Enhanced differential synthesis of proteins in a mammalian cell-free system by addition of polyamines

Growth responses of prostatic epithelial cells from male mice neonatally exposed to diethylstilbestrol in serum-free collagen gel culture

Growth of anterior and ventral prostatic epithelial cells from mice neonatally exposed to diethylstilbestrol (DES) and from unexposed control mice was compared at different time points in serum-free collagen gel culture. A longer maintenance of the initial plating density (lag in growth) was observed in cultured DES-exposed ventral prostatic cells. Neonatal DES exposure resulted in two colony types: one similar to colonies arising from unexposed cells and one which appears to be non-growing. Keratinization was observed in some DES-exposed anterior prostatic cell colonies. Removal of epidermal growth factor from the serum-free medium significantly decreased growth in 3 of the 4 groups compared with their growth in the complete serum-free medium.

Serum-free culture of enriched mouse anterior and ventral prostatic epithelial cells in collagen gel

Sustained growth of mouse ventral and anterior prostatic epithelial cells embedded within collagen gel matrix was achieved in a serum-free medium composed of Dulbecco's modified Eagle's medium and Ham's F12 medium, 1:1 (vol/vol), supplemented with bovine serum albumin fraction V, epidermal growth factor, transferrin, cholera toxin, prolactin, 5 alpha-dihydrotestosterone, cortisol, putrescine, fibroblast growth factor, and a trace element mixture. Three-dimensional growth of prostatic epithelial cells occurred inside the collagen gel matrix. This serum-free medium allowed cell growth greater than sevenfold over 10 d in culture. Tissue recombination and cell culture techniques were integrated to demonstrate that cultured cells retained prostatic characteristics. Following 10 d of culture, epithelial colonies from mouse ventral and anterior prostatic epithelial cell cultures were isolated and combined with rat fetal urogenital sinus mesenchyme and grown for 4 wk under the renal capsule of intact athymic male mice. These tissue recombinants showed distinctive prostatic histologic characteristics (alveoli and ducts lined with cuboidal or columnar epithelium surrounded by stroma). When histologic sections of recombinants were stained with the Hoechst 33258, epithelial cells of mouse origin were distinguishable from stromal cells of rat origin.

GFR increases before renal mass or ODC activity increase in rats fed high protein diets

Consumption of a high protein diet causes renal hypertrophy and increased glomerular filtration rate (GFR). To determine the relationship between increases in GFR, renal ornithine decarboxylase activity (ODC), arginase activity, and renal growth, dietary protein intake was increased from 8.5% to 40% in 50 male Sprague-Dawley rats (HP). Forty-one rats remained on 8.5% protein as time controls (LP). Eight to 17 animals were killed daily for measurement of kidney weight (kidney wt), ODC and arginase activities, total kidney protein and DNA content. GFR increased within the first 24 hours after the increase in dietary protein and reached a maximum within 48 hours, ODC increased from 9.7 +/- 0.8 U/g to a peak of 170 +/- 35 U/g at 48 hours, decreasing to a stable value of 28.6 +/- 8.0 U/g at 72 hours and 25.4 +/- 5.1 U/g at 168 hours, a value significantly greater than that at time zero. Arginase activity did not change. Kidney wt as percent body weight (body wt) increased after the initial increase in both GFR and in ODC activity. The peak in ODC activity corresponded with the maximum increase in GFR and preceded the increase in renal mass. After GFR stabilized, ODC activity decreased to a plateau and renal growth relative to body wt ceased. The increase in kidney weight was accompanied by a parallel increase in total kidney protein. Kidney protein/kidney DNA ratio increased significantly by 96 hours, indicating that renal hypertrophy had occurred. The sequence of these events suggests that increasing GFR may trigger the rise in ODC activity.

Polyamines and regulation of ornithine biosynthesis in Escherichia coli

The growth rate of several polyamine-deficient mutants of Escherichia coli was very low in minimal medium and increased markedly upon the addition of putrescine, spermidine, arginine, citrulline, or argininosuccinic acid. The endogenous content of polyamines was not significantly altered by the supplementation of polyamine-starved cultures with arginine or its precursors. In contrast, these compounds as well as putrescine or spermidine caused a 40-fold reduction in intracellular ornithine levels when added to polyamine-depleted bacteria. In vivo experiments with radioactive glutamic acid as a precursor and in vitro assays of the related enzymes showed that the decrease in ornithine levels was due to the inhibition of its biosynthesis rather than to an increase in its conversion to citrulline or delta 1-pyrroline-5-carboxylic acid and proline. High endogenous concentrations of ornithine were toxic for the E. coli strains tested. The described results indicate that the stimulatory effect of putrescine and spermidine on the growth of certain polyamine-starved bacteria may be partially due to the control of ornithine biosynthesis by polyamines.

