Ornithine decarboxylase antizyme induces hypomethylation of genome DNA and histone H3 lysine 9 dimethylation (H3K9me2) in human oral cancer cell line

The Synergistic Benefit of Combination Strategies Targeting Tumor Cell Polyamine Homeostasis

Mammalian polyamines, including putrescine, spermidine, and spermine, are positively charged amines that are essential for all living cells including neoplastic cells. An increasing understanding of polyamine metabolism, its molecular functions, and its role in cancer has led to the interest in targeting polyamine metabolism as an anticancer strategy, as the metabolism of polyamines is frequently dysregulated in neoplastic disease. In addition, due to compensatory mechanisms, combination therapies are clinically more promising, as agents can work synergistically to achieve an effect beyond that of each strategy as a single agent. In this article, the nature of polyamines, their association with carcinogenesis, and the potential use of targeting polyamine metabolism in treating and preventing cancer as well as combination therapies are described. The goal is to review the latest strategies for targeting polyamine metabolism, highlighting new avenues for exploiting aberrant polyamine homeostasis for anticancer therapy and the mechanisms behind them.

Polyamines: the pivotal amines in influencing the tumor microenvironment

Cellular proliferation, function and survival is reliant upon maintaining appropriate intracellular polyamine levels. Due to increased metabolic needs, cancer cells elevate their polyamine pools through coordinated metabolism and uptake. High levels of polyamines have been linked to more immunosuppressive tumor microenvironments (TME) as polyamines support the growth and function of many immunosuppressive cell types such as MDSCs, macrophages and regulatory T-cells. As cancer cells and other pro-tumorigenic cell types are highly dependent on polyamines for survival, pharmacological modulation of polyamine metabolism is a promising cancer therapeutic strategy. This review covers the roles of polyamines in various cell types of the TME including both immune and stromal cells, as well as how competition for nutrients, namely polyamine precursors, influences the cellular landscape of the TME. It also details the use of polyamines as biomarkers and the ways in which polyamine depletion can increase the immunogenicity of the TME and reprogram tumors to become more responsive to immunotherapy.

Changes in Whole Blood Polyamine Levels and Their Background in Age-Related Diseases and Healthy Longevity

The relationship between polyamines and healthy longevity has received much attention in recent years. However, conducting research without understanding the properties of polyamines can lead to unexpected pitfalls. The most fundamental consideration in conducting polyamine studies is that bovine serum used for cell culture contains bovine serum amine oxidase. Bovine serum amine oxidase, which is not inactivated by heat treatment, breaks down spermine and spermidine to produce the highly toxic aldehyde acrolein, which causes cell damage and activates autophagy. However, no such enzyme activity has been found in humans. Polyamine catabolism does not produce toxic aldehydes under normal conditions, but inflammation and some pathogens provoke an inducible enzyme, spermine oxidase, which only breaks down spermine to produce acrolein, resulting in cytotoxicity and the activation of autophagy. Therefore, spermine oxidase activation reduces spermine concentration and the ratio of spermine to spermidine, a feature recently reported in patients with age-related diseases. Spermine, which is increased by a long-term, continuous high polyamine diet, suppresses aberrant gene methylation and the pro-inflammatory status that progress with age and are strongly associated with the development of several age-related diseases and senescence. Changes in spermine concentration and the spermine/spermidine ratio should be considered as indicators of human health status.

KDM3A promotes oral squamous cell carcinoma cell proliferation and invasion via H3K9me2 demethylation-activated DCLK1

BACKGROUND

Oral squamous cell carcinoma (OSCC) is a frequently-diagnosed malignancy with high potential for proliferation and invasion. Histone methylation is known as a crucial mechanism that regulates pathological processes in various cancers, including OSCC.

OBJECTIVE

This study sought to delve into the molecular mechanism of lysine demethylase 3 A (KDM3A) in OSCC cell proliferation and invasion.

METHODS

Expression levels of KDM3A, lysin-9 of di-methylated histone H3 (H3K9me2), and doublecortin-like kinase 1 (DCLK1) in cells were determined by reverse-transcription quantitative polymerase chain reaction or Western blot analysis. Cell proliferation and invasion were evaluated by cell counting kit-8, colony formation, and Transwell assays. The enrichment of KDM3A and H3K9me2 on the DCLK1 promoter was determined by chromatin immunoprecipitation assay. The functional rescue experiment was performed with DCLK1 overexpression vector and si-KDM3A in CAL-27 and SCC-9 cells.

