Characterization of the interaction between the transcription factors human polyamine modulated factor (PMF-1) and NF-E2-related factor 2 (Nrf-2) in the transcriptional regulation of the spermidine/spermine N1-acetyltransferase (SSAT) gene

Polyamines and Their Metabolism: From the Maintenance of Physiological Homeostasis to the Mediation of Disease

The polyamines spermidine and spermine are positively charged aliphatic molecules. They are critical in the regulation of nucleic acid and protein structures, protein synthesis, protein and nucleic acid interactions, oxidative balance, and cell proliferation. Cellular polyamine levels are tightly controlled through their import, export, de novo synthesis, and catabolism. Enzymes and enzymatic cascades involved in polyamine metabolism have been well characterized. This knowledge has been used for the development of novel compounds for research and medical applications. Furthermore, studies have shown that disturbances in polyamine levels and their metabolic pathways, as a result of spontaneous mutations in patients, genetic engineering in mice or experimentally induced injuries in rodents, are associated with multiple maladaptive changes. The adverse effects of altered polyamine metabolism have also been demonstrated in in vitro models. These observations highlight the important role these molecules and their metabolism play in the maintenance of physiological normalcy and the mediation of injury. This review will attempt to cover the extensive and diverse knowledge of the biological role of polyamines and their metabolism in the maintenance of physiological homeostasis and the mediation of tissue injury.

Polyamine Homeostasis in Development and Disease

Polycationic polyamines are present in nearly all living organisms and are essential for mammalian cell growth and survival, and for development. These positively charged molecules are involved in a variety of essential biological processes, yet their underlying mechanisms of action are not fully understood. Several studies have shown both beneficial and detrimental effects of polyamines on human health. In cancer, polyamine metabolism is frequently dysregulated, and elevated polyamines have been shown to promote tumor growth and progression, suggesting that targeting polyamines is an attractive strategy for therapeutic intervention. In contrast, polyamines have also been shown to play critical roles in lifespan, cardiac health and in the development and function of the brain. Accordingly, a detailed understanding of mechanisms that control polyamine homeostasis in human health and disease is needed to develop safe and effective strategies for polyamine-targeted therapy.

Aberrant AZIN2 and polyamine metabolism precipitates tau neuropathology

Tauopathies display a spectrum of phenotypes from cognitive to affective behavioral impairments; however, mechanisms promoting tau pathology and how tau elicits behavioral impairment remain unclear. We report a unique interaction between polyamine metabolism, behavioral impairment, and tau fate. Polyamines are ubiquitous aliphatic molecules that support neuronal function, axonal integrity, and cognitive processing. Transient increases in polyamine metabolism hallmark the cell's response to various insults, known as the polyamine stress response (PSR). Dysregulation of gene transcripts associated with polyamine metabolism in Alzheimer's disease (AD) brains were observed, and we found that ornithine decarboxylase antizyme inhibitor 2 (AZIN2) increased to the greatest extent. We showed that sustained AZIN2 overexpression elicited a maladaptive PSR in mice with underlying tauopathy (MAPT P301S; PS19). AZIN2 also increased acetylpolyamines, augmented tau deposition, and promoted cognitive and affective behavioral impairments. Higher-order polyamines displaced microtubule-associated tau to facilitate polymerization but also decreased tau seeding and oligomerization. Conversely, acetylpolyamines promoted tau seeding and oligomers. These data suggest that tauopathies launch an altered enzymatic signature that endorses a feed-forward cycle of disease progression. Taken together, the tau-induced PSR affects behavior and disease continuance, but may also position the polyamine pathway as a potential entry point for plausible targets and treatments of tauopathy, including AD.

Genetic Polymorphisms Associated with Spontaneous Intracerebral Hemorrhage

Differences in the incidence of spontaneous intracerebral hemorrhage (ICH) between ethnicities exist, with an estimated 42% of the variance explained by ethnicity itself. Caucasians have a higher proportion of lobar ICH (LICH, 15.4% of all ICH) than do Asians (3.4%). Alterations in the causal factor exposure between countries justify part of the ethnic variance in ICH incidence. One third of ICH risk can be explained by genetic variation; therefore, genetic differences between populations can partly explain the difference in ICH incidence. In this paper, we review the current knowledge of genetic variants associated with ICH in multiple ethnicities. Candidate gene variants reportedly associated with ICH were involved in the potential pathways of hypertension, vessel wall integrity, lipid metabolism, endothelial dysfunction, inflammation, platelet function, and coagulopathy. Furthermore, variations in APOE (in multiple ethnicities), PMF1/SLC25A44 (in European), ACE (in Asian), MTHFR (in multiple ethnicities), TRHDE (in European), and COL4A2 (in European) were the most convincingly associated with ICH. The majority of the associated genes provide small contributions to ICH risk, with few of them being replicated in multiple ethnicities.

Corrected and Republished from: The COP9 Signalosome Interacts with and Regulates Interferon Regulatory Factor 5 Protein Stability

The transcription factor interferon regulatory factor 5 (IRF5) exerts crucial functions in the regulation of host immunity against extracellular pathogens, DNA damage-induced apoptosis, death receptor signaling, and macrophage polarization. Tight regulation of IRF5 is thus warranted for an efficient response to extracellular stressors and for limiting autoimmune and inflammatory responses. Here we report that the COP9 signalosome (CSN), a general modulator of diverse cellular and developmental processes, associates constitutively with IRF5 and promotes its protein stability. The constitutive CSN/IRF5 interaction was identified using proteomics and confirmed by endogenous immunoprecipitations. The CSN/IRF5 interaction occurred on the carboxyl and amino termini of IRF5; a single internal deletion (Δ455-466) was found to significantly reduce IRF5 protein stability. CSN3 was identified as a direct interacting partner of IRF5, and knockdown of this subunit with small interfering RNAs (siRNAs) resulted in enhanced degradation. Degradation was further augmented by knockdown of CSN1 and CSN3 together. The ubiquitin E1 inhibitor UBEI-41 or the proteasome inhibitor MG132 prevented IRF5 degradation, supporting that its stability is regulated by the ubiquitin-proteasome system. Importantly, activation of IRF5 by the death receptor ligand tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) resulted in enhanced degradation via loss of the CSN/IRF5 interaction. This study defines the CSN as a new interacting partner of IRF5 that controls its stability.

