Paraquat is not accumulated in B16 tumor cells by the polyamine transport system

We have examined the effect of difluoromethylornithine on the ability of B16 melanoma cells to take up putrescine and the 4,4'-dipyridyl herbicide paraquat. Pretreatment with difluoromethylornithine for 24 hr enhanced putrescine uptake by inducing the maximum capacity of the transport system without affecting the Km for the substrate. Paraquat uptake was minor compared with that of putrescine and was not affected by difluoromethylornithine. Neither putrescine, spermidine or spermine at concentrations up to 100 microM inhibited the accumulation of paraquat. However, paraquat competitively inhibited putrescine transport (Ki = 54 +/- 10 microM). Exposure of the B16 melanoma cells for 24 hr to increasing concentrations of paraquat produced a dose-dependent inhibition of DNA synthesis. Difluoromethylornithine pretreatment did not affect paraquat toxicity. These data show that paraquat is not taken up into B16 melanoma cells by the uptake system responsible for transporting putrescine. Moreover, it is likely that the difluoromethylornithine inducible polyamine transport system in B16 melanoma cells is characteristically different to that previously described in normal mammalian lung since the latter is reportedly capable of transporting both putrescine and paraquat.     

Polyamine uptake in cultured cerebellar granule neurons

In the present study, we have examined the transport of polyamines in cultured cerebellar granule cells. Our results suggest the existence of two different transporters for polyamines in these neurons. Putrescine and spermidine uptake (K ap m = 2.17 and 1.39 microM, respectively), were affected when extracellular sodium was replaced with choline (about 30% inhibition over controls) or sucrose (about 2.5-fold potentiation over controls). By contrast, the substitution of sodium by choline or sucrose did not modify spermine uptake (K ap m = 13.53 microM) in cerebellar granule cells. Accordingly, alteration of membrane potential with ouabain was able to block putrescine (50% inhibition) and spermidine (60% inhibition) uptake but not spermine uptake. These results indicate that putrescine and spermidine transport in cerebellar granule cells is membrane potential dependent, whereas spermine uptake is not modulated by membrane potential.     

Functional analysis of <Emphasis Type="Italic">OsPUT1</Emphasis>, a rice polyamine uptake transporter

Polyamines are nitrogenous compounds found in all eukaryotic and prokaryotic cells and absolutely essential for cell viability. In plants, they regulate several growth and developmental processes and the levels of polyamines are also correlated with the plant responses to various biotic and abiotic stresses. In plant cells, polyamines are synthesized in plastids and cytosol. This biosynthetic compartmentation indicates that the specific transporters are essential to transport polyamines between the cellular compartments. In the present study, a phylogenetic analysis was used to identify candidate polyamine transporters in rice. A full-length cDNA rice clone AK068055 was heterologously expressed in the Saccharomyces cerevisiae spermidine uptake mutant, agp2∆. Radiological uptake and competitive inhibition studies with putrescine indicated that rice gene encodes a protein that functioned as a spermidine-preferential transporter. In competition experiments with several amino acids at 25-fold higher levels than spermidine, only methionine, asparagine, and glutamine were effective in reducing uptake of spermidine to 60% of control rates. Based on those observations, this rice gene was named polyamine uptake transporter 1 (OsPUT1). Tissue-specific expression of OsPUT1 by semiquantitative RT-PCR showed that the gene was expressed in all tissues except seeds and roots. Transient expression assays in onion epidermal cells and rice protoplasts failed to localize to a cellular compartment. The characterization of the first plant polyamine transporter sets the stage for a systems approach that can be used to build a model to fully define how the biosynthesis, degradation, and transport of polyamines in plants mediate developmental and biotic responses.     

