Relationship of the expression of the S20 and L34 ribosomal proteins to polyamine biosynthesis in Escherichia coli

Polyamine biosynthesis in Escherichia coli is regulated transcriptionally and post-translationally. Antizyme and ribosomal proteins S20 and L34 participate in post-translational inhibition of the polyamine biosynthetic enzymes ornithine and arginine decarboxylase. The aim of the present study was to investigate the significance of S20 and L34 in polyamine regulation in vivo. In vivo overexpression of S20 and L34 lowered the activities of ornithine and arginine decarboxylases and decreased total polyamine production. The levels of cadaverine, a related diamine whose synthesis is not regulated by S20 and L34, did not decrease but increased. The diminished ornithine and arginine decarboxylase activities are shown to result from reversible post-translational inhibition since the enzymes could be reactivated to normal levels upon titration of the inhibitors. The effects were specific as overexpression of eight other ribosomal proteins had no influence. Overexpression of ornithine decarboxylase results in elevated polyamine production and it increases S20 and L34 levels but not those of other ribosomal proteins. Ornithine depletion decreases S20 and L34 to normal levels in the ornithine decarboxylase overproducing cells. Immunoprecipitation experiments coupled with immunoblots indicated that ornithine and arginine decarboxylases physically interact with S20 and L34. This study shows that ribosomal proteins S20 and L34 can inhibit ornithine and arginine decarboxylases and polyamine biosynthesis in vivo. It is concluded that, unlike other basic ribosomal proteins and polycationic compounds which inhibit the activities of these enzymes only in vitro, S20 and L34 are biologically relevant in the regulation of the polyamine biosynthetic pathway.

Post-translational and transcriptional regulation of polyamine biosynthesis in Escherichia coli

Ornithine and arginine decarboxylases (ODC and ADC) of Escherichia coli are inhibited post-translationally by antizyme and ribosomal proteins S20 and L34. The inhibition of either enzyme is relieved when excess of the other decarboxylase is added. Using this approach, in vitro as well as in vivo, we demonstrate that the extent of the post-translational inhibition of ODC and ADC in E. coli is at least 65 and 50%, respectively. The inhibited enzyme levels increase even further upon exposure of cells to polyamines. The post-translational mode of regulation can counteract a 4-fold increase of ODC protein in the cell. The negative transcriptional regulation of ODC and ADC expression by polyamines is mediated by transcription factors and not by direct polyamine effects on the promoters of their genes. Three proteins interacting with the ODC promoter region were found by southwestern blot analysis.

Identification, cloning, and nucleotide sequencing of the ornithine decarboxylase antizyme gene of Escherichia coli

The ornithine decarboxylase antizyme gene of Escherichia coli was identified by immunological screening of an E. coli genomic library. A 6.4-kilobase fragment containing the antizyme gene was subcloned and sequenced. The open reading frame encoding the antizyme was identified on the basis of its ability to direct the synthesis of immunoreactive antizyme. Antizyme shares significant homology with bacterial transcriptional activators of the two-component regulatory system family; these systems consist of a "sensor" kinase and a transcriptional regulator. The open reading frame next to antizyme is homologous to sensor kinases. Antizyme overproduction inhibits the activities of both ornithine and arginine decarboxylases without affecting their protein levels. Extracts from E. coli bearing an antizyme gene-containing plasmid exhibit increased antizyme activity. These data strongly suggest that (i) the cloned gene encodes the ornithine decarboxylase antizyme and (ii) antizyme is a bifunctional protein serving as both an inhibitor of polyamine biosynthesis as well as a transcriptional regulator of an as yet unknown set of genes.

Transcriptional effects of polyamines on ribosomal proteins and on polyamine-synthesizing enzymes in Escherichia coli

We find that the transcription of various ribosomal proteins can be differentially affected by polyamines and by changes in growth rates. Using strain MG1655 of Escherichia coli K-12 (F-, lambda-), we have determined the effects of polyamines and changes in growth rate on the transcription of several ribosomal genes and the polyamine-synthesizing enzymes ornithine decarboxylase (L-ornithine carboxy-lyase; EC 4.1.1.17) and arginine decarboxylase (L-arginine carboxylyase; EC 4.1.1.19). Ribosomal proteins S20 and L34 can be differentiated from the other ribosomal proteins studied; the transcription of S20 and L34 is especially sensitive to polyamines and less sensitive to changes in growth rates. In contrast, the transcription of S10, S15, S19, L2, L4, L20, L22, and L23 is insensitive to polyamines although it is particularly sensitive to changes in growth rates. Like S20 and L34, the transcription of ornithine decarboxylase and arginine decarboxylase is especially sensitive to polyamines. Polyamines specifically enhance the transcription of ribosomal proteins S20 and L34, and decrease that of ornithine decarboxylase and arginine decarboxylase. It is evident that polyamines can exert both positive and negative regulation of gene expression in E. coli that can be differentiated from the effects caused by changes in growth rates.

