Polyamine synthesis in mammalian tissues. Isolation and characterization of spermine synthase from bovine brain

Myosin Va interacts with the exosomal protein spermine synthase

Myosin Va (MyoVa) is an actin-based molecular motor that plays key roles in the final stages of secretory pathways, including neurotransmitter release. Several studies have addressed how MyoVa coordinates the trafficking of secretory vesicles, but why this molecular motor is found in exosomes is still unclear. In this work, using a yeast two-hybrid screening system, we identified the direct interaction between the globular tail domain (GTD) of MyoVa and four protein components of exosomes: the WD repeat-containing protein 48 (WDR48), the cold shock domain-containing protein E1 (CSDE1), the tandem C2 domain-containing protein 1 (TC2N), and the enzyme spermine synthase (SMS). The interaction between the GTD of MyoVa and SMS was further validated in vitro and displayed a K_d in the low micromolar range (3.5 ± 0.5 µM). SMS localized together with MyoVa in cytoplasmic vesicles of breast cancer MCF-7 and neuroblastoma SH-SY5Y cell lines, known to produce exosomes. Moreover, MYO5A knockdown decreased the expression of SMS gene and rendered the distribution of SMS protein diffuse, supporting a role for MyoVa in SMS expression and targeting.

A paternal methyl donor-rich diet altered cognitive and neural functions in offspring mice

Dietary intake of methyl donors, such as folic acid and methionine, shows considerable intra-individual variation in human populations. While it is recognized that maternal departures from the optimum of dietary methyl donor intake can increase the risk for mental health issues and neurological disorders in offspring, it has not been explored whether paternal dietary methyl donor intake influences behavioral and cognitive functions in the next generation. Here, we report that elevated paternal dietary methyl donor intake in a mouse model, transiently applied prior to mating, resulted in offspring animals (methyl donor-rich diet (MD) F1 mice) with deficits in hippocampus-dependent learning and memory, impaired hippocampal synaptic plasticity and reduced hippocampal theta oscillations. Gene expression analyses revealed altered expression of the methionine adenosyltransferase Mat2a and BK channel subunit Kcnmb2, which was associated with changes in Kcnmb2 promoter methylation in MD F1 mice. Hippocampal overexpression of Kcnmb2 in MD F1 mice ameliorated altered spatial learning and memory, supporting a role of this BK channel subunit in the MD F1 behavioral phenotype. Behavioral and gene expression changes did not extend into the F2 offspring generation. Together, our data indicate that paternal dietary factors influence cognitive and neural functions in the offspring generation.

S-adenosylmethionine in liver health, injury, and cancer

S-adenosylmethionine (AdoMet, also known as SAM and SAMe) is the principal biological methyl donor synthesized in all mammalian cells but most abundantly in the liver. Biosynthesis of AdoMet requires the enzyme methionine adenosyltransferase (MAT). In mammals, two genes, MAT1A that is largely expressed by normal liver and MAT2A that is expressed by all extrahepatic tissues, encode MAT. Patients with chronic liver disease have reduced MAT activity and AdoMet levels. Mice lacking Mat1a have reduced hepatic AdoMet levels and develop oxidative stress, steatohepatitis, and hepatocellular carcinoma (HCC). In these mice, several signaling pathways are abnormal that can contribute to HCC formation. However, injury and HCC also occur if hepatic AdoMet level is excessive chronically. This can result from inactive mutation of the enzyme glycine N-methyltransferase (GNMT). Children with GNMT mutation have elevated liver transaminases, and Gnmt knockout mice develop liver injury, fibrosis, and HCC. Thus a normal hepatic AdoMet level is necessary to maintain liver health and prevent injury and HCC. AdoMet is effective in cholestasis of pregnancy, and its role in other human liver diseases remains to be better defined. In experimental models, it is effective as a chemopreventive agent in HCC and perhaps other forms of cancer as well.

Spermine synthase deficiency leads to deafness and a profound sensitivity to alpha-difluoromethylornithine

Male gyro (Gy) mice, which have an X chromosomal deletion inactivating the SpmS and Phex genes, were found to be profoundly hearing impaired. This defect was due to alteration in polyamine content due to the absence of spermine synthase, the product of the SpmS gene. It was reversed by breeding the Gy strain with CAG/SpmS mice, a transgenic line that ubiquitously expresses spermine synthase under the control of a composite cytomegalovirus-IE enhancer/chicken beta-actin promoter. There was an almost complete loss of the endocochlear potential in the Gy mice, which parallels the hearing deficiency, and this was also reversed by the production of spermine from the spermine synthase transgene. Gy mice showed a striking toxic response to treatment with the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO). Within 2-3 days of exposure to DFMO in the drinking water, the Gy mice suffered a catastrophic loss of motor function resulting in death within 5 days. This effect was due to an inability to maintain normal balance and was also prevented by the transgenic expression of spermine synthase. DFMO treatment of control mice or Gy-CAG/SpmS had no effect on balance. The loss of balance in Gy mice treated with DFMO was due to inhibition of polyamine synthesis because it was prevented by administration of putrescine. Our results are consistent with a critical role for polyamines in regulation of Kir channels that maintain the endocochlear potential and emphasize the importance of normal spermidine:spermine ratio in the hearing and balance functions of the inner ear.

