Polyamine effects on DNA-directed RNA polymerases in the ciliate Tetrahymena thermophila. In vivo- and in vitro-experiments suggesting highly specific regulative interactions

Biogenic polyamines spermine and spermidine activate RNA polymerase and inhibit RNA helicase of hepatitis C virus

Influence of the biogenic polyamines spermine, spermidine, and putrescine as well as their derivatives on the replication enzymes of hepatitis C virus (HCV) was investigated. It was found that spermine and spermidine activate HCV RNA-dependent RNA polymerase (NS5B protein). This effect was not caused by the stabilization of the enzyme or by competition with template-primer complex, but rather it was due to achievement of true maximum velocity V(max). Natural polyamines and their derivatives effectively inhibited the helicase reaction catalyzed by another enzyme of HCV replication - helicase/NTPase (NS3 protein). However, these compounds affected neither the NTPase reaction nor its activation by polynucleotides. Activation of the HCV RNA polymerase and inhibition of the viral helicase were shown at physiological concentrations of the polyamines. These data suggest that biogenic polyamines may cause differently directed effects on the replication of the HCV genome in an infected cell.

Transcription in vitro of Tetrahymena class II and class III genes

A method for preparation of transcriptionally active nuclear extracts from the ciliated protozoan Tetrahymena thermophila is described. Cells were lysed in the presence of gum arabic, and nuclei were further purified in the presence of Ficoll 400. Highly concentrated nuclear extracts were prepared by ultracentrifugation of nuclei in a buffer containing potassium glutamate and spermidine. These extracts supported accurate transcription initiation of T. thermophila class II and III genes. Using the histone H3-II gene as a template, we demonstrated that physiologically induced changes in transcriptional activity in vivo were reflected in the transcriptional activity of the nuclear extract in vitro. By electrophoretic mobility shift assays, five conserved sequence elements in the upstream region of the histone H3-II gene were shown specifically to bind proteins in extracts from exponentially growing as well as from starved cells, and by UV cross-linking we further characterized the specific binding of two proteins to an oligonucleotide containing a conserved CCAAT box motif. Transcription competition experiments showed that addition of this oligonucleotide decreased transcription significantly. Competition with oligonucleotides corresponding to the two proximal conserved sequence elements almost completely abolished transcription of the H3-II gene suggesting that binding of transacting factors to these elements is crucial for initiation of transcription.

Structure of the human spermidine/spermine N1-acetyltransferase gene (exon/intron gene organization and localization to Xp22.1)

The super induction of spermidine/spermine N1-acetyltransferase (SSAT), has been implicated in the cytotoxic response of human solid tumors to the bis(ethyl)polyamines. The SSAT response is a phenotype specific response and is modulated at the level of increased steady-state mRNA levels and enzyme protein. The human genomic region (4,095 bases) containing the coding sequence of SSAT has been cloned and localized to the Xp22.1 region. Primer extension analysis indicates the transcription of SSAT starts 179 bases upstream from the translational start site and appears to be under the control of a "TATA-less" promoter. The availability of this human clone will facilitate the direct functional examination of the SSAT gene.

Characterization of DNA-directed RNA polymerases in isolated macronuclei of the ciliated protozoan Tetrahymena thermophila. Effects of purified ornithine decarboxylase and amine compounds