The Role of Nrf2 in Cardiovascular Function and Disease

Free radicals, reactive oxygen/nitrogen species (ROS/RNS), hydrogen sulphide, and hydrogen peroxide play an important role in both intracellular and intercellular signaling; however, their production and quenching need to be closely regulated to prevent cellular damage. An imbalance, due to exogenous sources of free radicals and chronic upregulation of endogenous production, contributes to many pathological conditions including cardiovascular disease and also more general processes involved in aging. Nuclear factor erythroid 2-like 2 (NFE2L2; commonly known as Nrf2) is a transcription factor that plays a major role in the dynamic regulation of a network of antioxidant and cytoprotective genes, through binding to and activating expression of promoters containing the antioxidant response element (ARE). Nrf2 activity is regulated by many mechanisms, suggesting that tight control is necessary for normal cell function and both hypoactivation and hyperactivation of Nrf2 are indicated in playing a role in different aspects of cardiovascular disease. Targeted activation of Nrf2 or downstream genes may prove to be a useful avenue in developing therapeutics to reduce the impact of cardiovascular disease. We will review the current status of Nrf2 and related signaling in cardiovascular disease and its relevance to current and potential treatment strategies.

Endoplasmic reticulum stress and unfolded protein response in infection by intracellular parasites

Perturbations of the physiological status of the endoplasmic reticulum (ER) trigger a specific response known as the ER stress response or unfolded protein response (UPR). In mammalian cells, the UPR is mediated by three ER transmembrane proteins (IRE1, PERK and ATF6) which activate three signaling cascades to restore ER homeostasis. In recent years, a cross-talk between UPR, inflammatory and microbial sensing pathways has been elucidated. Pathogen infection can lead to UPR activation; moreover, several pathogens subvert the UPR to promote their survival and replication. While the UPR in viral and bacterial infection has been characterized, little is known about the role of UPR in intracellular parasite infection. Here, we review recent findings on UPR induction/modulation by intracellular parasites in host cells.

Genetic Variants in the STMN1 Transcriptional Regulatory Region Affect Promoter Activity and Fear Behavior in English Springer Spaniels

Stathmin 1 (STMN1) is a neuronal growth-associated protein that is involved in microtubule dynamics and plays an important role in synaptic outgrowth and plasticity. Given that STMN1 affects fear behavior, we hypothesized that genetic variations in the STMN1 transcriptional regulatory region affect gene transcription activity and control fear behavior. In this study, two single nucleotide polymorphisms (SNPs), g. -327 A>G and g. -125 C>T, were identified in 317 English Springer Spaniels. A bioinformatics analysis revealed that both were loci located in the canine STMN1 putative promoter region and affected transcription factor binding. A statistical analysis revealed that the TT genotype at g.-125 C>T produced a significantly greater fear level than that of the CC genotype (P < 0.05). Furthermore, the H4H4 (GTGT) haplotype combination was significantly associated with canine fear behavior (P < 0.01). Using serially truncated constructs of the STMN1 promoters and the luciferase reporter, we found that a 395 bp (-312 nt to +83 nt) fragment constituted the core promoter region. The luciferase assay also revealed that the H4 (GT) haplotype promoter had higher activity than that of other haplotypes. Overall, our results suggest that the two SNPs in the canine STMN1 promoter region could affect canine fear behavior by altering STMN1 transcriptional activity.

Exogenous spermine inhibits the proliferation of human pulmonary artery smooth muscle cells caused by chemically-induced hypoxia via the suppression of the ERK1/2- and PI3K/AKT-associated pathways

Pulmonary vascular remodeling is a significant pathological feature of hypoxia-induced pulmonary hypertension (HPH), while pulmonary artery smooth muscle cell (PASMC) proliferation plays a leading role in pulmonary vascular remodeling. Spermine (Sp), a polyamine, plays a critical role in periodic cell proliferation and apoptosis. The present study was conducted to observe the association between hypoxia-induced PASMC proliferation and polyamine metabolism, and to explore the effects of exogenous Sp on PASMC poliferation and the related mechanisms. In the present study, PASMCs were cultured with cobalt chloride (CoCl2) to establish a hypoxia model, and Sp at various final concentrations (0.1, 1, 10 and 100 µM) was added to the medium of PASMCs 40 min prior to the induction of hypoxia. Cell proliferation was measured by 3-(4,5-dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide (MTT) assay, cell counting kit-8 assay and 5-bromo‑2'‑deoxyuridine (BrdU) incorporation assay. Cell cycle progression was determined by flow cytometry, and the protein expression levels of spermidine/spermine N1-acetyltransferase (SSAT; the key enzyme in the terminal degradation of polyamine), ornithine decarboxylase (ODC; the key enzyme of polyamine biosynthesis), cyclin D1 and p27 were measured by western blot analysis. The results revealed that the proliferation of the PASMCs cultured with CoCl2 at 50 µM for 24 h markedly increased. The expression of ODC was decreased and the expression of SSAT was increased in the cells under hypoxic conditions. Exogenous Sp at concentrations of 1 and 10 µM significantly inhibited hypoxia-induced PASMC proliferation, leading to cell cycle arrest at the G1/G0 phase. In addition, Sp decreased cyclin D1 expression, increased p27 expression, and suppressed the phosphorylation of extracellular signal‑regulated kinase 1/2 (ERK1/2), phosphatidylinositol 3-kinase (PI3K) and protein kinase B (AKT); however, the above-metioned parameters were not markedly affected by Sp at concentrations of 0.1 or 100 µM. These results suggest that hypoxia disrupts polyamine metabolism, and Sp at concentrations of 1 and 10 µM inhibits the increase in human PASMC proliferation caused by chemically-induced hypoxia via the suppression of the ERK1/2- and PI3K/AKT-associated pathways. This study thus offer new insight into the prevention and treatment of HPH.

