Differential crosslinking of histones and non-histones in nuclei by cis-Pt(II)

The internalization and degradation of human copper transporter 1 following cisplatin exposure

The human copper transporter 1 (hCTR1), the major transporter responsible for copper influx, mediates one component of the cellular accumulation of cisplatin (DDP). Both copper and DDP cause rapid down-regulation of hCTR1 expression in human ovarian carcinoma cells. In this study, we investigated the mechanism of this effect using digital deconvolution microscopy and Western blot analysis of cells stained with antibodies directed at both ends of the protein. Treatment of 2008 cells with DDP in combination with inhibitors of various endosomal pathways (amiloride, cytochalasin D, nystatin, and methyl-beta-cyclodextrin) showed that hCTR1 degradation was blocked by amiloride and cytochalasin D, indicating that hCTR1 was internalized primarily by macropinocytosis. Expression of transdominant-negative forms of dynamin I and Rac showed that loss of hCTR1 was not dependent on pathways regulated by either of these proteins. DDP-induced loss of hCTR1 was blocked by the proteasome inhibitors lactacystin, proteasome inhibitor 1, and MG132. This study confirms that DDP triggers the rapid loss of hCTR1 from ovarian carcinoma cells at clinically relevant concentrations. The results indicate that DDP-induced loss of hCTR1 involves internalization from the plasma membrane by macropinocytosis followed by proteasomal degradation. Because hCTR1 is a major determinant of early DDP uptake, prevention of its degradation offers a potential approach to enhancing tumor sensitivity.

Chromosome-protein interactions in polyomavirus virions

In this work, we sought to determine whether the components of the murine polyomavirus capsid establish specific interactions with the minichromosome encapsidated into the mature viral particles by using the cis-diamminedichloroplatinum(II) cross-linking reagent. Our data indicated that VP1, but not minor capsid proteins, interacts with the viral genome in vivo. In addition, semiquantitative PCR assays performed on cross-linked DNA complexes revealed that VP1 binds to all regions of the viral genome but significantly more to the regulatory region. The implications of such an interaction for viral infectivity are discussed.

In vivo cross-linking of nm23/nucleoside diphosphate kinase to the PDGF-A gene promoter

Human isoforms A and B of nm23/nucleoside diphosphate (NDP) kinase, functionally important in development and cancer, have been reported to bind to DNA, and in particular isoform A to the PDGF-A promoter and isoform B to the c-myc promoter and to telomeric repeats. However, no direct proof of the binding in vivo has yet been obtained. To demonstrate this interaction, human erythroleukemic K562 cells were incubated with two different cross-linking reagents, formaldehyde or cis-diammine dichloro platinum H. The DNA-protein covalent complexes were isolated and analyzed by Western blotting. The positive immunochemical staining showed that in both conditions NDP kinase isoforms A and B were efficiently cross-linked to DNA in vivo. NDP kinase-linked DNA fragments obtained by immunoprecipitation, subjected to hybridization with different probes, showed a definite enrichment in the nuclease-hypersensitive silencer element of the PDGF-A promoter. No conclusive evidence was found by this technique of preferential hybridization with a nuclease-hypersensitive element of the c-myc promoter and with the telomeric TTAGGG repeats. The immunoprecipitated NDP kinase-DNA complexes are a promising material for the detection of other specific DNA sequences interacting with NDP kinase.

DNA-protein cross-linking in nuclei of immature and mature chicken erythrocytes

DNA-protein cross-linkages were formed in isolated nuclei from immature and mature chicken erythrocytes by reaction with cis-diammine dichloroplatinum. On the basis of electrophoretic behaviour, the most abundant proteins involved in the cross-linking appeared to be present also in preparations of nuclear matrix. The maturation of the erythrocyte, which is accompanied by transcriptional inactivation, leads to a decrease in the amount of DNA-interacting proteins, to a loss of proteins capable of a specific recognition of DNA sequences and, unexpectedly, to the appearence of some new DNA-protein interactions. At least three cross-linked proteins were found predominantly or exclusively in nuclei of immature cells, and three others in those of mature ones. The three DNA-bound proteins, typical of mature erythrocytes, were not found among the components of a high-salt preparation of nuclear matrix. The results obtained suggest that, in addition to the well-known histone H5 and MENT protein, these newly identified DNA-bound proteins contribute to the formation of the condensed, inactive chromatin characteristic of mature erythrocyte.