Polyamine transport systems in the LLC-PK1 renal epithelial established cell line

LLC-PK1 cells were brought to a quiescent state by treatment with DL-2-difluoromethylornithine (DFMO), a specific inhibitor of L-ornithine decarboxylase (ODC). The inhibition of ODC, which is the key enzyme for polyamine synthesis, strongly reduced the cellular content of putrescine and spermidine. The cells resumed DNA-synthesis followed by mitosis when exogenous putrescine was added. DFMO treatment strongly stimulated the putrescine uptake capability. A kinetic analysis of the initial uptake rates revealed a saturable Na+-dependent and a saturable Na+-independent pathway on top of non-saturable diffusion. The stimulation by DFMO was exclusively due to an effect on the Vmax values of the saturable pathways. The Na+-dependent transporter had a higher affinity for putrescine (apparent Km = 4.7 +/- 0.7 microM) than the Na+-independent transporter (apparent Km = 29.8 +/- 3.5 microM). As a consequence, although the latter transporter had a higher Vmax, the Na+-dependent transport was more important at a physiological putrescine concentration. Putrescine uptake by both transporters was inhibited with similar relative affinities by spermidine, spermine as well as by the antileukemic agent, methylglyoxal bis(guanylhydrazone), but not by amino acids. The activity of the Na+-dependent transporter was very much dependent on SH-group reagents, whereas the Na+-independent transporter was not affected. Both transporters were inhibited by metabolic inhibitors and by ionophores but the Na+-dependent transporter was affected to a greater extent. For both transporters there was a down-regulation in response to exogenous putrescine. This suggests that the polyamine transporters in LLC-PK1 are adaptively regulated and may contribute to the regulation of the cellular polyamine level and cellular proliferation.     

AGP2 encodes the major permease for high affinity polyamine import in Saccharomyces cerevisiae

Polyamines play essential functions in many aspects of cell biology. Plasma membrane transport systems for the specific uptake of polyamines exist in most eukaryotic cells but have been very recently identified at the molecular level only in the parasite Leishmania. We now report that the high affinity polyamine permease in Saccharomyces cerevisiae is identical to Agp2p, a member of the yeast amino acid transporter family that was previously identified as a carnitine transporter. Deletion of AGP2 dramatically reduces the initial velocity of spermidine and putrescine uptake and confers strong resistance to the toxicity of exogenous polyamines, and transformation with an AGP2 expression vector restored polyamine transport in agp2delta mutants. Yeast mutants deficient in polyamine biosynthesis required >10-fold higher concentrations of exogenous putrescine to restore cell proliferation upon deletion of the AGP2 gene. Disruption of END3, a gene required for an early step of endocytosis, increased the abundance of Agp2p, an effect that was paralleled by a marked up-regulation of spermidine transport velocity. Thus, AGP2 encodes the first eukaryotic permease that preferentially uses spermidine over putrescine as a high affinity substrate and plays a central role in the uptake of polyamines in yeast.     

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.     

Characterization of putrescine- and spermidine-transport systems of a rat pancreatic acinar tumoral cell line (AR4-2J).

Polyamines are polycationic molecules essential for cell growth and differentiation. Recent work has focused on cell polyamine-transport systems as a way to regulate intracellular polyamine levels. In this study, we demonstrate the presence of two different active transporters for putrescine and spermidine in a rat tumoral cell line (AR4-2J). The first has a Km of 3.1 microM and a Vmax of 3.7 pmol/15 min per micrograms of DNA for putrescine and the second a Km of 0.42 microM and a Vmax of 4.7 pmol/15 min per micrograms of DNA for spermidine. Competition studies performed between the polyamines confirm the difference between these two carriers; one has an equal affinity for the three main polyamines, and the other has a lower affinity for putrescine. Amino acids do not share this transport system, which is Na(+)-independent. Choline chloride inhibits selectively and in a dose-responsive manner the uptake of putrescine without affecting that of spermidine. These data demonstrate that AR4-2J cells possess two polyamine transporters; one is specific for aminopropyl groups (spermidine and spermine), and the other is choline-sensitive, but cannot discriminate between aminobutyl (putrescine) and aminopropyl groups.     

Transport of putrescine across duodenal,jejunal and ileal brush-border membrane of chicks (Gallus domesticus)

