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Studies of inhibition of rat spermidine synthase and spermine synthase.

1. S-Adenosyl-l-methionine, S-adenosyl-l-homocysteine, 5'-methylthioadenosine and a number of analogues having changes in the base, sugar or amino acid portions of the molecule were tested as potential inhibitors of spermidine synthase and spermine synthase from rat ventral prostate. 2. S-Adenosyl-l-methionine was inhibitory to these reactions, as were other nucleosides containing a sulphonium centre. The most active of these were S-adenosyl-l-ethionine, S-adenosyl-4-methylthiobutyric acid, S-adenosyl-d-methionine and S-tubercidinylmethionine, which were all comparable in activity with S-adenosylmethionine itself, producing 70-98% inhibition at 1mm concentrations. Spermine synthase was somewhat more sensitive than spermidine synthase. 3. 5'-Methylthioadenosine, 5'-ethylthioadenosine and 5'-methylthiotubercidin were all powerful inhibitors of both enzymes, giving 50% inhibition of spermine synthase at 10-15mum and 50% inhibition of spermidine synthase at 30-45mum. 4. S-Adenosyl-l-homocysteine was a weak inhibitor of spermine synthase and practically inactive against spermidine synthase. Analogues of S-adenosylhomocysteine lacking either the carboxy or the amino group of the amino acid portion were somewhat more active, as were derivatives in which the ribose ring had been opened by oxidation. The sulphoxide and sulphone derivatives of decarboxylated S-adenosyl-l-homocysteine and the sulphone of S-adenosyl-l-homocysteine were quite potent inhibitors and were particularly active against spermidine synthase (giving 50% inhibition at 380, 50 and 20mum respectively). 5. These results are discussed in terms of the possible regulation of polyamine synthesis by endogenous nucleosides and the possible value of some of the inhibitory substances in experimental manipulations of polyamine concentrations. It is suggested that 5'-methylthiotubercidin and the sulphone of S-adenosylhomocysteine or of S-adenosyl-3-thiopropylamine may be particularly valuable in this respect.

Adenosine↗

Specificity of mammalian spermidine synthase and spermine synthase.

1. The specificity of rat prostatic spermidine synthase and spermine synthase with respect to the amine acceptor of the propylamine group was studied. 2. Spermidine synthase could use cadaverine (1,5-diaminopentane) instead of putrescine, but the Km for cadaverine was much greater and the rate with 1mM-cadaverine was only 10% of that with putrescine. 1,3-Diaminopropane was even less active (2% of the rate with putrescine) and no other compound tested (including longer alpha,omega-diamines, spermidine and its homologues and monoacetyl derivatives) was active. 3. Spermine synthase was equally specific. The only compounds tested that showed any activity were 1,8-diamino-octane, sym-homospermidine, sym-norspermidine and N-(3-aminopropyl)-cadaverine, which at 1mM gave rates 2, 17, 3 and 4% of the rate with spermidine respectively. 4. The formation of polyamine derivatives of cadaverine and to a very small extent of 1,3-diaminopropane was confirmed by exposing transformed mouse fibroblasts to these diamines when synthesis of putrescine was prevented by alpha-difluoromethylornithine. Under these conditions the cells accumulated significant amounts of N-(3-aminopropyl)cadaverine and NN'-bis(3-aminopropyl)cadaverine when exposed to cadaverine and small amounts of sym-norspermidine and sym-norspermine when exposed to 1,3-diaminopropane.

Animals↗

Effects of inhibitors of spermidine synthase and spermine synthase on polyamine synthesis in rat tissues.