Biosynthesis of polyamines in ornithine decarboxylase, arginine decarboxylase, and agmatine ureohydrolase deletion mutants of Escherichia coli strain K-12

Escherichia coli K-12 mutants that carry deletions in their genes for ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) (speC), arginine decarboxylase (L-arginine carboxy-lyase, EC 4.1.1.19) (speA), and agmatine ureohydrolase (agmatinase or agmatine amidinohydrolase, EC 3.5.3.11) (speB) can still synthesize very small amounts of putrescine and spermidine. The putrescine concentration in these mutants was found to be 1/2500th that in spe+ cells. The pathway of putrescine synthesis appears to be through the biodegradative arginine decarboxylase, which converts arginine to agmatine, in combination with a low agmatine ureohydrolase activity--1/2000th that in spe+ strains. These results suggest that even such low levels of polyamines permit a low level of protein synthesis. Evidence is presented that the polyamine requirement for the growth of the polyamine-dependent speAB, speC deletion mutants, which are also streptomycin resistant, is not due to a decreased ability to synthesize polyamines.

Induction of ornithine decarboxylase activity by insulin and growth factors is mediated by amino acids

The polypeptide growth factors, nerve growth factor, epidermal growth factor, and platelet-derived growth factor, as well as insulin do not induce ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) unless a minimal concentration of an ornithine decarboxylase-inducing amino acid, such as asparagine, is present in the medium. The effects of the growth factors were studied in appropriately responsive cell lines: pheochromocytoma (PC12) cells for nerve and epidermal growth factors, fibroblasts (NIH 3T3) for platelet-derived growth factor, and fibroblasts and hepatoma (KRC-7) cells for insulin. The nonmetabolizable amino acid analog alpha-aminoisobutyric acid can replace asparagine, indicating that the covalent modification of the inducing amino acid is not necessary for the induction of ornithine decarboxylase by these growth factors. For the same intracellular concentration of the inducing amino acid, the presence of the growth factors induces higher levels of ornithine decarboxylase. The evidence indicates that these growth factors do not induce ornithine decarboxylase by raising the intracellular concentration of amino acids but rather act synergistically with the inducing amino acid. Evidence is provided that the induction of polyamine-dependent growth by these growth factors is mediated by amino acids. The relationship of these results to the A and N amino acid transport systems and to the Na+ influxes in relation to growth is discussed.

Relationship of biochemical drug effects to their antitumor activity--II. Diacridines and membrane-related reactions

A method is presented that determines the degree of attachment of cancer cells to normal cells. This method may be useful in determining the extent to which treatment of normal cells (or of a tumor-bearing host) with a particular chemotherapeutic agent may affect the degree of attachment of cancer cells to the normal cells. The effects of several diacridines upon this process are described. In addition, we have determined the ability of individual diacridines to alter the permeability of P-388 cells; this effect has been related to their antitumor properties. In general, the most effective antitumor diacridines are those that cause minimal disruption of cell permeability. Conversely, diacridines that disrupt cell permeability tend to have poor antitumor properties. It is considered that the toxicity of these compounds may be a necessary consequence of the assays used for testing anticancer agents, and may not necessarily be related to their antitumor activity.

The effect of transport system A and N amino acids and of nerve and epidermal growth factors on the induction of ornithine decarboxylase activity

The induction of ornithine decarboxylase (EC 4.1.1.17) (ODC) by amino acids and by the peptide hormones nerve growth factor (NGF) and epidermal growth factor (EGF) in salts-glucose media has been studied. Only those neutral amino acids taken into the cell via one of the Na+ dependent transport systems stimulate ODC activity. Asparagine and the nonmetabolizable alpha-amino-isobutyric acid (AIB) were used as representatives of this class of inducing amino acids, and their intracellular concentrations were related to the levels of ODC induced. A threshold intracellular concentration of asparagine or AIB has to be attained before ODC can be induced. Further slight increases in intracellular concentrations of asparagine or AIB produce disproportionately large increases of ODC, resulting in a sigmoidal curve of ODC induction. These results, and the fact that the decrease in ODC levels caused by valine is associated with a concurrent decrease in the intracellular level of the inducing amino acid, suggest that the intracellular amino acid level is causally related to the induction of ornithine decarboxylase. Glutamic acid, EGF, and NGF do not induce ODC except in the presence of an inducing amino acid. They act synergistically with the inducing amino acid and produce higher ODC levels at the same intracellular concentration of the inducing amino acid.

