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PubMed1985

Methylglyoxal bis(guanylhydrazone) elimination of polyamine effects on protein synthesis.

The effect of methylglyoxal bis(guanylhydrazone) (MGBG), a structural analog of polyamines, on protein synthesis has been studied in the presence and absence of spermidine. The spermidine stimulation of polyphenylalanine- and MS2 RNA-directed RNA replicase synthesis in an Escherichia coli cell-free system and of globin synthesis in a rabbit reticulocyte cell-free system disappeared with the addition of MGBG. The spermidine reduction of misincorporation of leucine during polyphenylalanine synthesis in both E. coli and wheat germ cell-free systems was also disturbed by MGBG. MGBG noncompetitively interfered with polyamine stimulation of polyphenylalanine and globin synthesis, suggesting that MGBG could bind to both RNA and the complex of RNA and polyamine. MGBG was preferentially bound to ribosomal RNA among ribosomal RNA, poly(U), and calf thymus DNA, and strongly inhibited the amount of polyamine bound to ribosomal RNA. These results suggest that MGBG elimination of polyamine effects on protein synthesis may occur through the disturbance of polyamine binding to ribosomal RNA.

Animals↗

PubMed1978

Cellular polyamine depletion reduces DNA synthesis in isolated lymphocyte nuclei.

The accumulation of putrescine, spermidine and spermine in activated bovine lymphocytes was blocked by the combined action of two inhibitors of polyamine biosynthesis, methylglyoxal bis(guanylhydrazone) (MGBG) and alpha-methylornithine. Lymphocytes were cultured under three conditions: (1) alpha-methylornithine alone, (2) MGBG alone, or (3) alpha-methylornithine plus MGBG. DNA synthesis in nuclei isolated from these cells was reduced from control rates by approx. 10, 55 and 75%, respectively. In each case, the degree of inhibition was similar to that observed with the intact cells. Stimulation of nuclear DNA synthesis with the postnuclear supernatant fraction was not affected by polyamine depletion of the cells. Several experiments indicate that the reduced rate of in vitro DNA synthesis was caused by the lack of polyamines and not by alternate effects of the drugs. No inhibition was observed (1) when spermidine was added to inhibited cultures 12 h before harvest and nuclear isolation, (2) when the drugs were added after polyamines had accumulated, and (3) when the drugs were added directly to the in vitro assay. In addition, the degree of inhibition of in vitro DNA synthesis correlated with the degree of polyamine deficiency. These in vitro studies confirm the results obtained with whole cells and support the hypothesis that DNA synthesis is one cellular site of action of the naturally occurring polyamines.

Animals↗

PubMed1992

Polyamine N-acetyltransferase from Fasciola hepatica.

A cytosolic polyamine N-acetyltransferase which catalyses polyamine and diamine acetylation has been partially purified from the liver fluke Fasciola hepatica. The enzyme has an apparent Mr of 50,000 and unlike the corresponding mammalian liver counterpart is capable of putrescine acetylation. Among the substrates tested, spermidine had the highest reaction rate but putrescine had a lower Km value. The Km values for spermidine, spermine, norspermidine, putrescine, cadaverine and 1,3-diaminopropane were 20 microM, 1.30 mM, 20 microM, 7 microM, 10 microM and 50 microM, respectively. Acetylated polyamines were also substrates for the trematode acetylase, but histones were inactive. The partially purified enzyme had no deacetylase activity. The Km for acetyl-CoA was 4.4 microM. Coenzyme A was strongly inhibitory with a Ki value of 5.3 microM. Bis(benzyl)polyamine analogue MDL 27695 was a potent competitive inhibitor of the enzyme with a Ki of 22 microM. Inhibition by 1,4-dimethyl-putrescine was non-competitive and had a Ki value of 15 microM. The trematode acetylase is highly dependent on sulfhydryl groups for its activity. As had been reported in nematodes, polyamine acetylation could represent a process by which trematodes convert excess polyamines to forms suitable for transport and excretion. On the other hand, this could be the regulatory step of a functional interconversion pathway in these parasites.

Acetylation↗

PubMed1996

Effect of three novel polyamine oxa-analogues (MTR-OSPD, DIP-SPN and APPO-TFA) on the growth and proliferation of Swiss 3T3 cells.