Luminal polyamines and their absorption are essential for proliferation of the enterocytes and, therefore, nutrition, health and development of the animal. The transport systems that facilitate the uptake of putrescine were characterized in chick duodenal, jejunal and ileal brush-border membrane vesicles prepared by MgCl2 precipitation from three-week-old chicks. An inwardly-directed Na+ gradient did not stimulate putrescine uptake and, therefore, putrescine transport in chick intestine. In the duodenum, jejunum and ileum, kinetics of putrescine transport fitted a model with a single affinity component plus a non-saturable component. The affinity (Kt) for [3H]putrescine transport across the brush-border membrane increased along the length of the small intestine. A model of intermediate affinity converged to the data obtained for [3H]putrescine transport with Kt approximating 1.07 and 1.05 mM or duodenum and jejunum, respectively; and high affinity with a Kt of 0.35 mM for the ileum. The polyamines cadaverine, putrescine, spermidine and spermine strongly inhibited the uptake of [3H]putrescine into chick brush-border membrane vesicles, more so for the jejunum and ileum than the duodenum. The kinetics of cadaverine, spermidine and spermine inhibition are suggestive of competitive inhibition of putrescine transport. These uptake data indicate that a single-affinity system facilitates the intestinal transport of putrescine in the chick; and the affinity of transporter for putrescine is higher in the ileum than in the proximal sections of the small intestine. In addition, this study shows that the ileum of chicks plays an important role in regulating cellular putrescine concentration.     

Levels of polyamines and kinetic characterization of their uptake in the soybean pathogen Phytophthora sojae

Polyamines are ubiquitous biologically active aliphatic cations that are at least transiently available in the soil from decaying organic matter. Our objectives in this study were to characterize polyamine uptake kinetics in Phytophthora sojae zoospores and to quantify endogenous polyamines in hyphae, zoospores, and soybean roots. Zoospores contained 10 times more free putrescine than spermidine, while hyphae contained only 4 times as much free putrescine as spermidine. Zoospores contained no conjugated putrescine, but conjugated spermidine was present. Hyphae contained both conjugated putrescine and spermidine at levels comparable to the hyphal free putrescine and spermidine levels. In soybean roots, cadaverine was the most abundant polyamine, but only putrescine efflux was detected. The selective efflux of putrescine suggests that the regulation of polyamine availability is part of the overall plant strategy to influence microbial growth in the rhizosphere. In zoospores, uptake experiments with [1,4-(14)C]putrescine and [1,4-(14)C]spermidine confirmed the existence of high-affinity polyamine transport for both polyamines. Putrescine uptake was reduced by high levels of exogenous spermidine, but spermidine uptake was not reduced by exogenous putrescine. These observations suggest that P. sojae zoospores express at least two high-affinity polyamine transporters, one that is spermidine specific and a second that is putrescine specific or putrescine preferential. Disruption of polyamine uptake or metabolism has major effects on a wide range of cellular activities in other organisms and has been proposed as a potential control strategy for Phytophthora. Inhibition of polyamine uptake may be a means of reducing the fitness of the zoospore along with subsequent developmental stages that precede infection.     

Putrescine transport in a cyanobacterium Synechocystis sp. PCC 6803

The transport of putrescine into a moderately salt tolerant cyanobacterium Synechocystis sp. PCC 6803 was characterized by measuring the uptake of radioactively-labeled putrescine. Putrescine transport showed saturation kinetics with an apparent K(m) of 92 +/- 10 microM and V(max) of 0.33 +/- 0.05 nmol/min/mg protein. The transport of putrescine was pH-dependent with highest activity at pH 7.0. Strong inhibition of putrescine transport was caused by spermine and spermidine whereas only slight inhibition was observed by the addition of various amino acids. These results suggest that the transport system in Synechocystis sp. PCC 6803 is highly specific for polyamines. Putrescine transport is energy-dependent as evidenced by the inhibition by various metabolic inhibitors and ionophores. Slow growth was observed in cells grown under salt stress. Addition of low concentration of putrescine could restore growth almost to the level observed in the absence of salt stress. Upshift of the external osmolality generated by either NaCl or sorbitol caused an increased putrescine transport with an optimum 2-fold increase at 20 mosmol/kg. The stimulation of putrescine transport mediated by osmotic upshift was abolished in chloramphenicol-treated cells, suggesting possible involvement of an inducible transport system.     