Isoform-level brain expression profiling of the spermidine/spermine N1-Acetyltransferase1 (SAT1) gene in major depression and suicide

Low brain expression of the spermidine/spermine N-1 acetyltransferase (SAT1) gene, the rate-limiting enzyme involved in catabolism of polyamines that mediate the polyamine stress response (PSR), has been reported in depressed suicides. However, it is unknown whether this effect is associated with depression or with suicide and whether all or only specific isoforms expressed by SAT1, such as the primary 171 amino acid protein-encoding transcript (SSAT), or an alternative splice variant (SSATX) that is involved in SAT1 regulated unproductive splicing and transcription (RUST), are involved. We applied next generation sequencing (RNA-seq) to assess gene-level, isoform-level, and exon-level SAT1 expression differences between healthy controls (HC, N = 29), DSM-IV major depressive disorder suicides (MDD-S, N = 21) and MDD non-suicides (MDD, N = 9) in the dorsal lateral prefrontal cortex (Brodmann Area 9, BA9) of medication-free individuals postmortem. Using small RNA-seq, we also examined miRNA species putatively involved in SAT1 post-transcriptional regulation. A DSM-IV diagnosis was made by structured interview. Toxicology and history ruled out recent psychotropic medication. At the gene-level, we found low SAT1 expression in both MDD-S (vs. HC, p = 0.002) and MDD (vs. HC, p = 0.002). At the isoform-level, reductions in MDD-S (vs. HC) were most pronounced in four transcripts including SSAT and SSATX, while reductions in MDD (vs. HC) were pronounced in three transcripts, one of which was reduced in MDD relative to MDD-S (all p < 0.1 FDR corrected). We did not observe evidence for differential exon-usage (i.e. splicing) nor differences in miRNA expression. Results replicate the finding of low SAT1 brain expression in depressed suicides in an independent sample and implicate low SAT1 brain expression in MDD independent of suicide. Low expressions of both SSAT and SATX isoforms suggest that shared transcriptional mechanisms involved in RUST may account for low SAT1 brain expression in depressed suicides. Future studies are required to understand the functions and regulation of SAT1 isoforms, and how they relate to the pathogenesis of MDD and suicide.

Suicide and the polyamine system

Suicide is a significant worldwide public health problem. Understanding the neurobiology is important as it can help us to better elucidate underlying etiological factors and provide opportunities for intervention. In recent years, many lines of research have suggested that the polyamine system may be dysregulated in suicidal behaviors. Initial research in animals provided evidence of a dysfunctional polyamine stress response system, while later work using post-mortem human brain tissue has suggested that molecular mechanisms may be at play in the suicide brain. In this review, we will describe the research that suggests the presence of alterations in the polyamine system in mental disorders and behavioral phenotypes, with particular attention to work on suicide. In addition, we will also describe potential avenues for future work.

Meta-analysis of genome-wide association studies identifies 1q22 as a susceptibility locus for intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is the stroke subtype with the worst prognosis and has no established acute treatment. ICH is classified as lobar or nonlobar based on the location of ruptured blood vessels within the brain. These different locations also signal different underlying vascular pathologies. Heritability estimates indicate a substantial genetic contribution to risk of ICH in both locations. We report a genome-wide association study of this condition that meta-analyzed data from six studies that enrolled individuals of European ancestry. Case subjects were ascertained by neurologists blinded to genotype data and classified as lobar or nonlobar based on brain computed tomography. ICH-free control subjects were sampled from ambulatory clinics or random digit dialing. Replication of signals identified in the discovery cohort with p < 1 × 10(-6) was pursued in an independent multiethnic sample utilizing both direct and genome-wide genotyping. The discovery phase included a case cohort of 1,545 individuals (664 lobar and 881 nonlobar cases) and a control cohort of 1,481 individuals and identified two susceptibility loci: for lobar ICH, chromosomal region 12q21.1 (rs11179580, odds ratio [OR] = 1.56, p = 7.0 × 10(-8)); and for nonlobar ICH, chromosomal region 1q22 (rs2984613, OR = 1.44, p = 1.6 × 10(-8)). The replication included a case cohort of 1,681 individuals (484 lobar and 1,194 nonlobar cases) and a control cohort of 2,261 individuals and corroborated the association for 1q22 (p = 6.5 × 10(-4); meta-analysis p = 2.2 × 10(-10)) but not for 12q21.1 (p = 0.55; meta-analysis p = 2.6 × 10(-5)). These results demonstrate biological heterogeneity across ICH subtypes and highlight the importance of ascertaining ICH cases accordingly.

Cryptosporidium parvum induces an endoplasmic stress response in the intestinal adenocarcinoma HCT-8 cell line

Invasion of human intestinal epithelial cells (HCT-8) by Cryptosporidium parvum resulted in a rapid induction of host cell spermidine/spermine N(1)-acetyltransferase 1 (hSSAT-1) mRNA, causing a 4-fold increase in SSAT-1 enzyme activity after 24 h of infection. In contrast, host cell SSAT-2, spermine oxidase, and acetylpolyamine oxidase (hAPAO) remained unchanged during this period. Intracellular polyamine levels of C. parvum-infected human epithelial cells were determined, and it was found that spermidine remained unchanged and putrescine increased by 2.5-fold after 15 h and then decreased after 24 h, whereas spermine decreased by 3.9-fold after 15 h. Concomitant with these changes, N(1)-acetylspermine and N(1)-acetylspermidine both increased by 115- and 24-fold, respectively. Increased SSAT-1 has previously been shown to be involved in the endoplasmic reticulum (ER) stress response leading to apoptosis. Several stress response proteins were increased in HCT-8 cells infected with C. parvum, including calreticulin, a major calcium-binding chaperone in the ER; GRP78/BiP, a prosurvival ER chaperone; and Nrf2, a transcription factor that binds to antioxidant response elements, thus activating them. However, poly(ADP-ribose) polymerase, a protein involved in DNA repair and programmed cell death, was decreased. Cumulatively, these results suggest that the invasion of HCT-8 cells by C. parvum results in an ER stress response by the host cell that culminates in overexpression of host cell SSAT-1 and elevated N(1)-acetylpolyamines, which can be used by a parasite that lacks ornithine decarboxylase.