In order to investigate their biological function on cellular polyamine content, cell growth and proliferation, three novel polyamine oxa-analogues, 5-(4-methoxy-2,3,6-trimethylbenzenesulfonyl)-6-oxa-spermidine (MTR-OSPD); 6,9-dioxa-5,10-di-(2,2,5,7,8-pentamethylchroman-6-sulfonyl) spermine (DIP-SPN) and 3-aminopropyl N-(3-phthalimidopropyloxy) trifluoroacetimidate (APPO-TFA) were tested for their ability to stop or slow down the growth of Swiss 3T3 cells. Cells at 50-60% confluency were grown for 24 or 48 hr in the presence of a wide range of polyamine oxa-analogue concentrations and the number of cells counted. To determine whether the drugs were cytotoxic or cytostatic, the analogue-containing medium in some vials was replaced with fresh culture medium after 48 hr and the cells incubated for a further 24 hr. Cellular protein, RNA, DNA, polyamine contents and the activities of ornithine decarboxylase, S-adenosyl-L-methionine decarboxylase and spermidine/spermine N1-acetyltransferase were also determined at the lowest effective analogue concentration. All three inhibitors stopped cell proliferation at concentrations over 100 microM. Both MTR-OSPD and DIP-SPN were cytotoxic, since the cells could not be revived by removing the inhibitor from the medium, whereas APPO-TFA was only cytostatic. At the lowest effective concentration the analogues had little effect on protein, RNA and DNA content of the cells, but had varying effects on polyamine metabolism. The most interesting analogue was APPO-TFA. This drug showed concentration-dependent growth inhibition between concentrations of 5 nM and 5 microM. These novel analogues may be of value in elucidating the precise functions of polyamines in cellular metabolism. Their exact mode of action is now under investigation.

3T3 Cells↗

PubMed2004

Simultaneous determination of catecholamines and polyamines in PC-12 cell extracts by micellar electrokinetic capillary chromatography with ultraviolet absorbance detection.

A method for simultaneous determination of polyamines and catecholamines in cell extracts by micellar electrokinetic capillary chromatography with UV detection at 254 nm was established at the first time. The polyamines (putrescine, spermidine and spermine) and catecholamines (dopamine, serotonin, norepinephrine and epinephrine) were extracted from PC-12 cells and were derivatized with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate. Different derivatization conditions such as temperature, ratio of derivatization reagents and incubation time were investigated to find the best reaction condition which gave the highest detection sensitivity for polyamines and catecholamines. The influence of running buffer and additives on the separation such as pH, sodium dodecyl sulfate (SDS) concentrations and various additives was also investigated. Separation was achieved within 20 min with good repeatability in a 100mM boric acid buffer containing 10mM SDS and 10mM 18-crown-6 at a pH of 9.5. The detection limit ranged from 1.0 x 10(-7) to 9.0 x 10(-7) M, which is sufficient for determination of polyamines and catecholamines in many cell extracts. This technique can be easily applied to polyamine-related anticancer drug studies or clinical follow-ups after each dosage of these anticancer drugs, since these drugs not only have great inhibition on polyamine levels in blood, but also have a large influence on catecholamine levels in blood.

Animals↗

PubMed2006

Novel oral formulation safely improving intestinal absorption of poorly absorbable drugs: utilization of polyamines and bile acids.

In order to develop a novel oral formulation that can safely improve the intestinal absorption of poorly absorbable drugs, polyamines such as spermine (SPM) and spermidine (SPD) was examined as an absorption enhancing adjuvant in rats. The absorption of rebamipide, classified into BCS Class IV, from colon was significantly improved by SPM or SPD, and the enhancing ability of SPM was larger than that of SPD. As a possible mixing and/or interaction of polyamines with bile acids were expected, the combinatorial use of sodium taurocholate (STC) with polyamines was also examined. The absorption of rebamipide was drastically improved by the combinatorial use of SPM or SPD with STC. As STC itself did not enhance the absorption of rebamipide so much, it was considered that polyamines and STC had a synergistic enhancing effect. In-vivo oral absorption study was also performed to investigate the effectiveness and safety of polyamines and their combinatorial use with STC in rats. Although the enhancing effect slightly attenuated comparing with the in-situ loop study, the absorption of rebamipide was significantly improved and the combinatorial use of 10 mM SPM with 25 mM STC showed the largest enhancing effect. Histopathological studies clearly showed that any significant change in stomach and duodenum was not caused by SPM (10 mM), SPD (10 mM) or their combinatorial use with STC (25 mM) at 1.5 or 8.0 h after oral administration. Taken all together, polyamines, especially SPM, and its combinatorial use with STC could improve the absorption of poorly absorbable drugs without any significant changes in gastrointestinal tract after oral administration in rats.