Uptake of putrescine and spermidine by Gap1p on the plasma membrane in Saccharomyces cerevisiae

It has been reported that Gap1p on the plasma membrane of Saccharomyces cerevisiae can catalyze the uptake of many kinds of amino acids. In the present study, we found that Gap1p also catalyzed the uptake of putrescine and spermidine, but not spermine. The Km and Vmax values for putrescine and spermidine were 390 and 21 microM, and 4.6 and 0.59 nmol/min/mg protein, respectively. The uptake of putrescine was strongly inhibited by basic amino acids, lysine, arginine, and histidine, whose Ki values were 25-35 microM. Thus, it is deduced that spermidine and basic amino acids have almost the same affinity for Gap1p. When the concentrations of amino acids in the medium were reduced to one-third and 0.5 mM putrescine or 0.1 mM spermidine was added to the medium, accumulation of putrescine or spermidine by Gap1p was observed. Furthermore, when yeast was transformed with the GAP1 gene and cultured in the presence of 60 mM putrescine, cell growth was inhibited through overaccumulation of putrescine. GAP1 mRNA was found to be induced by polyamines. This is the first report of the identification, at a molecular level, of a polyamine uptake protein on the plasma membrane in eukaryotes.     

Histatin 5 uptake by Candida albicans utilizes polyamine transporters Dur3 and Dur31 proteins

Histatin 5 (Hst 5) is a salivary gland-secreted cationic peptide with potent fungicidal activity against Candida albicans. Hst 5 kills fungal cells following intracellular translocation, although its selective transport mechanism is unknown. C. albicans cells grown in the presence of polyamines were resistant to Hst 5 due to reduced intracellular uptake, suggesting that this cationic peptide may enter candidal cells through native yeast polyamine transporters. Based upon homology to known Saccharomyces cerevisiae polyamine permeases, we identified six C. albicans Dur polyamine transporter family members and propose a new nomenclature. Gene deletion mutants were constructed for C. albicans polyamine transporters Dur3, Dur31, Dur33, Dur34, and were tested for Hst 5 sensitivity and uptake of spermidine. We found spermidine uptake and Hst 5 mediated killing were decreased significantly in Δdur3, Δdur31, and Δdur3/Δdur31 strains; whereas a DUR3 overexpression strain increased Hst 5 sensitivity and higher spermidine uptake. Treatment of cells with a spermidine synthase inhibitor increased spermidine uptake and Hst 5 killing, whereas protonophores and cold treatment reduced spermidine uptake. Inhibition assays showed that Hst 5 is a competitive analog of spermidine for uptake into C. albicans cells, and that Hst 5 Ki values were increased by 80-fold in Δdur3/Δdur31 cells. Thus, Dur3p and Dur31p are preferential spermidine transporters used by Hst 5 for its entry into candidal cells. Understanding of polyamine transporter-mediated internalization of Hst 5 provides new insights into the uptake mechanism for C. albicans toxicity, and further suggests design for targeted fungal therapeutic agents.     

Epidermal growth factor: modulator of murine embryonic palate mesenchymal cell proliferation, polyamine biosynthesis, and polyamine transport

Polyamines (putrescine, spermidine, and spermine) are normal cellular constituents able to modulate cellular proliferation and differentiation in a number of tissues and cell types. This investigation explores the response of murine embryonic palate mesenchymal (MEPM) cells to epidermal growth factor (EGF) in terms of biosynthesis of putrescine and its transport across the plasma membrane and tests the hypothesis that polyamine transport can serve as an alternative mechanism (other than biosynthesis) for elevating intracellular polyamines during stimulation of MEPM cellular proliferation. MEPM cells treated with EGF were stimulated to proliferate and showed a dose- and time-dependent stimulation of ornithine decarboxylase (ODC) which was maximal at 4-6 hours. EGF also stimulated the initial rate of putrescine transport in a dose- and time-dependent manner. This stimulation was found to be maximal 3 hours after treatment and specific for the putrescine transport system. The kinetic parameters of putrescine transport shifted from 2.52 microM (Km) and 23.6 nmol/mg protein/15 minutes (Vmax) in nonstimulated cells to 4.48 microM (Km) and 39.8 nmol/mg protein/15 minutes (Vmax) in EGF-treated cells. This kinetic shift did not require de novo protein or RNA synthesis, as cycloheximide (10 micrograms/ml) and actinomycin D (50 micrograms/ml) had little effect on the ability of EGF to stimulate the initial rate of putrescine uptake. The rate of transport, however, was found to be inversely related to cell density. The addition of exogenous putrescine concomitantly with EGF blocked the induction of ODC, while in the presence of difluoromethylornithine (DFMO) (irreversible inhibitor of ODC) the initial rate of putrescine transport remained elevated throughout the time course studied. This stimulation of putrescine uptake caused by polyamine deprivation was reversed by exogenous putrescine and Ca++ while alpha-aminoisobutyric acid (AIB) further stimulated the rate of uptake. EGF's ability to stimulate cellular DNA synthesis was inhibited by DFMO. If DFMO-treated cells were stimulated with EGF in the presence of exogenous putrescine, this stimulatory effect was preserved. These studies indicate that the rate of polyamine transportation is highly responsive to a signal which initiates biosynthesis of polyamines. Further, this transportation system provides a compensatory mechanism allowing the cell to increase intracellular levels of polyamines when environmental conditions inhibit biosynthesis or when polyamines are abundant.     

