Nuclear Matrix-associated Proteins Research Articles

Fatty acids produced by the gut microbiota dampen host inflammatory responses by modulating intestinal SUMOylation

ABSTRACT The gut microbiota produces a wide variety of metabolites, which interact with intestinal cells and contribute to host physiology. The effect of gut commensal bacteria on host protein SUMOylation, an essential ubiquitin-like modification involved in various intestinal functions, remains, however, unknown. Here, we show that short chain fatty acids (SCFAs) and branched chain fatty acids (BCFAs) produced by the gut microbiota increase protein SUMOylation in intestinal cells in a pH-dependent manner. We demonstrate that these metabolites inactivate intestinal deSUMOylases and promote the hyperSUMOylation of nuclear matrix-associated proteins. We further show that BCFAs inhibit the NF-κB pathway, decrease pro-inflammatory cytokine expression, and promote intestinal epithelial integrity. Together, our results reveal that fatty acids produced by gut commensal bacteria regulate intestinal physiology by modulating SUMOylation and illustrate a new mechanism of dampening of host inflammatory responses triggered by the gut microbiota.

SATB2 drives glioblastoma growth by recruiting CBP to promote FOXM1 expression in glioma stem cells.

Nuclear matrix‐associated proteins (NMPs) play critical roles in regulating chromatin organization and gene transcription by binding to the matrix attachment regions (MARs) of DNA. However, the functional significance of NMPs in glioblastoma (GBM) progression remains unclear. Here, we show that the Special AT‐rich Binding Protein‐2 (SATB2), one of crucial NMPs, recruits histone acetyltransferase CBP to promote the FOXM1‐mediated cell proliferation and tumor growth of GBM. SATB2 is preferentially expressed by glioma stem cells (GSCs) in GBM. Disrupting SATB2 markedly inhibited GSC proliferation and GBM malignant growth by down‐regulating expression of key genes involved in cell proliferation program. SATB2 activates FOXM1 expression to promote GSC proliferation through binding to the MAR sequence of FOXM1 gene locus and recruiting CBP to the MAR. Importantly, pharmacological inhibition of SATB2/CBP transcriptional activity by the CBP inhibitor C646 suppressed GSC proliferation in vitro and GBM growth in vivo. Our study uncovers a crucial role of the SATB2/CBP‐mediated transcriptional regulation in GBM growth, indicating that targeting SATB2/CBP may effectively improve GBM treatment.

The significance of BLCA-4 in early diagnosis and postoperative monitoring of tumor recurrence in patients with bladder cancer

Objective To investigate the clinical significance of urinary bladder cancer specific nuclear matrix protein-4 (BLCA-4) for the diagnosis of bladder cancer and postoperative monitoring of bladder cancer recurrence. Methods From February 2012 to January 2016 in our hospital 87 patients with bladder cancer pathology confirmed cases (bladder cancer group), 30 patients with urinary tract benign lesions (benign group) and 30 cases of normal healthy people (control group), and the level of BLCA-4 in urine of three groups and recurrence 24 months postoperatively were detected. One month, 6 months and 24 months before and after surgery, the levels of urinary BLCA-4 were compared. Results Preoperative urine BLCA-4 level of bladder cancer group was significantly higher than that of the benign group and healthy group, the difference was statistically significant (P<0.05). The level of BLCA-4 in benign lesion in urine was significantly higher than that of healthy group (P<0.05). The sensitivity of urine BLCA-4 level in the differential diagnosis of bladder cancer was 95.00% and the specificity was 96.67%, the rate of misdiagnosis 5.00%, the misdiagnosis rate was 3.33%, the area under the ROC curve of AUC value consistency was 0.949, urine BLCA-4 level in the differential diagnosis of bladder cancer and the pathological results was 0.916. The recurrence of postoperative BLCA-4 level 6 months and 24 months in the urine was significantly higher than that for the non-recurrence group (P<0.05). Conclusions BLCA-4 level of urine in the differential diagnosis of bladder cancer has a certain clinical value, postoperative monitoring is conducive to the early detection of postoperative recurrence. Key words: Urinary Bladder Neoplasms; Nuclear Matrix-Associated Proteins; Neoplasm Recurrence, Local

FUS interacts with nuclear matrix-associated protein SAFB1 as well as Matrin3 to regulate splicing and ligand-mediated transcription.