RESULTS

KDM3A was elevated in OSCC cells. KDM3A knockdown suppressed OSCC proliferation and invasion, along with increased H3K9me2 level in OSCC cells. KDM3A and H3K9me2 were enriched on the DCLK1 promoter and inhibiting H3K9me2 improved DCLK1 expression levels. DCLK1 overexpression neutralized the inhibition of KDM3A knockdown on OSCC proliferation and invasion.

CONCLUSIONS

KDM3A facilitated OSCC proliferation and invasion by eliminating H3K9me2 to upregulate DCLK1 expression levels.

Methyl Group Metabolism in Differentiation, Aging, and Cancer

Methyl group metabolism belongs to a relatively understudied field of research. Its importance lies in the fact that methyl group metabolic pathways are crucial for the successful conversion of dietary nutrients into the basic building blocks to carry out any cellular methylation reaction. Methyl groups play essential roles in numerous cellular functions such as DNA methylation, nucleotide- and protein biosynthesis. Especially, DNA methylation is responsible for organizing the genome into transcriptionally silent and active regions. Ultimately, it is this proper annotation that determines the quality of expression patterns required to ensure and shape the phenotypic integrity and function of a highly specialized cell type. Life is characterized by constantly changing environmental conditions, which are addressed by changes in DNA methylation. This relationship is increasingly coming into focus as it is of fundamental importance for differentiation, aging, and cancer. The stability and permanence of these metabolic processes, fueling the supplementation of methyl groups, seem to be important criteria to prevent deficiencies and erosion of the methylome. Alterations in the metabolic processes can lead to epigenetic and genetic perturbations, causative for diverse disorders, accelerated aging, and various age-related diseases. In recent decades, the intake of methyl group compounds has changed significantly due to, e.g., environmental pollution and food additives. Based on the current knowledge, this review provides a brief overview of the highly interconnected relationship between nutrition, metabolism, changes in epigenetic modifications, cancer, and aging. One goal is to provide an impetus to additionally investigate changes in DNA methylation as a possible consequence of an impaired methyl group metabolism.

Nucleosome destabilization by polyamines

The roles and molecular interactions of polyamines (PAs) in the nucleus are not fully understood. Here their effect on nucleosome stability, a key regulatory factor in eukaryotic gene control, is reported, as measured in agarose embedded nuclei of H2B-GFP expressor HeLa cells. Nucleosome stability was assessed by quantitative microscopy [1,2] in situ, in close to native state of chromatin, preserving the nucleosome constrained topology of the genomic DNA. A robust destabilizing effect was observed in the millimolar concentration range in the case of spermine, spermidine as well as putrescine, which was strongly pH and salt concentration-dependent, and remained significant also at neutral pH. The integrity of genomic DNA was not affected by PA treatment, excluding DNA break-elicited topological relaxation as a factor in destabilization. The binding of PAs to DNA was demonstrated by the displacement of ethidium bromide, both from deproteinized nuclear halos and from plasmid DNA. The possibility that DNA methylation patterns may be influenced by PA levels is contemplated in the context of gene expression and DNA methylation correlations identified in the NCI-60 panel-based CellMiner database: methylated loci in subsets of high-ODC1 cell lines and the dependence of PER3 DNA methylation on PA metabolism.

Epigenetics in the Diagnosis and Therapy of Malignant Melanoma

Epigenetic mechanisms are fundamentally important for cancer initiation and development. However, a survey of the literature reveals that, to date, they appear less comprehensively investigated in melanoma than in many other cancers, e.g., prostate, breast, and colon carcinoma. The aim of this review is to provide a short summary of epigenetic aspects of functional relevance for melanoma pathogenesis. In addition, some new perspectives from epigenetic research in other cancers with potential for melanoma diagnosis and therapy are introduced. For example, the PrimeEpiHit hypothesis in urothelial carcinoma, which, similarly to malignant melanoma, can also be triggered by a single exogenous noxa, states that one of the first steps for cancer initiation could be epigenetic changes in key genes of one-carbon metabolism. The application of such insights may contribute to further progress in the diagnosis and therapy of melanoma, a deadly type of cancer.

Overview of Polyamines as Nutrients for Human Healthy Long Life and Effect of Increased Polyamine Intake on DNA Methylation

Polyamines, spermidine and spermine, are synthesized in every living cell and are therefore contained in foods, especially in those that are thought to contribute to health and longevity. They have many physiological activities similar to those of antioxidant and anti-inflammatory substances such as polyphenols. These include antioxidant and anti-inflammatory properties, cell and gene protection, and autophagy activation. We have first reported that increased polyamine intake (spermidine much more so than spermine) over a long period increased blood spermine levels and inhibited aging-associated pathologies and pro-inflammatory status in humans and mice and extended life span of mice. However, it is unlikely that the life-extending effect of polyamines is exerted by the same bioactivity as polyphenols because most studies using polyphenols and antioxidants have failed to demonstrate their life-extending effects. Recent investigations revealed that aging-associated pathologies and lifespan are closely associated with DNA methylation, a regulatory mechanism of gene expression. There is a close relationship between polyamine metabolism and DNA methylation. We have shown that the changes in polyamine metabolism affect the concentrations of substances and enzyme activities involved in DNA methylation. I consider that the increased capability of regulation of DNA methylation by spermine is a key of healthy long life of humans.