Crystal structure of human spermine synthase: implications of substrate binding and catalytic mechanism

The crystal structures of two ternary complexes of human spermine synthase (EC 2.5.1.22), one with 5'-methylthioadenosine and spermidine and the other with 5'-methylthioadenosine and spermine, have been solved. They show that the enzyme is a dimer of two identical subunits. Each monomer has three domains: a C-terminal domain, which contains the active site and is similar in structure to spermidine synthase; a central domain made up of four beta-strands; and an N-terminal domain with remarkable structural similarity to S-adenosylmethionine decarboxylase, the enzyme that forms the aminopropyl donor substrate. Dimerization occurs mainly through interactions between the N-terminal domains. Deletion of the N-terminal domain led to a complete loss of spermine synthase activity, suggesting that dimerization may be required for activity. The structures provide an outline of the active site and a plausible model for catalysis. The active site is similar to those of spermidine synthases but has a larger substrate-binding pocket able to accommodate longer substrates. Two residues (Asp(201) and Asp(276)) that are conserved in aminopropyltransferases appear to play a key part in the catalytic mechanism, and this role was supported by the results of site-directed mutagenesis. The spermine synthase.5'-methylthioadenosine structure provides a plausible explanation for the potent inhibition of the reaction by this product and the stronger inhibition of spermine synthase compared with spermidine synthase. An analysis to trace possible evolutionary origins of spermine synthase is also described.

The first agmatine/cadaverine aminopropyl transferase: biochemical and structural characterization of an enzyme involved in polyamine biosynthesis in the hyperthermophilic archaeon Pyrococcus furiosus

We report here the characterization of the first agmatine/cadaverine aminopropyl transferase (ACAPT), the enzyme responsible for polyamine biosynthesis from an archaeon. The gene PF0127 encoding ACAPT in the hyperthermophile Pyrococcus furiosus was cloned and expressed in Escherichia coli, and the recombinant protein was purified to homogeneity. P. furiosus ACAPT is a homodimer of 65 kDa. The broad substrate specificity of the enzyme toward the amine acceptors is unique, as agmatine, 1,3-diaminopropane, putrescine, cadaverine, and sym-nor-spermidine all serve as substrates. While maximal catalytic activity was observed with cadaverine, agmatine was the preferred substrate on the basis of the k(cat)/K(m) value. P. furiosus ACAPT is thermoactive and thermostable with an apparent melting temperature of 108 degrees C that increases to 112 degrees C in the presence of cadaverine. Limited proteolysis indicated that the only proteolytic cleavage site is localized in the C-terminal region and that the C-terminal peptide is not necessary for the integrity of the active site. The crystal structure of the enzyme determined to 1.8-A resolution confirmed its dimeric nature and provided insight into the proteolytic analyses as well as into mechanisms of thermal stability. Analysis of the polyamine content of P. furiosus showed that spermidine, cadaverine, and sym-nor-spermidine are the major components, with small amounts of sym-nor-spermine and N-(3-aminopropyl)cadaverine (APC). This is the first report in Archaea of an unusual polyamine APC that is proposed to play a role in stress adaptation.

Targeting polyamine metabolism and function in cancer and other hyperproliferative diseases

The polyamines spermidine and spermine and their diamine precursor putrescine are naturally occurring, polycationic alkylamines that are essential for eukaryotic cell growth. The requirement for and the metabolism of polyamines are frequently dysregulated in cancer and other hyperproliferative diseases, thus making polyamine function and metabolism attractive targets for therapeutic intervention. Recent advances in our understanding of polyamine function, metabolic regulation, and differences between normal cells and tumour cells with respect to polyamine biology, have reinforced the interest in this target-rich pathway for drug development.

Regulation of Polyamine and Cancer

This review describes my work in the field of polyamine research for the last 35 years. My research started with developing the improved synthesis of decarboxylated S-adenosylmethionine and then moved to the purification of spermidine synthase from rat prostate. I also took considerable efforts to find the synthetic procedure for various polyamines with high yield in order to prepare (15)N-labeled polyamines. On the basis of these methodological work, I searched for the inhibitor of spermidine synthase and found trans-4-methylcyclohexylamine (MCHA), the most effective one at the present time. I also developed a new analytical method for polyamines using stable isotope and ionspray ionization mass spectrometry (IS-MS). Based on these studies I examined the role of polyamines in liver regeneration and found that oral administration of MCHA effectively changed the concentration of polyamines and inhibited the hepatic growth. I also found the close relationship between the concentration ratio of spermidine to spermine and the extent of liver regeneration. These results may shed new light on the control of cell growth by polyamine in vivo.