Adjuvants, Pharmaceutic↗

PubMed1998

A unique interaction between polyamine and multidrug resistance (P-glycoprotein) transporters in cultured Chinese hamster ovary cells transfected with mouse mdr-1 gene.

We have shown that a functional link exists between the polyamine transporter and the multi-drug resistance (MDR) efflux transporter (P-glycoprotein, P-gp) in MDR-positive cancer cells. To further explore the nature of this interaction, we have examined the effect of reduced polyamine transport activity on cellular expression and activity of P-gp acquired by either selection or transfection. Chinese hamster ovary (CHO) cells and their polyamine transport-deficient mutants (CHOMGBG) were transfected with mouse mdr-1b gene. The activity of P-gp in these cells was quantified by measuring cellular accumulation of radiolabeled taxol and etoposide in the presence and absence of the P-gp modulator SDZ PSC-833 (valspodar; a semisynthetic undecapeptide derived from cyclosporin D). The mdr-1b-transfected CHO cells accumulated 2- to 3-fold less taxol and etoposide than the controls, an accumulation defect reversed by the potent MDR modulator PSC-833. Despite expression of P-gp on the surface of mdr-1b-transfected CHOMGBG cells, this classic MDR phenotype was not observed. Similarly, CHO cells, but not CHOMGBG cells, showed MDR activity after selection with doxorubicin as determined by reduced accumulation of radiolabeled taxol. Treatment with 50 microM of reduced polymer of spermine and glutaraldehyde, a selective blocker of the polyamine transport system, reduced MDR activity in mdr-1-transfected CHO cells and restored cellular accumulation of etoposide and taxol to control levels, effects not observed in mdr-1-transfected CHOMGBG cells. Notably, mdr-1-transfected CHO cells were 4- to 16-fold more resistant to the cytotoxic effects of the P-gp substrates doxorubicin, taxol, and etoposide than were the mdr-1-transfected CHOMGBG cells. CHO cells transfected with the mdr-1 gene exhibited a 23% reduction in cellular uptake of [14C]spermidine compared with untransfected controls; spermidine accumulation in CHOMGBG cells was no different than that in untransfected controls. These data suggest that the existence of a functioning polyamine transport system may be a requirement for MDR transporter activity, while the expression of functioning P-gp appears to reduce polyamine transporter activity.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2001

Expression of host S-adenosylmethionine decarboxylase gene and polyamine composition in aphid bacteriocytes.

Differential cDNA display and quantitative RT-PCR revealed that mRNA of host S-adenosylmethionine decarboxylase (SAMDC) was abundant only in the aphid endosymbiotic system well organized in young hosts, suggesting that SAMDC plays some important roles in the system. SAMDC is a key enzyme to synthesize polyamines that are known to be involved in a large array of biological events including protein synthesis, DNA stabilization, DNA replication, and cell proliferation. As the first step to investigate roles of polyamines in the endosymbiotic system, polyamine composition in bacteriocytes was determined by high performance liquid chromatography. As a result, we found that bacteriocytes contained virtually an only single polyamine, spermidine. The spermidine content of bacteriocytes fluctuated with time in the course of development and aging of the host aphid. This is the first report of polyamine assessment in a prokaryote-eukaryote endocellular symbiotic system, which demonstrated a unique polyamine composition.

Adenosylmethionine Decarboxylase↗

PubMed1997

Filarial DNA and its interaction with polyamines and antifilarial drugs.

The interaction of DNA from filarial parasite Setaria cervi with polyamines was monitored by melting temperature (Tm) profile, condensation and B to Z DNA transition and compared with DNA of Escherichia coli, Micrococcus luteus and calf thymus having different GC content. Polyamines, viz. spermine and spermidine, stabilized the secondary structure of all DNAs as indicated by increase in Tm value. UV absorption studies indicated B to Z DNA transition in the presence of polyamines. The amount of polyamines required for B to Z transition was dependent upon base composition of DNA and charge of the polyamine. Filarial DNA (AT rich) required six times higher concentration of spermine as compared to GC rich DNA for B to Z DNA transition. Spermidine was not effective in causing transition of S. cervi DNA even at Spd:DNA-P ratio of 20. The antifilarial compound suramin significantly decreased melting temperature of filarial DNA as compared to GC rich DNAs of other parasites. Suramin adversely affected condensation and B to Z DNA transition of various DNAs but prior addition of polyamines protected the DNAs from the destabilizing effect of suramin.