Cross-linked telomere-protein complexes from chicken erythrocyte nuclei: isolation by a new procedure

DNA-protein cross-linkages were produced in intact nuclei of chicken erythrocytes by the action of cis-diammine dichloroplatinum. The telomeric DNA-protein cross-linked complexes were then isolated by hybridization with a biotinylated oligonucleotide and selective binding on immobilized streptavidin. Two main nonhistone proteins were present in the purified complexes, migrating in SDS-gel electrophoresis with apparent molecular masses of 66 and 58 kDa, respectively. Although the identity of these two proteins is still unknown, it is significant that two proteins with similar electrophoretic behavior have been described as constituents of the human telomeric complexes. This procedure could also be applied to the isolation of DNA-protein cross-linked complexes containing any chosen DNA sequence.

Differentiation-specific nuclear matrix proteins cross-linked to DNA by cis-diammine dichloroplatinum

DNA-protein cross-linkages were performed in intact undifferentiated and differentiated-HL60 cells by the action of cis-diammine dichloroplatinum. Total nuclear matrix proteins and DNA cross-linked nuclear matrix proteins were resolved by two-dimensional gel electrophoresis. The comparison of the electrophoretic patterns allowed the identification of a set of differentiation-induced nuclear matrix proteins cross-linked to DNA. One of these proteins binds cloned histone SAR sequences. Our results outline an experimental strategy for isolating and characterizing nuclear matrix components that may play a fundamental role in the overall control and coordination of gene expression during differentiation.

Comparison of DNA-protein interactions in intact nuclei from avian liver and erythrocytes: a cross-linking study

DNA-protein cross-linkages were formed in intact nuclei of chicken erythrocytes and liver cells by the action of cis-diammine dichloroplatinum (II). Most cross-linked proteins were components of the nuclear matrix, and their heterogeneity reflected the different complexity of liver and erythrocytes matrices, respectively. Some basic proteins, including histones, were also cross-linked, particularly in erythrocyte nuclei. South-Western blotting revealed that a variety of proteins isolated from the cross-linked liver nuclei recognized DNA specifically. In this group of proteins two relatively abundant, acidic, species of 38 and 66 kDa, respectively, might represent novel DNA-binding proteins from the nuclear matrix. In the case of erythrocytes, only the basic proteins showed a DNA-recognition capacity, and among them there were some unidentified species, absent from liver. Lamin B2 was cross-linked but was unable to recognize DNA, and the same was true for other abundant, cross-linked proteins from both types of nuclei. This led to the hypothesis that for some DNA-nuclear matrix interactions the aggregation typical of matrix proteins is essential for the specificity of DNA recognition. Hybridization analysis of the DNA isolated from the cross-linked complexes showed that SARs (scaffold attachment regions) and telomeric sequences were well represented in the cross-linked fragments, that the cross-linked DNA of liver was partially different from that of erythrocytes and that two defined SAR sequences were found to be present only in the cross-linked DNA. These results are in agreement with the present views on DNA-nuclear matrix interactions, which are usually studied on isolated nuclear matrices or purified proteins. Instead, our results provide experimental evidence obtained directly from intact nuclei.

The presence of N-glycosylated proteins in cell nuclei

The protein-DNA crosslinking capability of cis-dichloro diammineplatinum has been exploited to check the intranuclear location of N-glycosylated proteins. When intact liver cells were treated with this reagent, a number of glycoproteins, recognized by Concanavalin A, have been shown to become crosslinked to DNA; many of them have been recognized as nuclear matrix components. The recognition by this lectin was abolished by treatment with N-glycosidase F, showing the presence of N-glycosidic bonds between the sugar moiety and the protein. Most of the glycoproteins appeared to have high mannose oligosaccharide chains, but sialic acid containing oligosaccharides were also identified.

Chemical and photochemical probing of DNA complexes

An overview of the chemical and photochemical probes which over the past ten years have been used in studies of DNA/ligand complexes and of non-B-form DNA conformations is presented with emphasis on the chemical reactions of the probes with DNA and on their present 'use-profile'. The chemical probes include: dimethyl sulfate, ethyl nitroso urea, diethyl pyrocarbonate, osmium tetroxide, permanganate, aldehydes, methidiumpropyl-EDTA-Fell (MPE), phenanthroline metal complexes and EDTA/FeII. The photochemical probes that have been used include: psoralens, UVB, acridines and uranyl salts. The biological systems analysed by use of these probes are reviewed by tabulation.