Several inhibitors of aminopropyltransferases, developed recently in this laboratory, were tested for their specificity by measuring their effects on six enzyme activities related to polyamine biosynthesis and interconversion. Two of them, trans-4-methylcyclohexylamine (4MCHA) and N-(3-aminopropyl)cyclohexylamine (APCHA), selectively and potently inhibited the activities of spermidine synthase and spermine synthase, respectively. They were subjected to in vivo studies using rats. Oral administration of 4MCHA or APCHA dissolved in drinking water (0.02 and 0.1%) available ad lib. for a period of 10 days or 4 months caused a specific and marked decrease in spermidine or spermine in tissues (such as a 95% decrease) with a compensatory increase of spermine or spermidine, respectively, but without any observable change in the growth of the treated rats. Also, with extreme reduction of spermidine or spermine, when their sum was approximately constant, the activity of S-adenosyl-methionine decarboxylase in these tissues was enhanced significantly with no change in the activity of ornithine decarboxylase. These results suggested a separate role for spermidine or spermine in the in vivo enhancement of S-adenosylmethionine decarboxylase activity.

Adenosylmethionine Decarboxylase↗

ACAULIS5, an Arabidopsis gene required for stem elongation, encodes a spermine synthase.

Polyamines have been implicated in a wide range of biological processes, including growth and development in bacteria and animals, but their function in higher plants is unclear. Here we show that the Arabidopsis: ACAULIS5 (ACL5) gene, whose inactivation causes a defect in the elongation of stem internodes by reducing cell expansion, encodes a protein that shares sequence similarity with the polyamine biosynthetic enzymes spermidine synthase and spermine synthase. Expression of the recombinant ACL5 protein in Escherichia coli showed that ACL5 possesses spermine synthase activity. Restoration of the acl5 mutant phenotype by somatic reversion of a transposon-induced allele suggests a non-cell-autonomous function for the ACL5 gene product. We also found that expression of the ACL5 cDNA under the control of a heat shock gene promoter in acl5 mutant plants restores the phenotype in a heat shock-dependent manner. The results of the experiments showed that polyamines play an essential role in promotion of internode elongation through cell expansion in Arabidopsis: We discuss the relationships to plant growth regulators such as auxin and gibberellins that have related functions.

Alleles↗

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

Spermine synthase, a propylamine transferase, which catalyses the biosynthesis of spermine from S-methyladenosylhomocystemine and spermidine has been purified to an apparent homogeneity (about 6000-fold) from bovine brain using spermine-Sepharose affinity chromatography. The enzyme preparation was free from S-adenosylmethionine decarboxylase and spermidine synthase activities. The molecular Stokes radius of the enzyme was calculated to be 4.16 nm. The enzyme has an apparent molecular weight of approximately 88 000, composing of two subunits of equal size. The enzyme showed a broad pH optimum between 7.0 and 8.0 and an acidic isoelectric point at pH 5.10. The apparent Km values for S-methyladenosylhomocysteamine was 0.6 microM and about 60 microM for spermidine. The enzyme showed strict specificity to spermidine as the propylamine acceptor. Both the reaction products, spermine and 5'-methylthioadenosine inhibited the enzyme activity, methylthioadenosine being a powerful competitive inhibitor with respect to S-methyladenosylhomocysteamine (Ki value of about 0.3 microM). Putrescine also inhibited competitively with respect to spermidine (Ki value of about 1.7 mM). Spermine synthase had no requirements for metal or other cofactors.

Animals↗

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.

Amino Acid Sequence↗

Effect of spermine synthase on the sensitivity of cells to anti-tumour agents.