Animals↗

PubMed2002

Peach (Prunus persica) fruit ripening: aminoethoxyvinylglycine (AVG) and exogenous polyamines affect ethylene emission and flesh firmness.

The effect of various concentrations of aminoethoxyvinylglycine (AVG; 0.32 and 1.28 mM), an ethylene biosynthesis inhibitor, and of the polyamines putrescine (10 mM), spermidine (0.1, 1 and 5 mM) and spermine (2 mM) on peach (Prunus persica L. Batsch cv. Redhaven) fruit ripening was evaluated under field conditions. Treatments were performed 19 (polyamines) and 8 (AVG) days before harvest. Fruit growth (diameter, fresh and dry weight), flesh firmness, soluble solids content and ethylene emission were determined on treated and untreated (controls) fruits. Moreover, endogenous polyamine content and S-adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.21) activity were determined to check for a possible competition between polyamines and ethylene for their common precursor S-adenosylmethionine (SAM). Both treatments strongly inhibited ethylene emission and delayed flesh softening. On a biochemical level, AVG and exogenous polyamines both reduced the free-to-conjugate ratio of endogenous polyamines, and transiently altered SAMDC activity. The possible use of these compounds to control fruit ripening is discussed also in the light of their rejuvenating effect on peach fruits.

Journal Article↗

PubMed1968

Studies on the role of polyamines associated with the ribosomes from Bacillus stearothermophilus.

1. Spermine and spermidine were the main polyamines detectable in Bacillus stearothermophilus. 2. When grown at 65 degrees B. stearothermophilus contained lower concentrations of polyamines per mg. of RNA than when grown at 45 degrees or at 55 degrees . 3. Ribosomes isolated from B. stearothermophilus in 0.01m-tris-hydrochloric acid buffer (pH7.4)-0.01m-magnesium chloride contained sufficient polyamines to neutralize between 4% and 9% of their RNA phosphorus. 4. Removal of polyamines from the ribosomes by dialysis against m-potassium chloride did not appreciably alter the hypochromicity or thermal denaturation profiles of the ribosomes when measured in 0.01m-tris-hydrochloric acid buffer (pH7.4)-0.01m-magnesium chloride, though it did cause a loss of ribosome particles sedimenting at greater than 78s. 5. When ribosomes were dialysed against acridine orange solutions acridine orange bound to the ribosomes and did not displace spermine, but when a mixture of ribosomal RNA and spermine was dialysed against acridine orange the acridine orange displaced the spermine. It is concluded that polyamines in the ribosomes are less accessible for displacement by acridine orange than when polyamines are bound to ribosomal RNA.

Acridines↗

PubMed1982

Regulation of tRNA methyltransferase activities by spermidine and putrescine. Inhibition of polyamine synthesis and tRNA methylation by alpha-methylornithine or 1,3-diaminopropan-2-ol in Dictyostelium.

Inhibitors of polyamine synthesis (alpha-methylornithine and 1,3-diaminopropan-2-ol) were used to study the relationship between polyamine synthesis and specific methylations of tRNA in Dictyostelium discoideum during vegetative growth. Polyamine concentrations were found to be 10 mM for putrescine, 1.6 mM for spermidine and 7 mM for 1,3-diaminopropane throughout the growth stage. On treatment of growing amoebae with alpha-methylornithine or with 1,3-diaminopropan-2-ol (each at 5 mM), the syntheses of putrescine, spermidine and 1,3-diaminopropane were arrested within 4h. After polyamine synthesis had ceased, the incorporation of methyl groups into tRNA was considerably decreased under conditions that had no effect on the incorporation of uridine into tRNA, or on net syntheses of protein and of DNA. The following nucleosides in tRNA were concerned: 1 methyladenosine, 5-methylcytidine, 7-methylguanosine, 2-methylguanosine, N2N2-dimethylguanosine and 5-methyluridine (ribosylthymine). The corresponding tRNA methyltransferases, determined in Mg2+-free enzyme extracts, proved to be inactive unless polyamines were added. Putrescine and/or spermidine at concentrations of 10 mM or 1-2 mM respectively stimulate the transmethylation reaction in vitro to a maximal rate and to an optimal extent at exactly the same concentrations as found in vegetative cells. In contrast, 1,3-diaminopropane, which is formed from spermidine, does not affect the methylation of tRNA in vitro at physiological concentrations. Putrescine and/or spermidine stabilize the tRNA methyltransferases in crude extracts in the presence but not in the absence of the substrate tRNA. The results support the view that S-adenosylmethionine-dependent transmethylation reactions can be regulated by alterations of polyamine concentrations in vivo.