FUS (Fused-in-Sarcoma) is a multifunctional DNA/RNA binding protein linked to familial amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD). Since FUS is localized mainly in the nucleus with nucleo-cytoplasmic shuttling, it is critical to understand physiological functions in the nucleus to clarify pathogenesis. Here we report a yeast two-hybrid screening identified FUS interaction with nuclear matrix-associated protein SAFB1 (scaffold attachment factor B1). FUS and SAFB1, abundant in chromatin-bound fraction, interact in a DNA-dependent manner. N-terminal SAP domain of SAFB1, a DNA-binding motif, was required for its localization to chromatin-bound fraction and splicing regulation. In addition, depletion of SAFB1 reduced FUS’s localization to chromatin-bound fraction and splicing activity, suggesting SAFB1 could tether FUS to chromatin compartment thorough N-terminal DNA-binding motif. FUS and SAFB1 also interact with Androgen Receptor (AR) regulating ligand-dependent transcription. Moreover, FUS interacts with another nuclear matrix-associated protein Matrin3, which is muted in a subset of familial ALS cases and reportedly interacts with TDP-43. Interestingly, ectopic ALS-linked FUS mutant sequestered endogenous Matrin3 and SAFB1 in the cytoplasmic aggregates. These findings indicate SAFB1 could be a FUS’s functional platform in chromatin compartment to regulate RNA splicing and ligand-dependent transcription and shed light on the etiological significance of nuclear matrix-associated proteins in ALS pathogenesis.

Rapid detection of bladder cancer using a point-of-care nuclear matrix protein 22 BladderChek control kit: a multicenter clinical trial

Objective To evaluate the clinical significance of nuclear matrix protein 22 (NMP22) test in rapid diagnosis of bladder cancer.Methods From February 2009 to November 2011,803 patients and 200 healthy individuals were included in this multicenter study from four urology centers in China.They provided a urine sample for test of NMP22 protein using a point-of-care NMP22 BladderChek control kit (colloidal gold method).All tests were evaluated in a blinded fashion.Patients were divided into three groups.Group 1 included 392 patients of bladder cancer; group 2 included 411 patients who had benign urinary disease with non-bladder cancer history or non-bladder cancer; group 3 included 200 healthy individuals.The sensitivity and specificity of NMP22 test were analyzed compared with pathologic results using Pearson Chi-square test.Results The overall sensitivity and specificity of the NMP22 test were 69.6％ (273/392,95％ CI 64.9％-74.0％) and 84.9％ (519/611,95％CI 81.1％-87.6％),respectively.In group 1,337 patients had pathologic stage data,and the sensitivities of the NMP22 test for each stage were Ta-T1 69.6％ (165/237) and T2-T4 82.0％ (82/100),respectively; 322 patients had pathologic grade data,and the sensitivities for each grade were G1 60.5％ (72/119),G2 66.2％ (47/71) and G3 90.9％ (120/132),respectively.The specificities for patients of benign urinary disease,of non-bladder cancer history or nonbladder cancer and healthy individuals were 87.8％ (324/369),69.0％ (29/42) and 97.5％ (195/200),respectively.Conclusion NMP22 BladderChek control kit had high sensitivity and specificity in detection of bladder cancer,and it can be used in early detection and rapid diagnosis of bladder cancer. Key words: Nuclear matrix-associated proteins; Urinary bladder neoplasms; Diagnosis; Reagent kits, diagnostic; Multicenter studies

Relationship between content of hepatocyte growth factor and nuclear matrix protein 22 in urine and the stage and grade of bladder uroepithelium carcinoma