The COP9 signalosome interacts with and regulates interferon regulatory factor 5 protein stability

The transcription factor interferon regulatory factor 5 (IRF5) exerts crucial functions in the regulation of host immunity against extracellular pathogens, DNA damage-induced apoptosis, death receptor signaling, and macrophage polarization. Tight regulation of IRF5 is thus warranted for an efficient response toward extracellular stressors and for limiting autoimmune and inflammatory responses. Here we report that the COP9 signalosome (CSN), a general modulator of diverse cellular and developmental processes, associates constitutively with IRF5 and promotes its protein stability. The constitutive CSN/IRF5 interaction was identified using proteomics and confirmed by endogenous immunoprecipitations. The CSN/IRF5 interaction occurred on the carboxyl and amino termini of IRF5; a single internal deletion from amino acids 455 to 466 (Δ455-466) was found to significantly reduce IRF5 protein stability. CSN subunit 3 (CSN3) was identified as a direct interacting partner of IRF5, and knockdown of this subunit with small interfering RNAs resulted in enhanced degradation. Degradation was further augmented by knockdown of CSN1 and CSN3 together. The ubiquitin E1 inhibitor UBEI-41 or the proteasome inhibitor MG132 prevented IRF5 degradation, supporting the idea that its stability is regulated by the ubiquitin-proteasome system. Importantly, activation of IRF5 by the death receptor ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) resulted in enhanced degradation via loss of the CSN/IRF5 interaction. This study defines CSN to be a new interacting partner of IRF5 that controls its stability.

Significant association between body composition phenotypes and the osteocalcin genomic region in normative human population

Osteocalcin, a major inorganic component of bone matrix and marker of bone formation, is also involved in regulation of glucose and fat mass metabolism. However, much uncertainty remains about whether the above effect on fat mass has a genetic component. Our main aim was to test whether a variation of body composition phenotypes is associated with BGLAP genomic region variants. To achieve this aim, we used an ethnically homogeneous discovery sample of 230 families consisting of 1112 apparently healthy individuals (561 males and 551 females) of European origin. We conducted association analysis between six SNPs and five obesity-related phenotypes: plasma levels of leptin, anthropometrical fat mass (FM), principal component scores of eight skinfold (SK_PC) and nine circumference (CR_PC) measurements, and body mass index (BMI). Two powerful and robust tools were applied: the pedigree disequilibrium test and variance component models, taking into account both familial and genetic effects. Significant association results were observed for all phenotypes. The most significant results were observed between the haplotype composed of three SNPs (rs2758605-rs1543294-rs2241106) and BMI (p=8.07(-7)), and CR_PC (p=5.29(-5)). The association with BMI was tested and confirmed in our replication study, including 2244 unrelated adult US Caucasians, who were previously assessed for whole genome SNP data. In addition, we obtained an evidence of potential non-additive interactions between the above three SNPs concerning their association with BMI. Bioinformatics sources suggest that the aforementioned interaction could originate from different genetic loci in this region; however, ascertaining the exact circumstances requires a detailed molecular-genetic study.

Polyamine-modulated factor-1 methylation predicts Bacillus Calmette-Guérin response in patients with high-grade non-muscle-invasive bladder carcinoma

BACKGROUND

Bacillus Calmette-Guérin (BCG) is a standard treatment to reduce tumor recurrence and delay progression of high-risk non-muscle-invasive (NMI) bladder tumors. However, it is not clear yet which patients are more likely to respond to BCG.

OBJECTIVE

The aim was to evaluate the role of polyamine-modulated factor-1 (PMF-1) methylation in predicting clinical outcome of T1 high-grade (T1HG) bladder tumors treated with BCG.

DESIGN, SETTING, AND PARTICIPANTS

In a retrospective design, PMF-1 methylation was analyzed on tumor specimens belonging to 108 patients with T1HG NMI bladder cancer undergoing BCG treatment. Median follow-up was 77 mo (range: 5-235 mo).

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

PMF-1 methylation was assessed by methylation-specific polymerase chain reactions. Recurrence, progression into muscle-invasive tumors, and disease-specific survival rates were analyzed using competing risks regression analysis.

RESULTS AND LIMITATIONS

Among the 108 patients analyzed, 35 had recurring disease (32.4%), 21 progressed (19.4%), and 16 died of disease (14.8%); 71.3% of tumors had PMF-1 methylation. Univariate analyses using cumulative incidence curves revealed that an unmethylated PMF-1 was significantly associated with increased recurrence (p=0.026), progression (p=0.01), and shorter disease-specific survival (log-rank, p=0.03). Multivariate analyses indicated that among sex, age, focality, tumor size, and concomitant carcinoma in situ, only PMF-1 methylation provided significant hazard ratios (HRs) for recurrence of (HR: 2.032; p=0.042), and progression (HR: 2.910; p=0.020). Limitations of the study include its retrospective design, lymphovascular invasion status not available, short maintenance BCG, and that a second transurethral resection was not performed.

CONCLUSIONS

Epigenetic analyses revealed that the methylation status of PMF-1 was associated with the clinical outcome of patients with T1HG tumors undergoing BCG treatment. An unmethylated PMF-1 correlated to recurrence and progression in T1HG disease using univariate and multivariate analyses. Thus, assessing the methylation status of PMF-1 may serve to distinguish patients responding to BCG from those who may require more aggressive therapeutic approaches.