Basic Hallmarks of Urothelial Cancer Unleashed in Primary Uroepithelium by Interference with the Epigenetic Master Regulator ODC1

Urothelial carcinoma (UC) is a common disease causing significant morbidity and mortality as well as considerable costs for health systems. Extensive aberrant methylation of DNA is broadly documented in early UC, contributing to genetic instability, altered gene expression and tumor progression. However the triggers initiating aberrant methylation are unknown. Recently we discovered that several genes encoding key enzymes of methyl group and polyamine metabolism, including Ornithine Decarboxylase 1 (ODC1), are affected by DNA methylation in early stage UC. In this study, we investigated the hypothesis that these epigenetic alterations act in a feed-forward fashion to promote aberrant DNA methylation in UC. We demonstrate that siRNA-mediated knockdown of ODC1 expression elicits genome-wide LINE-1 demethylation, induction of LINE-1 transcripts and double-strand DNA breaks and decreases viability in primary cultured uroepithelial cells. Similarly, following siRNA-mediated knockdown of ODC1, UC cells undergo double-strand DNA breaks and apoptosis. Collectively, our findings provide evidence that ODC1 gene hypermethylation could be a starting point for the onset of genome-wide epigenetic aberrations in urothelial carcinogenesis. Furthermore, LINE-1 induction enabled by ODC1 interference provides a new experimental model to study mechanisms and consequences of LINE-1 activation in the etiology and progression of UC as well as presumably other cancers.

Spermine and gene methylation: a mechanism of lifespan extension induced by polyamine-rich diet

The polyamines spermidine and spermine are synthesized in almost all organisms and are also contained in food. Polyamine synthesis decreases with aging, but no significant decrease in polyamine concentrations were found in organs, tissues, and blood of adult animals and humans. We found that healthy dietary patterns were associated with a preference for polyamine-rich foods, and first reported that increased polyamine intake extended the lifespan of mice and decreased the incidence of colon cancer induced by repeated administration of moderate amounts of a carcinogen. Recent investigations have revealed that changes in DNA methylation status play an important role in lifespan and aging-associated pathologies. The methylation of DNA is regulated by DNA methyltransferases in the presence of S-adenosylmethionine. Decarboxylated S-adenosylmethionine, converted from S-adenosylmethionine by S-adenosylmethionine decarboxylase, provides an aminopropyl group to synthesize spermine and spermidine and acts to inhibit DNMT activity. Long-term increased polyamine intake were shown to elevate blood spermine levels in mice and humans. In vitro studies demonstrated that spermine reversed changes induced by the inhibition of ornithine decarboxylase (e.g., increased decarboxylated S-adenosylmethionine, decreased DNA methyltransferase activity, increased aberrant DNA methylation), whose activity decreases with aging. Further, aged mice fed high-polyamine chow demonstrated suppression of aberrant DNA methylation and a consequent increase in protein levels of lymphocyte function-associated antigen 1, which plays a pivotal role on inflammatory process. This review discusses the relation between polyamine metabolism and DNA methylation, as well as the biological mechanism of lifespan extension induced by increased polyamine intake.

Dietary and Gut Microbiota Polyamines in Obesity- and Age-Related Diseases

The polyamines putrescine, spermidine, and spermine are widely distributed polycationic compounds essential for cellular functions. Intracellular polyamine pools are tightly regulated by a complex regulatory mechanism involving de novo biosynthesis, catabolism, and transport across the plasma membrane. In mammals, both the production of polyamines and their uptake from the extracellular space are controlled by a set of proteins named antizymes and antizyme inhibitors. Dysregulation of polyamine levels has been implicated in a variety of human pathologies, especially cancer. Additionally, decreases in the intracellular and circulating polyamine levels during aging have been reported. The differences in the polyamine content existing among tissues are mainly due to the endogenous polyamine metabolism. In addition, a part of the tissue polyamines has its origin in the diet or their production by the intestinal microbiome. Emerging evidence has suggested that exogenous polyamines (either orally administrated or synthetized by the gut microbiota) are able to induce longevity in mice, and that spermidine supplementation exerts cardioprotective effects in animal models. Furthermore, the administration of either spermidine or spermine has been shown to be effective for improving glucose homeostasis and insulin sensitivity and reducing adiposity and hepatic fat accumulation in diet-induced obesity mouse models. The exogenous addition of agmatine, a cationic molecule produced through arginine decarboxylation by bacteria and plants, also exerts significant effects on glucose metabolism in obese models, as well as cardioprotective effects. In this review, we will discuss some aspects of polyamine metabolism and transport, how diet can affect circulating and local polyamine levels, and how the modulation of either polyamine intake or polyamine production by gut microbiota can be used for potential therapeutic purposes.