：Objective To evaluatethe relationship of the hepatocyte growth factor (HGF) and the nuclear matrix protein 22(NMP22) in urine and the stage and grade of bladder uroepithelium carcinoma.Methods Atotal of 48 post-operative patients (males 39, females 9) with bladder cancer enrolled inthis study were perfused with THP. The voided urine of all the patients before and 6months after perfusion were recovered selectively. HGF and NMP22 ELISA kits were used todetect bladder cancer. Results The recurrence rate was 12.5 %. The HGF level had positivecorrelation with the stage and grade of bladder uroepithelium carcinoma (P ＜0.05). The NMP22 level hadpositive correlation with the grade of bladder cancer. The sensitivity and specificity ofHGF, NMP22 and cytology were 100 % (6/6), 83.3 % (5/6), 66.7 %(4/6) and 61.9 % (26/42),57.1% (24/42), 97.6 % (41/42), respectively. Conclusion The HGF and NMP22 are bothvaluable tumor markers in the urine of bladder uroepithelium carcinoma. They have intimaterelation with the stage and grade of bladder uroepithelium carcinoma. Hence combined withcytology, they could be selected as the significance level of early screening anddiagnosing. Key words: Urinary bladder neoplasms; Hepatocyte growth factor; ,Nuclear matrix-associated proteins

SAFB1 interacts with and suppresses the transcriptional activity of p53

A significant amount of nuclear p53 is found associated with the nuclear matrix in cells that were exposed to genotoxic stress. In this study we identified Scaffold attachment factor B1 (SAFB1), a nuclear matrix-associated protein that binds the scaffold or matrix attachment regions (S/MARs) of genomic DNA, as a novel p53-interacting protein. SAFB1 was able to associate with p53 through its C-terminal domain, while significant co-localization of the two proteins was observed in cells treated with 5-fluorouracil or mithramycin. Binding of p53 to SAFB1 had a significant functional outcome, since SAFB1 was shown to suppress p53-mediated reporter gene expression. These data suggest that nuclear matrix-associated proteins may play a critical role in regulating p53 localization and activity. Structured summaryp53physically interacts with SRPK1a: shown by two hybrid (view interaction)p53physically interacts with SRPK1a: shown by pull down (view interaction)p53physically interacts with SRPK1a: shown by anti bait coimmunoprecipitation (view interaction)p53physically interacts with SRPK1a: shown by anti tag coimmunoprecipitation (view interaction)SAFB1physically interacts with p53: shown by pull down (view interactions 1, 2)SAFB1physically interacts with p53: shown by anti bait coimmunoprecipitation (view interactions 1, 2)SAFB1 and p53colocalize: shown by fluorescence microscopy (view interaction)SAFB2physically interacts with p53: shown by pull down (view interaction)

Polypurine-repeat-containing RNAs: a novel class of long non-coding RNA in mammalian cells

In higher eukaryotic cells, long non-protein-coding RNAs (lncRNAs) have been implicated in a wide array of cellular functions. Cell- or tissue-specific expression of lncRNA genes encoded in the mammalian genome is thought to contribute to the complex gene networks needed to regulate cellular function. Here, we have identified a novel species of polypurine triplet repeat-rich lncRNAs, designated as GAA repeat-containing RNAs (GRC-RNAs), that localize to numerous punctate foci in the mammalian interphase nuclei. GRC-RNAs consist of a heterogeneous population of RNAs, ranging in size from ~1.5 kb to ~4 kb and localize to subnuclear domains, several of which associate with GAA.TTC-repeat-containing genomic regions. GRC-RNAs are components of the nuclear matrix and interact with various nuclear matrix-associated proteins. In mitotic cells, GRC-RNAs form distinct cytoplasmic foci and, in telophase and G1 cells, localize to the midbody, a structure involved in accurate cell division. Differentiation of tissue culture cells leads to a decrease in the number of GRC-RNA nuclear foci, albeit with an increase in size as compared with proliferating cells. Conversely, the number of GRC-RNA foci increases during cellular transformation. We propose that nuclear GRC-RNAs represent a novel family of mammalian lncRNAs that might play crucial roles in the cell nucleus.