Regulation of polyamine biosynthesis by antizyme and some recent developments relating the induction of polyamine biosynthesis to cell growth. Review

This review considers the role of antizyme, of amino acids and of protein synthesis in the regulation of polyamine biosynthesis. The ornithine decarboxylase of eukaryotic cells and of Escherichia coli can be non-competitively inhibited by proteins, termed antizymes, which are induced by di- and poly- amines. Some antizymes have been purified to homogeneity and have been shown to be structurally unique to the cell of origin. Yet, the E. coli antizyme and the rat liver antizyme cross react and inhibit each other's biosynthetic decarboxylases. These results indicate that aspects of the control of polyamine biosynthesis have been highly conserved throughout evolution. Evidence for the physiological role of the antizyme in mammalian cells rests upon its identification in normal uninduced cells, upon the inverse relationship that exists between antizyme and ornithine decarboxylase as well as upon the existence of the complex of ornithine decarboxylase and antizyme in vivo. Furthermore, the antizyme has been shown to be highly specific; its Keq for ornithine decarboxylase is 1.4 X 10(11) M-1. In addition, mammalian cells contain an anti-antizyme, a protein that specifically binds to the antizyme of an ornithine decarboxylase-antizyme complex and liberates free ornithine decarboxylase from the complex. In E. coli, in which polyamine biosynthesis is mediated both by ornithine decarboxylase and by arginine decarboxylase, three proteins (one acidic and two basic) have been purified, each of which inhibits both these enzymes. They do not inhibit the biodegradative ornithine and arginine decarboxylases nor lysine decarboxylase. The two basic inhibitors have been shown to correspond to the ribosomal proteins S20/L26 and L34, respectively. The relationship of the acidic antizyme to other known E. coli proteins remains to be determined. In mammalian cells, ornithine decarboxylase can be induced by a broad spectrum of compounds. These range from hormones and growth factors to natural amino acids such as asparagine and to non-metabolizable amino acid analogues such as alpha-amino-isobutyric acid. The amino acids that induce ornithine decarboxylase as well as those that promote polyamine uptake utilize the sodium dependent A and N transport systems. Consequently, they act in concert and increase intracellular polyamine levels by both mechanisms. The induction of ornithine decarboxylase by growth factors, such as NGF, EGF, and PDGF as well as by insulin requires the presence of these same amino acids and does not occur in their absence. However, the inducing amino acid need not be incorporated into protein nor covalently modified.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantitation of metabolic cooperation by measurement of HGPRTase activity

A method for the quantitation of metabolic cooperation between cells is described. The method depends upon measuring the increase in HGPRTase activity that occurs between HGPRT+ cells and the HGPRT-LN (Lesch-Nyhan) cells. The variables upon which this method depends and their effect on the final determination are discussed.

Comparison of the basic Escherichia coli antizyme 1 and antizyme 2 with the ribosomal proteins S20/L26 and L34

The two basic Escherichia coli proteins that inhibit ornithine and arginine decarboxylase and were named provisionally antizyme 1 and antizyme 2 (Heller, J.S., Rostomily, R., Kyriakidis, D.A., and Canellakis, E.S. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 5181-5184) are shown to have long identical sequences with the ribosomal proteins S20/L26 and L34, respectively. We have also isolated ribosomal proteins from purified E. coli ribosomes by established methodology and further purified them by our purification procedure for antizymes 1 and 2. Of the various basic ribosomal proteins, two were found to have the same properties as antizyme 1 and 2. These results indicate that these two basic E. coli antizymes are ribosomal proteins. The nature of the acidic antizyme remains to be elucidated.