The possible regulatory interactions of purified ornithine decarboxylase with DNA-directed RNA polymerases in isolated macronuclei from the ciliated protozoan Tetrahymena thermophila were studied. It has been found that highly purified ODC (specific activity 10.2 mumols CO2 x h-1 x mg-1), even at activities of 37,500 nmol CO2 x h-1 per ml failed to alter RNA polymerase activity in the in vitro transcription assay in the presence or absence of the substrate L-ornithine at 20mM. The naturally occurring di- and polyamines putrescine, spermidine, and spermine stimulated in-vitro-transcription in isolated macronuclei more at optimal Mg2+/Mn(2+)-concentrations than at suboptimal concentrations, suggesting that polyamines act via a mechanism which is distinct from that of the inorganic cations. Of the monovalent amine compounds tested, (NH4)+ at high concentrations between 40 and 50mM slightly stimulated activity whereas the onset of stimulation by the organic amine compounds, piperidine and cyclohexylamine, was inversely related to the hydrophobicity of each particular compound. In the series of divalent amines, the correct distance between the N-atoms appeared to be very important since ethylenediamine and piperazine did not stimulate significantly but did inhibit at concentrations above 5 mM. 1,3-Diaminopropane stimulated slightly but inhibited above 10 mM, whereas the 1,4-diamino compounds putrescine and 1,4-diaminocyclohexane (DAC) were equally potent stimulators with the more hydrophobic one, DAC, reaching the maximum at lower concentrations than putrescine. For the trivalent amines, the influence of correct spacing seems not to be as important: N-(2-aminoethyl)piperazine stimulated very similar to spermidine.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoaffinity polyamines: sequence-specific interactions with DNA

ANB-spermine is a photoaffinity analog of the naturally-occurring polyamine, acetylspermine. ANB-spermine was used to determine its binding sites on naked double stranded DNA, at the nucleotide level, using a modification of the primer extension technique. A total of 1,275 nucleotides was examined in 5 sequences of DNA from Saccharomyces cerevisiae. Binding sites were non-random. The primary determinant of binding was the presence of a thymidine residue. Secondary determinants appeared to depend on the secondary structure of the DNA, with runs of thymidines providing unusually poor binding sites while TA and, especially, TATA providing the strongest binding sites. The 'TATA element' upstream of the URA3 gene from S. cerevisiae was the strongest binding site. The data indicate that ANB-spermine binding to DNA is a probe for DNA secondary structure and suggest a role for polyamines in regulating the structure of chromatin in vivo.

Polyamine biosynthesis in arginine-starved and refed rats

Growth of rats fed with a synthetic diet was studied under control conditions (arginine-rich), arginine starvation, and arginine starvation/refeeding. Hepatic polyamine concentrations and ornithine decarboxylase (ODC-)activity were determined for each population. In the livers of arginine-starved rats putrescine was decreased to half the control content within 8 days; upon refeeding, it returned to control levels within another 8 days. Spermidine content in liver tissue of arginine-starved rats remained rather stable for 7 days, but thereafter dropped to half the original value within two days. Refeeding for a period of 11 days was not enough to restore the spermidine content. The effects of arginine starvation/refeeding on spermine were very similar to those of spermidine. ODC specific activity, when correlated with growth, was higher in livers of arginine-starved rats than in control animals. Refeeding caused a decrease in ODC-activity although growth arrest was completely released. This apparent uncoupling of growth and ODC stimulation supports the theory that ODC in rat liver is regulated at three levels: first the growth-related component which is observed after stimulation by growth-hormone; second the known feed back control by polyamines, e.g. via antizyme; third the regulation at the level of the substrate supply which has been shown in this work. This is not a unique finding since very similar results have been obtained in previous experiments with the protozoan Tetrahymena thermophila. A remarkable observation of these assays was that L-ornithine, when added to the arginine-free diet was not able to substitute for L-arginine in directing growth and growth related processes.

Regulation of ornithine decarboxylase activity in the growth cycle of Tetrahymena thermophila

Cells of the ciliated protozoan Tetrahymena thermophila, grown in proteose peptone medium up to late logarithmic phase, harvested by centrifugation, and resuspended in fresh medium to almost the same cell density, underwent one more division cycle within 5 h after inoculation, thereafter being definitely in full stationary phase. This growth cycle proved to be a useful tool to investigate the activation and deactivation of ornithine decarboxylase ODC1 in Tetrahymena: In late logarithmic phase the cells contained a very low specific activity of ODC of about 3 nmol CO2.h-1.mg-1 in the soluble protein fraction. After growth stimulation the activity was increased up to 100-fold within 1 h. This high activity was maintained for about 5 h-about as long as division activity-then rapidly declined with a half life time (t1/2) of about 15 min to the original low level. Inhibition assays with cycloheximide and actinomycin D revealed that: i. the rapid increase of ODC activity was biphasic with one component of translation of preexisting mRNA and one component of translation of newly transcribed mRNA; ii. the t1/2 of the mRNA of ODC was estimated to be about 2 h; iii. inhibition of protein biosynthesis before ODC inactivation at 5 h caused a decrease of ODC with a t1/2 of 55 min instead of 15 min. These findings suggest that ODC activity in Tetrahymena is regulated on both levels: transcription and translation and by an inactivating protein factor which is regulated at the level of biosynthesis.