Polyamine stimulation of ribosomal synthesis and activity in a polyamine-dependent mutant of Escherichia coli

A polyamine-dependent mutant of Escherichia coli KK101 was isolated by treatment of E. coli MA261 with N-methyl-N'-nitro-N-nitrosoguanidine. In the absence of putrescine, doubling time of the mutant was 496 min. The mutation was accompanied by a change in the nature of the 30 S ribosomal subunits. Addition of putrescine to the mutant stimulated the synthesis of proteins and subsequently, this led to stimulation of RNA and DNA synthesis. Under these conditions, we determined which proteins were preferentially synthesized. Putrescine stimulated the synthesis of ribosomal protein S1 markedly, but stimulated ribosomal proteins S4, L20, and X1, and RNA polymerase slightly. The amounts of initiation factors 2 and 3 synthesized were not influenced significantly by putrescine. The preferential stimulation of the synthesis of ribosomal protein S1 occurred as early as 20 min after the addition of putrescine, while stimulation of the synthesis of the other ribosomal proteins and RNA polymerase appeared at 40 min. The stimulation of the synthesis of ribosomal RNA also occurred at 40 min after addition of putrescine. Our results indicate that putrescine can stimulate both the synthesis and the activity of ribosomes. The increase in the activity of ribosomes was achieved by the association of S1 protein to S1-depleted ribosomes. The early stimulation of ribosomal protein S1 synthesis after addition of putrescine may be important for stimulation of cell growth by polyamines.

Effect of various polyamine analogs on in vitro polypeptide synthesis

Various polyamine analogs were examined for their ability to stimulate and to function as sparing agents for the Mg2+ requirement in polypeptide synthesis at various temperatures in Escherichia coli (37 and 47 degrees C) and the extremely thermophilic Thermus thermophilus (60 and 70 degrees C) cell-free systems. The optimal concentration of each polyamine analog increased as the incubation temperature was elevated. At a fixed temperature, the optimal concentration of polyamine analogs was in the order diamines greater than triamines greater than tetraamines greater than pentaamines. All diamines tested stimulated polypeptide synthesis almost equally but lowered the optimal Mg2+ concentration in the order diaminopropane greater than putrescine greater than cadaverine. The degree of diamine stimulation was maximal at 37 degrees C. The effects of three triamines were very similar in the E. coli system but in the T. thermophilus system spermidine was most effective in stimulation of polypeptide synthesis. From the results of experiments using tetraamines and pentaamines, it was deduced that the presence of both aminobutyl and aminopropyl groups in polyamine analogs is important for stimulation of polypeptide synthesis. In the E. coli system, triamines were the most effective polyamines for stimulation of polyphenylalanine synthesis at both 37 and 47 degrees C, while, in the T. thermophilus system, thermospermine, a tetraamine, was most effective at 60 degrees C and 3,4,4,3-pentaamine was most effective at 70 degrees C.

Serum albumin

The liver manufactures albumin at a massive rate and decreases production in times of environmental, nutritional, toxic and trauma stress. Osmotic pressure is a basic evolutionary regulatory factor, and hormonal control over albumin production has been demonstrated. Where and why new or old albumin is degraded are questions which have not been clarified, although the vascular endothelium may well be the degradative site. Albumin is important as a transport protein, as a measure of evolution and as a model to study secretion following synthesis without the intervening steps of glycosylation. Investigations as to how this protein enters the endoplasmic membrane may well answer some of the questions concerning signal peptide insertion (288). The role of the urea cycle intermediate ornithine and its participation in polyamine synthesis, which has a positive effect on albumin synthesis, is under study. Likewise, the inverse relation between acute-phase protein synthesis and albumin synthesis regulated by interleukin 1 and other cytokines will merit further study. These are a few of the concepts which will be tested in the future.

Regulation of protein synthesis by polyamines

Present experimental data show that the synthesis of ribosomal protein S1 and PI protein was stimulated greatly by polyamines at the early stage after addition of putrescine in polyamine-requiring mutants of E. coli. No macromolecular synthesis was stimulated at this stage. Polyamine stimulation of the synthesis of these proteins probably plays an important role for cell growth. In polyamine-deficient bovine lymphocytes, protein synthesis became perturbed before RNA and DNA synthesis. Among enzymes concerned with DNA replication, thymidine kinase activity was most strongly influenced by polyamines. The activity in polyamine-deficient cells was only 7% of the level in normal cells. Judging from the amount of thymidine kinase mRNA and its distribution in polysomes, it was concluded that polyamines mainly regulate the synthesis of thymidine kinase at the level of initiation of protein synthesis. A polyamine-free protein synthetic system, established from components of rabbit reticulocytes, consisted of globin mRNA, salt-washed ribosomes, partially purified initiation factors, and pH 5 enzymes. Spermidine added to this system not only lowered the optimal magnesium concentration required for globin synthesis, but it also stimulated the globin synthesis 8- to 10-fold. The optimal spermidine concentration was 0.4 to 0.6 mM, a concentration similar to that in intact rabbit reticulocytes. The ratio of alpha to beta globin chains synthesized in the presence of spermidine and Mg2+ was approximately 1.0, while the ratio in the presence of only Mg2+ was approximately 1.5. The results strongly suggest that polyamines play an important role in rabbit reticulocyte protein synthesis.

Polyamine binding sites on Escherichia coli ribosomes

To determine the binding sites of polyamines on Escherichia coli ribosomes, ribosomal proteins crosslinked with polyamines through bifunctional reagents were analyzed. When 1,5-difluoro-2,4-dinitrobenzene was used as a crosslinking reagent, spermine was bound to S3, S8, S9, L1, L2, L3, L5, L6, L13, L18, L24, and L27 proteins. When dimethyl suberimidate was used, spermine was bound to S1, S3, S4, S5, S7, S8, S9, S15, L1, L2, L3, L6, L18, and L24 proteins. In addition to crosslinking with the above proteins, spermidine, when crosslinked with dimethyl suberimidate, bound to S2, S14, S20, L4, L5, L9, L13, and L16 proteins. The relationship between the binding site(s) of polyamines on ribosomes and the function of polyamines is discussed.