The regulation of hypoxanthine guanine phosphoribosyl transferase activity through transfer of PRPP by metabolic cooperation

We have developed a method of relating changes in hypoxanthine guanine phosphoribosyl transferase (HGPRTase) activity to the rate of phosphoribosyl pyrophosphate (PRPP) synthesis in isolated cell lines and in co-cultures of different cell lines. Using this approach, we have determined the response of the HGPRTase activity of communication-competent and communication-incompetent cells to changes in PRPP content. The HGPRTase activity of HGPRT+ communication-competent NS cells responds to changes of their own PRPP level, as well as to changes of the PRPP level of HGPRT- cells with which they are co-cultured. In contrast, the HGPRTase activity of the HGPRT+, but communication-incompetent L929 cells responds to changes of their own PRPP content but not to changes of the PRPP content of the cocultured HGPRT- cells. These and other experiments show that PRPP is freely exchangeable between communication-competent cells and that the intracellular activity of HGPRTase in one cell can be regulated by changes in the levels of its substrate in another cell through metabolic cooperation. The results also indicate that HGPRTase normally functions at a small fraction of its total activity, and that this can be greatly increased by raising the intracellular PRPP levels. Furthermore, it is found that when communication-competent cells establish intercellular communication, they share a common pool of PRPP and of purine nucleotides. This approach can be used as the basis of a biochemical method for the quantitation of metabolic cooperation between cells.

Purification and properties of the antizymes of Escherichia coli to ornithine decarboxylase

The purification of the antizymes to ornithine decarboxylase of Escherichia coli to homogeneity is detailed. An acidic component, pI 3.8, and two basic histone-like proteins, pI above 9.5, are described. The two latter proteins constitute approximately 90% of the total antizyme activity.

Regulation of polyamine biosynthesis in Escherichia coli by basic proteins

In Escherichia coli, the biosynthetic ornithine and arginine decarboxylases (EC 4.1.1.17 and 4.1.1.19, respectively) are responsible for the biosynthesis of polyamines from ornithine and arginine, respectively. When E. coli cells are grown in the presence of increasing amounts of polyamines, a progressive increase in the amount of antizyme 1 and antizyme 2 occurs. The amino acid compositions of antizymes 1 and 2 show them to be basic proteins; antizyme 1 has an amino acid composition similar to that of the E. coli histone-like protein HU and of the eukaryotic histone H2B; antizyme 2 is characterized by an unusually high arginine content. We find these proteins to be specific inhibitors of both the biosynthetic ornithine decarboxylase and the biosynthetic arginine decarboxylase. They do not inhibit the corresponding biodegradative ornithine and arginine decarboxylases, nor do they inhibit lysine decarboxylase or S-adenosylmethionine decarboxylase. These properties of the antizymes favor their function in the regulation of polyamine biosynthesis in E. coli. The ability of the purified antizymes to inhibit the ornithine and arginine decarboxylases is stabilized in acidic buffers and is lost upon prolonged exposure to solutions at neutral or basic pH.

Biochemical assay of inhibitors of metabolic cooperation

A significant and reproducible enhancement of purine nucleotide synthesis from hypoxanthine occurs in HAT medium, when communication-competent hypoxanthine-guanine phosphoribosyltransferase (HGPRT+) cells are co-cultured with communication-competent (HGPRT-) LN cells. This enhancement of purine nucleotide synthesis is dependent upon the hypoxanthine concentration and upon the ratio of (HGPRT-): (HGPRT+) cells. Based upon these results a simple biochemical method for the detection of inhibitors of metabolic cooperation between (HGPRT+) cells and (HGPRT-) LN cells is presented. The biochemical method distinguishes inhibitors of metabolic cooperation from inhibitors of hypoxanthine uptake, of hypoxanthine phosphorylation and of nucleic acid synthesis, as well as from general metabolic inhibitors. This method has the advantage that it can be used on a relatively large number of cells, it is simple and not time-consuming, and distinguishes the inhibition of metabolic cooperation by compounds that have a variety of sites of inhibition.

Studies on the role of protein synthesis and of sodium on the regulation of ornithine decarboxylase activity

The minimum requirements for eliciting or enhancing ornithine decarboxylase activity (EC. 4.1.1.17); L-ornithine carboxylase) in neuroblastoma cells incubated in salts-glucose solutions have been investigated. These incubation conditions permit the study of changes in ornithine decarboxylase activity independently of the growth-associated reactions that occur in cell culture media (Chen, K.Y. and Canellakis, E.S. (1977) Proc. Natl, Acad. Sci. U.S.A. 74, 3791-3795). Ornithine decarboxylase activity can be elicited by a variety of asparagine and other amino acid analogs, including alpha-aminoisobutyric acid, that cannot participate in protein synthesis. Of the eleven asparagine analogs tested, alpha-N-CH3-DL-asparagine is the most potent in eliciting ornithine decarboxylase activity and is equivalent to asparagine in this regard. Inclusion of polar groups into the asparagine molecule results in the loss of its ability to elicit ornithine decarboxylase activity. With the use of these analogs and of analogs of other amino acids it is shown that the rapid fall in ornithine decarboxylase activity that is noted following cycloheximide treatment may not be a consequence of the inhibition of protein synthesis. The rapid fall in ornithine decarboxylase activity is primarily due to the removal of the agent that elicits and stabilizes its activity. These results, the finding that alpha-aminoisobutyric acid stimulates ornithine decarboxylase activity and that sodium is required for the stimulation of ornithine decarboxylase activity are discussed in relation to the "A" amino acid transport system.