In vivo crosslinking of nuclear proteins to DNA by cis-diamminedichloroplatinum (II) in differentiating rat myoblasts

When cells are briefly exposed to cis-diamminedichloroplatinum (II) before lysis in high sodium dodecyl sulfate-urea solutions, the high molecular-weight nucleic acids pelleted by ultracentrifugation contain an increased level of bound proteins when compared to a similar fraction from untreated cells. Subsequent shearing of the pelleted DNA followed by treatment with DNase permits electrophoretic and immunoblot analysis of the crosslinked proteins. In the present study such experiments were carried out with reference to nuclear envelope pore complex proteins in the differentiating L8 rat skeletal muscle cells. The results show that (i) whereas the major lamin proteins crosslinked to DNA in both myoblast and myotubes, lamin B is crosslinked to a greater extent to DNA in myotubes; (ii) a 62-kDa lectin-binding glycoprotein is apparently situated differently with respect to DNA in myotube nuclei; and (iii) the crosslinking pattern of the nuclear matrix proteins to DNA is qualitatively similar in myoblast and myotubes. In addition, lamin C', a modified form of lamin C, not observed in intact nonmuscle cells previously [Glass et al. (1985) J. Biol. Chem. 260, 1895-1900], exists as a native component of the nuclear lamina in rat skeletal myotubes but not in myoblasts. These results point to significant structural alterations in the proteins of the nuclear lamina-pore complex during myogenesis.

Mechanisms of cellular resistance to cisplatin

Treatment of cancer patients often fails because of the resistance in the tumor to chemotherapeutic drugs. A better understanding of mechanisms which are active in resistant cells might lead to measures to circumvent the resistance. This review deals with the mechanisms of action of cisplatin (CDDP) and the various causes for CDDP resistance in the tumor cells. Also, possibilities to circumvent CDDP resistance in vitro and in vivo are presented.

DNA-protein crosslinking by heavy metals in Novikoff hepatoma

Crosslinking of proteins to DNA was studied in live intact Novikoff ascites hepatoma cells exposed in vitro to salts of chromium VI, III, and II, nickel II, cadmium II, and to CoCl2, As2O3, and AlK(SO4)2. DNA-protein complexes were separated by high-speed centrifugation of cells solubilized in buffered 4% sodium dodecyl sulfate and assayed by polyacrylamide gel electrophoresis. Hexavalent chromium compounds formed DNA-protein complexes very efficiently. The trivalent, poorly soluble, cupric chromite was nearly as efficient crosslinker as hexavalent Cr, perhaps because phagocytosis facilitated its entry into the cells. The more basic divalent form produced hardly any crosslinks. Most of the crosslinked proteins were common to all of the chromium salts employed. Nickel salts formed DNA-protein crosslinks less efficiently. Most proteins crosslinked by this metal had a high molecular weight ranging from 94,000 to 200,000. There was little qualitative difference between the crosslinked protein patterns for several various nickel (II) salts. Similar results were obtained for cells incubated with cadmium salts. Most of the proteins crosslinked by cadmium had high molecular weights and were similar to those crosslinked by nickel (II). Relatively weak, but significant, crosslinking was also observed when the Novikoff hepatoma cells were exposed to CoCl2, As2O3, or AlK(SO4)2.

Cross-linking of cytokeratins to DNA in vivo by chromium salt and cis-diamminedichloroplatinum(II)

The in vivo cross-linking of cytokeratins to DNA in intact Novikoff ascites hepatoma cells exposed to the chromium salt K2CrO4 and cis-diamminedichloroplatinum(II) (cis-DDP) was studied. Cytokeratin-DNA complexes were obtained by high-speed centrifugation of cells solubilized in buffered 4% sodium dodecyl sulfate. The cytokeratins were identified electrophoretically and immunologically by use of polyclonal and monoclonal antibodies. Time dependence experiments showed that detectable cross-linking occurred after cells were exposed to K2CrO4 for at least 4 h, and the amount of keratin-DNA complexes increased with the incubation time. Each of the three Novikoff ascites hepatoma cytokeratins (p39, p49, and p56) showed a different apparent rate of cross-link formation with DNA. Cytokeratin-DNA complexes were detectable in our system only with K2CrO4 concentrations of 200 microM or greater, and saturation in cross-linking was effected at approximately 2 mM. Higher K2CrO4 concentrations (up to 5 mM) did not produce further significant increases in the amount of cross-linked cytokeratins. Chromium and cis-DDP cross-linked the same cytokeratins at approximately the same ratios; however, both agents cross-linked the major cytokeratins selectively, since not all cytokeratins present in Novikoff hepatoma cell lysates could be cross-linked to DNA. Further evidence of DNA-cytokeratin complexes was obtained by CsCl gradient centrifugation. Our results document the ability of chromate and cis-DDP to produce DNA-cytokeratin cross-links in vivo and show that in live Novikoff hepatoma cells some, but not all, of the components of intermediate filaments are within cross-linking distance of DNA.