Extracellular Spermine Activates DNA Methyltransferase 3A and 3B

We first demonstrated that long-term increased polyamine (spermine, spermidine, putrescine) intake elevated blood spermine levels in mice and humans, and lifelong consumption of polyamine-rich chow inhibited aging-associated increase in aberrant DNA methylation, inhibited aging-associated pathological changes, and extend lifespan of mouse. Because gene methylation status is closely associated with aging-associated conditions and polyamine metabolism is closely associated with regulation of gene methylation, we investigated the effects of extracellular spermine supplementation on substrate concentrations and enzyme activities involved in gene methylation. Jurkat cells and human mammary epithelial cells were cultured with spermine and/or D,L-alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase. Spermine supplementation inhibited enzymatic activities of adenosylmethionine decarboxylase in both cells. The ratio of decarboxylated S-adenosylmethionine to S-adenosyl-L-methionine increased by DFMO and decreased by spermine. In Jurkat cells cultured with DFMO, the protein levels of DNA methyltransferases (DNMTs) 1, 3A and 3B were not changed, however the activity of the three enzymes markedly decreased. The protein levels of these enzymes were not changed by addition of spermine, DNMT 3A and especially 3B were activated. We show that changes in polyamine metabolism dramatically affect substrate concentrations and activities of enzymes involved in gene methylation.

Polyamine Metabolism and Gene Methylation in Conjunction with One-Carbon Metabolism

Recent investigations have revealed that changes in DNA methylation status play an important role in aging-associated pathologies and lifespan. The methylation of DNA is regulated by DNA methyltransferases (DNMT1, DNMT3a, and DNMT3b) in the presence of S-adenosylmethionine (SAM), which serves as a methyl group donor. Increased availability of SAM enhances DNMT activity, while its metabolites, S-adenosyl-l-homocysteine (SAH) and decarboxylated S-adenosylmethionine (dcSAM), act to inhibit DNMT activity. SAH, which is converted from SAM by adding a methyl group to cytosine residues in DNA, is an intermediate precursor of homocysteine. dcSAM, converted from SAM by the enzymatic activity of adenosylmethionine decarboxylase, provides an aminopropyl group to synthesize the polyamines spermine and spermidine. Increased homocysteine levels are a significant risk factor for the development of a wide range of conditions, including cardiovascular diseases. However, successful homocysteine-lowering treatment by vitamins (B6, B12, and folate) failed to improve these conditions. Long-term increased polyamine intake elevated blood spermine levels and inhibited aging-associated pathologies in mice and humans. Spermine reversed changes (increased dcSAM, decreased DNMT activity, aberrant DNA methylation, and proinflammatory status) induced by the inhibition of ornithine decarboxylase. The relation between polyamine metabolism, one-carbon metabolism, DNA methylation, and the biological mechanism of spermine-induced lifespan extension is discussed.

Aberrant methylated key genes of methyl group metabolism within the molecular etiology of urothelial carcinogenesis

Urothelial carcinoma (UC), the most common cancer of the urinary bladder causes severe morbidity and mortality, e.g. about 40.000 deaths in the EU annually, and incurs considerable costs for the health system due to the need for prolonged treatments and long-term monitoring. Extensive aberrant  DNA methylation is described to prevail in urothelial carcinoma and is thought to contribute to genetic instability, altered gene expression and tumor progression. However, it is unknown how this epigenetic alteration arises during carcinogenesis. Intact methyl group metabolism is required to ensure maintenance of cell-type specific methylomes and thereby genetic integrity and proper cellular function. Here, using two independent techniques for detecting DNA methylation, we observed DNA hypermethylation of the 5'-regulatory regions of the key methyl group metabolism genes ODC1, AHCY and MTHFR in early urothelial carcinoma. These hypermethylation events are associated with genome-wide DNA hypomethylation which is commonly associated with genetic instability. We therefore infer that hypermethylation of methyl group metabolism genes acts in a feed-forward cycle to promote additional DNA methylation changes and suggest a new hypothesis on the molecular etiology of urothelial carcinoma.