The role of spermine in the sensitivity of cells to various established and experimental anti-tumour agents was examined, using paired cell lines that possess or lack spermine synthase. All spermine-synthase-deficient cells had no detectable spermine, and elevated spermidine, content. Spermine content did not alter the cell growth rate. There was little or no difference in sensitivity of immortalized mouse embryonic fibroblasts to doxorubicin, etoposide, cisplatin, methylglyoxal bis(guanylhydrazone) or H(2)O(2) and only a slight increase in sensitivity to vinblastine and nocodazole. However, the absence of spermine clearly increased the sensitivity to 1,3-bis(2-chloroethyl)- N -nitrosourea, suggesting that depletion of spermine may be a useful way to increase the anti-neoplastic effects of anti-tumour agents that form chloroethyl-mediated interstrand DNA cross-links. The effects of spermine on the response to polyamine analogues (which have been proposed to be useful anti-neoplastic agents) were complex, and depended on the compound examined and on the cells tested. Sensitivity to CHENSpm ( N (1)-ethyl- N (11)-[(cycloheptyl)methyl]-4,8-diazaundecane) was substantially greater in immortalized fibroblasts that lack spermine. In contrast, BE-3-4-3 [ N (1), N (12)-bis(ethyl)spermine] and BE-3-3-3 [ N (1), N (11)-bis(ethyl)norspermine] were more active against cells that contained spermine. The presence of spermine correlated with a greater induction of spermidine/spermine- N (1)-acetyltransferase by BE-3-3-3, which is consistent with suggestions that this induction is important for the response to this drug. These findings support the concepts that different polyamine analogues have different sites of action and that CHENSpm has a different site of action from BE-3-3-3.

Animals↗

Spermine is not essential for growth of Saccharomyces cerevisiae: identification of the SPE4 gene (spermine synthase) and characterization of a spe4 deletion mutant.

Spermine, ubiquitously present in most organisms, is the final product of the biosynthetic pathway for polyamines and is synthesized from spermidine. In order to investigate the physiological roles of spermine, we identified the SPE4 gene, which codes for spermine synthase, on the right arm of chromosome XII of Saccharomyces cerevisiae and prepared a deletion mutant in this gene. This mutant has neither spermine nor spermine synthase activity. Using the spe4 deletion mutant, we show that S. cerevisiae does not require spermine for growth, even though spermine is normally present in the wild-type organism. This is in striking contrast to the absolute requirement of S. cerevisiae for spermidine for growth, which we had previously reported using a mutant lacking the SPE3 gene (spermidine synthase) [Hamasaki-Katagiri, N., Tabor, C. W., Tabor, H., 1997. Spermidine biosynthesis in Saccharomyces cerevisiae: Polyamine requirement of a null mutant of the SPE3 gene (spermidine synthase). Gene 187, 35-43].

Amino Acid Sequence↗

Characterization of transgenic mice with widespread overexpression of spermine synthase.

A widespread increase in SpmS (spermine synthase) activity has been produced in transgenic mice using a construct in which the human SpmS cDNA was placed under the control of a composite CMV-IE (cytomegalovirus immediate early gene) enhancer-chicken beta-actin promoter. Four separate founder CAG/SpmS mice were studied. Transgenic expression of SpmS was found in all of the tissues examined, but the relative SpmS activities varied widely according to the founder animal and the tissue studied. Very large increases in SpmS activity were seen in many tissues. SpdS (spermidine synthase) activity was not affected. Although there was a statistically significant decline in spermidine content and increase in spermine, the alterations were small compared with the increase in SpmS activity. These results provide strong support for the concept that the levels of the higher polyamines spermidine and spermine are not determined only by the relative activities of the two aminopropyltransferases. Other factors such as availability of the aminopropyl donor substrate decarboxylated S-adenosylmethionine and possibly degradation or excretion must also influence the spermidine/spermine ratio. No deleterious effects of SpmS overexpression were seen. The mice had normal growth, fertility and behaviour up to the age of 12 months. However, breeding the CAG/SpmS mice with MHC (alpha-myosin heavy chain)/AdoMetDC (S-adenosylmethionine decarboxylase) mice, which have a large increase in S-adenosylmethionine decarboxylase expression in heart, was lethal. In contrast, breeding the CAG/SpmS mice with MHC/ODC (L-ornithine decarboxylase) mice, which have a large increase in cardiac ornithine decarboxylase expression, had a protective effect in preventing the small decrease in viability of the MHC/ODC mice.

Animals↗

Partial deletion of both the spermine synthase gene and the Pex gene in the X-linked hypophosphatemic, gyro (Gy) mouse.

