Biological functions of SLC5A8, a candidate tumour suppressor

Exploring monocarboxylate transporter inhibition for cancer treatment

Cells are separated from the environment by a lipid bilayer membrane that is relatively impermeable to solutes. The transport of ions and small molecules across this membrane is an essential process in cell biology and metabolism. Monocarboxylate transporters (MCTs) belong to a vast family of solute carriers (SLCs) that facilitate the transport of certain hydrophylic small compounds through the bilipid cell membrane. The existence of 446 genes that code for SLCs is the best evidence of their importance. In-depth research on MCTs is quite recent and probably promoted by their role in cancer development and progression. Importantly, it has recently been realized that these transporters represent an interesting target for cancer treatment. The search for clinically useful monocarboxylate inhibitors is an even more recent field. There is limited pre-clinical and clinical experience with new inhibitors and their precise mechanism of action is still under investigation. What is common to all of them is the inhibition of lactate transport. This review discusses the structure and function of MCTs, their participation in cancer, and old and newly developed inhibitors. Some suggestions on how to improve their anticancer effects are also discussed.

In vitro evaluation of the anti‑breast cancer properties and gene expression profiles of Thai traditional formulary medicine extracts

Breast cancer is a leading cause of cancer-related deaths worldwide. Moreover, standard treatments are limited, so new alternative treatments are required. Thai traditional formulary medicine (TTFM) utilizes certain herbs to treat different diseases due to their dominant properties including anti-fungal, anti-bacterial, antigenotoxic, anti-inflammatory and anti-cancer actions. However, very little is known about the anti-cancer properties of TTFM against breast cancer cells and the underlying molecular mechanism has not been elucidated. Therefore, the present study, evaluated the metabolite profiles of TTFM extracts, the anti-cancer activities of TTFM extracts, their effects on the apoptosis pathway and associated gene expression profiles. Liquid chromatography with tandem mass spectroscopy analysis identified a total of 226 compounds within the TTFM extracts. Several of these compounds have been previously shown to have an anti-cancer effect in certain cancer types. The MTT results demonstrated that the TTFM extracts significantly reduced the cell viability of the breast cancer 4T1 and MDA-MB-231 cell lines. Moreover, an apoptosis assay, demonstrated that the TTFM extracts significantly increased the proportion of apoptotic cells. Furthermore, the RNA-sequencing results demonstrated that 25 known genes were affected by TTFM treatment in 4T1 cells. TTFM treatment significantly up-regulated Slc5a8 and Arhgap9 expression compared with untreated cells. Moreover, Cybb, and Bach2os were significantly downregulated after TTFM treatment compared with untreated cells. Reverse transcription-quantitative PCR demonstrated that TTFM extract treatment significantly increased Slc5a8 and Arhgap9 mRNA expression levels and significantly decreased Cybb mRNA expression levels. Moreover, the mRNA expression levels of Bax and Casp9 were significantly increased after TTFM treatment in 4T1 cells compared with EpH4-Ev cells. These findings indicated anti-breast cancer activity via induction of the apoptotic process. However, further experiments are required to elucidate how TTFM specifically regulates genes and proteins. This study supports the potential usage of TTFM extracts for the development of anti-cancer drugs.

Effect of diet and genotype on the miRNome of mice with altered lipoprotein metabolism

The molecular mechanism by which lipid/lipoprotein biosynthesis is regulated in mammals involves a very large number of genes that are subject to multiple levels of regulation. miRNAs are recognized contributors to lipid homeostasis at the post-transcriptional level, although the elucidation of their role is made difficult by the multiplicity of their targets and the ability of more miRNAs to affect the same mRNAs. In this study, an evaluation of how miRNA expression varies in organs playing a key role in lipid/lipoprotein metabolism was conducted in control mice and in two mouse models carrying genetic ablations which differently affect low-density lipoprotein metabolism. Mice were fed a lipid-poor standard diet and a diet enriched in cholesterol and saturated fat. The results obtained showed that there are no miRNAs whose expression constantly vary with dietary or genetic changes. Furthermore, it appears that diet, more than genotype, impacts on organ-specific miRNA expression profiles.

Targeted demethylation of the SLC5A7 promotor inhibits colorectal cancer progression

Background

SLC5A7 (solute carrier family 5 member 7), also known as choline transporter 1 (CHT1), is downregulated in colorectal cancer (CRC) and functions as a tumor suppressor. However, the mechanisms underlying the inactivation of SLC5A7 in CRC remain to be elucidated.