Epimutagenesis: A prospective mechanism to remediate arsenic-induced toxicity

Arsenic toxicity is a global issue, addressed by the World Health Organization as one of the major natural calamities faced by humans. More than 137 million individuals in 70 nations are affected by arsenic mainly through drinking water and also through diet. Chronic arsenic exposure leads to various types of patho-physiological end points in humans including cancers. Arsenic, a xenobiotic substance, is biotransformed in the body to its methylated species by using the physiological S-adenosyl methionine (SAM). SAM dictates methylation status of the genome and arsenic metabolism leads to depletion of SAM leading to an epigenetic disequilibrium. Since epigenetics is one of the major phenomenon at the interface between the environment and human health impact, its disequilibrium by arsenic inflicts upon the chromatin compaction, gene expression, genomic stability and a host of biomolecular interactions, the interactome within the cell. Since arsenic is not mutagenic but is carcinogenic in nature, arsenic induced epimutagenesis has come to the forefront since it determines the transcriptional and genomic integrity of the cell. Arsenic toxicity brings forth several pathophysiological manifestations like dermatological non-cancerous, pre-cancerous and cancerous lesions, peripheral neuropathy, DNA damage, respiratory disorders and cancers of several internal organs. Recently, several diseases of similar manifestations have been explained with the relevant epigenetic perspectives regarding the possible molecular mechanism for their onset. Hence, in the current review, we comprehensively try to intercalate the information on arsenic-induced epigenetic alterations of DNA, histones and microRNA so as to understand whether the arsenic-induced toxic manifestations are brought about by the epigenetic changes. We highlight the need to understand the aspect of epimutagenesis and subsequent alterations in the cellular interactome due to arsenic-induced molecular changes, which may be utilized to develop putative therapeutic strategies targeting both oxidative potential and epimutagenesis in humans.

Say what? The activity of the polyamine biosynthesis inhibitor difluoromethylornithine in chemoprevention is a result of reduced thymidine pools?

In this issue of Cancer Discovery, Witherspoon and colleagues use an unbiased metabolite profiling approach to study the effects of polyamine depletion by 2-difluoromethylornithine in colon cancer cells. Their surprising findings indicate that it is a decrease in thymidine pools resulting from altered tetrahydrofolate availability rather than decreases in polyamines that produces cytostasis.

Assay of OAZ1 mRNA levels in chronic myeloid leukemia combined with application of leukemia PCR array identified relevant gene changes affected by antizyme

Ornithine decarboxylase antizyme (OAZ) has recently emerged as a potential therapeutic target in various malignant tumors because it plays vital roles in cellular functions including proliferation, differentiation, apoptosis and genomic stability. Therefore, there is a significant interest in discovering its function in chronic myeloid leukemia (CML). Firstly, OAZ1 mRNA was measured by qRT-PCR in 43 cases with CML and 23 controls, and we demonstrated that it is significantly down-regulated in CML patients. To further understand its functions in CML pathogenesis, OAZ1 was overexpressed, and the human leukemia PCR array analysis was used to monitor the expression of key genes commonly involved in leukemia development, classification and therapeutic response. We found several favorable up-regulation factors including CXCL10, DAPK1 and IKZF3. In conclusion, OAZ1 may be a useful therapeutic target in CML due to its potential ability to induce erythroid differentiation and cell apoptosis. These functions were proven to be associated with several gene changes that were directly or indirectly caused by OAZ1. The mechanism of how OAZ1 affects other genes remains to be elucidated.

Unbiased metabolite profiling indicates that a diminished thymidine pool is the underlying mechanism of colon cancer chemoprevention by alpha-difluoromethylornithine

The ornithine decarboxylase inhibitor α-difluoromethylornithine (DFMO) is a highly effective chemopreventive agent for colorectal cancer thought to act via polyamine depletion. However, in DFMO-treated patients, mucosal polyamine levels do not directly correlate with colorectal cancer risk. Untargeted metabolite profiling was used to broadly survey DFMO actions on colon cancer cell metabolism. We found that DFMO treatment of Apc(Min) intestinal tumors and human colorectal cancer cells is associated with reduced levels of folate-dependent metabolites, including S-adenosylmethionine (SAM), thymidine pools, and related pathway intermediates. We hypothesized that unrestrained SAM consumption/regeneration constitutes a futile DFMO-triggered cascade that can steal tetrahydrofolate from thymidylate synthase and thereby diminish thymidine pools. In accord with this hypothesis, DFMO treatment altered the folate cofactor balance and thymidine supplementation prevented DFMO-elicited cytostasis without restoring polyamine levels. These findings suggest that thymidine metabolite pool insufficiency is a fundamental mechanism of DFMO cytostatic activity.