Aminoalkyl affinity matrices

Aminoalkyl matrices are used in affinity chromatography of amine oxidases and other proteins with affinity for amino groups. Under appropriate circumstances chromatography on aminoalkyl matrices may yield purification factors around 100 to 1000, and they have been used in affinity purification of many members of the amine oxidase family. Other proteins with affinity for aminoalkyl matrices include thiol ester proteins, lactoferrin, and proteins with lysine-binding kringles (plasminogen, plasminogen activator, apolipoprotein A). The affinity of thiol ester proteins for aminoalkyl matrices is abolished after inactivation of the thiol ester group by reaction with low molecular weight amines including ammonia. Due to this, an ammonium sulphate precipitation step should be included in purification schemes for amine oxidases. The affinity of lactoferrin for aminoalkyl matrices stems from an affinity for the repeating amino groups in glycosaminoglycans, and this explains why lactoferrin requires diamines for efficient elution. The affinity of plasminogen for aminoalkyl groups is exploited in a one-step purification from plasma, and is also utilised in purification schemes for angiostatin, an angiogenesis-inhibiting fragment of plasminogen. Apolipoprotein A is homologous to plasminogen, and also has affinity for aminohexyl columns. The common binding motif for these proteins are lysine-binding kringles. Due to the properties of the amino group itself, aminoalkyl matrices will inevitably also function as anion exchangers, and this must be taken into consideration in the choice of conditions for sample loading, column washing and elution of bound proteins. Depending on the length of the alkyl chain, the matrices also have a potential for hydrophobic interactions. This property has been exploited in the purification of several proteins but must be minimized during affinity chromatography of amine oxidases. In conclusion, aminoalkyl matrices are valuable tools for affinity chromatography of several different proteins, and simple variations of sample pretreatment, sample loading, and column washing and elution conditions allow efficient selective purification of proteins with different affinities for the matrices.

Polyamines. An overview

The polyamines spermine, spermidine, and putrescine are small organic molecules one or more of which are present in all living organisms. Many natural products contain polyamine residues. Polyamines are synthesized by a highly regulated pathway from arginine or ornithine and also can be transported in and out of cells. Polyamines are degraded to a variety of compounds the functions of which are largely unknown. Polyamines influence the transcriptional and translational stages of protein synthesis, stabilize membranes, and, in mammalian systems, modulate neurophysiological functions and may act as intracellular messengers. However, at the molecular level the mode of action of the polyamines is largely unknown.

Cloning of nicotianamine synthase genes, novel genes involved in the biosynthesis of phytosiderophores

Nicotianamine synthase (NAS), the key enzyme in the biosynthetic pathway for the mugineic acid family of phytosiderophores, catalyzes the trimerization of S-adenosylmethionine to form one molecule of nicotianamine. We purified NAS protein and isolated the genes nas1, nas2, nas3, nas4, nas5-1, nas5-2, and nas6, which encode NAS and NAS-like proteins from Fe-deficient barley (Hordeum vulgare L. cv Ehimehadaka no. 1) roots. Escherichia coli expressing nas1 showed NAS activity, confirming that this gene encodes a functional NAS. Expression of nas genes as determined by northern-blot analysis was induced by Fe deficiency and was root specific. The NAS genes form a multigene family in the barley and rice genomes.

Cloning and expression of Escherichia coli 5'-methylthioadenosine/S-adenosylhomocysteine nucleosidase: identification of the pfs gene product

The enzyme 5'-methylthioadenosine/S-adenosylhomocysteine nucleosidase (EC 3.2.2.9) is responsible for cleavage of the glycosidic bond in both 5'-methylthioadenosine (MTA) and S-adenosylhomocysteine (SAH). Based on amino acid sequence analysis of this enzyme from Klebsiella, we recently speculated that an open reading frame found in E. coli (designated pfs) encoded MTA/SAH nucleosidase. To explore this possibility, we amplified, cloned, and expressed the complete pfs gene from E. coli genomic DNA. The recombinant protein exhibited a molecular weight and Michaelis constants for MTA that are in agreement with those reported for native enzyme. From this biochemical evidence we confirm our original assignment of the pfs gene as encoding MTA/SAH nucleosidase.

Molecular cloning of a cDNA encoding human spermine synthase

We have isolated and sequenced cDNA clones that encode human spermine synthase (EC 2.5.1.22). The total length of the sequenced cDNA was 1,612 nucleotides, containing an open reading frame encoding a polypeptide chain of 368 amino acids. All of the previously sequenced peptide fragments of human and bovine spermine synthase proteins could be located within the coding region derived from the cDNA. An unusual sequence of AATTAA apparently signaled the initiation of polyadenylation. Sequence comparisons between human spermine synthase and spermidine synthases from bacterial and mammalian sources revealed a nearly complete lack of similarity between the primary structures of these two enzymes catalyzing almost identical reactions. A modest similarity found was restricted to a relatively short peptide domain apparently involved in the binding of decarboxylated S-adenosylmethionine, the common substrate for both enzymes. The apparent lack of an overall similarity may indicate that spermine synthase, the enzyme found only in eukaryotes, and spermidine synthase with more universal distribution, although functionally closely related, have evolved separately.