Results

In the present study, two broad-spectrum demethylation agents (azacitidine and decitabine) employed to treat CRC cells significantly upregulated SLC5A7 expression. Further results based on the CRC cohort and TCGA database indicated that SLC5A7 promoter methylation inversely correlated with SLC5A7 expression, and the status of SLC5A7 promotor methylation showed a promising prognostic value for patients with CRC. Next, the dCas9-multiGCN4/scFv-TET1CD-based precision demethylation system was constructed, which could significantly and specifically promote SLC5A7 expression in CRC cells through sgRNA targeting the SLC5A7 promoter. Both in vitro and in vivo experiments demonstrated that targeted demethylation of SLC5A7 by dCas9-multiGCN4/scFv-TET1CD-sgSLC5A7 inhibited tumor growth by stabilizing p53 and regulating downstream targets.

Conclusions

Collectively, DNA promoter methylation caused inactivation of SLC5A7 in CRC, and targeted demethylation of SLC5A7 might be a therapeutic target for CRC and other cancers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-022-01308-5.

Microbial short-chain fatty acids: a bridge between dietary fibers and poultry gut health

The maintenance of poultry gut health is complex depending on the intricate balance among diet, the commensal microbiota, and the mucosa, including the gut epithelium and the superimposing mucus layer. Changes in microflora composition and abundance can confer beneficial or detrimental effects on fowl. Antibiotics have devastating impacts on altering the landscape of gut microbiota, which further leads to antibiotic resistance or spread the pathogenic populations. By eliciting the landscape of gut microbiota, strategies should be made to break down the regulatory signals of pathogenic bacteria. The optional strategy of conferring dietary fibers (DFs) can be used to counterbalance the gut microbiota. DFs are the non-starch carbohydrates indigestible by host endogenous enzymes but can be fermented by symbiotic microbiota to produce short-chain fatty acids (SCFAs). This is one of the primary modes through which the gut microbiota interacts and communicate with the host. The majority of SCFAs are produced in the large intestine (particularly in the caecum), where they are taken up by the enterocytes or transported through portal vein circulation into the bloodstream. Recent shreds of evidence have elucidated that SCFAs affect the gut and modulate the tissues and organs either by activating G-protein-coupled receptors or affecting epigenetic modifications in the genome through inducing histone acetylase activities and inhibiting histone deacetylases. Thus, in this way, SCFAs vastly influence poultry health by promoting energy regulation, mucosal integrity, immune homeostasis, and immune maturation. In this review article, we will focus on DFs, which directly interact with gut microbes and lead to the production of SCFAs. Further, we will discuss the current molecular mechanisms of how SCFAs are generated, transported, and modulated the pro-and anti-inflammatory immune responses against pathogens and host physiology and gut health.

Choline-induced SLC5A7 impairs colorectal cancer growth by stabilizing p53 protein

The members of the solute carrier (SLC) superfamily are vital membrane transporters in human cells. In the present study, we determine the expression and function of SLC5 family members in colorectal cancer (CRC). Expression analysis based on The Cancer Genome Atlas database and potential clinical relation analysis based on the Oncomine database indicate that SLC5A7 is downregulated and is predicted to correlate with the staging, and prognosis response of CRC. Additional results demonstrate that SLC5A7 is downregulated and correlates with good prognosis in patients with CRC. Ectopic expression of SLC5A7 either by overexpression, or uptake of choline efficiently inhibits CRC growth. Examination of the molecular mechanism reveals that SLC5A7 promotes p53 protein expression by directly interacting with and modifying p53 and disrupting the interaction between p53 and MDM2 in wild type p53 CRC cells. Our findings establish the clear correlation between SLC5A7 and tumour growth, providing a novel potential therapeutic target for CRC.