SIGNIFICANCE

A previously unappreciated metabolic linkage between polyamine and thymidine biosynthesis is revealed, based on the competing requirement of these pathways for a limited pool of tetrahydrofolate cofactor. This study identifies the fi rst shared mechanism for colorectal cancer chemoprevention and chemotherapy, suggesting a common metabolic target for both premalignant and malignant colon cells.

Increased polyamine intake inhibits age-associated alteration in global DNA methylation and 1,2-dimethylhydrazine-induced tumorigenesis

Polyamines (spermine and spermidine) play many important roles in cellular function and are supplied from the intestinal lumen. We have shown that continuous high polyamine intake inhibits age-associated pathologies in mice. The mechanism by which polyamines elicit these effects was examined. Twenty-four week old Jc1:ICR male mice were fed one of three experimental chows containing different polyamine concentrations. Lifetime intake of high polyamine chow, which had a polyamine content approximately three times higher than regular chow, elevated polyamine concentrations in whole blood, suppressed age-associated increases in pro-inflammatory status, decreased age-associated pathological changes, inhibited age-associated global alteration in DNA methylation status and reduced the mortality in aged mice. Exogenous spermine augmented DNA methyltransferase activity in Jurkat and HT-29 cells and inhibited polyamine deficiency-induced global alteration in DNA methylation status in vitro. In addition, increased polyamine intake was associated with a decreased incidence of colon tumors in BALB/c mice after 1,2-demethylhydrazine administration; 12 mice (60%) in the low polyamine group developed tumors, compared with only 5 mice (25%) in the high polyamine group (Fisher's exact probability = 0.027, p = 0.025). However, increased polyamine intake accelerated the growth of established tumors; maximal tumor diameter in the Low and High groups was 3.85±0.90 mm and 5.50±1.93 mm, respectively (Mann-Whitney test, p = 0.039). Spermine seems to play important roles in inhibiting age-associated and polyamine-deficient induced abnormal gene methylation as well as pathological changes including tumorigenesis.

Epigenetic mechanisms in oral carcinogenesis

Dysregulation of gene expression is a frequent occurrence in oral squamous cell carcinoma (OSCC). However, accumulating evidence suggests that in contrast to genetics, epigenetic modifications consisting of aberrant DNA methylation, histone modifications and altered expression of miRNAs induce OSCC tumorigenesis and perhaps play a more central role in the evolution and progression of this disease. The unifying theme among these three epigenetic mechanisms remains the same, which is aberrant regulation of gene expression. In this article, we provide a comprehensive review of the impact of epigenetics on oral tumorigenesis with a systematic report on aberrant DNA methylation, histone modifications and miRNA regulation in the pathogenesis of OSCC. We provide insights into recent studies on the prospect of biomarkers for early detection and indication of disease recurrence, and novel treatment modalities.

Polyamines and cancer: implications for chemotherapy and chemoprevention

Polyamines are small organic cations that are essential for normal cell growth and development in eukaryotes. Under normal physiological conditions, intracellular polyamine concentrations are tightly regulated through a dynamic network of biosynthetic and catabolic enzymes, and a poorly characterised transport system. This precise regulation ensures that the intracellular concentration of polyamines is maintained within strictly controlled limits. It has frequently been observed that the metabolism of, and the requirement for, polyamines in tumours is frequently dysregulated. Elevated levels of polyamines have been associated with breast, colon, lung, prostate and skin cancers, and altered levels of rate-limiting enzymes in both biosynthesis and catabolism have been observed. Based on these observations and the absolute requirement for polyamines in tumour growth, the polyamine pathway is a rational target for chemoprevention and chemotherapeutics. Here we describe the recent advances made in the polyamine field and focus on the roles of polyamines and polyamine metabolism in neoplasia through a discussion of the current animal models for the polyamine pathway, chemotherapeutic strategies that target the polyamine pathway, chemotherapeutic clinical trials for polyamine pathway-specific drugs and ongoing clinical trials targeting polyamine biosynthesis.