Effect of polyamines on in vitro reconstitution of ribosomal subunits

The effect of polyamines on in vitro reconstitution of Escherichia coli 30S and 50S ribosomal subunits has been studied. Spermidine stimulated the reconstitution of 30S particles from 16S rRNA lacking the methyl groups on two neighboring adenines and total proteins of 30S subunits at least 1.6-fold. The reconstitution of 30S particles from normal 16S rRNA and total proteins of 30S subunits exhibited only slight spermidine stimulation. However, the optimal Mg2+ concentration of the reconstitution was decreased from 20 mM to 16 mM in the presence of 3 mM spermidine. In the absence of spermidine the assembly of 30S particles from normal 16S rRNA was more rapid than the assembly from 16S rRNA lacking the methyl groups on two neighboring adenines. The reconstitution of 50S particles from 23S and 5S rRNA and total proteins of 50S subunits was not influenced greatly by spermidine. Gel electrophoresis results, from reconstitution experiments of 30S particles from 16S rRNA lacking the methyl groups on two neighboring adenines and total proteins of 30S subunits, showed that the assembly of S1 and S9 proteins to 23S core particles was stimulated by spermidine during reconstitution. The relationship of polyamine effects on in vitro ribosome assembly from its constituents to in vivo ribosome assembly is discussed. The reconstitution of Bacillus subtilis 30S particles from 16S rRNA and total proteins of 30S subunits was also stimulated approximately 1.3-fold by 3 mM spermidine.

pH dependence of kinetic parameters for oxalacetate decarboxylation and pyruvate reduction reactions catalyzed by malic enzyme

Both chicken liver NADP-malic enzyme and Ascaris suum NAD-malic enzyme catalyze the metal-dependent decarboxylation of oxalacetate. Both enzymes catalyze the reaction either in the presence or in the absence of dinucleotide. The presence of dinucleotide increases the affinity of oxalacetate for the chicken liver NADP-malic enzyme, but this information could not be obtained in the case of A. suum NAD-malic enzyme because of the low affinity of free enzyme for NAD. The kinetic mechanism for oxalacetate decarboxylation by the chicken liver NADP-malic enzyme is equilibrium ordered at pH values below 5.0 with NADP adding to enzyme first. The Ki for NADP increases by a factor of 10 per pH unit below pH 5.0. An enzyme residue is required protonated for oxalacetate decarboxylation (by both enzymes) and pyruvate reduction (by the NAD-malic enzyme), but the beta-carboxyl of oxalacetate must be unprotonated for reaction (by both enzymes). The pK of the enzyme residue of the chicken liver NADP-malic enzyme decreases from a value of 6.4 in the absence of NADP to about 5.5 with Mg2+ and 4.8 with Mn2+ in the presence of NADP. The pK value of the enzyme residue required protonated for either oxalacetate decarboxylation or pyruvate reduction for the A. suum NAD-malic enzyme is about 5.5-6.0. Although oxalacetate binds equally well to protonated and unprotonated forms of the NADP-enzyme, the NAD-enzyme requires that oxalacetate or pyruvate selectively bind to the protonated form of the enzyme. Both enzymes prefer Mn2+ over Mg2+ for oxalacetate decarboxylation.(ABSTRACT TRUNCATED AT 250 WORDS)

H4 histone messenger RNA decay in cell-free extracts initiates at or near the 3' terminus and proceeds 3' to 5'

The relative decay of four human messenger RNAs, gamma globin, delta globin, c-myc and H4 histone, were compared in a cell-free system. Under appropriate conditions, they are degraded in vitro in approximately the same relative order as in vivo: histone faster than c-myc and delta globin faster than gamma globin. Degradation of polysome-associated H4 histone mRNA and of deproteinized histone mRNA begins at or near the 3' terminus. At least a portion of the mRNA then continues to be degraded in a 3' to 5' direction. Discrete 3'-terminal degradation hold-up points are observed, suggesting that 3' to 5' degradation occurs non-uniformly. Cycloheximide and puromycin inhibit protein synthesis but do not affect the rate or directionality of histone mRNA decay in vitro. We conclude that the rate-limiting step in H4 histone mRNA decay occurs at or near the 3' terminus and that at least a portion of the mRNA molecule is subsequently degraded 3' to 5', probably via a processive exonuclease.

Effect of polyamines on translation fidelity in vivo

Polyamines, when added to cell-free protein-synthesizing systems, have been shown either to reduce mistranslation or to increase it depending upon the composition of the reaction mixture. To study this question under conditions as natural as possible we investigated the effects of polyamines on the fidelity of protein synthesis in intact Escherichia coli bacterial cells, using strains which were auxotrophic for polyamine synthesis. Error was measured in two ways: the incorporation of [3H]histidine into coat protein of bacteriophage MS2, the gene of which does not code for histidine, and the synthesis of a basic variant of MS2 coat protein in which a lysine erroneously replaces an asparagine, causing a change in isoelectric point. We found that when cell cultures were supplemented with polyamines there was no effect on the first type of error and the second type decreased twofold. The measured errors occurred at the level of translation because their frequency increased in the presence of streptomycin and decreased in cells bearing a streptomycin-resistance mutation known to lower the occurrence of translational misreading. The average erroneous incorporation per mol coat protein in the presence of polyamines was 1.43 +/- 0.59 mmol histidine and 25-34 mmol lysine/asparagine substitution. The reason for the different effect of polyamines on the two types of error is not known but could be related to the difference between their corresponding frequencies or to codon-specific effects.