Butyrate and the Intestinal Epithelium: Modulation of Proliferation and Inflammation in Homeostasis and Disease

The microbial metabolite butyrate serves as a link between the intestinal microbiome and epithelium. The monocarboxylate transporters MCT1 and SMCT1 are the predominant means of butyrate transport from the intestinal lumen to epithelial cytoplasm, where the molecule undergoes rapid β-oxidation to generate cellular fuel. However, not all epithelial cells metabolize butyrate equally. Undifferentiated colonocytes, including neoplastic cells and intestinal stem cells at the epithelial crypt base preferentially utilize glucose over butyrate for cellular fuel. This divergent metabolic conditioning is central to the phenomenon known as “butyrate paradox”, in which butyrate induces contradictory effects on epithelial proliferation in undifferentiated and differentiated colonocytes. There is evidence that accumulation of butyrate in epithelial cells results in histone modification and altered transcriptional activation that halts cell cycle progression. This manifests in the apparent protective effect of butyrate against colonic neoplasia. A corollary to this process is butyrate-induced inhibition of intestinal stem cells. Yet, emerging research has illustrated that the evolution of the crypt, along with butyrate-producing bacteria in the intestine, serve to protect crypt base stem cells from butyrate’s anti-proliferative effects. Butyrate also regulates epithelial inflammation and tolerance to antigens, through production of anti-inflammatory cytokines and induction of tolerogenic dendritic cells. The role of butyrate in the pathogenesis and treatment of intestinal neoplasia, inflammatory bowel disease and malabsorptive states is evolving, and holds promise for the potential translation of butyrate’s cellular function into clinical therapies.

The effect of delayed feeding post-hatch on caeca development in broiler chickens

1. Broiler chicks are frequently deprived of food up to 72 h due to uneven hatching rates, management procedures and transportation to farms. Little is known about the effect of delayed feeding due to extended hatching times on the early neonatal development of the caeca. Therefore, the objective of this study was to investigate the developmental changes and effects of a 48-h delay in feed access immediately post-hatch (PH) on the caeca.2. After hatch, birds (Ross 708) were randomly divided into two treatment groups (n = 6 battery pen/treatment). One group (early fed; EF) received feed and water immediately after hatch, while the second group (late fed; LF) had access to water but had delayed access to feed for 48 h. Contents averaging across all regions of the caeca were collected for mRNA expression as well as for histological analysis at -48, 0, 4 h PH and then at 1, 2, 3, 4, 6, 8, 10, 12 and 14 days PH.3. Expression of MCT-1 (a nutrient transporter), Cox7A2 (related to mitochondrial function) IgA, pIgR, and ChIL-8 (immune function) genes was affected by delayed access to feed that was dependent by the time PH. Expression of immune and gut barrier function-related genes (LEAP2 and MUC2, respectively) was increased in LF group. There was no effect of feed delay on expression of genes related to mitochondrial functions in the caeca, although developmental changes were observed (ATP5F1B, Cox4|1). Caecal mucus and muscle thickness were affected by delayed access to feed during caeca development.4. The data suggested a limited effect of delayed feed access PH on the developmental changes in caecal functions. However, the caeca seemed to be relatively resistant to delayed access to feed early PH, with only a few genes affected.

Postbiotics, Metabolic Signaling, and Cancer

Postbiotics are health-promoting microbial metabolites delivered as a functional food or a food supplement. They either directly influence signaling pathways of the body or indirectly manipulate metabolism and the composition of intestinal microflora. Cancer is the second leading cause of death worldwide and even though the prognosis of patients is improving, it is still poor in the substantial part of the cases. The preventable nature of cancer and the importance of a complex multi-level approach in anticancer therapy motivate the search for novel avenues of establishing the anticancer environment in the human body. This review summarizes the principal findings demonstrating the usefulness of both natural and synthetic sources of postbotics in the prevention and therapy of cancer. Specifically, the effects of crude cell-free supernatants, the short-chain fatty acid butyrate, lactic acid, hydrogen sulfide, and β-glucans are described. Contradictory roles of postbiotics in healthy and tumor tissues are highlighted. In conclusion, the application of postbiotics is an efficient complementary strategy to combat cancer.

Critical transporters of methionine and methionine hydroxyl analogue supplements across the intestine: What we know so far and what can be learned to advance animal nutrition