Conformational changes in DNA upon ligand binding monitored by circular dichroism

Circular dichroism (CD) spectroscopy is an optical technique that measures the difference in the absorption of left and right circularly polarized light. This technique has been widely employed in the studies of nucleic acids structures and the use of it to monitor conformational polymorphism of DNA has grown tremendously in the past few decades. DNA may undergo conformational changes to B-form, A-form, Z-form, quadruplexes, triplexes and other structures as a result of the binding process to different compounds. Here we review the recent CD spectroscopic studies of the induction of DNA conformational changes by different ligands, which includes metal derivative complex of aureolic family drugs, actinomycin D, neomycin, cisplatin, and polyamine. It is clear that CD spectroscopy is extremely sensitive and relatively inexpensive, as compared with other techniques. These studies show that CD spectroscopy is a powerful technique to monitor DNA conformational changes resulting from drug binding and also shows its potential to be a drug-screening platform in the future.

Regulation of polyamine metabolism by translational control

Polyamines are low molecular weight, positively charged compounds that are ubiquitous in all living cells. They play a crucial role in many biochemical processes including regulation of transcription and translation, modulation of enzyme activities, regulation of ion channels and apoptosis. A strict balance between synthesis, catabolism and excretion tightly controls the cellular concentration of polyamines. The concentrations of rate-limiting enzymes in the polyamine synthesis and degradation pathways are regulated at different levels, including transcription, translation and degradation. Polyamines can modulate the translation of most of the enzymes required for their synthesis and catabolism through feedback mechanisms that are unique for each enzyme. Translational control is associated with cis-acting and trans-acting factors that can be influenced by the concentration of polyamines through mechanisms that are not completely understood. In this review, we present an overview of the translational control mechanisms of the proteins in the polyamine pathway, including ornithine decarboxylase (ODC), ODC antizyme, S-adenosylmethionine decarboxylase and spermidine/spermine N(1) acetyltransferase, highlighting the areas where more research is needed. A better understanding of the translational control of these enzymes would offer the possibility of a novel pharmacological intervention against cancer and other diseases.

Tissue-specific alternative splicing of spermidine/spermine N1-acetyltransferase

The polyamines, spermidine and spermine, are abundant organic cations participating in many important cellular processes. We have previously shown that the rate-limiting enzyme of polyamine catabolism, spermidine/spermine N(1)-acetyltransferase (SSAT), has an alternative mRNA splice variant (SSATX) which undergoes degradation via nonsense-mediated mRNA decay (NMD) pathway, and that the intracellular polyamine level regulates the ratio of the SSATX and SSAT splice variants. The aim of this study was to investigate the effect of SSATX level manipulation on SSAT activity in cell culture, and to examine the in vivo expression levels of SSATX and SSAT mRNA. Silencing SSATX expression with small interfering RNA led to increased SSAT activity. Furthermore, transfection of SSAT-deficient cells with mutated SSAT gene (which produced only trace amount of SSATX) yielded higher SSAT activity than transfection with natural SSAT gene (which produced both SSAT and SSATX). Blocking NMD in vivo by protein synthesis inhibitor cycloheximide resulted in accumulation of SSATX mRNA, and like in cell culture, the increase of SSATX mRNA was prevented by administration of polyamine analog N(1),N(11)-diethylnorspermine. Although SSATX/total SSAT mRNA ratio did not correlate with polyamine levels or SSAT activity between different tissues, increasing polyamine levels in a given tissue led to decreased SSATX/total SSAT mRNA ratio and vice versa. Taken together, the regulated unproductive splicing and translation of SSAT has a physiological relevance in modulating SSAT activity. However, in addition to polyamine level there seems to be additional factors regulating tissue-specific alternative splicing of SSAT.

Antitumor agent PX-12 inhibits HIF-1α protein levels through an Nrf2/PMF-1-mediated increase in spermidine/spermine acetyl transferase

PURPOSE

Thioredoxin-1 (Trx-1) redox signaling regulates multiple aspects of cell growth and survival, and elevated tumor levels of Trx-1 have been associated with decreased patient survival. PX-12, an inhibitor of Trx-1 currently in clinical development, has been found to decrease tumor levels of the HIF-1α transcription factor. SSAT1 has been reported to bind to HIF-1α and RACK1, resulting in oxygen-independent HIF-1 ubiquitination and degradation. SSAT2, a related protein, stabilizes the interaction of the VHL protein and elongin C with HIF-1 leading to oxygen-dependent HIF-1α ubiquitination and degradation. We investigated the effects of PX-12 and Trx-1 on SSAT1, SSAT2, and inhibition of HIF-1α.

METHODS

A panel of cell lines was treated with PX-12 to investigate its effects on SSAT1 and SSAT2 expression, and on HIF-1α protein levels. We also evaluated the regulation of SSAT1 through the Nrf2 and PMF-1, two trans-acting transcription factors.

RESULTS

We found that PX-12 increased nuclear Nrf2 activity and antioxidant response element binding. PX-12 also increased the expression of SSAT1 but not SSAT2 in a PMF-1-dependent manner that was independent of Trx-1. Inhibition of Nrf2 or PMF-1 prevented the increase in SSAT1 caused by PX-12.

CONCLUSIONS

The results show that PX-12, acting independently of Trx-1, increases nuclear Nrf2, which interacts with PMF-1 to increase the expression of SSAT1. The degradation of HIF-1α that results from binding with SSAT1 may explain the decrease in HIF-1α caused by PX-12 and could contribute to the antitumor activity of PX-12.