N1-monoacetylation abolishes the inhibitory effect of spermine and spermidine in the reticulocyte lysate translation system

At optimum magnesium, the translation of rat heart mRNA in the nuclease treated rabbit reticulocyte lysate system was inhibited by low concentrations of spermidine or spermine but not of putrescine. Spermidine and spermine cause a general reduction in the translation of all the heart mRNAs since no differential effects were observed when the translation products were examined by gel electrophoresis. Spermine was a five times more potent inhibitor than spermidine but no inhibition was obtained with N1-acetylspermidine or N1-acetylspermine. Since analyses of endogenous polyamines demonstrate that the inhibitory concentrations of spermine could be obtained by converting a small fraction of the endogenous spermidine to spermine, these results indicate that interconversions of the polyamines might be a sensitive regulatory mechanism for protein synthesis.

Ribosomes are stalled during in vitro translation of alfalfa mosaic virus RNA 1

In the presence of plant tRNAs the full-length translation product of alfalfa mosaic virus RNA 1 is produced in rabbit reticulocytes only at low mRNA concentration. At higher mRNA concentration translation is restricted to the 5' half of RNA 1. At high mRNA concentration the full-length product can be formed when additional plant tRNA and glutamine are supplied to the translation mixture. In contrast, in the presence of yeast or calf liver tRNA the translation pattern of alfalfa mosaic virus RNA 1 always results in the synthesis of the full-length product. Pulse-chase experiments in the presence of plant tRNAs show that the ribosomes pause at several positions in the 5' half of RNA 1. The pausing time is different at the different 'halting places'. Protein synthesis is resumed upon addition of glutamine, even when the addition is delayed for more than 3 h after the start of protein synthesis. Only one tRNA species, purified from wheat germ or tobacco, could promote full-length translation of RNA 1. This tRNA can be charged with glutamine. Analysis of the position of glutamine codons on RNA 1 shows a correlation between the positions of the CAA codons and the halting places of the ribosomes. The CAA codon (for any other codon) on its own cannot be responsible for the pausing of the ribosomes, since a variety of RNAs, known to contain all sense codons, are translated efficiently in rabbit reticulocyte lysates in the presence of plant tRNAs. Apparently other elements can restrict decoding of normal codons during protein chain elongation.

The effects of dicyclohexylamine on polyamine biosynthesis and incorporation into turnip yellow mosaic virus in Chinese cabbage protoplasts infected in vitro

We have reported (R. Balint and S. S. Cohen, 1985, Virology 144, 181-193) that protoplasts from plants infected with turnip yellow mosaic virus (TYMV) continue to produce virus in culture and that newly formed virus particles contained predominantly newly synthesized spermidine and spermine. Inhibition of spermidine synthesis by dicyclohexylamine (DCHA), however, led to incorporation of preexisting spermidine and increased amounts of spermine into newly formed virions. We now report similar results with healthy protoplasts infected in vitro, in which essentially all of the virus is newly formed. Again, newly synthesized spermidine and spermine were preferentially incorporated into virus. DCHA inhibited spermidine synthesis by 85%, leading in 20 hr to a 60% depletion of the cellular spermidine and a 30% reduction in the amount of spermidine per virion. Spermine synthesis increased, however, producing a 40% increase in cellular spermine and 50-100% increase in the amount of spermine per virion. Thus, in spite of spermidine depletion, the total positive charge contributed by polyamines to the virus was essentially conserved.

Ribosomal protein phosphorylation induced during Q fever or by lipopolysaccharide: in vitro translation is stimulated by infected liver ribosomes

Q fever, as well as the lipopolysaccharide prepared from the rickettsial agent Coxiella burnetii, stimulates the phosphorylation of guinea pig liver ribosomal protein S6. In vitro mRNA and ribosome-dependent rabbit reticulocyte lysate translation systems reconstituted with ribosomes and mRNAs from infected animal livers were more active than those with mRNAs and ribosomes from uninfected animals. Treatment of ribosomes with a ribosomal supernatant phosphatase reduced the in vitro translation activities; the largest decreases occurred in systems with ribosomes and mRNAs from infected liver. These experiments provide a basis for explaining the increased hepatic protein synthesis during Q fever and demonstrate, perhaps for the first time, the phosphorylation of ribosomal protein in response to lipopolysaccharide. The implications of these observations are discussed in the context of previous studies on stimulated transcription and translation during Q fever.

Characteristics of the translation of thymosin alpha 1 precursor mRNA by cell-free wheat germ system. Evidence for the acetylation of thymosin alpha 1 precursor

At the optimal concentrations of Mg2+ and K+ to translate total thymus PolyA+-RNA, the purified thymosin alpha 1 precursor mRNA saturate the protein synthetic activity at lower concentration than the total thymus mRNAs. The polyamine spermidine increases the translation rate of the messenger, which is modulated by magnesium, rather than improve the yield in full-length chains of thymosin alpha 1 precursor. As other eukariotic mRNAs, this messenger presents the "cap" modification at the 5'-end terminal position. The incorporation of [3H]acetate into the translation product of the messenger, shows an evidence for the acetylation of the thymosin alpha 1 precursor during its biosynthesis in vitro.

