in the fractions of repressed chromatin. E-hypovitaminosis leads to changes in the fatty acid spectrum of chromatin fractions which correlated with the shifts in the process of lipid peroxidation. Antioxidant deficiency produces changes in the activities of endogenous DNA- and RNA-polymerases in chromatin fractions and in the nuclear matrix. In the fraction of the transcriptionally active liver chromatin of E-deficient animals the endogenous total DNA-polymerase activity and the activity of DNA-polymerases alpha and beta decrease, while in the fractions of repressed chromatin the total RNA-polymerase activity increases. In E-hypovitaminosis the endogenous DNA- and RNA-polymerase activities in the nuclear matrix decrease. Addition of alpha-tocopherol to the preparations of the isolated nuclear matrix results in an increase of the DNA- and RNA-polymerase activities which is more vivid in preparations made of the E-hypovitaminous animal liver.

Animals↗
PubMed1987

Protein disulfide crosslinking stabilizes a polyoma large T antigen-host protein complex on the nuclear matrix.

We have investigated the effects of intermolecular disulfide crosslinking and temperature-dependent insolubilization of nuclear proteins in vitro on the association of the polyoma large T antigen with the nuclear matrix in polyomavirus-infected mouse 3T6 cells. Nuclear matrices, prepared from polyomavirus-infected 3T6 cells by sequential extraction of isolated nuclei with 1% Triton X-100 (Triton wash), DNase I, and 2 M NaCl (high salt extract) at 4 degrees C, represented 18% of total nuclear protein. Incubation of nuclei with 1 mM sodium tetrathionate (NaTT) to induce disulfide crosslinks or at 37 degrees C to induce temperature-dependent insolubilization prior to extraction, transferred an additional 9-18% of the nuclear protein from the high salt extract to the nuclear matrix. This additional protein represented primarily an increased recovery of the same nuclear protein subset present in nuclear matrices prepared from untreated nuclei. Major constituents of chromatin including histones, hnRNP core proteins, and 98% of nuclear DNA were removed in the high salt extract following either incubation. Polyoma large T antigen was quantified in subcellular fractions by immunoblotting with rat anti-T ascites. Approximately 60-70% of the T antigen was retained in nuclei isolated in isotonic sucrose buffer at pH 7.2. Most (greater than 95%) of the T antigen retained in untreated nuclei was extracted by DNase-high salt treatment. Incubation at 37 degrees C or with NaTT transferred most (greater than 95%) of the T antigen to the nuclear matrix. T antigen solubilized from NaTT-treated matrices with 1% SDS sedimented on sucrose gradients as a large (50-S) complex. These complexes, isolated by immunoprecipitation with anti-T sera, were dissociated by reduction with 2-mercaptoethanol, and SDS-PAGE analysis revealed that T antigen was crosslinked in stoichiometric amounts to several host proteins: 150, 129, 72, and 70 kDa. These host proteins were not present in anti-T immunoprecipitates of solubilized nuclear matrices prepared from iodoacetamide-treated cells. Our results suggest that the majority of polyomavirus large T antigen in infected cells is localized to a specific subnuclear domain which is distinct from the bulk chromatin and is closely associated with the nuclear matrix.

Animals↗
PubMed1996

Anchoring of c-myc on nuclear matrix proteins in process of mouse thymic T lymphocyte proliferation induced by ConA.

Isolation and characterization of functional nuclear matrix proteins involved in DNA anchoring and gene expression is one of the major subjects of current nuclear matrix research. Southwestern blotting (DNA-protein hybridization) was applied to studying the anchoring of c-myc on the nuclear matrix proteins in mouse thymic T lymphocytes. The results showed that c-myc bound to the lamin, p34 and p36 nuclear matrix proteins specifically. In the process of mouse thymic PNA-T lymphocytes proliferation induced by ConA, the anchoring of c-myc on p34 and p36 nuclear matrix proteins changed dynamically.

Animals↗
PubMedDate not supplied

[Analysis of cellular nucleoproteins by the nucleoprotein-celite chromatography method. III. Two types of DNA-nuclear matrix interaction].

There are two types of DNA-nuclear matrix interactions in animal cells as revealed by the release of DNA from isolated nuclei by three successive gradients: NaCl, LiCl-urea and temperature. Nuclei were treated with dissociating agents while being adsorbed on the Celite columns. "Weak" DNA-matrix interactions which dissociate in 1.5 M LiCl-3 M urea at 2 degrees appear to be sensitive to ethidium bromide and resistant to exogeneous nucleases (DNAase I, DNAase II and micrococcal nuclease), to DNA-damaging agents, including alkylators and gamma-irradiation, and also to psoralen-induced cross-links. "Strong" DNA-matrix interactions proved to be very different. They dissociate in 4 M LiCl-8 M urea at approximately 90 degrees, are very sensitive to DNAase I and other nucleases, slightly sensitive to chemicals and irradiation at doses stimulating single-stranded DNA breaks, but resistant to ethidium bromide. DNA strand separation seems to be necessary prerequisite for DNA release from its "strong" complex with nuclear matrix. A model for the topological link between DNA and the nuclear matrix involved in DNA replication complex is discussed.