DL-methionine (DL-Met) and its analogue DL-2-hydroxy-4-(methylthio) butanoic acid (DL-methionine hydroxyl analogue or DL-MHA) have been used as nutritional supplements in the diets of farmed raised animals. Knowledge of the intestinal transport mechanisms involved in these products is important for developing dietary strategies. This review provides updated information of the expression, function, and transport kinetics in the intestine of known Met-linked transporters along with putative MHA-linked transporters. As a neutral amino acid (AA), the transport of DL-Met is facilitated by multiple apical sodium-dependent/-independent high-/low-affinity transporters such as ASCT2, B⁰AT1 and rBAT/b^0,+AT. The basolateral transport largely relies on the rate-limiting uniporter LAT4, while the presence of the basolateral antiporter y⁺LAT1 is probably necessary for exchanging intracellular cationic AAs and Met in the blood. In contrast, the intestinal transport kinetics of DL-MHA have been scarcely studied. DL-MHA transport is generally accepted to be mediated simply by the proton-dependent monocarboxylate transporter MCT1. However, in-depth mechanistic studies have indicated that DL-MHA transport is also achieved through apical sodium monocarboxylate transporters (SMCTs). In any case, reliance on either a proton or sodium gradient would thus require energy input for both Met and MHA transport. This expanding knowledge of the specific transporters involved now allows us to assess the effect of dietary ingredients on the expression and function of these transporters. Potentially, the resulting information could be furthered with selective breeding to reduce overall feed costs.

Lactose-Induced Chronic Diarrhea Results From Abnormal Luminal Microbial Fermentation and Disorder of Ion Transport in the Colon

Diarrhea is one of the major abdominal symptoms in lactose-intolerant subjects. The changes in the large intestinal luminal environment and disorder of the epithelial ion transport in lactose-induced diarrhea remain unclear. The present study aimed to investigate the effect of an incremental high-lactose diet (IHLD, 30%/40%/50%) on luminal microbiota, microbiota-derived metabolite concentrations and colonic ion transport. Gut microbiota were analyzed by 16S rRNA amplicon sequencing and the concentration of SCFAs by gas chromatography, galactose, lactose and lactic acid through assay kit; Ussing chamber was performed to detect basal and stimulated ion transport; The expression and location of SCFA transporters, the Na-H exchanger 3(NHE3), cystic fibrosis transporter regulater (CFTR) and NKCC1 in the colon mucosa were analyzed by western and immunostaining. The concentrations of lactose, galactose and lactic acid of the cecal content were markedly increased (P < 0.01) and SCFA concentration was significantly decreased (P < 0.01). This was associated with depletion of the Lachnospiraceae NK4A136 group and Ruminococcaceae UCG-005 and increased relative abundance of Lactobacillus, escherichia-shigella and megamonas in the cecal microbiota. The expression of monocarboxylate transporter 1 was decreased in the colonic mucosa of the IHLD group. Low NHE3 expression and phosphorylation levels, and decreases in delta basal short circuit current after apical Na⁺ removal in the colonic mucosa of the IHLD group contributed to Na⁺ accumulation in the lumen and decrease stimulated Cl^– secretion with low CFTR and NKCC1 expression would compensate for water and electrolyte loss during the diarrhea process. These results indicated that the persistence of the diarrhea state was maintained by abnormal colonic microbiota fermentation leading to high concentrations of lactose, galactose and lactic acid and low SCFAs in the lumen, and decreased Na⁺ absorption with the low NHE3 expression and phosphorylation levels.

Deficiency of Dietary Fiber in Slc5a8-Null Mice Promotes Bacterial Dysbiosis and Alters Colonic Epithelial Transcriptome towards Proinflammatory Milieu

Inflammatory bowel disease (IBD) is characterized by chronic inflammation in the intestinal tract due to disruption of the symbiotic relationship between the host immune system and microbiota. Various factors alter the gut microbiota which lead to dysbiosis; in particular, diet and dietary fibers constitute important determinants. Dietary fiber protects against IBD; bacteria ferment these dietary fibers in colon and generate short-chain fatty acids (SCFAs), which mediate the anti-inflammatory actions of dietary fibers. SLC5A8 is a high-affinity transporter in the apical membrane of colonic epithelium which mediates the entry of SCFAs from the lumen into cells in Na⁺-coupled manner. Due to the unique transport kinetics, the function of the transporter becomes important only under conditions of low dietary fiber intake. Here, we have examined the impact of dietary fiber deficiency on luminal microbial composition and transcriptomic profile in colonic epithelium in wild-type (WT) and Slc5a8-null (KO) mice. We fed WT and KO mice with fiber-containing diet (FC-diet) or fiber-free diet (FF-diet) and analyzed the luminal bacterial composition by sequencing 16S rRNA gene in feces. Interestingly, results showed significant differences in the microbial community depending on dietary fiber content and on the presence or absence of Slc5a8. There were also marked differences in the transcriptomic profile of the colonic epithelium depending on the dietary fiber content and on the presence or absence of Slc5a8. We conclude that absence of fiber in diet in KO mice causes bacterial dysbiosis and alters gene expression in the colon that is conducive for inflammation.