Interaction of spermidine with viral RNA and its influence on protein synthesis

Addition of spermidine to a cell-free protein synthesizing system from wheat germ programmed with total brome mosaic virus (BMV) RNA resulted in a several-fold stimulation of amino acid incorporation. Increasing the spermidine concentration in the system led to inhibition of the overall protein synthesis, but the production of longer polypeptides was inhibited much more than that of the coat protein (shorter product). Analysis of the products synthesized under direction of BMV RNA 3 (longer product) and RNA 4 (coat protein) revealed that optimal translation of RNA 3 occurred at a much lower concentration of spermidine than that of RNA 4. Binding experiments with radioactive spermidine and BMV RNAs showed that the saturation of spermidine binding is achieved at a lower concentration of spermidine for RNA 3 than for RNA 4, which may suggest that the structure of RNA 4 is more compact than that of RNA 3. Taking into account the binding obtained at a spermidine concentration corresponding to optimal conditions of protein synthesis, it may be concluded that the optimum translation of these two mRNAs occurs when there is a similar level of RNA charge neutralisation, which implies a similar level of RNA structure stabilisation.

Differential inhibition of protein synthesis: a possible biochemical mechanism of thalidomide teratogenesis

A theory concerning the chemical and biochemical mechanisms of thalidomide teratogenesis is presented. A considerable body of evidence suggests that the glutarimide ring of thalidomide may exert its biological activity because of its resemblance to the imide pyrimidines thymine and uracil. In addition to the glutarimide ring, thalidomide contains a moderately reactive phthalimide moiety, which allows the spontaneous formation of various glutarimide derivatives in fetal tissues. A model is proposed in which the phthalimide group reacts with small nucleophiles, most likely the polyamines, to produce a derivative(s) having a similar biochemical potential to that of cycloheximide, a glutarimide which is a powerful inhibitor of the elongation phase of protein synthesis. Interference in the elongation phase results in the selective inhibition of the translation of messages which have a high translational efficiency. Evidence is reviewed concerning the differential inhibition or protein synthesis by cycloheximide and the effects of this inhibition on various biochemical and biological processes which are critical during development and differentiation. A similar biochemical activity by the putative thalidomide derivative(s) could explain its extreme teratogenic potential. A number of parallels between the biological effects of thalidomide and cycloheximide are discussed which support the idea that a similar biochemical activity is involved. The theory readily explains many of the observed biological effects of thalidomide including the large difference between fetal and adult toxicity. In addition, evidence is reviewed which suggests that the teratogenic properties of a number of drugs which are structurally related to thalidomide may have a common chemical basis due to the similarity of their imide core structures to thymine and uracil.

Cellular proliferation and hypusine synthesis

Hypusine (N(-)-(4-amino-2-hydroxybutyl) lysine), a spermidine-dependent post-translational protein modification, is synthesized by various mammalian cells in culture. Experiments described in this paper demonstrated a relationship between rates of cellular growth and the synthesis of hypusine. Cells that divide at fast rates have a high rate of hypusine synthesis. In kinetic experiments, a positive relationship is evident between the rates of protein, DNA and hypusine synthesis. Cells seeded at high density, growing non-exponentially, synthesized less hypusine than logarithmically growing cells seeded at low density. Slowing the growth rate of cells by modification of the external milieu also results in a decreased rate of hypusine synthesis. These results provide additional evidence of the association of hypusine with cell proliferation in cultured cell lines and suggest a possible role for this unusual post-translational modification in the complex macromolecular events leading to cellular growth.

Necessity of polyamines for maximum in vivo synthesis of beta beta' subunits of RNA polymerase

The possibility that polyamines can stimulate the in vivo synthesis of beta beta' subunits of RNA polymerase has been examined through the use of a polyamine-requiring mutant of Escherichia coli. Results from autoradiographic estimation and activity measurement of RNA polymerase in cell extracts prepared from polyamine starved and unstarved bacteria showed that polyamines stimulate the synthesis of beta beta' subunits of RNA polymerase 2- to 3.6-fold.

Polyamine requirement for microbial protein synthesis: structural specificity in cell-free systems of Escherichia coli

Cell-free protein synthesis was performed with synthetic or natural mRNA in an E. coli system containing physiological concentrations of Ca2, Mg2 and either one or both of the two natural polyamines of E. coli, spermidine and putrescine, or corresponding homologues. Putrescine does not permit poly(U)-dependent poly(Phe) synthesis unless spermidine or nor-spermidine is added. Spermidine supports homopeptide synthesis sufficiently well, its effect being stimulated by putrescine or homologous diamines with increasing chain length from 4 to 7 carbon atoms. Diaminopropane completely inhibits the spermidine-activated system in a competitive manner. Translation of MS2 phage RNA is supported by putrescine, the rate and quality (read through to the termination signal) of translation is optimized by spermidine or triamine homologues. MS2 phage RNA translation is supported by spermidine, putrescine has no further stimulatory effect but diaminoheptane enhances the rate of translation. In this case, however, premature chain termination does occur. The results indicate that spermidine is necessary for optimal poly(U) and MS2 phage RNA translation, that the aminopropyl moiety is important for its function and that the remaining side chain can be extended from C4 to C8. Putrescine may cooperate with spermidine but its chain length is rather critical, it cannot substitute for spermidine. The results indicate that the polyamines facilitate mRNA/tRNA/ribosome interactions in a specific manner.