Suppression of LFA-1 expression by spermine is associated with enhanced methylation of ITGAL, the LFA-1 promoter area

Spermine and spermidine, natural polyamines, suppress lymphocyte function-associated antigen 1 (LFA-1) expression and its associated cellular functions through mechanisms that remain unknown. Inhibition of ornithine decarboxylase, which is required for polyamine synthesis, in Jurkat cells by 3 mM D,L-alpha-difluoromethylornithine hydrochloride (DFMO) significantly decreased spermine and spermidine concentrations and was associated with decreased DNA methyltransferase (Dnmt) activity, enhanced demethylation of the LFA-1 gene (ITGAL) promoter area, and increased CD11a expression. Supplementation with extracellular spermine (500 µM) of cells pretreated with DFMO significantly increased polyamine concentrations, increased Dnmt activity, enhanced methylation of the ITGAL promoter, and decreased CD11a expression. It has been shown that changes in intracellular polyamine concentrations affect activities of -adenosyl-L-methionine-decaroboxylase, and, as a result, affect concentrations of the methyl group donor, S-adenosylmethionine (SAM), and of the competitive Dnmt inhibitor, decarboxylated SAM. Additional treatments designed to increase the amount of SAM and decrease the amount of decarboxylated SAM–such as treatment with methylglyoxal bis-guanylhydrazone (an inhibitor of S-adenosyl-L-methionine-decaroboxylase) and SAM supplementation–successfully decreased CD11a expression. Western blot analyses revealed that neither DFMO nor spermine supplementation affected the amount of active Ras-proximate-1, a member of the Ras superfamily of small GTPases and a key protein for regulation of CD11a expression. The results of this study suggest that polyamine-induced suppression of LFA-1 expression occurs via enhanced methylation of ITGAL.

Oligoamine analogues in combination with 2-difluoromethylornithine synergistically induce re-expression of aberrantly silenced tumour-suppressor genes

Epigenetic gene silencing is an important mechanism in the initiation and progression of cancer. Abnormal DNA CpG island hypermethylation and histone modifications are involved in aberrant silencing of tumour-suppressor genes. LSD1 (lysine-specific demethylase 1) was the first enzyme identified to specifically demethylate H3K4 (Lys⁴ of histone H3). Methylated H3K4 is an important mark associated with transcriptional activation. The flavin adenine dinucleotide-binding amine oxidase domain of LSD1 is homologous with two polyamine oxidases, SMO (spermine oxidase) and APAO (N¹-acetylpolyamine oxidase). We have demonstrated previously that long-chain polyamine analogues, the oligoamines, are inhibitors of LSD1. In the present paper we report the synergistic effects of specific oligoamines in combination with DFMO (2-difluoromethylornithine), an inhibitor of ornithine decarboxylase, in human colorectal cancer cells. DFMO treatment depletes natural polyamines and increases the uptake of exogenous polyamines. The combination of oligoamines and DFMO results in a synergistic re-expression of aberrantly silenced tumour-suppressor genes, including SFRP2 (secreted frizzled-related protein 2), which encodes a Wnt signalling pathway antagonist and plays an anti-tumorigenic role in colorectal cancer. The treatment-induced re-expression of SFRP2 is associated with increased H3K4me2 (di-methyl H3K4) in the gene promoter. The combination of LSD1-inhibiting oligoamines and DFMO represents a novel approach to epigenetic therapy of cancer.

Molecular characterization, tissue expression and nucleotide variation of the porcine AZ1 gene

Antizyme 1 (AZ1) is a member of the antizyme family that is involved in many biological processes. As a natural inhibitor, AZ1 controls the normal level of polyamines, which is indispensable to cellular function. Our prior research showed that the expression of the AZ1 gene in Longissimus doris of Landrace pigs was higher (P<0.05) than in Lantang pigs. The AZ1 gene might be involved in the development of muscle and potentially serves as an important target for muscle improvement in pigs. In this study, the molecular characterization, tissue expression, and sequence variation of porcine AZ1 gene were analyzed. A 4082 bp sequence including the 5'-flanking region and gene sequence was obtained through RACE and sequencing. The genomic sequence of AZ1 gene consists of six exons and five introns. The mRNA of AZ1 gene contains three elements: 5'-untranslated regions (UTR, 79 bp), CDS (684 or 207 bp), and 3'-UTR (161 or 423 bp for the two transcripts). Three termination signals of AATAAA were found in the longer 3'-UTR. The mRNA sequence of the AZ1 gene contained two ORFs with a frameshifting site at the 69th codon. The amino acid sequence from the porcine AZ1 gene was similar to other vertebrates and exhibited the highest similarity to cattle. The partial 5'-flanking region was 852 bp with typical cis-regulatory elements such as TATA boxes and CAAT boxes. By DNA pooling and sequencing, nine and 12 single nucleotide polymorphisms (SNPs) were detected in the 5'-flanking region and introns, respectively. Except the SNP at -713, the other eight SNPs were found in putative cis-acting elements and might alter the binding of trans-acting factors. Expression patterns showed that in Lantang pig, the AZ1 gene is differentially expressed in various tissues and displayed higher expression in lung and skeletal muscle.