Regulation of the Na(+)-dependent and the Na(+)-independent polyamine transporters in renal epithelial cells (LLC-PK1)

We have studied the regulation of the Na(+)-dependent and Na(+)-independent polyamine transport pathways in the renal LLC-PK1 cell line. Most of the experiments were performed in the presence of 5 mM DL-2-difluoromethylornithine (DFMO) in order to inhibit the cellular synthesis of polyamines. The activity of both transporters as measured by putrescine uptake was increased by growth-promoting stimuli and decreased by exogenous polyamines. The time course of the increase in uptake activity induced by fetal calf serum could be fitted by a single exponential, and the process was three times faster for the Na(+)-dependent than for the Na(+)-independent transporter. Maximum activity was reached after more than 24 h. This increase could be inhibited by actinomycin D and by cycloheximide. Other growth-promoting stimuli, such as subconfluent cell density, as well as growth factors also induced an increase in the transport activity. Particularly, there was a marked stimulation of the Na(+)-dependent pathway by epidermal growth factor in combination with insulin. On the other hand, the transport activity decayed very rapidly upon addition of exogenous polyamines (t1/2 less than 60 min). The diamine putrescine was much less effective in this respect than the polyamines spermidine and spermine. The non-metabolizable substrate methylglyoxal bis(guanylhydrazone) did not induce a decay of the transport activity, but it protected the Na(+)-dependent pathway against the polyamine-induced decay. Inhibition of the protein synthesis by cycloheximide did not induce a rapid decrease of the transport activity; neither did it affect the polyamine-induced decay. These observations suggest that this polyamine-induced decay is not owing to an inhibitory effect on the rate of synthesis of the transporters, but rather to a degradation or an inactivation of the transporters. The polyamine-induced decay slowed down at lower cell density. This effect was particularly pronounced for the Na(+)-dependent transporter. Since the uptake of polyamines was increased at low cell density, the decreased rate of decay in this condition pleads against a simple mechanism of transinhibition by the substrate. In conclusion, both transport pathways were similarly affected by the regulatory parameters, but the Na(+)-dependent transporter was more rapidly and more effectively regulated. The numerous interacting regulatory steps furthermore suggest a physiological role for these transporters, such as an involvement in urinary polyamine disposal.     

Levels of Polyamines and Kinetic Characterization of Their Uptake in the Soybean Pathogen Phytophthora sojae

Polyamines are ubiquitous biologically active aliphatic cations that are at least transiently available in the soil from decaying organic matter. Our objectives in this study were to characterize polyamine uptake kinetics in Phytophthora sojae zoospores and to quantify endogenous polyamines in hyphae, zoospores, and soybean roots. Zoospores contained 10 times more free putrescine than spermidine, while hyphae contained only 4 times as much free putrescine as spermidine. Zoospores contained no conjugated putrescine, but conjugated spermidine was present. Hyphae contained both conjugated putrescine and spermidine at levels comparable to the hyphal free putrescine and spermidine levels. In soybean roots, cadaverine was the most abundant polyamine, but only putrescine efflux was detected. The selective efflux of putrescine suggests that the regulation of polyamine availability is part of the overall plant strategy to influence microbial growth in the rhizosphere. In zoospores, uptake experiments with [1,4-¹⁴C]putrescine and [1,4-¹⁴C]spermidine confirmed the existence of high-affinity polyamine transport for both polyamines. Putrescine uptake was reduced by high levels of exogenous spermidine, but spermidine uptake was not reduced by exogenous putrescine. These observations suggest that P. sojae zoospores express at least two high-affinity polyamine transporters, one that is spermidine specific and a second that is putrescine specific or putrescine preferential. Disruption of polyamine uptake or metabolism has major effects on a wide range of cellular activities in other organisms and has been proposed as a potential control strategy for Phytophthora. Inhibition of polyamine uptake may be a means of reducing the fitness of the zoospore along with subsequent developmental stages that precede infection.     