Identification of the multivalent PDZ protein PDZK1 as a binding partner of sodium-coupled monocarboxylate transporter SMCT1 (SLC5A8) and SMCT2 (SLC5A12)

Sodium-coupled monocarboxylate transporters SMCT1 (SLC5A8) and SMCT2 (SLC5A12) mediate the high- and low-affinity transport of lactate in the kidney, but their regulatory mechanism is still unknown. Since these two transporters have the PDZ-motif at their C-terminus, the function of SMCTs may be modulated by a protein-protein interaction. To investigate the binding partner(s) of SMCTs in the kidney, we performed yeast two-hybrid (Y2H) screenings of a human kidney cDNA library with the C-terminus of SMCT1 (SMCT1-CT) and SMCT2 (SMCT2-CT) as bait. PDZK1 was identified as a partner for SMCTs. PDZK1 coexpression in SMCT1-expressing HEK293 cells enhanced their nicotinate transport activity. PDZK1, SMCT1, and URAT1 in vitro assembled into a single tri-molecular complex and their colocalization was confirmed in the renal proximal tubule in vivo by immunohistochemistry. These results indicate that the SMCT1-PDZK1 interaction thus plays an important role in both lactate handling as well as urate reabsorption in the human kidney.

Fatty and hydroxycarboxylic acid receptors: The missing link of immune response and metabolism in cattle

Fatty and hydroxycarboxylic acids are one of the main intermediates of energy metabolism in ruminants and critical in the milk production of cattle. High production demands on a dairy farm can induce nutritional imbalances and metabolism disorders, which have been widely associated with the onset of sterile inflammatory processes and increased susceptibility to infections. The literature suggests that short-chain fatty acids (SCFA), long-chain fatty acids (LCFA) and hydroxycarboxylic acids are relevant modulators of the host innate inflammatory response. For instance, increased SCFA and lactate levels are associated with subacute ruminal acidosis (SARA) and the activation of pro-inflammatory processes mediated by diverse leukocyte and vascular endothelial cells. As such, free LCFA and the ketone body β-hydroxybutyrate are significantly increased in the plasma 1-2 weeks postpartum, coinciding with the time period in which cows are more susceptible to acquiring infectious diseases that the host innate immune system should actively oppose. Today, many of these pro-inflammatory responses can be related to the activation of specific G protein-coupled receptors, including GPR41/FFA3 and GPR43/FFA2 for SCFA; GPR40/FFA1 and GPR120/FFA4 for LCFA, GPR109A/HCA2 for ketone body β-hydroxybutyrate, and GPR81/HCA₁ for lactate, all expressed in different bovine tissues. The activation of these receptors modulates the release of intracellular granules [e.g., metalloproteinase-9 (MMP-9) and lactoferrin], radical oxygen species (ROS) production, chemotaxis, and the production of relevant pro-inflammatory mediators. The article aimed to review the role of natural ligands and receptors and the resulting impact on the host innate immune reaction of cattle and, further, to address the most recent evidence supporting a potential connection to metabolic disorders.

Circulating tumor cells in thyroid carcinoma - the prognostic role of this biomarker. Review of the literature

Thyroid cancer is a disease with a good prognosis and high survival rates, but having a marked growth of incidence all over the world in the last years. This fact requires special attention of researchers for understanding the behavior of this disease and to establish a correct therapy. Analysis of circulating tumor cells in patients with different malignancies is nowadays a new and exciting research tool, which can improve the diagnosis and prevent the metastatic disease. In the case of thyroid carcinoma there are few studies which explore these biomarkers and investigate the prognostic significance of circulating tumor cells. With this review we seek to emphasize the role of these cells to better understand the mechanisms of invasion or metastasis and to establish a new research base to treat aggressive forms of this type of cancer. Most of the included studies demonstrate the efficacy of these markers for diagnosis and follow up.