Monitoring of the uptake and metabolism of aminooxy analogues of polyamines in cultured cells by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of polyamines and their aminooxy analogues is described. Oxime derivatization with a ketone is used to protect the aminooxy group during post-column reaction with o-phthalaldehyde. The amount of the polyamines and of the oximes of their aminooxy analogues can be determined simultaneously in cultured cells and cell culture media. The limit of detection is 20-30 pmol, and the response of the fluorescence detection is linear up to 4 nmol. The separation of the aminooxy analogues from the naturally occurring polyamines can be varied by using different ketones for oxime formation. The method was used to measure the stability of aminooxy analogues of putrescine (1-aminooxy-3-aminopropane) and spermidine [N-(2-aminooxyethyl)-1,4-diaminobutane and 1-aminooxy-3-N-(3-aminopropyl)aminopropane] in cell culture media and the uptake into cultured baby hamster kidney (BHK21/C13) cells.

Human spermidine synthase: cloning and primary structure

Using a synthetic deoxyoligonucleotide mixture constructed for a tryptic peptide of the bovine enzyme as a probe, cDNA coding for the full-length subunit of spermidine synthase was isolated from a human decidual cDNA library constructed on phage lambda gt11. After subcloning into the Eco RI site of pBR322 and propagation, both strands of the insert were sequenced using a shotgun strategy. Starting from the first start codon, which was immediately preceded by a GC-rich region including four overlapping CCGCC consensus sequences, an open reading frame for a 302-amino-acid polypeptide was resolved. This peptide had an Mr of 33,827, started with methionine, and ended with serine. The identity of the isolated cDNA was confirmed by comparison of the deduced amino acid sequence with resolved sequences of the tryptic peptides of bovine spermidine synthase. The coding strand of the cDNA revealed no special regulatory or ribosome-binding signals within 82 nucleotides preceding the start codon and no polyadenylation signal within 247 nucleotides following the stop codon. The coding region, containing a 13-nucleotide repeat close to the 5' end, was longer than, and very different from, that of the bacterial counterpart. This region seems to be of retroviral origin and shows marked homology with sequences found in a variety of human, mammalian, avian, and viral genes and mRNAs. By computer analysis, the first 200 nucleotides of the 5' end of the coding strand appear able to form a very stable secondary structure with a free energy change of -157.6 kcal/mole.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and partial characterization of human polyamine synthases

Spermidine synthase was purified to apparent homogeneity from human spleens (8700-fold) by affinity chromatography. The native enzyme was composed of two subunits of identical Mr (35,000) and showed an apparent Mr of 62,000 in pore-gradient gel electrophoresis. Its pI was 5.1, Spermine synthase was purified to apparent homogeneity from placenta (5300-fold) and from kidney (4600-fold). The native enzyme was composed of two subunits of identical Mr (45,000) and showed an apparent Mr of 78,000 in pore-gradient gel electrophoresis. In isoelectric focusing it revealed two bands, with pI values of 4.9 and 5.0. Both synthases were present in all human tissues studied, but revealed a clear tissue-specific pattern. Mouse antisera against spermidine synthase revealed only one band, of Mr 35,000, in all purified enzyme preparations and in crude human tissue extracts in immunoblotting. Antisera against spermine synthase showed an immunoreactive band corresponding to the Mr of the subunit of spermine synthase. These antisera did not indicate any cross-reactivity in immunoblotting. Thus spermine synthase and spermidine synthase do not share homologous antigenic sites and are totally different proteins.

Fluorinated analogues of spermidine as substrates of spermine synthase

A series of mono- and geminal difluorinated analogues of spermidine (4-azaoctane-1,8-diamine) have been tested as potential substrates of partially purified rat hepatoma (HTC) cell or pure bovine spleen spermine synthase (EC 2.5.1.22). Substitution of the hydrogen atoms of the methylene group at position 7 by one or two fluorine atoms decreases 8-fold and 160-fold the apparent Km values for the HTC cell enzyme respectively. Similarly, the Km values of 7-monofluoro and 7,7-difluorospermidine for the pure bovine enzyme are reduced 8-fold and 100-fold respectively, in comparison with spermidine. Di-, but not monofluoro substitution, in the 6-position causes a 5-fold reduction in the affinity for the HTC cell enzyme. Gem-fluorine substitution in the 2-position abolishes substrate capability. In addition to their high affinity for spermine synthase, 7-monofluorospermidine and 7,7-difluorospermidine cause substrate inhibition. This phenomenon, which is more pronounced in the case of the difluorinated analogues is pH-dependent. These enzymatic findings are discussed with regard to the protonation sites of the spermidine analogues, determined by potentiometric titration, which vary as a function of the number and position of the fluorine substituents relative to the basic amino groups.