Large T Antigen Promotes JC Virus Replication in G2-arrested Cells by Inducing ATM- and ATR-mediated G2 Checkpoint Signaling

Large T antigen (TAg) of the human polyomavirus JC virus (JCV) possesses DNA binding and helicase activities, which, together with various cellular proteins, are required for replication of the viral genome. We now show that JCV-infected cells expressing TAg accumulate in the G(2) phase of the cell cycle as a result of the activation of ATM- and ATR-mediated G(2) checkpoint pathways. Transient transfection of cells with a TAg expression vector also induced G(2) checkpoint signaling and G(2) arrest. Analysis of TAg mutants with different subnuclear localizations suggested that the association of TAg with cellular DNA contributes to the induction of G(2) arrest. Abrogation of G(2) arrest by inhibition of ATM and ATR, Chk1, and Wee1 suppressed JCV genome replication. In addition, abrogation of the G(2)-M transition by Cdc2 depletion disabled Wee1 depletion-induced suppression of JCV genome replication, suggesting that JCV replication is facilitated by G(2) arrest resulting from G(2) checkpoint signaling. Moreover, inhibition of ATM and ATR by caffeine suppressed JCV production. The observation that oligodendrocytes productively infected with JCV in vivo also undergo G(2) arrest suggests that G(2) checkpoint inhibitors such as caffeine are potential therapeutic agents for JCV infection.

Glutamate receptor signaling pathway in melanoma cells and its effect on cytoskeleton protein.

Objective To investigate the effects of glutamate receptor signaling on melanoma cell dendrite morphology and cytoskeleton protein. Methods A metastatic human malignant melanoma cell line WM451LU was cultured and transfected by recombinant adenovirus vector carrying a cDNA encoding microtubule-associated protein 2a (MAP2a). MK-801, an antagonist of N-methyl-D-aspartate receptor (NMDAR), and CPCCOEt, an antagonist of metabotropie glutamate receptor 1 (mGluR1), were used to treat transfected or untrausfeeted WM451LU cells. Confocal microscopy and three dimensional atomic force microscopy were used to assess subcellular location of NMDAR2A, mGluR1 and MAP2a as well as the dis-tribution of α-tubulin in and dendrite morphology of WM451LU cells. The proliferation of WM451LU cells was estimated by cell survival growth curve. Results Confocal laser microscopy revealed that NMDAR2A, mGluRl and MAP2a were mainly co-localized in melanoma cell dendrites. Both MK-801 and CPCCOEt increased the density of microtubules in cell dendrites and dendritic branching of WM451LU cells, and both effects of MK-801 and CPCCOEt were enhanced by the expression of MAP2a. Furthermore, the proliferation of WM451LU cells was significantly inhibited by MK-801 of 100 μmol/L and CPCCOEt of 10 μmol/L. Conclusions In melanoma cells, glutamate receptors may participate in the development of dendrites, and anta- gonists of glutamate receptors could inhibit the proliferation of melanoma cells. Key words: Melanoma; Dendrite; Receptors, glutamate; Nuclear matrix-associated proteins

Ret Finger Protein: An E3 Ubiquitin Ligase Juxtaposed to the XY Body in Meiosis

During prophase I of male meiosis, the sex chromosomes form a compact structure called XY body that associates with the nuclear membrane of pachytene spermatocytes. Ret Finger Protein is a transcriptional repressor, able to interact with both nuclear matrix-associated proteins and double-stranded DNA. We report the precise and unique localization of Ret Finger Protein in pachytene spermatocytes, in which Ret Finger Protein takes place of lamin B1, between the XY body and the inner nuclear membrane. This localization of Ret Finger Protein does not seem to be associated with O-glycosylation or sumoylation. In addition, we demonstrate that Ret Finger Protein contains an E3 ubiquitin ligase activity. These observations lead to an attractive hypothesis in which Ret Finger Protein would be involved in the positioning and the attachment of XY body to the nuclear lamina of pachytene spermatocytes.