The inhibition of the serum-stimulated increase of ornithine decarboxylase by ionophores and local anesthetics

The addition of fresh serum-containing growth medium to L1210 mouse leukemic cells in culture resulted in a 5-fold increase in ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) activity. The presence of microtubule disrupting agents (colchicine, vinblastine) or cations (5-10 mM K+, Na+ or Mg2+) abolishes this increase of ornithine decarboxylase activity. (Chen, K.Y., Heller, J.S. and Canellakis, E.S. (1976) Biochem. Biophys. Res. Commun. 70, 212-219). Based on these observations we proposed that fluctuation in cellular cation concentrations may act as a link between the membrane structure and ornithine decarboxylase. To test this proposal, we studied the effects of selective membrane perturbing agents such as ionophores and local anesthetics, on the serum-stimulated increase of ornithine decarboxylase activity in L1210 cells. Among the six ionophores tested, valinomycin was the most potent one, with I50 value (concentration that gives 50% inhibition of ornithine decarboxylase activity) of 6.10(-9) M. Dibucaine and tetracaine were also effective inhibitors at 10(-4)-10(-5) M. The I50 values of valinomycin on the protein synthesis and RNA synthesis, however, were greater than 1.10(-6) M. These results substantiate the notion that ornithine decarboxylase activity can be regulated at plasma membrane level and such regulation is related to the perturbation of cellular cation pools.

The complexity of regulation of ornithine decarboxylase

Evidence is provided from Escherichia coli, from mammalian cells as well as from germinating barley seeds that there exist positive and negative macromolecular effectors of ODC (ornithine decarboxylase) that modify its activity. These effectors interact with ODC either by forming inactive complexes or by lowering its KmORN resulting in the activation of ODC. These facts, in addition to other evidence presented, argue for the existence of an equilibrium between: (Formula: see text) Such an equilibrium would result in the modulation of ODC activity independently of the net synthesis or degradation of ODC molecules.

Cellular control of ornithine decarboxylase activity by its antizyme

Conditions have been established under which the antizyme of ornithine decarboxylase (E.C. 4.1.1.17, L-ornithine carboxy-lyase, ODC) a non-competitive protein inhibitor of ODC, can be detected in cells in response to as little as 10(-7) M putrescine. The maintenance of intracellular antizyme activity depends upon the continued presence of putrescine in the medium. Removal of putrescine results in a rapid decline of antizyme activity. These phenomena are unaffected by the presence of cycloheximide and are comparable to the requirement of L-asparagine for the maintenance of ODC activity. The extent to which the antizyme level is increased is inversely related to the preexisting level of intracellular ODC at the time of addition of putrescine. The time of appearance of free antizyme is delayed in cells that have high levels of ODC; the amount of free antizyme that can be assayed for in these cells, at any particular time is correspondingly less. The converse is also true. In cells that have high levels of antizyme, the delay in appearance of ODC is greater and the amount of ODC that can be assayed for is correspondingly less than in cells with low levels of antizyme. These experiments, as well as others, indicate that the ODC antizyme and ODC interact in vivo with each other to modify their respective activities.

The surface glycoproteins of the HeLa cell. Internalization of wheat germ agglutinin-receptors

The sensitivity of 125I-labeled sialoglycoproteins to neuraminidase digestion was used to monitor the loss of specific membrane glycoproteins from the cell surface in to the cytoplasmic compartment during lectin-mediated endocytosis. These studies demonstrated that a major portion of the surface glycoproteins had undergone internalization concurrently with wheat germ agglutinin in a time- and temperature-dependent process. The internalized 125I-labeled glycoproteins were associated with the small vesicle fraction and were present in the same relative proportion as they existed in the plasma membrane isolated from control untreated cells. Many of the 125I-labeled membrane proteins were shown to be receptors and were isolated after affinity chromatography of the solubilized plasma membranes on wheat germ agglutinin-agarose columns.