Studies of non-metabolizable polyamines that support growth of SV-3T3 cells depleted of natural polyamines by exposure to alpha-difluoromethylornithine

A number of synthetic polyamine derivatives that included five achiral gem-dimethylspermidines and two analogous tetramethylated spermines were tested for their abilities to serve as substrates for enzymes metabolizing polyamines and for their capacities to substitute for the natural polyamines in cell growth. It was found that none of the compounds were effective substrates for spermine synthase, and only one, namely 8,8-dimethylspermidine, was a substrate for spermidine/spermine N1-acetyltransferase. However, all of the spermidine derivatives and 1,1,12,12-tetramethylspermine were able to support the growth of SV-3T3 cells in which endogenous polyamine synthesis was prevented by the addition of alpha-difluoromethylornithine. These results suggest that either spermidine or spermine can support cell growth without the need for metabolic interconversion. In contrast with the result with 1,1,12,12-tetramethylspermine, 3,3,10,10-tetramethylspermine did not restore growth of polyamine-depleted SV-3T3 cells. Comparison of the properties of these derivatives may prove valuable in understanding the physiological role of polyamines.

Purification and characterization of propylamine transferase from Sulfolobus solfataricus, an extreme thermophilic archaebacterium

The enzyme propylamine transferase, catalyzing the transfer of the propylamine moiety from S-adenosyl(5')-3-methylthiopropylamine to several amine acceptors, has been purified 643-fold in 20% yield from Sulfolobus solfataricus, an extreme thermophilic archaebacterium optimally growing at 87 degrees C. The purified enzyme (specific activity 2.05 units/mg protein), is homogeneous by criteria of gel electrophoresis, gel filtration, isoelectric focusing and ultracentrifugation analysis. The molecular mass of the native enzyme was estimated to be about 110 kDa by gel permeation and ultracentrifugation analysis. The protein migrates on SDS/polyacrylamide gel electrophoresis as a single band of 35 kDa, suggesting that the enzyme is a trimer composed by identical subunits. An optimum pH of 7.5 and an acidic isoelectric point of 5.3 have been calculated. The optimum temperature was 90 degrees C and no loss of activity is observable even after exposure of the purified enzyme to 100 degrees C for 1 h. No reducing agents are required for enzymatic activity. Substrate specificity towards the amine acceptors is rather broad in that 1,3-diaminopropane (Km = 1675 microM), putrescine (Km = 3850 microM), sym-norspermidine (Km = 954 microM) and spermidine (Km = 1539 microM) are recognized as substrates. Conversely S-adenosyl(5')-3-methylthiopropylamine is the only propylamine donor (Km = 7.9 microM) and the deamination of the sulfonium compound prevents the recognition by the enzyme. The reaction is irreversible and initial-rate kinetic studies indicate that the propylamine transfer is operated through a sequential mechanism. 5'-Methylthioadenosine, a product of the reaction, acts as a powerful competitive inhibitor with a Ki of 3.7 microM. Enzyme-substrate binding sites have been investigated with the aid of several substrate analogs and products. Among the compounds assayed, 5'-methylthiotubercidin, S-adenosyl(5')-3-thiopropylamine and S-adenosyl-3-thio-1,8-diaminooctane are the most active inhibitors.

Polyamine depletion increases cellular ribonucleotide levels

Depletion of the putrescine and spermidine content of Ehrlich ascites tumor cells by alpha-difluoromethylornithine (DFMO) treatment results in at least a 1 500-fold increase in the decarboxylated S-adenosylmethionine (deSAM) content. The accumulation of this adenine nucleoside occurs because of the absence of putrescine and spermidine to act as aminopropyl group acceptors in the spermidine and spermine synthase reactions and because of an increase in S-adenosylmethionine decarboxylase activity. The fact that the synthesis of deSAM continues in DFMO-treated cells makes the pathway an adenine trap. This prompted a study of the adenine nucleotide pools. High-performance liquid chromatographic analysis showed that the total adenine nucleotide pool increased, rather than decreased, as a result of DFMO treatment; the major contributors to the increase being ATP and ADP, which increased 2.6 and 1.9 times, respectively. The cellular content of other ribonucleotides increased as well, particularly that of UTP and CTP. When putrescine was added together with DFMO, the increases in cellular ribonucleotide contents were prevented, showing that they were indeed caused by polyamine depletion.

Growth of mammalian cells in the absence of the accumulation of spermine

Mammalian spermine synthase activity was strongly inhibited by S-methyl-5'-methylthioadenosine. This nucleoside was readily taken up by SV-3T3 cells and blocked the synthesis of spermine by these cells. However, there was a corresponding increase in spermidine content and there was no effect on cell growth. These results indicate that S-methyl-5'-methylthioadenosine should be a useful compound to evaluate the role of spermine in mammalian cell physiology and that in at least one cell line the synthesis of spermine is not required for a normal growth rate.