Nuclear matrix proteins and hereditary diseases

The review summarizes literature data on alterations of structure or expression of different nuclear matrix proteins in hereditary syndromes. From the point of view of involvement of nuclear matrix proteins in etiology and pathogenesis of the disease hereditary pathologies can be classified in pathologies with pathogenesis associated with defects of nuclear matrix proteins and pathologies associated to changes of the nuclear matrix protein spectrum. The first group includes laminopathies, hereditary diseases with abnormal nuclear-matrix associated proteins and triplet extension diseases associated with accumulation of abnormal proteins in the nuclear matrix. Laminopathies are hereditary diseases coupled to structural defects of the nuclear lamina. These diseases include Emery-Dreifuss muscular dystrophy, limb girdle muscular dystrophy, dilated cardiomyopathy (DCM) with conduction system disease, familial partial lipodystrophy (FPLD), autosomal recessive axonal neuropathy (Charcot-Marie-Tooth disorder type 2, CMT2), mandibuloacral dysplasia (MAD), Hutchison Gilford Progeria syndrome (HGS), Greenberg Skeletal Dysplasia, and Pelger-Huet anomaly (PHA). Most of them are due to mutations in the lamin A/C gene, one - to mutations in emerin gene, some are associated with mutations in Lamin B receptor gene. In Werner's, Bloom's, Cockayne's syndromes, Fanconi anemia, multiple carboxylase deficiency mutations in nuclear matrix protein or enzyme gene lead to deficient DNA repair, abnormal regulation of cell growth and differentiation or other specific metabolic functions. Proteins with a long polyglutamic tract synthesized in the cells of patients with dentato-rubral and pallido-luysian atrophy, myotonic dystrophy and Huntington disease interfere with transcription on the nuclear matrix. Down's syndrome is a representative of the group of diseases with altered nuclear matrix protein spectrum.

NMPdb: Database of Nuclear Matrix Proteins

The nuclear matrix (NM) is a structure resulting from the aggregation of proteins and RNA in the nucleus of eukaryotic cells; it is the ‘sticky bit’ that remains after aggressive DNAse digestion and salt extraction protocols. Owing to the important role of the NM in DNA replication, DNA transcription and RNA splicing, the expression pattern of NM proteins has become an important early indicator for numerous cancers/tumors. Recent descriptions of the NM structure distinguish between a network-like ‘internal nuclear matrix’ (INM) and a ‘nuclear shell’ that connects the INM to the inner and outer nuclear membranes. A cautious NM preparation protocol reveals a coat of proteins on top of the INM; these proteins are usually referred to as the ‘nuclear matrix-associated proteins’. Here, we describe a new database (NMPdb at http://www.rostlab.org/db/NMPdb/) that currently contains details of 398 NM proteins. We collected these data through a semi-automated analysis of over 3000 scientific articles in PubMed. We could match these 398 proteins to 302 protein sequences in UniProt or GenBank. Our NMPdb repository annotates these links along with the following annotations: organism, cell type, PubMed identifier, sequence-based predictions of structural and functional features and for some entries the explicit sequence segment that is responsible for localization (nuclear matrix targeting signal).

Nuclear Coactivator-62 kDa/Ski-interacting Protein Is a Nuclear Matrix-associated Coactivator That May Couple Vitamin D Receptor-mediated Transcription and RNA Splicing

Nuclear coactivator-62 kDa/Ski-interacting protein (NCoA62/SKIP) is a putative vitamin D receptor (VDR) and nuclear receptor coactivator protein that is unrelated to other VDR coactivators such as those in the steroid receptor coactivator (SRC) family. The mechanism through which NCoA62/SKIP functions in VDR-activated transcription is unknown. In the present study, we identified a nuclear localization sequence in the COOH terminus of NCoA62/SKIP and showed that NCoA62/SKIP was targeted to nuclear matrix subdomains. Chromatin immunoprecipitation studies revealed that endogenous NCoA62/SKIP associated in a 1,25-dihydroxyvitamin D3-dependent manner with VDR target genes in ROS17/2.8 osteosarcoma cells. A cyclic pattern of promoter occupancy by VDR, SRC-1, and NCoA62/SKIP was observed, with NCoA62/SKIP entering these promoter complexes after SRC-1. These studies provide strong support for the proposed role of NCoA62/SKIP as a VDR transcriptional coactivator, and they indicate that key mechanistic differences probably exist between NCoA62/SKIP and SRC coactivators. To explore potential mechanisms, NCoA62/SKIP-interacting proteins were purified from HeLa cell nuclear extracts and identified by mass spectrometry. The identified proteins represent components of the spliceosome as well as other nuclear matrix-associated proteins. Here, we show that a dominant negative inhibitor of NCoA62/SKIP (dnNCoA62/SKIP) interfered with appropriate splicing of transcripts derived from 1,25-dihydroxyvitamin D3-induced expression of a growth hormone minigene cassette. Taken together, these data show that NCoA62/SKIP has properties that are consistent with those of nuclear receptor coactivators and with RNA spliceosome components, thus suggesting a potential role for NCoA62/SKIP in coupling VDR-mediated transcription to RNA splicing.