Structural limitations on the bifunctional intercalation of diacridines into DNA

An homologous series of diacridines containing two 9-aminoacridine chromophores linked via a simple methylene chain has been studied in order to investigate the minimum interchromophore separation required to permit bifunctional intercalation. Viscometric, sedimentation, and electric dichroism experiments show that compounds having one to four methylene groups in the linker are restricted to monofunctional intercalation, whereas the interaction becomes bifunctional when the chain length is increased to six carbons or more. The results indicate that bifunctional reaction occurs with an interchromophore distance not exceeding 8.8 A, implying that intercalation by these compounds is not subject to neighbor exclusion if the mode of binding is of the classical intercalation type.

Modulation of ornithine decarboxylase activity in Escherichia coli by positive and negative effectors

Two effectors of ornithine decarboxylase (ODC; L-ornithine carboxy-lyase, EC 4.1.1.17) have been extracted from an ODC- (speC-) mutant, Escherichia coli MA 255. One of these is an ODC inhibitor (Mr 15,000 +/- 2000) that is labile to trypsin; its activity increases 20-fold in response to increased polyamine levels in the growth medium. It has additional characteristics similar to those of the ODC antizyme of eukaryote cells: it is a noncompetitive inhibitor of ODC; the complex formed between ODC and the ODC inhibitor can be dissociated with salt to provide active ODC and active ODC inhibitor; furthermore, this E. coli ODC inhibitor is inhibitory to eukaryote ODC. A thermostable nondialyzable factor that activates ODC in vitro has also been extracted from MA255; increased polyamine levels in the growth medium caused a 1.6-fold increase in the activity of this ODC activator. Effectors with comparable activities have also been identified in the parent ODC+ (speC+) strain MA197. The fluctuations of the intracellular levels of these two ODC effectors during the growth of E. coli MA255 have been related to the temporal changes of the activity of ODC in the parent ODC+ MA197 strain. The mode of interaction of these three macromolecules, as reflected in the changes of the activity of ODC, appears to be complex. The results suggest that ODC activity may be controlled post-translationally by macromolecules that act as positive and negative effectors and whose levels fluctuate in response to the concentration of the end products of the reaction.

Diacridines, bifunctional intercalators. Chemistry and antitumor activity

The synthesis and the characterization of a number of diacridines connected through the 9-amino position of the acridine rings by alkyl chains of varying lengths and with various substituents on the acridine ring are described. An interesting chemical property has been noted; whereas the 3-amino monoacridines cannot form stable dihydrochloride salts, the corresponding diacridines can form stable trihydrochloride salts. The biological activity of the diacridines encompasses a broad spectrum of action. Their antitumor activity (% ILS) and their toxicity have been correlated with their biological actions. The % ILS, as measured by inhibition of growth of P-388 ascites cells in BDF/1 mice, shows no significant correlation with their ability to inhibit the growth of P-388 cells in culture (I50). The toxicity of the diacridines does not correlate with the inhibition of DNA or RNA synthesis, the uptake of the diacridines by P-388 cells, or with % ILS. The only significant correlation that has been found to date between the antitumor effectiveness of the diacridines and their effects on intact cells occurs between % ILS and cell agglutination. These results emphasize that caution should be used in attributing the "antitumor activity" of a single compound or of a small number of congeners of a given chemical structure to a particular site of biological inhibition. Furthermore, the results suggest that effective antitumor drugs are those that affect the host-tumor interaction and that the toxicity of the drugs may not be essential to their antitumor properties.

Isolation and characterization of surface glycoproteins from L-1210, P-388 and HeLa cells

A method is described that permits the rapid extraction of the cell surface glycoproteins of two murine leukemic cells, the P-388 and the L-1210 cells as well as those of the human adenocarcinoma cells, the HeLa cells. Proof of the surface location of these glycoproteins is provided by labeling the intact cells; (a) with 125I by the lactoperoxidase iodination technique; (b) with 3H by the galactose oxidase-reductive tritiation method. Most of these glycoproteins were also shown to incorporate radioactive glucosamine and fucose. By these criteria as well as by the distribution of molecular weights, the surface glycoproteins of the two murine cells are indistinguishable; however, they differ markedly from the surface glycoproteins of HeLa cells. The extracts of the murine cells were shown to contain lectin receptor activity as determined by their ability to inhibit the lectin-induced agglutination of the intact cells.