Regulation of growth and polyamine biosynthesis of the ciliated protozoan Tetrahymena thermophila. Effects of L-arginine metabolites and polyamines

Growth of Tetrahymena thermophila in a synthetic nutrient medium with or without the essential amino acid L-arginine was studied in the presence or absence of the arginine metabolites L-citrulline and L-ornithine and the polyamines putrescine, spermidine, and spermine. The effects of the growth conditions on the stimulations of the enzymes of the arginine metabolic and polyamine biosynthetic pathway, arginine deiminase (ADI), citrulline hydrolase (CH), ornithine decarboxylase (ODC), and ornithine-oxo-acid aminotransferase were determined. Tetrahymena cells were unable to grow in the absence of L-arginine and the amino-acid utilization was greatly impaired. None of the metabolites or polyamines was able to substitute for arginine. In the presence of arginine, Tetrahymena cultures grew well and citrulline and ornithine did not alter the growth behaviour in any way. In the presence of putrescine, the lag period was decreased from 3 h to 2 h. Spermidine and spermine acted similar to putrescine but less pronounced. The stimulation of the activity of ADI, the key enzyme of arginine degradation, was absolutely dependent upon the presence of arginine in the medium: in the absence of arginine, the low ADI activity which was present in the cells before inoculation was decreased to zero levels within 30 min. In the presence of arginine, the stimulation of ADI was not altered by citrulline and ornithine but putrescine, spermidine, and spermine decreased ADI-stimulation to half of the control values. The stimulation of CH activity in the presence of arginine was not altered by any added metabolite or polyamine. In the media without arginine, stimulation of CH was greatly reduced, in the presence of ornithine more than in its absence, and even more in the presence of putrescine and spermidine. Stimulation of ODC activity in the presence of arginine was not affected by citrulline and ornithine but in the presence of polyamines it was rapidly decreased to unstimulated levels after an initial ca. 10-fold increase. The "hyperstimulation" of ODC in the absence of free arginine was reduced to normal in the presence of citrulline, the stimulation was decreased even below normal levels in the presence of ornithine and polyamines decreased ODC activity to zero levels. O delta T activity was stimulated more in the presence of arginine than in its absence. In both cases the stimulation was enhanced in the presence of polyamines and only in the absence of arginine--by ornithine.(ABSTRACT TRUNCATED AT 400 WORDS)

Properties of purified L-ornithine decarboxylase (EC 4.1.1.17) from Tetrahymena thermophila

Ornithine decarboxylase (ornithine carboxy lyase; EC 4.1.1.17) (ODC) from Tetrahymena thermophila was purified 6,300 fold employing fractionated ammonium sulfate precipitation, gel permeation chromatography on Sephadex G-150, ion exchange chromatography on DEAE-Sepharose CL-6B, and preparative isoelectric focussing. The product obtained in 24% yield was a preparation of the specific activity of 10,200 nmol CO2.h-1.mg-1. The purified enzyme was rather stable at 37 degrees C (14% loss of activity within 1 h). The molecular and catalytic properties of this enzyme were investigated. The isoelectric point was 5.7 and the molecular weight (MW) was estimated to be 68,000 under nondenaturing conditions. The pH optimum was between 6.0 and 7.0, the Km for the substrate L-ornithine was 0.11 mM, and the Km for the cofactor pyridoxal 5-phosphate was 0.12 microM; the product of ODC catalysis, putrescine, was a poor inhibitor with an estimated Ki of about 10 mM. The enzyme was inhibited competitively by D-ornithine with a Ki of 1.6 mM and by alpha-difluoromethylornithine with a Ki of 0.15 mM. The latter one, an enzyme activated irreversible inhibitor of mammalian ODC, inactivated the enzyme from T. thermophila at high concentrations with a half life time of 14 min. Other basic amino acids, e.g. L-lysine, L-arginine, and L-histidine, were neither substrates nor inhibitors of the enzyme, as were the diamines 1,3-diaminopropanol and cadaverine, the polyamines spermidine and spermine and the cosubstrate analogues pyridoxal and pyridoxamine-5-phosphate.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of L-arginine iminohydrolase (EC 3.5.3.6) from Tetrahymena thermophila by putrescine and spermidine: feedback control of polyamine biosynthesis