PRb2/p130 and p107 control cell growth by multiple strategies and in association with different compartments within the nucleus.

It has been recently reported that retinoblastoma family proteins suppress cell growth by regulating not only E2F-dependent mRNA transcription but also rRNA and tRNA transcription and, through HDAC1 recruitment, chromatin packaging. In the present study we report data showing that these various control strategies are correlated, at least in part, with nuclear compartmentalization of retinoblastoma proteins. In a first series of experiments, we showed that pRb2/p130 and p107 are not evenly distributed within the nucleus and that cell cycle-dependent binding with E2F4 changes also as a function of their subnuclear localization. Namely, in the nucleoplasm pRb2/p130-E2F4 complexes are more numerous during G0/G1 while in the nucleolus they increase in S phase. Partially different functions for p107 are suggested since p107-E2F4 complexes in the nucleoplasm are more numerous is S phase with respect to G0/G1 and no cell cycle change is observed in the nucleolus. In a second series of experiments we showed that pRb2/p130, p107, E2F4, and pRb2/p130-HDAC1 complexes are all inner nuclear matrix-associated proteins and localize to sites different from pRb/p105 ones. We provide further evidence of multiple and partially distinct retinoblastoma protein family functional roles during cell cycle. Moreover, our data support emerging evidence for functional interrelationships between nuclear structure and gene expression.

The protein composition of the hepatocyte nuclear matrix is differentiation-stage specific.

The protein composition of hepatocyte nuclear matrices was examined in rats from the 16th day of gestation to 75 days after birth (adult). An overall increase in size of the nuclear matrix was accompanied by quantitative and qualitative changes in its protein content. Quantitative changes of the major proteins of the peripheral lamina surrounding the isolated nuclear matrix were detected. By Western analysis we established that in pre- and postnatal nuclear matrices the relative concentrations of lamin C were greater than lamin A. After birth, the relative concentrations of both lamins progressively increased. In the adult nuclear matrix, the concentration of lamin A was greater than lamin C. In contrast, the relative concentrations of lamin B remained unchanged throughout development and growth. The relative concentrations of two nuclear matrix-associated regulatory proteins studied changed with development and growth: transcription factor C/EBPalpha isoforms, which were detected during the gestation period, increased notably after the first postnatal day, attaining a maximum at the adult stage; the high concentrations of the proliferating cell nuclear antigen (PCNA) perceptibly decreased after the 21st prenatal day. Changes in the composition of the nuclear matrix protein suggest that this structure coordinates nuclear functioning during cell differentiation.

Nuclear matrix associated DNA-binding proteins of ocular lens epithelial cells.

Association of transcription factors with the nuclear matrix represents a mechanism by which nuclear architecture may influence transcriptional control of gene expression. This investigation examines nuclear matrix associated proteins (NMP's) isolated from ocular lens epithelial cells by monitoring DNA binding activities using consensus oligonucleotides recognized by the transcription factors YY1, AML-1, AP-1, SP-1 and ATF. The nuclear matrix fractions tested included an immortilized human lens epithelial cell line containing the SV40 large T-antigen, and two mouse lens epithelial cell lines derived from either a normal mouse or a cataract mouse. A rabbit epidermal epithelial cell line and HeLa cells were also included in this study for comparison. The data from these experiments reveal that ubiquitously represented and tissue restricted regulatory proteins are associated with nuclear matrix of lens epithelial cells. The functional significance of the nuclear matrix association of these transcription factors remains to be determined. However, our findings raise the possibility that the transcription factors associated with the nuclear matrix could have specific roles in gene regulation and eye tissue development.

