Stimulation of transcription of mouse kidney chromatin by sulfated polysaccharides

Nuclear translocation of heparan sulfate proteoglycans and their functional significance

BACKGROUND

Heparan sulfate proteoglycans (HSPGs) are important constituents of the cell membrane and they act as co-receptors for cellular signaling. Syndecan-1, glypican and perlecan also translocate to the nucleus in a regulated manner. Similar nuclear transport of growth factors and heparanase indicate a possible co-regulation and functional significance.

SCOPE OF REVIEW

In this review we dissect the structural requirement for the nuclear translocation of HSPGs and their functional implications.s

MAJOR CONCLUSIONS

The functions of the nuclear HSPGs are still incompletely understood. Evidence point to possible functions in hampering cell proliferation, inhibition of DNA topoisomerase I activity and inhibition of gene transcription.

GENERAL SIGNIFICANCE

HSPGs influence the behavior of malignant tumors in many different ways. Modulating their functions may offer powerful tools to control fundamental biological processes and provide the basis for subsequent targeted therapies in cancer. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

A detective story in drug discovery: elucidation of a screening artifact reveals polymeric carboxylic acids as potent inhibitors of RNA polymerase

Chasing the active impurity: In the validation of a screening hit it was discovered that a polymeric trace impurity was responsible for the biological activity. Such a side product can be formed with similar compounds. During the investigations it was discovered that the negatively charged macromolecule interacts very efficiently with the protein surface of E. coli RNAP via electrostatic interactions.

Heparin binds to intact mononucleosomes and induces a novel unfolded structure

It has been previously shown that heparin can bind to chromatin and enhance transcriptional activity. To characterize this phenomenon further, we have studied the interaction of heparin with isolated core mononucleosomes from avian reticulocytes. The results of these studies suggest that heparin bound reversibly to intact core mononucleosomes to induce a new structure, identified by decreased electrophoretic mobility and altered circular dichroism spectra. This altered nucleosome conformation exhibits 3-5-fold increased sensitivity to digestion by the nuclease, DNase I, and allows more efficient passage of RNA polymerase. At higher concentrations of heparin, core histones were completely removed from DNA. The finding of a reversible nucleosome-heparin complex in which core DNA is readily accessible to both RNA polymerase and the nuclease DNase I is discussed in the context of transcriptionally active chromatin.

Response of skeletal muscle RNA polymerases I and II to tumour growth

The muscle wasting which occurs in animals bearing a transplantable tumour is accompanied by a decrease in the level of protein synthesis and a loss in RNA. This paper examines the behaviour of RNA polymerases I and II (EC 2.7.7.6) in nuclei isolated from skeletal muscle of rats bearing a Walker 256 carcinoma. Marked decreases were observed in template-engaged RNA polymerase I and II activities and in free RNA polymerase I activity. Free RNA polymerase II activity was unaltered. When assays were carried out at high (NH4)2SO4 concentration or in the presence of heparin the diminished RNA polymerase I activity was still apparent, but heparin and high ionic strength overcame the inhibition of RNA polymerase II. Loss of RNA polymerase I activity was associated with a decrease in the number of template-engaged enzyme molecules and in the polynucleotide elongation rate. The number of template-engaged RNA polymerase II molecules was unaltered by tumour growth, but the polynucleotide elongation rate was significantly reduced. No evidence was obtained for any alteration in ribonuclease activity in nuclei or whole muscles of tumour-bearing rats. These results demonstrate an effect of the tumor on transcription in skeletal muscle of its host.

Dietary sugar promotes gene activation in intestinal cell chromatin of adult rats

The effect of dietary sucrose on transcription activity of chromatin from intestinal cells of adult rats was investigated. Chromatin-bound RNA polymerase II activity was significantly enhanced after feeding sucrose to rats. RNA polymerase II transcribes the genes coding for pre-messenger RNA. The results indicate that feeding of sucrose increased the synthesis of pre-messenger RNA molecules coding for specific proteins which are involved in the adaptive processes of sucrose hydrolysis in intestinal cells.

The effect of induction of hemoglobin synthesis in cultured Friend cells on the number of initiation sites for replication and transcription

It was found that differentiation of murine erythroleukemia cells can be induced by 5-fluorodeoxyuridine (FudR), amethopterin and alpha-aminoisobutyrate. Each of these compounds is believed to delay the onset of DNA synthesis. Since relief of the FudR block to DNA synthesis by addition of thymidine can increase the number of initiation sites for replication (Taylor, 1977), the effect of various inducers and inhibitors of differentiation of Friend cells upon the relative number of initiation sites for replication and transcription was investigated. Very efficient inducers of hemoglobin synthesis, hexamethylene bisacetamide (HMBA) and dimethylsulfoxide (DMSO), increase the number of initiation sites for transcription and HMBA also increases the number of functional initiation sites for replication. Two other compounds that induce differentiation of Friend cells, low levels of actinomycin D and FudR, did not increase the number of initiation sites for transcription. Compounds that prevent induction of hemoglobin synthesis by HMBA and DMSO include 5-bromodeoxyuridine (BrdU) and novobiocin. Both of these compounds were found to decrease the number of functional initiation sites for transcription and it is known that both compounds reduce the number of initiation sites for replication. The relation between initiation of replication and transcription, and its effect upon differentiation of erythroleukemia cells is discussed.