Preferential stimulation of the in vivo synthesis of a protein by polyamines in Escherichia coli: purification and properties of the specific protein

The possibility that polyamines can stimulate the synthesis of special kinds of proteins has been examined by using a polyamine-requiring mutant of Escherichia coli. It was found that the synthesis of some proteins, particularly one with a molecular weight (Mr) of 62K, was significantly stimulated following polyamine supplementation of polyamine-starved cells. The preferential stimulation of the synthesis of this polyamine-induced protein of Mr 62K (PI protein) was followed by the stimulation of overall protein synthesis by polyamines. PI protein was purified to homogeneity and some of its properties were examined. From studies on the effect of PI protein on MS2 RNA directed protein synthesis, it was shown that this protein stimulated the synthesis of RNA replicase by 2.2-fold in the presence of 1 mM spermidine.

Anti-inflammatory effects of polyamines in serotonin and carrageenan paw edemata - possible mechanism to increase vascular permeability inhibitory protein level which is regulated by glucocorticoids and superoxide radical

Serotonin paw edema of mice and carrageenan paw edema of rats were inhibited by subcutaneously or orally administered certain polyamines. They must be given at least 2 h before serotonin challenge to get inhibitions which were blocked by the concomitant injections of cycloheximide. Thirty percent inhibitory dose (ID30) of polyamines (s.c.) 3 h before serotonin (s.c.) were: spermidine (8 mg/kg), spermine 28 mg/kg) and putrescine (55 mg/kg). Agmatine, cadaverine, ornithine, citrulline, lysine and arginine were not inhibitory even at 200 mg/kg. Three inhibitory polyamines were effective by oral administration but were not inhibitory by local administration into the paws. Intravenous injections of spermidine also required 2 h of lag period for inhibitions. Serotonin edema was inhibited by dexamethasone (1 mg/kg), prednisolone (1 mg/kg) or by superoxide dismutase (SOD, 5 mg/kg) in lag period requiring manner (s.c. and i.v.). High dose of cyclo-oxygenase inhibitors indomethacin and diclofenac sodium, lipo-oxygenase inhibitor BW755C (30 mg/kg s.c., respectively) and phospholipase A2 inhibitor quinacrine (100 mg/kg s.c.) failed to inhibit serotonin edema, suggesting that arachidonate metabolites are not participating in this model. ID30 of polyamines which were administered (s.c. and oral) to rats 3 h before carrageenan and determined at 3 h by paw weight were: spermidine (28 and 100 mg/kg), spermine (18 and 90 mg/kg) and putrescine (both greater than 200 mg/kg). Adrenalectomized rats responded to polyamines just as normal rats. Local vascular permeability, irritancy and acute toxicity were also tested in mice. Polyamines were proved to be glucocorticoid-type anti-inflammatory drugs. Polyamines may be mediators of glucocorticoids for the synthesis of the postulated vascular permeability inhibitory protein (called as 'vasoregulin' for convenience). Anti-inflammatory effect of glucocorticoid is recently explained by its capacity to induce phospholipase A2 inhibitory protein(s) (macrocortin or lipomodulin). However, this hypothesis has not yet been proved by in vivo experiment and our data suggest that there is induction by glucocorticoid of another kind of protein which does not inhibit phospholipase A2 activity.

Resolution of the discrepancy between a gene translation--termination codon and the deduced sequence for release of the encoded polypeptide

The translation-termination codon of the synthetase gene of the RNA phage MS2 has been determined, by nucleotide sequencing and suppression studies in vitro, to be UAG. However in one of the only two studies on the signals for polypeptide chain release at the end of genes, Capecchi and Klein [(1970) Nature (Lond.) 226, 1029-1033] deduced that the synthetase of an almost identical phage, R17, is released at UAA. Here we show that under certain conditions the synthetase is released at the UAG terminator but that this UAG is especially prone to read-through with resulting release at the downstream UAA codon. The possible significance of the UAG being in a context prone to leakiness is discussed but is unresolved.

Uridine-33 in yeast tRNA not essential for amber suppression

The nucleotide at position 33 on the 5' side of the anticodon of almost all tRNAs is a uridine. Crystallographic studies of different tRNAs reveal that although the precise orientation of uridine-33 is not always the same, it connects the anticodon stacked along the 3' side of the loop with the pyrimidine-32 stacked on the 5' side of the loop. The remarkably conserved nature of uridine-33 and its unique position in the anticodon loop structure has led to suggestions that this nucleotide has an essential role in the translational mechanism. We have developed a biochemical procedure to replace nucleotides 33-35 in yeast tRNATyr with any desired sequence and used it to construct amber suppressor tRNAs having different nucleotides at position 33. As all of these synthetic amber suppressor tRNAs functioned well in eukaryotic in vitro suppression assays, we conclude that uridine-33 does not have an obligatory role in the translation mechanism.

Differential stimulation by polyamines of phage DNA-directed in vitro synthesis of proteins

The effect of polyamines on T7- and lambda rifd18 DNA-directed synthesis of proteins in an Escherichia coli cell-free system has been studied. When T7 DNA was used as a template, the degree of stimulation by spermidine of protein synthesis was larger with T7 RNA polymerase than with Mr 42 K protein, while the synthesis of Mr 13.5 K protein was not stimulated significantly by spermidine. The synthesis of T7 RNA polymerase was stimulated approx. 10-fold by 1 mM spermidine. When lambda rifd18 DNA was used as a template, the synthesis of beta beta' subunits of RNA polymerase was stimulated greatly by spermidine, while the synthesis of elongation factor Tu and ribosomal proteins was not stimulated significantly by spermidine. Spermidine stimulation of T7 DNA-directed synthesis of T7 RNA polymerase was at the level of both translation and transcription. The degree of stimulation by spermidine was greater at the level of translation. Putrescine stimulated the synthesis of T7 RNA polymerase and Mr 42 K protein to a small degree at the level of translation.