DNA supercoiling changes and nuclear matrix-associated proteins: Possible role in oncogene-mediated radioresistance

Purpose : Transfection with either H- ras or H- ras and c- myc has been shown to confer radioresistance in rat embryonal cells (REC). REC primary, transfected with either c- myc or cotransfected with c- myc and H- ras (in ascending order of radioresistance and tumorigenicity), were used as an in vitro model system to determine if nuclear matrix-mediated higher order DNA organization contributes to oncogene-mediated radioresistance. Methods and Materials : DNA damage induction and repair were measured by the alkaline and neutral filter elution assays. Analysis of the ability of DNA loop domains to undergo supercoiling changes in the presence of radiation-induced damage was determined by the fluorescent halo assay 9FHA). Because DNA loops are organized by the nuclear matrix (NM), a study of NM-associated proteins by high resolution two0dimensional gel electrophoresis was performed. Results: Induction and repair rates of DNA single- and double-strand breaks were similar for the relatively radiosensitive c- myc transfected and the radioresistant c- myc + H- ras transfected cells. However, the degree of inhibition of DNA supercoil rewinding in the presence of radiation-induced damage was less in the radioresistant cells and was inversely correlated with survival. A. progressive loss of NM-associated proteins was observed, which correlated with increasing radioresistance and tumorigenicity in these cell lines. In addition, some protein changes were consistent with the possibility that these changes could be involved in DNA anchoring. Conclusions : Increased radioresistance associated with increasing tumorigenicity in these oncogene-transfected cell lines could be due to changes in NM-mediated DNA organization, possibly via differences in NM protein composition that occur following oncogenic transfection.

Nuclear Matrix and the Cell Cycle

The facts that the nuclear matrix represents a structural framework of the cell nucleus and that nuclear events, such as DNA replication, transcription, and DNA repair, are associated with this skeletal structure suggest that its components are subject to cell cycle-regulatory mechanisms. Cell cycle regulation has been shown for nuclear lamina assembly and disassembly during mitosis and chromatin reorganization. Little attention has so far been paid to internal nuclear matrix proteins and matrix-associated proteins with respect to the cell cycle. This survey attempts to summarize available data and presents experimental evidence that important metabolic functions of the nucleus are regulated by the transient, cell cycle-dependent attachment of enzymes and regulatory proteins to the nuclear matrix. Results on thymidine kinase and RNA polymerase during the synchronous cell cycle of Physarum polycephalum demonstrate that reversible binding to the nuclear matrix represents an additional level of regulation for nuclear processes.

Avian nuclear matrix proteins bind very tightly to cellular DNA of the .beta.-globin gene enhancer in a tissue-specific fashion

We have previously shown that a cloned 480 bp DNA fragment that spans the 3'-enhancer region of the avian beta-globin gene cluster can become very tightly, perhaps covalently, bound to protein in avian nuclear matrices in vitro [Zenk et al. (1990) Biochemistry 29, 5221-5226]. This binding was not tissue-specific and was probably not mediated by topoisomerase enzymes. In the present study, we have examined avian nuclear matrices (or scaffolds) for the presence of very tight cellular DNA-protein complexes in the region of the beta-globin gene enhancer and of several other avian genes. Nuclear matrices were prepared by both high- and low-salt methods, and protein-DNA complexes were isolated by SDS/K+ precipitation after restriction enzyme digestion. In adult reticulocytes, up to 30% of the intact 3800 bp HindIII-EcoRI fragment that encompasses the beta-globin enhancer element may be very tightly bound to nuclear matrix protein. In adult avian thymus nuclei, the beta-globin enhancer is neither matrix-associated nor tightly bound to protein. In contrast, a 5.0-kb HindIII fragment of the malic enzyme gene is very tightly bound to nuclear matrix-associated protein in thymus cells, but not reticulocytes. The malic enzyme gene is active in thymus cells, and not in reticulocytes. These results suggests that certain regions of cellular DNA are very tightly, perhaps covalently, attached to nuclear matrix-associated proteins. Attachment follows a tissue-specific pattern that is associated with transcriptional activity.