Effects of atmospheric pollutants on the Nrf2 survival pathway

BACKGROUND, AIM, AND SCOPE

Atmospheric pollution is a worldwide problem. Exposure to atmospheric pollutants causes toxic cellular effects. One of the mechanisms of toxicity by these pollutants is the promotion of oxidative stress. Several signaling pathways control cellular redox homeostasis. In this respect, nuclear factor erythroid 2-related factor 2 (Nrf2) is a crucial transcription factor in the cell's response to oxidative stress.

MAIN FEATURES

In cellular animal models, exposure to atmospheric pollutants activates Nrf2, attenuating its toxic and even its carcinogenic effects. Therefore, we have reviewed the scientific literature in order to indicate that air pollutants, such as particulate matter, polycyclic aromatic hydrocarbons, and gaseous matter, are Nrf2 pathway inductors, triggering self-defense through the establishment of proinflammatory and antioxidant responses.

RESULTS AND DISCUSSION

Exposure to reactive molecules as atmospheric pollutants causes the activation of Nrf2 and the subsequent regulation of the expression of cytoprotective and detoxifying enzymes, as well as antioxidants. Moreover, induction of Nrf2 prior to exposure reduces the harmful effects of pollutants. The present article discusses the protective role of the Nrf2 pathway against different atmospheric pollutant insults.

CONCLUSIONS

Nrf2 regulates the expression of numerous cytoprotective genes that function to detoxify reactive species produced during atmospheric pollutant metabolic reactions. From the papers highlighted in this review, we conclude that Nrf2 has an important role in the defense against atmospheric pollutant-induced toxicity.

PERSPECTIVES

Further studies are needed to understand the signaling events that turn on the system in response to atmospheric pollutant stress. This could allow for the possibility of targeting the pathway for prevention benefits in the near future.

Polyamine catabolism and disease

In addition to polyamine homoeostasis, it has become increasingly clear that polyamine catabolism can play a dominant role in drug response, apoptosis and the response to stressful stimuli, and contribute to the aetiology of several pathological states, including cancer. The highly inducible enzymes SSAT (spermidine/spermine N1-acetyltransferase) and SMO (spermine oxidase) and the generally constitutively expressed APAO (N1-acetylpolyamine oxidase) appear to play critical roles in many normal and disease processes. The dysregulation of polyamine catabolism frequently accompanies several disease states and suggests that such dysregulation may both provide useful insight into disease mechanism and provide unique druggable targets that can be exploited for therapeutic benefit. Each of these enzymes has the potential to alter polyamine homoeostasis in response to multiple cell signals and the two oxidases produce the reactive oxygen species H2O2 and aldehydes, each with the potential to produce pathological states. The activity of SSAT provides substrates for APAO or substrates for the polyamine exporter, thus reducing the intracellular polyamine concentration, the net effect of which depends on the magnitude and rate of any increase in SSAT. SSAT may also influence cellular metabolism via interaction with other proteins and by perturbing the content of acetyl-CoA and ATP. The goal of the present review is to cover those aspects of polyamine catabolism that have an impact on disease aetiology or treatment and to provide a solid background in this ever more exciting aspect of polyamine biology.

SAT-1 -1415T/C polymorphism and susceptibility to schizophrenia

Patients suffering from psychosis show increased blood and fibroblast total polyamine levels. Spermidine/spermine N1-acetyltransferase (SSAT-1) and its coding gene (SAT-1) are the main factors regulating polyamine catabolism. The aim of the present study was to examine the association between the SAT-1 -1415T/C single nucleotide polymorphism (SNP) and schizophrenia. A case-control design was used in order to compare the genotypes for the SNP between schizophrenia patients (n=180, 83 females and 97 males), other non-psychotic psychiatric patients (n=413, 256 females and 157 males), and healthy controls (n=251, 101 females and 150 males). No significant differences in the distribution of the genotypes of the SAT-1 -1415T/C SNP were found groups among groups. We failed to demonstrate a significant association between the SAT-1 -1415T/C SNP and schizophrenia, but a mild association between allele C and psychopathology was found in the female group.

The polymine spermine regulates osteogenic differentiation in adipose stem cells

For bone tissue engineering, it is important that mesenchymal stem cells (MSCs) differentiate into osteoblasts. To develop a method for differentiation of adipose tissue-derived mesenchymal stem cells (AT-MSCs) along the osteogenic lineage, we studied the effect of polyamines, which are organic cations implicated in bone growth and development, on differentiation of AT-MSCs. Treatment of goat-derived AT-MSCs with 1,25-dihydroxyvitamin-D3 (1,25(OH)₂D₃), which stimulates osteogenic differentiation, for 7 days induced gene expression of the polyamine-modulated transcription factor-1 (PMF-1) and spermidine/spermine N (1)-acetyltransferase (SSAT), which are both involved in polyamine metabolism, suggesting that polyamines are involved in osteogenic differentiation of AT-MSCs. Furthermore, treatment of AT-MSCs with the polyamine spermine-regulated gene expression of runx-2, a transcription factor involved in early stages of osteogenic differentiation, and that of osteopontin, a bone matrix protein expressed in later stages of osteogenic differentiation. Runx-2 gene expression was increased 4 and 14 days after a short 30 min. treatment with spermine, while osteopontin gene expression was only increased 4 days after spermine treatment. Finally, alkaline phosphatase activity, which is intimately involved in the formation of extracellular matrix of bone, was increased 4 weeks after the 30 min.-spermine treatment of AT-MSCs. In conclusion, this study shows for the first time that the polyamine spermine regulates differentiation of AT-MSCs along the osteogenic lineage, which can be used as a new method for differentiation of AT-MSCs along the osteogenic lineage. Therefore, polyamines may constitute a promising tool for bone tissue engineering approaches using AT-MSCs, such as a one-step surgical procedure for spinal interbody fusion.