Gy, along with Hyp, is a dominant mutation of the normal gene Pex causing X-linked hypophosphatemia in the mouse. Hemizygous Gy male mice, however, have greater defects in survival, bodily growth, skeletal mineralization, and neurological function than those found in heterozygous Gy females or in Hyp mice. Since the gene for spermine synthase is immediately upstream of the homologous human gene PEX, we compared the effects of the Gy and Hyp mutations on both the spermine synthase gene and the Pex gene. Barely detectable levels of spermine (< 5% of normal) with elevated levels of its precursor, spermidine, were found in organs of Gy male mice compared to normal male littermates. Neither Gy females nor Hyp male mice were significantly affected. Four missing introns of the spermine synthase gene were identified in Gy male mice, suggesting extensive gene disruption. A pseudogene for spermine synthase was also identified in the mouse genome. Pex mRNA was found in several but not all tissues studied in adult normal mice. Pex mRNA was altered in both Gy and Hyp mice. All male Hyp mice were lacking the 3' end of the Pex message, whereas all male Gy mice were deficient at the 5' end. In summary, the Gy mutation is associated with a recessively expressed mutation of the spermine synthase gene, leading to spermine deficiency, and a dominantly expressed mutation of the Pex gene, leading to hypophosphatemia. Alterations in two contiguous genes in Gy may explain the additional phenotypic abnormalities present in the Gy male mouse.

Animals↗

Polyamine-linked sepharoses: preparation and application to mammalian spermine synthase.

Seven different polyamine-linked Sepharose derivatives were prepared for the affinity chromatography of spermidine and spermine binding macromolecules: Spermine synthase from rat and hog brain was used as a model protein with a spermidine binding site. Comparative studies of the affinities of the enzymes for the seven matrixes suggested that two negative charges, three to four methylene groups apart, should be present at the decarboxylated S-adenosylmethionine binding site and should improve the binding of the enzyme to the Sepharose derivative. Two negative charges at the spermidine binding site would be expected to do the same. Three affinity matrixes linked with 1,17-diamino-4,9,14-triazaheptadecane, 1,21-diamino-4,9,13,18-tetraazaheneicosane, and 5-spermine carboxylic acid, respectively, had an affinity for spermine synthases higher than that of spermine-Sepharose, which has been used for the purification of spermine synthase. The first of these matrixes was used and proved to be effective for the purification.

Animals↗

Effect of spermine synthase deficiency on polyamine biosynthesis and content in mice and embryonic fibroblasts, and the sensitivity of fibroblasts to 1,3-bis-(2-chloroethyl)-N-nitrosourea.

Mutant Gy male mice, which have previously been described as having disruption of the phosphate-regulating Phex gene and a spermine synthase gene [Meyer, Henley, Meyer, Morgan, McDonald, Mills and Price (1998) Genomics, 48, 289-295; Lorenz, Francis, Gempel, Böddrich, Josten, Schmahl and Schmidt (1998) Hum. Mol. Genet. 7, 541-547], as well as mutant Hyp male mice, which have disruption of the Phex gene only, were examined along with their respective normal male littermates. Biochemical analyses of extracts of brains, hearts and livers of 5-week-old mice showed that Gy males lacked any significant spermine synthase activity as well as spermine content. Organs of Gy males had a higher spermidine content. This was caused not only by the lack of conversion of spermidine into spermine, but also because of compensatory increases in the activities of other polyamine biosynthetic enzymes. Gy males were half the body weight of their normal male littermates at weaning age. Hyp males, however, were no different in size when compared with their controls. High mortality of Gy males occurs by weaning age and this mortality was shown to be largely post-natal. Embryonic fibroblasts were isolated from Gy males and their normal male littermates and were similarly shown to lack any significant spermine synthase activity as well as spermine content. The lack of spermine, however, had no significant effect on the growth of immortalized fibroblasts or of primary fibroblast cultures. Similarly, there was no difference in the time of senescence of primary fibroblast cultures from Gy males compared with cultures derived from normal male littermates. However, the lack of spermine did increase the sensitivity of immortalized fibroblasts to killing by the chloroethylating agent 1, 3-bis(2-chloroethyl)-N-nitrosourea. Therefore both the Gy male mice and derived embryonic fibroblasts provide valuable models to study the importance of spermine and spermine synthase, without the use of inhibitors which may have additional side effects.