Animals↗
PubMed1999

Monoclonal antibody to prostate cancer nuclear matrix protein (PRO:4-216) recognizes nucleophosmin/B23.

BACKGROUND: The nuclear protein B23, nucleophosmin, is an RNA-associated nucleolar phosphoprotein reported to be more abundant in malignant and growing cells than in normal nondividing cells. We examined the levels of B23 in fresh human prostate tissue and in five human prostate cancer cell lines with monoclonal antibodies (mAb) to nucleophosmin (alpha-B23) and to human prostate cancer nuclear matrix proteins (PRO:4-216). METHODS: mAb PRO:4-216 and mAb alpha-B23 were used for protein level detection. Nuclear matrix proteins (NMPs) were prepared from prostate tumor and five human prostate cancer cell lines: LNCaP, TSU, DU145, PC-3, and PPC-1. The NMPs were run on one-dimensional and two-dimensional (2D) electrophoresis gels for Western blot analysis with the two mAbs. Histologic sections from paraffin-embedded normal and cancerous prostate tissue were stained immunohistochemically with both mAbs. RESULTS: PRO:4-216 and B23 mAbs identified a 40-kD protein (pI approximately 5.0) by Western blot analysis in the human prostate cancer cell lines and on two-dimensional blots of human prostate cancer NMPs. Immunohistochemical staining demonstrated large punctate nuclear dots in most cancer nuclei, while staining of normal tissue was less intense or absent. Predominant reactivity was of epithelial nuclei, with some minor reactivity of stromal nuclei. Red blood cells (RBCs) and white blood cells (WBCs) were routinely negative. CONCLUSIONS: PRO:4-216, previously characterized as recognizing prostate cancer nuclear matrix proteins, recognized B23/nucleophosmin. PRO:4-216 and alpha-B23 showed intense immunohistochemical staining of B23/nucleophosmin in cancer nuclei compared to adjacent normal cells in paraffin-embedded prostate tissue. This preliminary study showed the potential of B23 as a tumor marker for human prostate cancer.

Antibodies, Monoclonal↗
PubMed1988

Hyperthermia blocks DNA processing at the nuclear matrix.

The capacity of control and heated HeLa cells to process newly polymerized DNA at the nuclear matrix was measured. DNA which had been pulse-labeled with [3H]thymidine was enriched by a factor of up to 6 at the cell's nuclear matrix. During continuous exposure to [3H]thymidine at 37 degrees C this enrichment for pulse-labeled DNA was reversed with a half-time of 7 min. We interpret this processing of newly replicated DNA to be a distribution of newly polymerized DNA throughout replicon-sized nuclear DNA domains. Both processing of newly polymerized DNA at the nuclear matrix and ligation of replicon clusters into the interphase cell chromosome were halted by incubation of cells at temperatures at or above 43 degrees C. When HeLa cells were pulse-labeled during a 30-min incubation at 45 degrees C and replaced at 37 degrees C, the enrichment for 3H-labeled DNA at the nuclear matrix was reversed with an initial half-time of 4 h. The results indicate that exposure of cells to hyperthermic temperatures blocks ongoing nascent DNA processing at the nuclear matrix and results in a retardation of DNA processing in preheated cells replaced at 37 degrees C.

Carbon Radioisotopes↗
PubMed2000

Nuclear matrix proteins associated with DNA in situ in hormone-dependent and hormone-independent human breast cancer cell lines.

The nuclear matrix is a dynamic RNA-protein complex that organizes chromatin and regulates nuclear DNA metabolism. Nuclear matrix proteins informative in the diagnosis of cancer have been identified. Here, the nuclear matrix breast cancer proteins (NMBCs) cross-linked to nuclear DNA in situ with cisplatin in human breast cancer cell lines were analyzed by two-dimensional gel electrophoresis. We identified NMBCs that were differentially associated with nuclear DNA of hormone-dependent and -independent breast cancer cell lines. Three DNA cross-linked NMBCs were found to be exclusive to estrogen receptor-positive, hormone-dependent breast cancer cells, whereas two NMBCs were observed only in estrogen receptor-negative, hormone-independent breast cancer cells. Changes in these NMBCs were observed when hormone-dependent breast cancer cells became hormone independent. Furthermore, we show that the intermediate filament protein vimentin is associated with the nuclear DNA of MDA-MB-231 breast cancer cells, an estrogen receptor-negative, hormone-independent breast cancer cell line with high metastatic potential. These nuclear matrix DNA-binding proteins may play important roles in breast tumorigenesis.

Breast↗