Diamines↗

PubMed1986

Localization and biosynthesis of polyamines in insulin-producing cells.

Two recently developed fluorescence cytochemical methods, specific for spermidine and spermine, were used to localize polyamines in the endocrine pancreas. The polyamines were restricted to the insulin-producing beta-cells and were mainly associated with the secretory granules. Chemical polyamine determinations carried out on isolated rat and mouse pancreatic islets revealed large amounts of polyamines. Compared with extracts of whole pancreas, the islets contained very high concentrations of spermine relative to spermidine. Biosynthesis of polyamines from [3H]ornithine or from [3H]putrescine in isolated islets was significantly stimulated at high glucose concentrations. Moreover, significant incorporation of label from [3H]putrescine was also detected in gamma-aminobutyric acid. This incorporation, however, was not stimulated by high glucose. Possible roles for polyamines associated with the secretory granules in insulin-producing cells are discussed.

Animals↗

PubMed1992

Regulation of pyruvate dehydrogenase by insulin and polyamines within electropermeabilized fat-cells and isolated mitochondria.

1. Regulation of the mammalian pyruvate dehydrogenase (PDH) complex by insulin and polyamines has been examined by using electropermeabilized rat epididymal fat-cells and isolated mitochondria. The complex could be regulated within the permeabilized cells not only by insulin, but also by certain low-M(r) species, including Ca2+ and the polyamine spermidine. 2. Both spermine and spermidine increased the level of active dephosphorylated PDH (PDHa) in isolated adipose-tissue mitochondria 2-3-fold, with half-maximal effects at 0.9 mM and 1.7 mM respectively. By contrast, PDH activity in rat heart mitochondria was essentially insensitive to the effects of these polyamines. 3. The effects on PDH activity of incubation of adipose-tissue mitochondria with spermine persisted through re-isolation and re-incubation of the mitochondria in the absence of the polyamine. 4. No evidence was found of any increase in the concentration of spermine associated with purified mitochondrial fractions prepared from insulin-treated tissue. 5. Overall, the data provide further evidence against a role for polyamines in the rapid stimulation of PDH by insulin, but suggest that polyamines may be important in mediating longer-term changes in the activity of the complex.

Adipose Tissue↗

PubMed1969

The polyamine content of the tRNA of E. coli.

A sensitive method of polyamine estimation has been adapted to the study of the organic cations of small amounts of nucleic acid. A procedure utilizing phenol extraction, alcohol precipitation, and separation on Sephadex G100 has been devised for the isolation of tRNA at low ionic strength. The procedure is applicable to the isolation of tRNA from liter batches of bacterial culture. With these methods we have examined the polyamines of tRNA isolated from polyauxotrophic strains of E. coli incubated under various physiological conditions and have found the following: (1) The tRNA from relaxed bacteria (TAU rel) harvested during exponential growth is heterogeneous with respect to polyamine content. Some portions of the population contain about one mole of spermidine per mole of tRNA. Some putrescine and an unknown amine are also present in low concentration. (2) After exponential TAU rel is incubated with thymine and uracil in the absence of arginine, the tRNA population is far more homogeneous with respect to polyamine content. The various fractions contain two moles of spermidine per mole of tRNA and a small amount of putrescine. (3) After exponential TAU rel is incubated in the absence of both arginine and uracil, the polyamine pattern of the tRNA resembles that isolated from exponential cells. (4) The tRNA from stringent bacterias harvested during exponential growth is heterogeneous with respect to polyamine distribution and some fractions contain relatively high concentrations of the unknown amine.

Amines↗

PubMed1997

The NR2B-specific interactions of polyamines and protons with the N-methyl-D-aspartate receptor.