1-Aminooxy-3-aminopropane, a new and potent inhibitor of polyamine biosynthesis that inhibits ornithine decarboxylase, adenosylmethionine decarboxylase and spermidine synthase

1-Aminooxy-3-aminopropane was shown to be a potent competitive inhibitor (Ki = 3.2 nM) of homogenous mouse kidney ornithine decarboxylase, a potent irreversible inhibitor (Ki = 50 microM) of homogeneous liver adenosylmethionine decarboxylase and a potent competitive (Ki = 2.3 microM) of homogeneous bovine brain spermidine synthase. It did not inhibit homogeneous bovine brain spermine synthase and it did not serve as a substrate for spermidine synthase. The compound did not inhibit tyrosine aminotransferase, alanine aminotransferase or aspartate aminotransferase, which are pyridoxal phosphate-containing enzymes like ornithine decarboxylase. The inactivation of adenosylmethionine decarboxylase was partially prevented by pyruvate, which is the coenzyme of adenosylmethionine decarboxylase, and by the substrate, adenosylmethionine. 1-Aminooxy-3-aminopropane at 0.5 mM concentration inhibited the growth of HL-60 promyelocytic leukemia cells and this inhibition was prevented by spermidine but not by putrescine.

5'-Deoxy-5'-methylthioadenosine phosphorylase--III. Role of the enzyme in the metabolism and action of 5'-halogenated adenosine analogs

5'-Deoxy-5'-halogenated adenosines are alternative substrates for 5'-deoxy-5'-methylthioadenosine phosphorylase (MTAPase), an enzyme responsible for the metabolism of 5'-deoxy-5'-methylthioadenosine (MTA), a by-product of polyamine biosynthesis. The relative reactivity of these nucleosides with MTAPase from HL-60 human promyelocytic leukemia cells is MTA greater than 5'-deoxy-5'-fluoroadenosine (5'-FlAdo) greater than 5'-chloro-5'-deoxyadenosine (5'-ClAdo) greter than 5'-bromo-5'-deoxyadenosine (5'-BrAdo) greater than 5'-deoxy-5'-iodoadenosine (5'-IAdo). In MTAPase-containing cells, the adenine released from the 5'-halogenated adenosine was incorporated into adenine nucleotide pools; cleavage by (MTAPase appeared to be the rate-limiting step in this process. 5'-BrAdo and 5'-IAdo were growth inhibitors (EC50 values less than 10 microM) of MTAPase-containing cell lines (HL-60 human promyelocytic leukemia and the L5178Y murine lymphoblastic leukemia) but were much less active (EC50 values greater than 65 microM) against MTAPase-deficient cell lines (the CCRF-CEM human T cell leukemia and the L1210 murine leukemia). The full cytotoxicity of these compounds, therefore, appeared to be related to their phosphorolysis by MTAPase. Indirect evidence suggests that 5-halogenated ribose-1-phosphate derivatives of 5'-BrAdo or 5'-IAdo produced by the MTAPase reaction were the active metabolites of these 5'-halogenated adenosines.

Effects of (2R, 5R)-6-heptyne-2,5-diamine, a potent inhibitor of L-ornithine decarboxylase, on rat hepatoma cells cultured in vitro

DL-alpha-Difluoromethylornithine (F2MeOrn), the most widely-used inhibitor of L-ornithine decarboxylase, has been a useful tool to demonstrate that polyamine biosynthesis is required to maintain maximum rates of cell proliferation. However, in most eukaryotic cell systems, F2MeOrn exerts cytostatic rather than cytotoxic effects. This may be due to the fact that this inhibitor creates only incomplete polyamine deficiency. In particular, F2MeOrn scarcely depletes intracellular spermine levels. We now demonstrate in rat hepatoma tissue culture (HTC) cells that (2R, 5R)-6-heptyne-2,5-diamine, a more potent irreversible inhibitor of L-ornithine decarboxylase than F2MeOrn, decreases the concentrations of all polyamines including spermine. In parallel with the depletion of these amines, there is a progressive decrease in the rate of cell proliferation and in cell viability. Restoration of the intracellular polyamine content, by addition to the medium of polyamines or a high concentration of L-ornithine, the substrate of L-ornithine decarboxylase, further demonstrates that the antiproliferative effects of (2R, 5R)-6-heptyne-2,5-diamine do result from polyamine deficiency. These findings support the concept that polyamines play an essential function in the cell division processes and emphasize the vital function of spermine in mammalian cells.

Polyamines and heparin do not appreciably influence phosphorylation of chromatin proteins HMG 14 and HMG 17 by nuclear protein kinase II

Phosphorylation of acidic substrates such as casein and phosvitin by nuclear protein kinase II is stimulated by polyamines and inhibited by heparin, which mimics an endogenous proteoglycan inhibitor. The phosphorylation in vitro of the chromatin proteins HMG 14 and HMG 17 by nuclear protein kinase II were examined in this study focusing on the modifying effects of polyamines and heparin. Both HMG proteins were phosphorylated by the enzyme, but polyamines did not appreciably influence the extent of their phosphorylation. In addition, heparin did not inhibit the kinase reaction with the HMG proteins as substrates. These results indicate that the nuclear protein kinase II does actively phosphorylate HMG 14 and HMG 17 in vitro but that in contrast to some model substrates, polyamines and heparin do not appreciably affect their phosphorylation.