Stimulation of hepatic and renal ornithine decarboxylase activity by selected amino acids

The activity of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine synthesis, increases after a protein meal. The effect of amino acid mixtures on hepatic and renal ODC activity and polyamine content was studied in postabsorptive and 72-hour fasted rats. Fasting decreased ODC activity in liver and in kidney by approximately 50%. Hepatic ODC activity increased tenfold 4 hours after intraperitoneal injection of either 1 g/kg of a synthetic mixture of 17 amino acids or of casein hydrolysate to fed rats and about 20-fold in fasted rats. Renal ODC activity increased four- and tenfold respectively. A mixture of glutamate, aspartate, and alanine at concentrations given in the hydrolysate reproduced the full amino acid effect. No amino acid was effective when given alone, nor were mixtures of the other amino acid constituents of the hydrolysate. Glutamate + alanine was ineffective as were glucose or various combinations of arginine, ornithine, aspartate and NH3. Ornithine + glutamate or aspartate + glutamate were active but stimulated less than aspartate + glutamate + alanine. Hepatic and renal putrescine content increased in parallel with ODC activity. The data suggest that specific amino acids possess the full ODC-stimulating capability of a high quality protein and that polyamine synthesis is linked to urea cycle activity.

Polyamine inhibition of gastric ulceration and secretion in rats

The effect of polyamines on gastric ulceration and secretion in rats was studied. Stress-induced gastric ulceration and ulceration in pylorus-ligated rats were inhibited by subcutaneous or oral administration of spermine; spermidine's inhibitory effect was somewhat less. Histamine-induced ulceration was also inhibited by the subcutaneous injection of spermine. In addition, the daily oral administration of spermine for 10 days was therapeutic against an acetic acid-induced ulcer (chronic ulcer). Gastric secretion in pylorus-ligated rats and in rats with fistulae and stimulated by histamine injection was decreased by the subcutaneous injection of spermine.

The study of spermidine-stimulated polypeptide synthesis in cell-free translation of mRNA from lactating mouse mammary gland

The stimulatory effect of spermidine on the translation of poly(A)+ mRNA from lactating mouse mammary glands in a wheat germ system was studied. Spermidine stimulated total polypeptide synthesis about 2.5-fold relative to that occurring in the presence of an optimal concentration of Mg2+ alone. The size and the number of polysomes were about 1.6-times larger in the presence of spermidine than in its absence. A similar magnitude of increase in peptide chain initiation, 1.4-fold, was found when the extent of peptide chain initiation was measured by determining the residual polypeptide synthesis subsequent to the addition of inhibitor(s) of peptide chain initiation to the in vitro translation system with or without spermidine at various times of the incubation. Time-course study of the release of polypeptide from polysomes showed that spermidine stimulated this process to a much greater extent than peptide chain initiation, indicating that the polyamine also increases the rate of peptide chain elongation. The extent of stimulation of peptide chain elongation by spermidine was estimated to be about 1.5-fold when the disappearance of isotope-labeled nascent peptides from polysomes was measured by pulse-chase experiments. These results indicate that spermidine stimulates the cell-free translation of mammary mRNA by increasing the rates of both initiation and elongation of polypeptide synthesis to almost the same extent. The polyamine also reduced the relative amount of incomplete polypeptides, thereby increasing the yield of full-length translational products.

Polyamines enhance readthrough of the UGA termination codon in a mammalian messenger RNA

The polyamines spermidine and spermine stimulate the readthrough of the UGA termination codon of rabbit beta-globin mRNA when it is translated in a rabbit reticulocyte cell-free system. The other major polyamine, putrescine, does not show this effect. The polyamine induced readthrough is specific for UGA as the UAA termination codon of alpha-globin mRNA is not read through and general translational misreading errors are not occurring in the presence of spermidine or spermine. The probable mechanism of this effect and some possible regulatory implications are discussed.

Phosphorylation of troponin and myosin light chain by cAMP-independent casein kinase-2 from rabbit skeletal muscle

Casein kinase-2 from rabbit skeletal muscle was found to phosphorylate, in addition to glycogen synthase, troponin from skeletal muscle, and myosin light chain from smooth muscle. Troponin T and the 20,000 Mr myosin light chain are phosphorylated by casein kinase-2 at much greater rates than glycogen synthase. The V values for the phosphorylation of troponin and myosin light chain are nearly an order of magnitude greater than that of glycogen synthase; however, the Km values for these two substrates are greater than that for glycogen synthase. The kinase activities with the various protein substrates are stimulated approximately three- and fivefold by 5 mM spermidine and 3 mM spermine, respectively. Heparin is a potent inhibitor of the kinase when casein, glycogen synthase, or myosin light chain is the substrate. However, with troponin as substrate the kinase is relatively insensitive to inhibition by heparin. The amount of heparin required for 50% inhibition with troponin as substrate is at least 10 times greater than with casein as substrate. The phosphorylation of troponin by casein kinase-2 results in the incorporation of phosphate into two major tryptic peptides, which are different from those phosphorylated by casein kinase-1. The site in myosin light chain phosphorylated by casein kinase-2 is different from that phosphorylated by myosin light chain kinase.