Animals↗

Effect of S-adenosyl-1,12-diamino-3-thio-9-azadodecane, a multisubstrate adduct inhibitor of spermine synthase, on polyamine metabolism in mammalian cells.

The effects of the potent spermine synthase inhibitor S-adenosyl-1,12-diamino-3-thio-9-azadodecane (AdoDatad) on polyamine biosynthesis have been studied in transformed mouse fibroblasts (SV 3T3 cells) and in mouse leukemia cells (L1210). A dose-dependent decrease in intracellular spermine concentration was observed in both cell lines when grown in the presence of the inhibitor. A major difference in the effects seen in these two cell lines was the cytotoxicity observed in L1210 cells exposed to the inhibitor, which contrasted with little or no effects on growth of SV 3T3 cells treated similarly. Oxidative metabolism of the drug in L1210 cells was suggested by the fact that addition of aminoguanidine, an amine oxidase inhibitor, to the cell cultures ablated the cytotoxic effects of the inhibitor. Complete analysis of intracellular polyamines was carried out, together with analysis of S-adenosylmethionine, decarboxylated S-adenosylmethionine, and the inhibitor. These analyses revealed that, although the inhibitor had a dramatic effect on spermine biosynthesis in the cells studied, a compensatory increase in spermidine biosynthesis was observed. This resulted in no change in total polyamine concentrations in cells treated with inhibitors of either spermine synthase or spermidine synthase (Pegg et al., 1982) alone or in combination. In all cases, the concentration of the aminopropyl donor decarboxylated S-adenosylmethionine increased dramatically, thus allowing for the observed maintenance of total polyamine levels even in the presence of either one or both potent inhibitors of the aminopropyltransferases. Oxidative metabolism of the inhibitor complicates the interpretation of experiments carried out in the absence of amine oxidase inhibitors such as aminoguanidine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗

Role of unsaturated derivatives of spermidine as substrates for spermine synthase and in supporting growth of SV-3T3 cells.

Synthetic unsaturated analogues of the natural polyamine were examined as possible substrates for spermine synthase and as replacements for spermidine in supporting the growth of SV-3T3 cells. It was found that N-(3-aminopropyl)-1,4-diamino-cis-but-2-ene [the cis isomer of the alkene analogue of spermidine] was a good substrate for spermine synthase, but that the trans isomer [N-(3-aminopropyl)-1,4-diamino-trans-but-2-ene] and the alkene analogue [N-(3-aminopropyl)-1,4-diaminobut-2-yne] were not substrates. These results provide the first demonstration of stereospecificity in the spermine synthase reaction. All three of the unsaturated spermidine analogues described above and the cis-alkene analogue of spermine [N1N4-bis-(3-aminopropyl)-1,4-diamino-cis-but-2-ene] were able to support the growth of SV-3T3 cells that were prevented from the endogenous synthesis of spermidine by treatment with alpha-difluoromethylornithine. Since N-(3-aminopropyl)-1,4-diamino-trans-but-2-ene] and N-(3-aminopropyl)-1,4-diaminobut-2-yne were not converted into a spermine derivative, it is apparent that this conversion is not needed for the stimulation of growth. However, since N1N4-bis-(3-aminopropyl)-1,4-diamino-cis-but-2-ene was also able to support growth and was not degraded to the spermidine derivative, it appears that either polyamine can be effective in this respect. All of the unsaturated analogues tested accumulated in the SV-3T3 cells to a much greater extent than spermidine itself. This indicates that these compounds are substrates for the polyamine transport system, but that they are less effective than the natural polyamines in the feedback regulation of this system.

Animals↗