Bifunctional intercalators: relationship of antitumor activity of diacridines to the cell membrane

The in vivo antitumor effectiveness [as measured by the percentage increase in life-span (ILS%)] of 28 diacridine bis-intercalators of nucleic acids shows a highly significant correlation with their effect on phenomena associated with plasma membrane as well as a high degree of structural specificity. In contrast, the ILS% does not correlate with the uptake of these diacridines by cells, nor with the inhibition of RNA synthesis or of DNA synthesis or with the inhibition of growth of cells in culture. The possibility that the antitumor effectiveness of actinomycin D, another DNA intercalator, is associated with sites of action other than the hibition of RNA synthesis is discussed.

Enzyme regulation in neuroblastoma cells in a salts/glucose medium: induction of ornithine decarboxylase by asparagine and glutamine

L-Asparagine is necessary and sufficient for the maximal induction of ornithine decarboxylase (ODC) (L-ornithine carboxy-lyase, EC 4.1.1.17) activity in confluent N18 mouse neuroblastoma cells in a salts/glucose medium; L-asparagine also induces maximal ODC activity when added to a tissue culture medium. L-Glutamine is about one-half as effective as asparagine. Cholera toxin and agents that are known to raise intracellular cyclic AMP concentrations have no effect on the induction of ODC activity unless suboptimal concentrations of asparagine are present in the salts/glucose medium. Whereas actinomycin D does not inhibit induction of ODC activity by asparagine, it inhibits the induction of ODC activity in association with cyclic AMP. In the salts/glucose medium, the rate of loss of ODC activity following the inhibition of protein synthesis by cycloheximide or puromycin depends upon the presence or absence of asparagine; loss is rapid only in the absence of asparagine and does not appear to be related to the inhibition of protein synthesis. These results are discussed in the context that the overlay of the growth medium tends to mask the minimal requirements for enzyme induction, because the composition of the medium defines: (a) the requirements for the induction of ODC activity; (b) the effect, or lack of effect, of cyclic AMP (and of inducers of intracellular cyclic AMP) on the induction of ODC activity; (c) the effect, or lack of effect, of actinomycin D on the induction of ODC activity; and (d) the action of puromycin and of cycloheximide on the rate of loss of ODC activity. It will be interesting to determine whether these results are uniquely applicable to ODC, whether many of the reactions attributed to cyclic AMP in the literature may be mediated by asparagine and glutamine, and whether actinomycin D, cycloheximide, and puromycin can be relied upon to differentiate between transcriptional and post-transcriptional control.

The mechanism of inhibition of bacteriophage T7 RNA synthesis by acridines, diacridines and actinomycin D

A homologous series of diacridines, as well as 9-amino acridine, were assayed for their ability to interfere with the synthesis of RNA (bands U-VI) by bacteriophage T7 DNA-dependent RNA polymerase transcribing T7 DNA in vitro; their action was compared to that of actinomycin D. It was found that, in contrast to actinomycin D which inhibits chain elongation, the acridines tested inhibited chain initiation only; no evidence for inhibition of chain elongation was noted. No clear-cut differentiation between single and double intercalators on the mechanism of inhibition of RNA synthesis could be determined, except that the latter are more potent inhibitors. However, it appears that diacridines connected with a diethyldiamine and a butyldiamine chain are less inhibitory to the synthesis of the RNA of Bands III and IV. The results furthermore indicate that the estimation of the number average molecular weight alone, without identification of the product RNA, is a potentially misleading method of determining the mode of action of these drugs.

Iodination of chloroplasts. I. Properties of iodinated chloroplasts

Spinach chloroplasts exposed to iodide can be washed free of the bulk of the iodide. In the presence of lactoperoxidase and H2O2, iodide can be introduced into chloroplasts in high amounts and in non diffusible forms. The resultant particles, which have been named iodochloroplasts, extrude their iodide upon stimulation by light. The form and the amount of extruded iodide bears a definite relationship to the amount of incident light. A flash of marginally effective light is additive to the next such flash even after a lapse of 10 min of darkness. These and other properties of iodochloroplasts may make them of great use in the study of intermediate reactions of photosynthesis.

Induction of a protein inhibitor to ornithine decarboxylase by the end products of its reaction

Putrescine, the end-product of ornithine decarboxylase (ODC: L-ornithine carboxylyase, EC; 4.1.1.17) action, induces the synthesis of a protein(s), in L1210, neuroblastoma, and H-35 cells as well as in rat liver, which inhibits ODC activity. Spermidine and spermine, distal products of ODC activity, also induce the synthesis of a similar protein in H-35 cells. These ODC-inhibitors are heat-labile, trypsin-sensitive, and their induction is dependent upon protein synthesis. They have short half-lives which range from 18 to 66 min; these half-lives are similar to those of the ODC derived from the same source. They are noncompetitive inhibitors of ODC activity with an apparent molecular weight of 26,500. Each inhibitor crossreacts with the ODC's of the other cells and forms an enzyme-inhibitor complex which is stable during Sephadex chromatography; however, after treatment with ammonium sulfate, enzyme and inhibitor activities can be dissociated and recovered intact from the same column. We propose the name antizyme for proteins whose synthesis is induced by the proximal or distal products of the enzyme they inhibit.