Helicobacter pylori Infection Is Associated with Decreased Expression of SLC5A8, a Cancer Suppressor Gene, in Young Children

Background:Helicobacter pylori infects half of the world's population and causes gastric cancer in a subset of infected adults. Previous blood microarray findings showed that apparently healthy children, persistently infected with H. pylori have differential gene expression compared to age-matched, non-infected children. SLC5A8, a cancer suppressor gene with decreased expression among infected children, was chosen for further study based on bioinformatics analysis. Methods: A pilot study was conducted using specific qRT-PCR amplification of SLC5A8 in blood samples from H. pylori infected and non-infected children, followed by a larger, blinded, case-control study. We then analyzed gastric tissue from H. pylori infected and non-infected children undergoing endoscopy for clinical purposes. Results: Demographics, clinical findings, and family history were similar between groups. SLC5A8 expression was decreased in infected vs. non-infected children in blood, 0.12 (IQR: 0-0.89) vs. 1.86 (IQR: 0-8.94, P = 0.002), and in gastric tissue, 0.08 (IQR: 0.04-0.15) vs. 1.88 (IQR: 0.55-2.56; P = 0.001). Children who were both stool positive and seropositive for H. pylori had the lowest SLC5A8 expression levels. Conclusions:H. pylori infection is associated with suppression of SCL5A8, a cancer suppressor gene, in both blood and tissue samples from young children. Key Points: Young children, persistently infected with Helicobacter pylori show decreased expression of SLC5A8 mRNA in both blood and tissue samples as compared to non-infected children.

Downregulation of SLC5A8 inhibits hepatocellular carcinoma progression through regulation of Wnt/β-catenin signaling

SLC5A8 has been shown to be associated with a large number of cancer progressions. However, the biological functions of SLC5A8 in hepatocellular carcinoma (HCC) remain largely unclear. Therefore, we performed this research to explore the functions of SLC5A8 in HCC progression. In this study, SLC5A8 protein and mRNA expression were examined by immunohistochemistry and quantitative real-time PCR, respectively, and we found significantly lower expression levels in HCCs than in the corresponding normal liver tissues. Low SLC5A8 expression was significantly correlated with the clinicopathological features of HCC patients. Patients with low SLC5A8 expression have a shorter overall survival time. This interpretation is confirmed by the results obtained from our in vitro experiments; functional assays indicated that overexpression of SLC5A8, by infection with a recombinant plasmid containing SLC5A8, significantly suppressed HCC cell growth, invasion, and migration and induced HCC cell apoptosis. Moreover, the expression levels of beta-catenin, cyclin D1, c-Myc, MMP-2, and FAK detected by western blotting were downregulated in SLC5A8-transfected HCC cells compared with control-transfected cells, indicating that SLC5A8 has a tumor-suppressive function that acts by interfering with Wnt/β-catenin signaling in HCC.

Slc5a8, a Na+-coupled high-affinity transporter for short-chain fatty acids, is a conditional tumour suppressor in colon that protects against colitis and colon cancer under low-fibre dietary conditions

Mammalian colon harbours trillions of bacteria under physiological conditions; this symbiosis is made possible because of a tolerized response from the mucosal immune system. The mechanisms underlying this tolerogenic phenomenon remain poorly understood. In the present study we show that Slc5a8 (solute carrier gene family 5a, member 8), a Na(+)-coupled high-affinity transporter in colon for the bacterial fermentation product butyrate, plays a critical role in this process. Among various immune cells in colon, dendritic cells (DCs) are unique not only in their accessibility to luminal contents but also in their ability to induce tolerogenic phenotype in T-cells. We found that DCs exposed to butyrate express the immunosuppressive enzymes indoleamine 2,3-dioxygenase 1 (IDO1) and aldehyde dehydrogenase 1A2 (Aldh1A2), promote conversion of naive T-cells into immunosuppressive forkhead box P3(+) (FoxP3(+)) Tregs (regulatory T-cells) and suppress conversion of naive T-cells into pro-inflammatory interferon (IFN)-γ-producing cells. Slc5a8-null DCs do not induce IDO1 and Aldh1A2 and do not generate Tregs or suppress IFN-γ-producing T-cells in response to butyrate. We also provide in vivo evidence for an obligatory role for Slc5a8 in suppression of IFN-γ-producing T-cells. Furthermore, Slc5a8 protects against colitis and colon cancer under conditions of low-fibre intake but not when dietary fibre intake is optimal. This agrees with the high-affinity nature of the transporter to mediate butyrate entry into cells. We conclude that Slc5a8 is an obligatory link between dietary fibre and mucosal immune system via the bacterial metabolite butyrate and that this transporter is a conditional tumour suppressor in colon linked to dietary fibre content.