Crosslinking of chromosomal antigen common in human tumors to DNA by cis-diamminedichloroplatinum (II)

The antisera specific for dehistonized HeLa cell chromatin were obtained by injecting rabbits or goats. Treatment of chromatin with cis-DDP crosslinked the active proteins to DNA thus preventing dissociation of the proteins in a high salt environment. Immunochemical staining of electrophoretically separated chromosomal proteins transferred to nitrocellulose sheets revealed that cis-DDP among others crosslinked the protein with m.w. of about 81 000. This protein is the only major protein antigen presented in several human tumors and absent in normal human tissues.

cis-Diamminedichloroplatinum-mediated crosslinking of nuclear proteins to DNA is cell cycle specific

Immunochemical analysis was employed to investigate the cell cycle-dependent protein-DNA crosslinking by cis-diamminedichloroplatinum II (cis-DDP), in HeLa-S3 cells. Cells synchronized by double thymidine block or hydroxyurea were released into S phase and incubated at 2-h intervals with cis-DDP as they progressed through S1, G2, M, and then into G1 and S phases of the subsequent cycle. Immunoblots of the DNA-crosslinked antigens reacted with antisera to 0.35 M NaCl extract or residue of HeLa S-phase nuclei revealed that several antigens changed their DNA-crosslinking pattern during the progression of HeLa cells through their reproductive cycle.

In vitro interaction of 63-nickel(II) with chromatin and DNA from rat kidney and liver nuclei

The interaction of nickel(II) with chromatin was studied in vitro and in isolated nuclei from rat liver and kidney. Nickel(II) bound to chromatin, polynucleosomes (DNA + histone octamer protein complex), and to deproteinized DNA both in intact nuclei and in vitro. The amount of nickel(II) bound depended on the concentration of nickel(II), the presence of chromosomal proteins and the binding sites on DNA which provide a stable coordination environment for nickel(II). The binding of nickel(II) to chromatin and to DNA in whole nuclei was much slower than in vitro indicating that assessibility of the DNA binding sites was influenced by the presence of the nuclear membrane, nuclear matrix and nuclear proteins and/or by the condensed nuclear structure of chromatin. Since DNA containing bound nickel(II) was isolated from chromatin, nickel(II) directly interacted with stable binding sites on the DNA molecule in chromatin. Nickel(II) was associated with the histone and non-histone nuclear proteins as well as the DNA in rat liver and kidney chromatin. Nickel(II) was found to bind to calf thymus histones in vitro. Nickel(II)-nuclear protein and -DNA interactions were investigated by gel electrophoretic analysis of in vitro incubation products. Although nickel-histone and nickel-non-histone protein interactions were completely disrupted by the electrophoretic conditions, fluorography revealed the presence of inert nickel(II)-DNA and/or nickel(II)-DNA-protein complexes.

The differential effects produced by cis- and trans-DDP on DNA in calf thymus nucleosomes

Calf thymus nucleosomes containing H1 were treated with dichlorodiammineplatinum (DDP) at low binding ratios (r = 0.05-0.15). Change in the electrophoretic mobility of the extracted nucleosomal DNA was observed following treatment with cis-DDP and little change with trans-DDP. There was a decrease in the electrophoretic mobility of the nucleosomal DNA as well as obliteration of the nucleosomal repeat distance. The fluorescence intensity of terbium binding to the extracted DNA showed minimal change following drug treatment. However, the thermal melting behavior of the nucleosomal DNA was altered to a greater extent following cis-DDP treatment at 280 rather than 260 nm and a destabilization of the DNA helix was observed. These data suggest that in the whole nucleosome, cis-DDP produces greater structural effects on the packaged DNA than trans-DDP, although similar amounts of drug are bound with both isomers.

Association of cytokeratin p39 with DNA in intact Novikoff hepatoma cells

The relationship between the rat tumor-associated cytokeratin p39 (Mr 39,000) and cellular DNA has been studied in intact cells. Using a DNA-protein crosslinking technique, incubation with cis-dichlorodiammineplatinum, we present evidence for the association of p39 with DNA in intact Novikoff ascites hepatoma cells. The cells were treated with cis-dichlorodiammineplatinum and solubilized in NaDodSO4-containing buffer, and the DNA was pelleted by high-speed centrifugation. By immunotransfer analysis, the cytokeratin was found in the DNA pellet of the crosslinked samples while absent from the controls. This result was further substantiated by CsCl density-gradient centrifugation. Collectively, these results suggest a cytokeratin-DNA association at the filament binding sites on or near the nuclear lamina.

Crosslinking of chromosomal proteins to DNA in HeLa cells by UV gamma radiation and some antitumor drugs

Immunochemical techniques were used to investigate the protein-DNA crosslinking by ultraviolet (UV) and gamma radiation as well as 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) or cis- and trans-diamminedichloroplatinum II (cis-DDP and trans-DDP). Antisera to 0.35 M NaCl extract and 0.35 M NaCl residue of HeLa nuclei were employed. Both gamma and UV irradiation, exposure to cis- or trans-DDP and, to a lesser extent, BCNU, resulted in crosslinking of various antigens to the DNA. Although several antigens were crosslinked by all the employed agents, other exhibited agent-specific crosslinking patterns.