Polyamines Modulate Nitric Oxide Production andCox-2Gene Expression in Response to Mechanical Loading in Human Adipose Tissue-Derived Mesenchymal Stem Cells

For bone tissue engineering, it is important that mesenchymal stem cells (MSCs) display a bone cell-like response to mechanical loading. We have shown earlier that this response includes increased nitric oxide (NO) production and cyclooxygenase-2 (COX-2) gene expression, both of which are intimately involved in mechanical adaptation of bone. COX-2 gene expression is likely regulated by polyamines, which are organic cations implicated in cell proliferation and differentiation. This has led to the hypothesis that polyamines may play a role in the response of adipose tissue-derived MSCs (AT-MSCs) to mechanical loading. The aim of this study was to investigate whether genes involved in polyamine metabolism are regulated by mechanical loading and to study whether polyamines modulate mechanical loading-induced NO production and COX-2 gene expression in human AT-MSCs. Human AT-MSCs displayed a bone cell-like response to mechanical loading applied by pulsating fluid flow (PFF), as demonstrated by increased NO production and increased gene expression of COX-2. Furthermore, PFF increased gene expression of spermidine/spermine N (1)-acetyltransferase, which is involved in polyamine catabolism, suggesting that mechanical loading modulates polyamine levels. Finally, the polyamine spermine was shown to inhibit both PFF-induced NO production and COX-2 gene expression, suggesting that polyamines modulate the response of human AT-MSCs to mechanical loading. In conclusion, this is the first study implicating polyamines in the response of human AT-MSCs to mechanical loading, creating opportunities for the use of polyamines in tissue engineering approaches targeting skeletal defects.

Analysis of the interactions of Nrf-2, PMF-1, and CSN-7 with the 5'-flanking sequence of the mouse 4E-BP1 gene

Nuclear factor erythroid 2-related factor 2 (Nrf-2) binds to a specific polyamine responsive element (PRE) in the promoter region of the spermidine-spermine acetyltransferase (SSAT) gene, a key component of the polyamine catabolic pathway. Regulation of SSAT gene transcription requires the additional interaction of Nrf-2 with polyamine modulated factor 1 (PMF-1). Likewise, transcription of the eukaryotic initiation factor 4E binding protein 1 (4E-BP1) gene is regulated in a polyamine-dependent manner, but the actual mechanism has not previously been determined. Analysis of the 5'-flanking sequence of the murine 4E-BP1 gene indicated the presence of several potential PRE sites, which might be involved in regulating its transcription. Our goal in this research was to determine potential interactions between Nrf-2, PMF-1, the human homologue of the Arabidopsis signalosome complex (CSN-7), and these potential PRE sites. Four PCR fragments containing regions with considerable homology (78%) to the human PRE were generated from the 5'-flanking sequence of the mouse 4E-BP1 gene and the fragments were used in electrophoretic gel mobility shift and supershift assays. Purified Nrf-2 interacted with all four of these fragments, and similar gel shifts were observed with both cytoplasmic and nuclear fractions of NIH-3T3 cells. However, polyamine depletion with difluoromethylornithine (DFMO) eliminated the gel shift. Supershift assays indicated that the shift was due to the binding of Nrf-2, and the binding was competitive with a known Nrf-2 binding sequence. Purified PMF-1 did not bind any of the PCR fragments alone, but when added with Nrf-2, decreased the magnitude of the gel shift for one of the fragments (PRE located at -2060 relative to the transcription start site). CSN-7 did not interact with the sequences, nor did it inhibit protein/DNA interaction. These data indicate a possible mechanism by which polyamines enhance the binding of a Nrf-2/PMF-1 complex to the 5'-flanking region of the 4E-BP1 gene. Since polyamines increase expression of the 4E-BP1 gene, it seems likely that formation of this complex is involved in its transcriptional regulation.

Induction of human spermine oxidase SMO(PAOh1) is regulated at the levels of new mRNA synthesis, mRNA stabilization and newly synthesized protein

The oxidation of polyamines induced by antitumour polyamine analogues has been associated with tumour response to specific agents. The human spermine oxidase, SMO(PAOh1), is one enzyme that may play a direct role in the cellular response to the antitumour polyamine analogues. In the present study, the induction of SMO(PAOh1) enzyme activity by CPENSpm [N1-ethyl-N11-(cyclopropyl)methyl-4,8,diazaundecane] is demonstrated to be a result of newly synthesized mRNA and protein. Inhibition of new RNA synthesis by actinomycin D inhibits both the appearance of SMO(PAOh1) mRNA and enzyme activity. Similarly, inhibition of newly synthesized protein with cycloheximide prevents analogue-induced enzyme activity. Half-life determinations indicate that stabilization of SMO(PAOh1) protein does not play a significant role in analogue-induced activity. However, half-life experiments using actinomycin D indicate that CPENSpm treatment not only increases mRNA expression, but also leads to a significant increase in mRNA half-life (17.1 and 8.8 h for CPENSpm-treated cells and control respectively). Using reporter constructs encompassing the SMO(PAOh1) promoter region, a 30-90% increase in transcription is observed after exposure to CPENSpm. The present results are consistent with the hypothesis that analogue-induced expression of SMO(PAOh1) is a result of increased transcription and stabilization of SMO(PAOh1) mRNA, leading to increased protein production and enzyme activity. These data indicate that the major level of control of SMO(PAOh1) expression in response to polyamine analogues exposure is at the level of mRNA.