Polyamine synthesis in mammalian tissues. Isolation and characterization of spermidine synthase from bovine brain

Spermidine synthase (EC 2.5.1.16) was purified to apparent homogeneity (about 11 000-fold) from bovine brain by affinity chromatography, with S-adenosyl-(5')-3-thiopropylamine linked to Sepharose as the adsorbent. The enzyme preparation was free from S-adenosylmethionine decarboxylase (EC 4.1.1.50) and spermine synthase (EC 2.5.1.22) activities. The native enzyme had an apparent Mr of 70 000, was composed of two subunits of equal size, and had an isoelectric point at pH 5.22. The apparent Km values for putrescine and decarboxylated adenosylmethionine [S-adenosyl-(5')-3-methylthiopropylamine] were 40 microM and 0.3 microM respectively. Cadaverine and 1,6-diaminohexane could replace putrescine as the aminopropyl acceptor, although the reaction rates were only 6% and 1% respectively of that obtained with putrescine. Ethyl, propyl and carboxymethyl analogues of decarboxy-S-adenosylmethionine could act as propylamine donors. Both the reaction products, spermidine and 5'-methylthioadenosine, were mixed-type inhibitors of the enzyme. On the basis of initial-velocity and product-inhibition studies, a ping-pong reaction mechanism for the spermidine synthase reaction was ruled out.

Kinetic properties of spermine synthase from bovine brain

A kinetic analysis including initial-velocity and product-inhibition studies were performed with spermine synthase purified from bovine brain. The enzyme activity was assayed in the presence of 5'-methylthioadenosine phosphorylase as an auxiliary enzyme to prevent the accumulation of the inhibitory product, 5'-methylthioadenosine, and thus to obtain linearity of the reaction with time. Initial-velocity studies gave intersecting or converging linear double-reciprocal plots. No substrate inhibition by decarboxylated S-adenosylmethionine was observed at concentrations up to 0.4 mM. Apparent Michaelis constants were 60 microM for spermidine and 0.1 microM for decarboxylated S-adenosylmethionine. Spermine was a competitive product inhibitor with respect to decarboxylated S-adenosylmethionine, but a mixed one with respect to the other substrate, spermidine. 5'-Methylthioadenosine showed a mixed inhibition with both substrates, predominantly competitive with respect to decarboxylated S-adenosylmethionine and predominantly uncompetitive with respect to spermidine. The observed kinetic and inhibition patterns are consistent with a compulsory-order mechanism, where both substrates add to the enzyme before products can be released.

Polyamines in Trichomonas vaginalis

Trichomonas vaginalis was grown in a modified Bushby's medium and putrescine, spermidine and spermine levels were determined in extracts from 24- and 48-h cultures and also in the culture media. All three polyamines were present in T. vaginalis extracts; the putrescine level and putrescine/spermidine ratio were much higher than those reported for other protozoa or for mammalian tissues. There were no significant differences between 24-h and 48-h amine levels per mg protein in these extracts, but amine levels per cell were higher at 24 than at 48 h. The spent culture media had a much higher putrescine content than corresponding uninoculated media and it was concluded that T. vaginalis secreted putrescine into the culture medium.

Biochemistry of the polyamines

The naturally-occurring polyamines exist in the free form, as N-acetyl derivatives and bound to protein. Their biosynthesis is subject to sensitive control, particularly of ornithine decarboxylase. This enzyme may be multifunctional and a key regulatory protein. Studies, principally with selective inhibitors, have elucidated the roles of polyamines in cell proliferation. Oxidized polyamines, in contrast, can be potent mitotic inhibitors. These effects are reviewed in terms of their chemistry and biochemistry. Their principal distinctions are that they can be made or degraded intracellularly, they can associate electrostatically with macromolecules by means of their spaced cationic groups, and these can be readily converted to covalent bonds.

5'-deoxy-5'-methylthioadenosine phosphorylase--II. Role of the enzyme in the metabolism and antineoplastic action of adenine-substituted analogs of 5'-deoxy-5'-methylthioadenosine

The biological activities of several previously synthesized [J. A. Montgomery et al., J. med. Chem. 17, 1197 (1974)] adenine-substituted analogs of 5'-deoxy-5'-methylthio- or 5'-deoxy-5'-ethyl-thioadenosine, including the 2-fluoroadenine, 2-chloroadenine, 2,6-diaminopurine, 8-azaadenine, and 4-aminopyrazolo [3,4-d]pyrimidine-containing derivatives, have been reexamined. It is demonstrated that many of these analogs are cleaved to their respective free base analogs by 5'-deoxy-5'-methyl-thioadenosine phosphorylase (MTAPase), an enzyme associated with polyamine biosynthesis, and that this reaction is necessary for the cytotoxic action of these MTA analogs to be fully expressed. Evidence to support this includes: (1) the growth of two MTAPase-containing human colon carcinoma cell lines (the HCT-15 and DLD-1 lines) was inhibited by these analogs, whereas an MTAPase-deficient cell line, the CCRF-CEM human T-cell leukemia, was relatively insensitive to their cytotoxic action; (2) extracts of the MTAPase-containing colon carcinoma cell lines were able to cleave these analogs to their respective free base analogs; in contrast, extracts of MTAPase-deficient CCRF-CEM cells were unable to cleave these analogs; (3) intact colon carcinoma cells converted these MTA analogs to their corresponding 5'-phosphorylated analog nucleotides, whereas CCRF-CEM cells did not, at least to detectable levels; and (4) the MTA analog, 5'-deoxy-5'-ethylthio-4-aminopyrazolo [3,4-d]pyrimidine ribonucleoside, which is not a substrate of MTAPase, did not form analog nucleotides and was essentially noncytotoxic to all cell lines tested, whereas the corresponding adenine analog, 4-aminopyrazolo [3,4-d]pyrimidine, readily formed analog nucleotides and was highly cytotoxic to all the lines. It is postulated that the corresponding adenine analog 5'-phosphorylated nucleotides are the primary active metabolites of these MTA analogs, having been formed by the cleavage of these nucleosides to free adenine analogs by MTAPase, followed by the conversion of these base analogs to analog nucleotides by adenine phosphoribosyltransferase and the enzymes of adenine nucleotide phosphorylation. This pathway represents a novel drug-activation system for the synthesis of analog nucleotides and has the potential to be exploited chemotherapeutically.