Effects of partial hepatectomy on RNA polymerase activities in mouse liver

Chromatin-bound and poly[d(A-T)]dependent RNA polymerase I plus III and II activities of mouse liver were analysed 24 and 48 hr after partial hepatectomy. Chromatin-bound RNA polymerase I plus III activity showed an increase of 57% at 24 hr and 51% at 48 hr after partial hepatectomy. There was a decrease in chromatin-bound RNA polymerase II activity of 15% at 24 hr and 34% at 48 hr after partial hepatectomy. There was no significant changes in poly[d(A-T)]dependent RNA polymerase activities. Heparin caused an approximately 10-fold increase in chromatin-bound RNA polymerase II activity. The stimulation by heparin was significantly increased 48 h after partial hepatectomy. Anaesthesia and/or surgery had great influence on RNA polymerase activities. At 24 hr after operation, chromatin-bound RNA polymerase I plus III and II activities were depressed, and the liver cell chromatin was more susceptible to stimulation by heparin.

Non-random effect on RNA synthesis in liver chromatin by administration of dimethylnitrosamine to mice

The effect of dimethylnitrosamine on functional activities of liver chromatin was studied in mice. After a single dose of dimethylnitrosamine injected i.v. (25 mg/kg body wt, 45 min before sacrifice) liver nuclei were isolated and incubated with micrococcal nuclease (EC 3.1.4.7) to an acid-solubility of 2.5% of total DNA. Chromatin was fractionated into a 1,200 g pellet P1, 102,000 g pellet P2 and supernatant fraction S2. Chromatin-bound RNA polymerase I plus III activity decreased 15% in the P1 and 25% in the P2 fraction. No changes in activity were observed in the S2 fraction. Chromatin-bound RNA polymerase II activity decreased 19% in the P1, 49% in the P2 and 32% in the S2 fraction. Heparin stimulated RNA polymerase II activity decreased 10% in the P1 and 44% in the P2 fraction. Formation of initiation in nuclear lysates with RNA polymerase from Escherichia coli increased after administration of dimethylnitrosamine suggesting an increase in the number of sites available for the start of new RNA chains. The results show that limited digestion of nuclei with endonuclease cleaves chromatin regions which are more affected by dimethylnitrosamine than the total chromatin suggesting a non-random effect of the hepatotoxin on chromatin. Modifications of the DNA template by dimethylnitrosamine is indicated by the change in number of initiation complexes.

Influences of anionic polysaccharides on DNA synthesis in isolated nuclei and by DNA polymerase alpha: correlation of observed effects with properties of the polysaccharides

The basis of the differential effect of anionic polysaccharides on replicative DNA synthesis in liver and hepatoma cell nuclei was investigated. The differential effect of heparin was lost when more than 40% of its sulfate was removed. DNA synthesis in liver nuclei was optimally stimulated by heparin of molecular weight 22600 and sulfate to hexosamine ratio 2.42, but inhibited by heparin of molecular weight 4300 and sulfate to hexosamine ratio 2.35. A heparin fragment (molecular weight 2800 and sulfate to hexosamine ratio 1.81), prepared by partial nitrous acid treatment was a potent inhibitor of DNA synthesis in hepatoma nuclei. There was no significant difference in the rate of entry of heparin or its subfractions into either liver or hepatoma nuclei. In both cases less than 15% of added polysaccharide entered the nuclei and only about 4.5% was found associated with the chromatin. The influence of the anionic polysaccharides on DNA synthesis was correlated with their ability to complex with histones as determined by relative light scattering in a laser nephelometer. The relative light scattered on mixing with histones (H1, H2A + H3, H4) was high for DNA synthesis stimulators (heparin, dextran sulfate); medium for DNA synthesis inhibitors (chondroitin 4- and 6-sulfates, heparan sulfate) and low for non-effectors (keratan sulfate, hyaluronic acid). Heparin and chondroitin sulfate H, which at low concentrations stimulate DNA synthesis in liver nuclei, inhibited DNA synthesis by calf thymus DNA polymerase alpha at all concentrations. This inhibition was not simply due to electrostatic interactions.