Changes in polyamine metabolism during experimental periodontitis in dogs and the role of putrescine in recovery

There are many reports showing a close relationship between polyamine metabolism and tissue growth or the recovery of damaged tissues, such as that occurring after partial hepatectomy. Therefore, it was proposed that the metabolism of polyamines might change in periodontitis induced by attaching surgical ligatures below the gingival margin of dog molars. One to two days after fixing the ligatures, the putrescine content and activity of ornithine decarboxylase in the tissue rose to about twice the control levels and then decreased gradually to control levels on day 7. No significant change in spermidine or spermine concentration was observed during this period. When the ligatures were removed on day 7, the putrescine content increased to about 2.5 times the normal level within 12 h. Ornithine decarboxylase activity changed in parallel with the change in putrescine content. Clinical and histopathological indications of periodontitis then started to decrease and had almost disappeared 2 weeks after removal of the ligatures. On the other hand, when the ligatures were removed on day 14, no significant increase in putrescine content was observed within 36 h and the rate of recovery from periodontitis was significantly slower than when the ligatures were removed on day 7. However, application of putrescine to the periodontal pocket immediately after removal of the ligatures on day 14 increased the rate of recovery, as determined by histological criteria. These findings suggest that putrescine or its metabolites are important in the process of recovery from periodontitis.

Ornithine decarboxylase may be a multifunctional protein

Ornithine decarboxylase may undergo posttranslational modifications which alter its function. Both transamidation of glutamine residues in the enzyme catalyzed by TGase and phosphorylation of serine and threonine residues catalyzed by a polyamine-stimulated protein kinase have been demonstrated. Data are presented which suggest that these modifications result in translocation of the modified protein to the nucleolus where it regulates the activity of RNA polymerase I to transcribe rDNA, the only active nucleolar genes. Transamidation of specific proteins with primary amines catalyzed by intracellular TGase may be an important posttranslational modification, capable of altering genetic transcription. The rapid half-life of ODC (10-15 min) may be related to rapid posttranslational modification with loss of enzymatic activity rather than to protein degradation.

Increase of fidelity of polypeptide synthesis by spermidine in eukaryotic cell-free systems

The mechanism of spermidine-induced increase of fidelity of polypeptide synthesis in a wheat germ cell-free system has been studied. It was found that the increase of fidelity in the presence of spermidine occurred mainly at the level of binding of aminoacyl-tRNA to ribosomes, that reduction of misreading was more marked at the 5'-base than at the 3'-base of the codon and that misreading caused by paromomycin and kanamycin C was not significantly decreased by spermidine. It was deduced from these results that spermidine inhibited low-frequency misreading more strongly than high-frequency misreading. In addition, spermidine was found to stimulate the rejection of non-cognate aminoacyl-tRNA mainly at an initial discrimination step during the binding of amino-acyl-tRNA to ribosomes, and slightly at a subsequent GTP-dependent discrimination step, the so-called proofreading step. In yeast, rabbit reticulocyte, and Artemia salina cell-free systems, spermidine was found to increase the fidelity of protein synthesis.

Stabilization of 30 S ribosomal subunits of Bacillus subtilis W168 by spermidine and magnesium ions

An explanation for the fragility of 30 S ribosomal subunits of Bacillus subtilis has been studied. Degradation of 16 S ribosomal RNA, rather than degradation of ribosomal proteins, was found to cause the inactivation of 30 S subunits. Although RNAases were bound specifically to 30 S ribosomal subunits, the RNAases were able to function. Spermidine was found to contribute to the stabilization of 30 S ribosomal subunits by inhibiting the degradation of 16 S ribosomal RNA. A high concentration of Mg2+ also stabilized the 30 S ribosomal subunits of Bacillus subtilis. The polypeptide synthetic activity of 30 S ribosomal subunits prepared in the presence of spermidine was at least 4-times greater than that of 30 S ribosomal subunits prepared in the absence of spermidine; this activity was maintained without any loss for 3 months at -70 degrees C.

Polyamines inhibit the protein kinase 380--catalyzed phosphorylation of eukaryotic initiation factor 2 alpha

Polyamines putrescine, spermidine, and spermine specifically inhibit the PK 380--catalyzed phosphorylation of eukaryotic initiation factor 2 alpha (eIF-2 alpha). Since te PK 380--dependent phosphorylation of eIF-2 alpha inhibits the initiation or protein synthesis, the possibility exists that the polyamines enhance protein synthesis by inhibiting the phosphorylation of eIF-2 alpha by PK 380.

Differential stimulation by polyamines of phage RNA-directed synthesis of proteins

The effect of polyamines on Q beta and MS2 phage RNA-directed synthesis of three kinds of protein in an Escherichia coli cell-free system has been studied. With both phage RNAs, the degree of stimulation of protein synthesis by spermidine was in the order RNA replicase greater than A protein, while the synthesis of coat protein was not stimulated significantly by spermidine. The synthesis of RNA replicase was stimulated by 1 mM spermidine approx. 8-fold. From the results of Q beta RNA direct alanyl-tRNA and seryl-tRNA binding to ribosomes and initiation dipeptide synthesis, it is suggested that the preferential stimulation of the synthesis of RNA replicase by spermidine is due at least partially to the stimulation of the initiation of RNA replicase synthesis.