Many compounds exhibit NR2B-specific modulation of the N-methyl-D-aspartate receptor, although their mechanism(s) of action are largely unknown. Using chimeric NR2A/NR2B subunits, we have located a region of NR2B (amino acids 138-238) which regulated glycine-independent polyamine stimulation. Mutation of glutamate 201 in this region affected stimulation by polyamines in the order E201D < E201A < E201N < E201R. The relief of proton inhibition of the N-methyl-D-aspartate-induced currents mediated by these mutant receptors correlated with the reduction in glycine-independent polyamine stimulation. Electrophysiological evidence with a triple mutant of NR2A further supports the hypothesis that polyamine stimulation may be linked to the relief of tonic inhibition by protons and demonstrates the crucial role of amino acids 200 and 201 in polyamine stimulation. Polyamines and protons, therefore, share common NR2B determinants.

Amino Acid Sequence↗

PubMed1998

Correlation of polyamine and growth responses to N1,N11-diethylnorspermine in primary fetal fibroblasts derived from transgenic mice overexpressing spermidine/spermine N1-acetyltransferase.

A recently generated transgenic mouse line having activated polyamine catabolism due to systemic overexpression of spermidine/spermine N1-acetyltransferase (SSAT) was used to isolate primary fetal fibroblasts as a means to further elucidate the cellular consequences of activated polyamine catabolism. Basal levels of SSAT activity and steady-state mRNA in the transgenic fibroblasts were about approximately 20- and approximately 40-fold higher than in non-transgenic fibroblasts. Consistent with activated polyamine catabolism, there was an overaccumulation of putrescine and N1-acetylspermidine and a decrease in spermidine and spermine pools. Treatment with the polyamine analogue N1,N11-diethylnorspermine (DENSPM) increased SSAT activity in the transgenic fibroblasts approximately 380-fold, whereas mRNA increased only approximately 3-fold, indicating post-mRNA regulation. SSAT activity in the nontransgenic fibroblasts increased approximately 200-fold. By Western blot, enzyme protein was found to increase approximately 46 times higher in the treated transgenic fibroblasts than non-transgenic fibroblasts: a value comparable to 36-fold differential in enzyme activity. With DENSPM treatment, spermidine pools were more rapidly depleted in the transgenic fibroblasts than in nontransgenic fibroblasts. Similarly, transgenic fibroblasts were much more sensitive to DENSPM-induced growth inhibition. This was not diminished by co-treatment with an inhibitor of polyamine oxidase, suggesting that growth inhibition was due to polyamine depletion per se as opposed to oxidative stress. Since the two fibroblasts were genetically identical except for the transgene, the various metabolic and growth response differences are directly attributable to overexpression of SSAT.

Acetyltransferases↗

PubMed2005

Regulation of apoptosis signal-regulating kinase 1 (ASK1) by polyamine levels via protein phosphatase 5.

Recent evidence has implicated the protein phosphatase PP5 in a variety of signaling pathways. Whereas several proteins have been identified that interact with PP5 and regulate its activity, a possibility of its regulation by second messengers remains speculative. Activation of PP5 in vitro by polyunsaturated fatty acids (e.g. arachidonic acid) and fatty acyl-CoA esters (e.g. arachidonoyl-CoA) has been reported. We report here that PP5 is strongly inhibited by micromolar concentrations of a natural polyamine spermine. This inhibition was observed both in assays with a low molecular weight substrate p-nitrophenyl phosphate as well as phosphocasein and apoptosis signal-regulating kinase 1 (ASK1), thought to be a physiological substrate of PP5. Furthermore, a decrease in polyamine levels in COS-7 cells induced by alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, led to accelerated dephosphorylation of oxidative stress-activated ASK1. This effect was suppressed by okadaic acid and by siRNA-mediated PP5 depletion, indicating that the effect of polyamine levels on ASK1 dephosphorylation was mediated by PP5. In line with the decreased ASK1 activation, polyamine depletion in COS-7 cells abrogated oxidative stress-induced activation of caspase-3, which executes ASK1-induced apoptosis, as well as caspase-3 activation induced by ASK1 overexpression, but had no effect on basal caspase-3 activity. These results implicate polyamines, emerging intracellular signaling molecules, as potential physiological regulators of PP5. Our findings also suggest a novel mechanism of the anti-apoptotic action of a decrease in polyamine levels via de-inhibition of PP5 and accelerated dephosphorylation and deactivation of ASK1.

Animals↗