Effect of heparin on the porcine lymphocyte chromatin--II. Comparative study of sedimentation of chromatin DNA and isolated DNA

1. Sedimentation of chromatin DNA and isolated deproteinized DNA was compared in neutral and alkaline sucrose density gradients after incubation of chromatin or DNA with various concentrations of heparin. 2. Irrespective of the molecular weight of DNA, an increase in the sedimentation constant of DNA was found with increasing concentration of the polyanion employed.

The effect of heparin on the porcine lymphocyte chromatin--I. The comparative study of DNA in different chromatin fractions

1. Porcine lymphocyte chromatin in the solution of 0.15 M NaCl + 0.01 M Tris, pH 7 treated with heparin liberated 30% protein and 7.5% DNA to the supernatant. 2. DNA from the supernatant and the pellet fractions as well as from control chromatin were isolated in identical conditions. 3. No significant changes were observed in spectral properties and melting points in SSC of comparable DNA specimens. 4. It was noted, however, that DNA of the supernatant is subject to denaturation in the process of isolation, which, apart from the difference in protein composition of the supernatant and the pellet fractions, suggests different chromatin structure of these fractions.

Influence of glycosaminoglycans on endogenous DNA synthesis in isolated normal and cancer cell nuclei. Differential effect of heparin

The influence of exogenously-added glycosaminoglycans and glycoproteins on DNA synthesis in isolated nuclei, from normal and malignant tissues, was investigated. Heparin stimulated DNA synthesis in normal cell nuclei at concentrations (heparin/DNA (w/w) less than 0.9) which inhibited DNA synthesis in tumor cell nuclei. At higher concentrations (heparin/DNA (w/w greater than 0.9) heparin inhibited DNA synthesis in both normal and tumor cell nuclei. The chondroitin-4 and 6-sulfates, heparin sulfate, cartilage proteoglycan, N-desulfated heparin, and glycophorin caused inhibition of DNA synthesis at all concentrations tested and in all nuclei examined. Hyaluronic acid, dermatan sulfate, keratan sulfate, alpha 1-acid glycoprotein and fetuin had no significant influence on DNA synthesis in isolated nuclei.

Relative base composition of initiation sites for transcription in developing frog embryos

The use of an inhibitor (0.4 N (NH4)2SO4) and an activator (sodium polydextran sulfate) of initiation of transcription in nuclei of frog embryos in vitro indicated that initiation sites for transcription are relatively A--T-rich. Comparison of incorporation of labeled ATP, UTP, and GTP, when initiation of transcription is prevented, indicates that initiation sites become relatively less A--T-rich as development proceeds. Inhibition of initiation of transcription in isolated nuclei blocks the normal increase in rate of transcription that occurs when cells enter the S phase, showing that an increased level of transcription depends upon a greater number of initiation sites.

Action of heparin on mammalian nuclei. I. Differential extraction of histone H1 and cooperative removal of histones from chromatin

Heparin interacts strongly with the histone component of chromatin, forming heparin-histone complexes which resist dissociation by 0.2 M H2SO4. Heparin treatment of unfractionated histones isolated from nuclei of Chinese hamster cells indicates that the affinities of the histone classes for heparin appear in the order from greatest to least: (H3, H4) greater than (H2A, H2B) greater than H1. However, when isolated nuclei are treated with heparin, H1 is released from the chromatin more readily than the other four histone classes. The release of these four histones (H2A, H2B, H3, and H4) is coordinate and occurs in a highly cooperative manner, as indicated by (1) dependence of the initial kinetics of histone removal upon heparin concentration, (2) analysis of DNA and histones in the fractions obtained from differential sedimentation of heparin-treated nuclei, and (3) analysis of the products from heparin-treated nuclei by equilibrium centrifugation in metrizamide density gradients. The results suggest rapid procedures for using heparin as an agent for studying the accessibility of histones in chromatin of intact nuclei. The relationship of these results to current models of chromatin structure is discussed.

Mast cell activation and tissue cell proliferation

The effect of mast cell activation and degranulation on the proliferation in the intact mesentery was studied in Sprague-Dawley rats. Mast cell activation was achieved by a single intraperitoneal injection of Compound 48/80. The proliferation was studied using three independent methods for estimation of cell production and DNA synthesis: 1. the mitotic index, 2. the relative number of cells having a DNA content in the S and G2 regions, by Feulgen photometric measurement in individual cells, and 3. the specific DNA activity, employing a method which combines a liquid scintillation technique after an intravenous injection of 3H-thymidine and Feulgen photometric determination of the DNA content per membrane preparation. It was found that the proliferation of the normal mesenchymal cells adjacent to the activated and degranulated mast cells in the mesentery was significantly increased within 24 and 32 h, the maximum increase being more than 20-fold compared to untreated controls. The results suggest that the common type of mast cell may have a pathophysiological function related to stimulation of local cell proliferation.