Efficacy of QCDCR formulated CpG ODN 2007 in Nile tilapia against Streptococcus iniae and identification of upregulated genes

The potential of using a QCDCR (quilA:cholesterol:dimethyl dioctadecyl ammonium bromide:carbopol:R1005 glycolipid) formulated CpG oligodeoxynucleotide (ODN), ODN 2007, to confer protection in Nile tilapia against Streptococcus iniae infection was evaluated in this study. At two days post treatment, QCDCR formulated ODN 2007 elicited significant (P<0.05) protection to Nile tilapia, with relative percent survival of 63% compared to fish treated by QCDCR alone. To understand the molecular mechanisms involved in the protective immunity elicited by ODN 2007, suppression subtractive cDNA hybridization technique was used to identify upregulated genes induced by ODN 2007. A total of 69 expressed sequence tags (ESTs) were identified from the subtractive cDNA library. Quantitative PCR revealed that 44 ESTs were significantly (P<0.05) upregulated by ODN 2007, including 29 highly (>10-fold) and 15 moderately (<10-fold) upregulated ESTs. Of all ESTs, putative peroxisomal sarcosine oxidase was upregulated the highest. The 69 ESTs only included six genes that had putative functions related to immunity, of which only two (putative glutaredoxin-1 and carboxypeptidase N catalytic chain) were confirmed to be significantly upregulated. Our results suggest that the protection elicited by ODN 2007 is mainly through innate immune responses directly or indirectly related to immunity.

Evidence of a role for antizyme and antizyme inhibitor as regulators of human cancer

Antizyme and its endogenous antizyme inhibitor have recently emerged as prominent regulators of cell growth, transformation, centrosome duplication, and tumorigenesis. Antizyme was originally isolated as a negative modulator of the enzyme ornithine decarboxylase (ODC), an essential component of the polyamine biosynthetic pathway. Antizyme binds ODC and facilitates proteasomal ODC degradation. Antizyme also facilitates degradation of a set of cell cycle regulatory proteins, including cyclin D1, Smad1, and Aurora A kinase, as well as Mps1, a protein that regulates centrosome duplication. Antizyme has been reported to function as a tumor suppressor and to negatively regulate tumor cell proliferation and transformation. Antizyme inhibitor binds to antizyme and suppresses its known functions, leading to increased polyamine synthesis, increased cell proliferation, and increased transformation and tumorigenesis. Gene array studies show antizyme inhibitor to be amplified in cancers of the ovary, breast, and prostate. In this review, we summarize the current literature on the role of antizyme and antizyme inhibitor in cancer, discuss how the ratio of antizyme to antizyme inhibitor can influence tumor growth, and suggest strategies to target this axis for tumor prevention and treatment.

Independent evolutionary origins of functional polyamine biosynthetic enzyme fusions catalysing de novo diamine to triamine formation

We have identified gene fusions of polyamine biosynthetic enzymes S-adenosylmethionine decarboxylase (AdoMetDC, speD) and aminopropyltransferase (speE) orthologues in diverse bacterial phyla. Both domains are functionally active and we demonstrate the novel de novo synthesis of the triamine spermidine from the diamine putrescine by fusion enzymes from β-proteobacterium Delftia acidovorans and δ-proteobacterium Syntrophus aciditrophicus, in a ΔspeDE gene deletion strain of Salmonella enterica sv. Typhimurium. Fusion proteins from marine α-proteobacterium Candidatus Pelagibacter ubique, actinobacterium Nocardia farcinica, chlorobi species Chloroherpeton thalassium, and β-proteobacterium D. acidovorans each produce a different profile of non-native polyamines including sym-norspermidine when expressed in Escherichia coli. The different aminopropyltransferase activities together with phylogenetic analysis confirm independent evolutionary origins for some fusions. Comparative genomic analysis strongly indicates that gene fusions arose by merger of adjacent open reading frames. Independent fusion events, and horizontal and vertical gene transfer contributed to the scattered phyletic distribution of the gene fusions. Surprisingly, expression of fusion genes in E. coli and S. Typhimurium revealed novel latent spermidine catabolic activity producing non-native 1,3-diaminopropane in these species. We have also identified fusions of polyamine biosynthetic enzymes agmatine deiminase and N-carbamoylputrescine amidohydrolase in archaea, and of S-adenosylmethionine decarboxylase and ornithine decarboxylase in the single-celled green alga Micromonas.