A perspective of polyamine metabolism

Polyamines are essential for the growth and function of normal cells. They interact with various macromolecules, both electrostatically and covalently and, as a consequence, have a variety of cellular effects. The complexity of polyamine metabolism and the multitude of compensatory mechanisms that are invoked to maintain polyamine homoeostasis argue that these amines are critical to cell survival. The regulation of polyamine content within cells occurs at several levels, including transcription and translation. In addition, novel features such as the +1 frameshift required for antizyme production and the rapid turnover of several of the enzymes involved in the pathway make the regulation of polyamine metabolism a fascinating subject. The link between polyamine content and human disease is unequivocal, and significant success has been obtained in the treatment of a number of parasitic infections. Targeting the polyamine pathway as a means of treating cancer has met with limited success, although the development of drugs such as DFMO (alpha-difluoromethylornithine), a rationally designed anticancer agent, has revolutionized our understanding of polyamine function in cell growth and provided 'proof of concept' that influencing polyamine metabolism and content within tumour cells will prevent tumour growth. The more recent development of the polyamine analogues has been pivotal in advancing our understanding of the necessity to deplete all three polyamines to induce apoptosis in tumour cells. The current thinking is that the polyamine inhibitors/analogues may also be useful agents in the chemoprevention of cancer and, in this area, we may yet see a revival of DFMO. The future will be in adopting a functional genomics approach to identifying polyamine-regulated genes linked to either carcinogenesis or apoptosis.

Regulatory mechanisms controlling gene expression mediated by the antioxidant response element

The expression of genes encoding antioxidative and Phase II detoxification enzymes is induced in cells exposed to electrophilic compounds and phenolic antioxidants. Induction of these enzymes is regulated at the transcriptional level and is mediated by a specific enhancer, the antioxidant response element or ARE, found in the promoter of the enzyme's gene. The transcription factor Nrf2 has been implicated as the central protein that interacts with the ARE to activate gene transcription constitutively or in response to an oxidative stress signal. This review focuses on the molecular mechanisms whereby the transcriptional activation mediated by the interaction between the ARE and NF-E2-related factor 2 (Nrf2) is regulated. Recent studies suggest that the sequence context of the ARE, the nature of the chemical inducers, and the cell type are important for determining the activity of the enhancer in a particular gene.

Lytic infection of pseudorabies virus in the presence of spermine, spermidine, or DFMO

The effects of polyamines (spermine or spermidine) and DFMO (an ornithine decarboxylase inhibitor) on the infection of LM (tk-) cells by pseudorabies virus (PRV) were investigated. Results from radioactive methionine labeling showed that the synthesis of viral proteins was not affected; however, the expression of a distinctive cellular protein ( approximately 27 kDa) was induced after the treatment of spermine or spermidine. Using plaque assay, we found that the plaque formation of PRV was not affected by these three reagents either. Furthermore, the effects of these drugs on the transcription of PRV immediate-early gene (IE) promoter were examined by CAT assay, and results showed weak stimulation of transcription by these drugs. Taken together, our results demonstrated that lytic infection of PRV was not influenced by addition of exogenous polyamines or depletion of endogenous polyamines; this conclusion was similar to earlier studies by using herpes simplex virus.

Functional characterization of the human spermidine/spermine N(1)-acetyltransferase gene promoter

Spermidine/spermine N(1)-acetyltransferase (SSAT), the key enzyme of polyamine catabolism, is induced by antiproliferative stresses. We analyzed the 5' flanking region of the human SSAT gene, and clarified that the binding of Sp1 to the GC-box located 42 to 51 bp upstream from the transcription start site is essential for transcription in HeLa S3 cells. A polyamine-responsive element (PRE) seemed to be responsible for the elevated transcription after X-ray irradiation.

Effects of polyamines on the thermal stability and formation kinetics of DNA duplexes with abnormal structure

The effects of ions (i.e. Na+, Mg2+ and polyamines including spermidine and spermine) on the stability of various DNA oligonucleotides in solution were studied. These synthetic DNA molecules contained sequences that mimic various cellular DNA structures, such as duplexes, bulged loops, hairpins and/or mismatched base pairs. Melting temperature curves obtained from the ultraviolet spectroscopic experiments indicated that the effectiveness of the stabilization of cations on the duplex formation follows the order of spermine > spermidine > Mg2+ > Na+ > Tris-HCl buffer alone at pH 7.3. Circular dichroism spectra showed that salts and polyamines did not change the secondary structures of those DNA molecules under study. Surface plasmon resonance (SPR) observations suggested that the rates of duplex formation are independent of the kind of cations used or the structure of the duplexes. However, the rate constants of DNA duplex dissociation decrease in the same order when those cations are involved. The enhancement of the duplex stability by polyamines, especially spermine, can compensate for the instability caused by abnormal structures (e.g. bulged loops, hairpins or mismatches). The effects can be so great as to make the abnormal DNAs as stable as the perfect duplex, both kinetically and thermodynamically. Our results may suggest that the interconversion of various DNA structures can be accomplished readily in the presence of polyamine. This may be relevant in understanding the role of DNA polymorphism in cells.

Cloning and characterization of the mouse polyamine-modulated factor-1 (mPMF-1) gene: an alternatively spliced homologue of the human transcription factor

The natural polyamines and their analogues have been implicated in transcriptional regulation of specific genes. Human polyamine-modulated factor-1 (hPMF-1) was the first polyamine-responsive transcription factor identified. Here the mouse homologue of the hPMF-1 gene is described. Interestingly, the mouse gene (mPMF-1) codes for two alternatively spliced mRNAs. Both of the mouse splice variants, mPMF-1S and mPMF-1L, possess C-terminal coiled-coil domains nearly identical to that found in hPMF-1 and are highly homologous with the human protein. The C-terminal coiled-coil structure is necessary for transcriptional activation. However, the shorter protein, mPMF-1S, does not contain an N-terminal coiled-coil region as do both hPMF-1 and the longer mPMF-1L. mPMF-1L mRNA codes for a protein of 202 amino acids, 37 amino acids longer than the human protein. By contrast, mPMF-1S codes for only 133 amino acids, as a result of two exons being omitted compared with mPMF-1L. Both mouse transcription factors can interact with Nrf-2 (nuclear factor-E2-related factor 2), the normal partner of hPMF-1, substantiating the importance of the C-terminal coiled-coil region responsible for this interaction. Finally, the expression of mPMF-1 is induced when mouse M1 myeloid leukaemia cells are exposed to polyamine analogues, suggesting control similar to that observed for the hPMF-1.