The appearance of an ornithine decarboxylase inhibitory protein upon the addition of putrescine to cell cultures

Quiescent, contact inhibited H-35 rat hepatoma cell cultures maintained in minimal essential medium contain a very low level of ornithine decarboxylase activity. However, 2 h after the addition of 10% fetal calf serum to the culture medium, the enzyme activity increases by approx. 100-fold. This increase can be completely inhibited by the simultaneous addition of 10(-2) M putrescine. The presence of putrescine elicits the appearance of an intracellular inhibitor of ornithine decarboxylase. This inhibitor of ornithine decarboxylase has a molecular weight of 26500, is sensitive to the action of chymotrypsin and is noncompetitive with respect to ornithine. The intracellular appearance of this inhibitor is sensitive to cycloheximide but is only partially inhibited by actinomycin D.

Diacridines: bifunctional intercalators. III. Definition of the general site of action

Electron microscopy of HeLa cells exposed to spermine diacridine shows nucleolar distortions which disappear after several days despite the persistence of the metabolic changes promoted by spermine diacridine. This compound inhibits ribosomal RNA synthesis and appears to act independently of any particular phase of the cell cycle. The DNA content of the HeLa cells remains unchanged and the cell distribution is not significantly disturbed from its normal distribution in the various phases of the cell cycle. Spermine diacridine and other diacridines inhibit primarily chain initiation but also chain elongation by DNA-directed RNA polymerase of Azotobacter vinelandii.

Diacridines: bifunctional intercalators. I. Chemistry, physical chemistry and growth inhibitory properties

The synthesis, as well as the rationale for synthesis of diacridines, double intercalators, as potential inhibitors of nucleic acid synthesis is presented. The syntheses of (9-acridyl)-putrescine and -spermine, and bis(-9-acridyl)-putrescine, -spermidine, -spermine diamines and of bis(6-chloro-2-methoxy-9-acridyl)-putrescine and -spermine diamines, all substituted on the terminal NH2 groups are described. In addition, the homologous series of diacridines connected by the amino groups of the diamines NH2(CH2)nNH2 (where n = 2,3,4,6,8,10,12,14,16,18) to the C-9 of the diacridines has been synthesized. The chemical properties of these compounds as well as their molecular relationship to DNA are presented. The effect of the double intercalators on the Tm of DNA and of (A)n - (U)n, (dA)n - (dT)n, (G)n - (C)n and on (dG)n - (dC)n have been determined. The double acridine intercalators produce a much greater increase of the Tm of these nucleic acids than do the single acridine intercalators. They also profoundly affect the Tm of DNA in physiological salt concentrations; under these latter conditions the single intercalators have no effect. The relationship between the length of the chain connecting the two acridine rings and the inhibition of the growth of P-388 cells in vitro and vivo is presented. Their growth inhibitory properties appear, in general, to parallel their intercalative abilities.

Diacridines: bifunctional intercalators. II. The biological effects of putrescine, sperimidine and spermine diacridines on HeLa cells and on the L-1210 and P-388 leukemia cells

The effect of putrescine, spermidine and spermine diacridines on the growth of HeLa cells and of P-388 and L-1210 leukemia cells has been evaluated and compared to that of the parent compound, 9-aminoacridine. The diacridines are more effective growth inhibitors than 9-aminoacridine. The primary site of action appears to be the inhibition of RNA synthesis.

Stable multisubstrate adducts as enzyme inhibitors. Potent inhibition of ornithine decarboxylase by N-(5'-phosphopyridoxyl)-ornithine

The synthesis of several N-(5'-phosphopyridoxyl)-amino acids is described. These compounds, analogs of the Schiff base intermediate involved in enzyme-catalyzed decarboxylation, are potent inhibitors of the cognate amino acid decarboxylases. Kinetic studies using partially purified rat liver ornithine decarboxylase, have shown that N-(5'-phosphopyridoxyl)-ornithine inhibits the enzyme in a non-competitive manner with respect to both ornithine and pyridoxal-5'-phosphate. These findings suggest that the inhibitor binds to the holoenzyme active site in place of the Schiff base intermediate.