Inhibition of bacterial aminopropyltransferases by S-adenosyl-1,8-diamino-3-thiooctane and by dicyclohexylamine

Bacterial aminopropyltransferases from Escherichia coli, Serratia marcescens and Pseudomonas aeruginosa were strongly inhibited by S-adenosyl-1,8-diamino-3-thiooctane (AdoDATO) and by dicyclohexylamine. The sensitivity to these drugs in vitro was comparable to that of mammalian spermidine synthase, but AdoDATO was much less potent in reducing spermidine content in the bacteria than in mammalian cells. Although AdoDATO was a stronger inhibitor than dicyclohexylamine in vitro, dicyclohexylamine was more active in reducing bacterial spermidine levels in vivo, suggesting that it is taken up better or is more stable in the cell and is the preferable compound for in vivo studies in microorganisms. The strong inhibition of spermidine synthases by AdoDATO which is a transition state analog supports the concept that these enzymes proceed by a single displacement reaction, rather than by a ping-pong mechanism.

Synthesis of Semliki-forest virus in polyamine-depleted baby-hamster kidney cells

The role of polyamines in macromolecular synthesis has been studied using the synthesis of Semliki-Forest virus (SF virus) in normal and alpha-difluoromethylornithine-treated baby-hamster kidney (BHK21) cells as a model system. The activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase, the rate-limiting enzymes in polyamine biosynthesis, decreased rapidly in mock- and SF-virus-infected cells, indicating that virus production in BHK21 cells was not dependent on polyamines formed after infection. A prolonged treatment of BHK21 cells with alpha-difluoro-methylornithine, a specific inhibitor of polyamine synthesis, resulted in a marked inhibition of the initial rate of virus production, which appeared 72 h after the beginning of the treatment. This inhibition was reversed by putrescine, spermidine and spermine, and at last partially by several other diamines and polyamine homologues. Polyamine-depletion also markedly reduced viral RNA polymerase activity in SF-virus infected cells. Addition of spermidine to the culture medium rapidly increased viral RNA polymerase activity in the inhibitor-treated cells but had no effect on the enzyme activity when added directly to the assay mixture. The results indicated that polyamines are needed for maximum initial rate of SF-virus replication and suggest that the inhibition of virus production in polyamine-depleted cells is at least partly due to malfunction of the protein-synthetic machinery of the host cell.

Inhibition of the synthesis of polyamines and macromolecules by 5'-methylthioadenosine and 5'-alkylthiotubercidins in BHK21 cells

5'-Methylthioadenosine and four 5'-alkylthiotubercidins were tested for their ability to inhibit polyamine synthesis in vitro and to decrease polyamine concentration and prevent growth of baby-hamster-kidney (BHK21) cells. 5'-Methylthioadenosine and 5'-methylthiotubercidin decreased the activity of spermidine synthase from brain to roughly the same extent, whereas brain spermine synthase was much more strongly inhibited by 5'-methylthioadenosine compared with 5'-methylthiotubercidin. These nucleoside derivatives also inhibited the growth of BHK21 cells and increased the concentration of putrescine. 5'-Methylthioadenosine decreased cellular spermine concentration, whereas 5'-methylthiotubercidin lowered the concentration of spermidine. The activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase were enhanced in cells grown in the presence of 5'-methylthiotubercidin. The growth inhibition produced by these nucleoside derivatives was not reversed by exogenous spermidine or spermine. 5'-Ethylthiotubercidin, 5'-propylthiotubercidin and 5'-isopropylthiotubercidin did not appreciably inhibit spermidine or spermine synthase in vitro or decrease the cellular polyamine content, but effectively prevented the growth of BHK21 cells. All nucleoside derivatives at concentrations of 0.2-1 mm caused a rapid inhibition of protein synthesis. It is concluded that the growth inhibition produced by 5'-methylthioadenosine and 5'-alkylthiotubercidins was not primarily due to polyamine depletion but other target sites, for instance the cellular nucleotide pool, cell membranes etc. must be considered.