Cell-based screening assay for anti-inflammatory activity of bioactive compounds

Excess dietary intake may induce metabolic inflammation which is associated with insulin resistance and cardiovascular disease. Recent evidence indicates that dietary bioactive compounds may diminish metabolic inflammation. To identify anti-inflammatory bioactives, we developed a screening assay using the human H293-NF-κB-RE-luc2P reporter cell line. Under optimised conditions we determined the anti-inflammatory activity of vegetables and purified bioactives, by monitoring their potency to inhibit TNF-α-induced NF-κB activity, as assessed by sensitive chemiluminescence detection in a 96-well assay format. Minced broccoli seedlings reduced NF-κB activity by 16%, while sulphoraphane, the dominant bioactive in broccoli seedlings, inhibited NF-κB activity with an IC₅₀ of 5.11 μmol/l. Short-chain fatty acids also reduced NF-κB activity in the order butyrate>propionate≫acetate with IC₅₀ of 51, 223, and 1300 μmol/l, respectively. The H293-NF-κB-RE-luc2P reporter cell line is a sensitive tool for rapid high-throughput screening for bioactives with anti-inflammatory activity.

The role of short-chain fatty acids in health and disease

There is now an abundance of evidence to show that short-chain fatty acids (SCFAs) play an important role in the maintenance of health and the development of disease. SCFAs are a subset of fatty acids that are produced by the gut microbiota during the fermentation of partially and nondigestible polysaccharides. The highest levels of SCFAs are found in the proximal colon, where they are used locally by enterocytes or transported across the gut epithelium into the bloodstream. Two major SCFA signaling mechanisms have been identified, inhibition of histone deacetylases (HDACs) and activation of G-protein-coupled receptors (GPCRs). Since HDACs regulate gene expression, inhibition of HDACs has a vast array of downstream consequences. Our understanding of SCFA-mediated inhibition of HDACs is still in its infancy. GPCRs, particularly GPR43, GPR41, and GPR109A, have been identified as receptors for SCFAs. Studies have implicated a major role for these GPCRs in the regulation of metabolism, inflammation, and disease. SCFAs have been shown to alter chemotaxis and phagocytosis; induce reactive oxygen species (ROS); change cell proliferation and function; have anti-inflammatory, antitumorigenic, and antimicrobial effects; and alter gut integrity. These findings highlight the role of SCFAs as a major player in maintenance of gut and immune homeostasis. Given the vast effects of SCFAs, and that their levels are regulated by diet, they provide a new basis to explain the increased prevalence of inflammatory disease in Westernized countries, as highlighted in this chapter.

Circulating cell-free DNA, SLC5A8 and SLC26A4 hypermethylation, BRAF(V600E): A non-invasive tool panel for early detection of thyroid cancer

PURPOSE

In the latest years, high levels of circulating cell-free DNA (cf-DNA) have been found to be associated with cancer diagnosis and progression, and cf-DNA has become a potential candidate as biomarker for tumor detection. cf-DNA has been investigated in plasma or serum of many tumor patients affected by different malignancies, but not yet in thyroid cancer (TC). Furthermore, in TC cells the capability to metabolize iodine is frequently lost. SLC5A8 and SLC26A4 genes are both involved in the iodine metabolism, and SLC5A8 hypermethylation status is associated with the BRAF(V600E) mutation, which is the most frequent genetic event underlying the development of papillary TC. The aim of our study is the development of a new non-invasive tool for the diagnosis and prognosis of TC based on cf-DNA, SLC5A8 and SLC26A4 hypermethylation, and BRAF(V600E) analysis.

METHODS

cf-DNA was measured by quantitative real-time PCR in nine cases of anaplastic thyroid cancer (ATC), 58 medullary thyroid cancers (MTC), five of synchronous medullary and follicular thyroid cancers (SMFC), 23 follicular adenomas (FA), 86 papillary thyroid cancers (PTC). A control group of 19 healthy subjects was taken. Moreover, in the PTC group we analyze the state of hypermethylation of SLC5A8 and SLC26A4, BRAF(V600E) mutation, and their involvement in the loss of function of the thyroid.

RESULTS

cf-DNA showed a high ability to discriminate healthy individuals from cancer patients. cf-DNAALU83 and cf-DNAALU244 values were significantly correlated with the histological type of TC (P-value < 0.0001). A significant increase in the amount of cf-DNAALU83 and cf-DNAALU244 when methylation occurs was observed (P-value = 0.02). A correlation between BRAF(V600E) and cf-DNAALU244/ALU83 was also found (P-value = 0.02).