Pulmonary alveolar macrophages express a polyamine transport system

Polyamine transport is an important mechanism by which cells regulate their intracellular polyamine content. It is well established that the lung has a high capacity for polyamine transport, and recently the polyamine putrescine has been shown to be selectively accumulated into the type II pneumocyte of rabbit lung slices (Saunders et al.: Lab. Invest., 95:380-386, 1988). In addition, it has been suggested that there may be more than one polyamine transport system in lung tissue (Byers et al.: Am. J. Physiol., 252:C663-C669, 1987). In the present study, we have examined whether there are differences in the distribution of putrescine and spermidine uptake activities in isolated rabbit lung cells. We report that pulmonary alveolar macrophages have a greater rate of uptake of both putrescine and spermidine than the total lung cell population. Kinetic analysis of the polyamine uptake system present in macrophages showed putrescine uptake consisted of a saturable (Km = 2.1 microM) and nonsaturable component whilst spermidine uptake consisted of both a high- and a low-capacity saturable component (Km = 0.16 microM and 1.97 microM, respectively). The rate of polyamine transport was similar to those reported for many proliferative or tumor cell-lines and appears to be greater than any other major lung cell type. Inhibition studies of the transport of polyamines into pulmonary alveolar macrophages suggested that the uptake of both putrescine and spermidine was mediated by the same system, which could not be described by simple Michaelis-Menten kinetics. The transport appears to be reversible due to significant efflux. This is the first study to describe the presence of multiple polyamine transport systems in pulmonary alveolar macrophages.     

Insensitivity of cardiac phosphofructokinase to adrenergic activation in Zucker rats. A post-receptor defect.

Glyoxal bis(guanylhydrazone), the parent compound of methylglyoxal bis(guanylhydrazone), was synthesized and tested for its ability to inhibit the biosynthesis of polyamines. It was found to be a powerful competitive inhibitor of adenosylmethionine decarboxylase (EC 4.1.1.50), yet the lack of the methyl group at the glyoxal portion increased the apparent Ki value for the enzyme by about 30-fold in comparison with methylglyoxal bis(guanylhydrazone). Glyoxal bis(guanylhydrazone) inhibited diamine oxidase (EC 1.4.3.6) activity as effectively as did methylglyoxal bis(guanylhydrazone). The cellular accumulation curves of glyoxal bis(guanylhydrazone) in L1210 cells were practically superimposable with those of methylglyoxal bis(guanylhydrazone), and the uptake of both compounds was distinctly stimulated by a prior treatment with 2-difluoromethylornithine. The drug decreased the concentration of spermidine in a dose-dependent manner and, in contrast with methylglyoxal bis(guanylhydrazone), without a concomitant accumulation of putrescine. The fact that putrescine concentrations were decreased in cells exposed to glyoxal bis(guanylhydrazone) was, at least in part, attributable to an inhibition of ornithine decarboxylase (EC 4.1.1.17) activity in cells treated with the compound. Under these experimental conditions equivalent concentrations of methylglyoxal bis(guanylhydrazone) [1,1'-[(methylethanediylidine)dinitrilo]diguanidine] elicited large increases in the enzyme activity. When combined with difluoromethylornithine, glyoxal bis(guanylhydrazone) potentiated the growth-inhibitory effect of that drug. Taking into consideration the proven anti-leukaemic activity of glyoxal bis(guanylhydrazone), its effectiveness to inhibit spermidine biosynthesis (without raising the concentration of putrescine) as well as its suitability for combined use with inhibitors of ornithine decarboxylase, this drug is apparently worthy of further testing in tumour-bearing animals, especially in combination with difluoromethylornithine or related inhibitors of ornithine decarboxylase.     