L-Arginine iminohydrolase (arginine deiminase, ADI) from Tetrahymena thermophila was purified approx. 75-fold by means of gel permeation chromatography. The Km of the purified enzyme for L-arginine was 412 +/- 25 microM and L-ornithine inhibited the reaction competitively with a Ki of 985 +/- 105 microM. D-Ornithine was a weak inhibitor with a Ki of greater than 10mM. The polyamines putrescine and spermidine inhibited ADI incompetitively with a Kii of 2.8mM for putrescine and 4.3mM for spermidine. Since the concentrations required for inhibition were within the range of the normal intracellular polyamine concentrations in Tetrahymena (maximally 14mM putrescine and 4mM spermidine), it is suggested that the polyamine effects on ADI are of regulatory nature. Thus, polyamine biosynthesis in Tetrahymena thermophila is regulated not only on the level of ornithine decarboxylase activity, but also on an earlier step, the supply of ODC with substrates.

Stimulation of growth and polyamine biosynthesis of the ciliated protozoan Tetrahymena thermophila. Regulation by L-arginine

Tetrahymena thermophila cells grown in a synthetic nutrient medium for 9 h removed 97% of the free L-arginine but less than 50% of any of the other essential amino acids. The major portion of the arginine was degraded rapidly (76-92%) whereas 5-15% was conserved as intact and only 2.5-10% were incorporated into protein. However, if bovine serum albumin (BSA) was present in the medium as a macromolecular arginine source the incorporation of free arginine into protein was reduced to less than 1% but the degraded fraction was increased. Apparently, the uptake mode of arginine determines its fate: arginine taken up by phagocytosis is bound for protein biosynthesis, arginine taken up by membrane receptors is chanelled to degradation. Media without arginine did not support growth of Tetrahymena. Citrulline and ornithine, the precursors of arginine biosynthesis in yeast and vertebrates, were not able to substitute for arginine. Pronounced morphological changes, e.g. greatly reduced ribosome content, were observed in Tetrahymena cells after 24 h of arginine starvation in otherwise complete medium, but not in cells starved in water, salt solution, or buffer. Thus, arginine is an essential nutrient component for Tetrahymena and the rapid degradation of this compound involving the enzymes arginine deiminase (ADI) and citrulline hydrolase (CH) might be of regulatory importance for the unicellular, as it is the case with acetylcholine and catecholamines in mammalian organisms. Since the product of these enzymes, L-ornithine, is the substrate for the regulatory key enzyme of polyamine biosynthesis, ornithine decarboxylase (ODC), the effects of the presence of absence of arginine on the activities of each particular enzyme of the pathway were studied, including ODC and the enzyme ornithine-oxo-acid aminotransferase (O delta T), which is a competitor of ODC for the common substrate. The arginine-degradative pathway was stimulated by extracellular free but not by peptide-bound arginine and was modulated by extracellular protein which induced phagocytosis; O delta T was stimulated with a time lag. The stimulation of ODC was in a reciprocal relation to the arginine concentration and enhanced by phagocytosis and previous arginine starvation.(ABSTRACT TRUNCATED AT 400 WORDS)