Characterization of the inducible polyamine transporter in bovine lymphocytes

The polyamine uptake system in bovine lymphocytes was activated by concanavalin A. The system was common to putrescine, spermidine and spermine. The Kt values for uptake activities of putrescine, spermidine and spermine were 3.7 microM, 0.38 microM and 0.23 microM in that order. The uptake activity was inhibited by carbonyl cyanide m-chlorophenylhydrazone, gramicidin D or valinomycin in the presence of 20 mM K+ suggesting that polyamine uptake depends on the membrane potential. The uptake activity appeared 10 h after addition of concanavalin A, and the maximum was reached at 28 h indicating that induction of the polyamine transporter precedes the initiation of DNA synthesis. Addition of polyamine antimetabolites, such as alpha-difluoromethylornithine and ethylglyoxal bis(guanylhydrazone), to the medium enhanced at least eightfold the induction of the polyamine transporter. The induction was repressed by addition of 50 microM spermidine or spermine, but not putrescine. We propose here that the induction of the membrane-potential-dependent polyamine transporter is regulated by the intracellular level of spermidine and spermine.     

Intracellular putrescine and spermidine deprivation induces increased uptake of the natural polyamines and methylglyoxal bis(guanylhydrazone).

Inhibition of polyamine synthesis by alpha-difluoromethylornithine in cultured Ehrlich ascites-carcinoma cells rapidly enhanced the uptake of exogenous putrescine, spermidine and spermine from the culture medium. In tumour cells exposed to the drug for 2 days, the intracellular concentration of spermidine was decreased to less than 10% of that found in untreated cells. However, the strikingly stimulated transport system brought the concentration of spermidine to the control values in less than 2h after supplementation of the cells with micromolar concentrations of the polyamine. In the absence of polyamine deprivation, tumour cells did not accumulate extracellular polyamines to any appreciable extent. Ascites-tumour cells deprived of putrescine and spermidine likewise concentrated methylglyoxal bis(guanylhydrazone) [1,1'-[methylethanedylidine)dinitrilo]diguanidine] at a greatly enhanced rate. A previous "priming of tumour cells with difluoromethylornithine followed by an exposure of the cells to methylglyoxal bis(guanylhydrazone) resulted in a marked and rapid anti-proliferative effect.     

Characterization of lipid-protein interactions in acetylcholinesterase lipoprotein extracted from bovine erythrocytes.

1. The activation of human peripheral blood lymphocytes by phytohaemagglutinin in vitro was accompanied by striking increases in the concentrations of the natural polyamines putrescine, spermidine and spermine. 2. The enhanced accumulation of polyamines could be almost totally abolished by dl-alpha-difluoromethylornithine, a newly discovered irreversible inhibitor of l-ornithine decarboxylase (EC 4.1.1.17), or by methylglyoxal bis(guanylhydrazone) {1,1'-[(methylethanediylidene)dinitrilo]diguanidine}, an inhibitor of S-adenosyl-l-methionine decarboxylase (EC 4.1.1.50). The inhibition of polyamine accumulation was associated with a marked suppression of DNA synthesis, which was partially or totally reversed by low concentrations of exogenous putrescine, spermidine, spermine and cadaverine and by higher concentrations of 1,3-diaminopropane. 3. In contrast with some earlier studies, we found that methylglyoxal bis(guanylhydrazone), at concentrations that were sufficient to prevent polyamine accumulation, also caused a clear inhibition of protein synthesis in the activated lymphocytes. Similar results were obtained with difluoromethylornithine. The decrease in protein synthesis caused by both compounds preceded the impairment of DNA synthesis. The inhibition of protein synthesis by difluoromethylornithine was fully reversed by exogenous putrescine, spermidine and spermine, and that caused by methylglyoxal bis(guanylhydrazone) by spermidine and spermine. In further support of the idea that the inhibition of protein synthesis by these compounds was related to the polyamine depletion, we found that difluoromethylornithine caused a dose-dependent decrease in the incorporation of [(14)C]leucine into lymphocyte proteins which closely correlated with the decreased concentrations of cellular spermidine. 4. Difluoromethylornithine and methylglyoxal bis(guanylhydrazone) also elicited a variable depression in the incorporation of [(3)H]uridine and [(14)C]adenine into total RNA. The apparent turnover of lymphocyte RNA remained essentially unchanged in spite of severe polyamine depletion brought about by difluoromethylornithine. 5. The present results, as well as confirming the anti-proliferative action of the inhibitors of polyamine biosynthesis, suggest that polyamine depletion may interfere with reactions at different levels of gene expression.