CONCLUSIONS

According to our experimental results, the panel including cf-DNA, SLC5A8 and SLC26A4 hypermethylation, and BRAF(V600E) analysis appears easy, reproducible, and non-invasive for the diagnosis on TC. Its possible implication in clinical setting remains to be elucidated.

The plasma membrane transporter SLC5A8 suppresses tumour progression through depletion of survivin without involving its transport function

SLC5A8 (solute carrier gene family 5A, member 8) is a sodium-coupled transporter for monocarboxylates. Among its substrates are the HDAC (histone deacetylase) inhibitors butyrate, propionate and pyruvate. Expression of SLC5A8 is silenced in cancers via DNA methylation, and ectopic expression of SLC5A8 in cancer cells induces apoptosis in the presence of its substrates that are HDAC inhibitors. In the present study we show that ectopic expression of SLC5A8 in cancer cells translocates the anti-apoptotic protein survivin to the plasma membrane through protein-protein interaction resulting in depletion of nuclear survivin and also decreases cellular levels of survivin through inhibition of transcription. These SLC5A8-induced changes in the location and levels of survivin result in cell-cycle arrest, disruption of the chromosome passenger complex involved in mitosis, induction of apoptosis and enhancement in chemosensitivity. These effects are seen independently of the transport function of SLC5A8 and histone acetylation status of the cell; in the presence of pyruvate, a SLC5A8 substrate and also an HDAC inhibitor, these effects are amplified. Ectopic expression of SLC5A8 in the breast cancer cell line MB231 inhibits the ability of cells to form colonies in vitro and to form tumours in mouse xenografts in vivo. The suppression of survivin transcription occurs independently of HDAC inhibition, and the underlying mechanism is associated with decreased phosphorylation of STAT3 (signal transducer and activator of transcription 3). The observed effects are specific for survivin with no apparent changes in expression of other inhibitor-of-apoptosis proteins. The present study unravels a novel, hitherto unrecognized, mechanism for the tumour-suppressive role of a plasma membrane transporter independent of its transport function.

Gene silencing of SLC5A8 identified by genome-wide methylation profiling in lung cancer

BACKGROUND

Aberrant DNA hypermethylation has been implicated as a component of an epigenetic mechanism that silences genes in cancers.

METHODS

We performed a genome-wide search to identify differentially methylated loci between 26 tumor and adjacent non-tumor paired tissues from same lung cancer patients using restriction landmark genomic scanning (RLGS) analysis. Among 229 loci which were hypermethylated in lung tumors as compared to adjacent non-tumor tissues, solute carrier family 5, member 8 (SLC5A8) was one of the hypermethylated genes, and known as a tumor suppressor gene which is silenced by epigenetic changes in various tumors. We investigated the significance of DNA methylation in SLC5A8 expression in lung cancer cell lines, and 23 paired tumor and adjacent non-tumor lung tissues by reverse transcription-PCR (RT-PCR), quantitative methylation specific PCR (QMSP) and bisulfite modified DNA sequencing analyses.

RESULTS

Reduced or lost expression of SLC5A8 was observed in 39.1% (9/23) of the tumor tissues as compared with paired adjacent non-tumor tissues. Bisulfite sequencing results of lung cancer cell lines and tissues which did not express SLC5A8 showed a densely methylated promoter region of SLC5A8. SLC5A8 was reactivated by treatment with DNA methyltransferase inhibitor, 5-Aza and/or HDAC inhibitor, trichostatin A (TSA) in lung cancer cell lines, which did not express SLC5A8. Hypermethylation was detected at the promoter region of SLC5A8 in primary lung tumor tissues as compared with adjacent non-tumor tissues (14/23, 60.9%).

CONCLUSION

These results suggest that DNA methylation in the SLC5A8 promoter region may suppress the expression of SLC5A8 in lung tumor.

SLC5A8 nuclear translocation and loss of expression are associated with poor outcome in pancreatic ductal adenocarcinoma

OBJECTIVES

This study aimed to assess the role of SLC5A8 expression in the survival of pancreatic cancer.

METHODS

We determined SLC5A8 expression in pancreatic ductal adenocarcinoma and adjacent non-neoplastic pancreas (NNP) obtained from 110 patients who underwent pancreatectomy. Formalin-fixed paraffin-embedded core sections in a tissue microarray were immunostained using polyclonal anti-SLC5A8 antibody, and a semiquantitative measure of SLC5A8 expression was determined.

RESULTS

SLC5A8 expression was low in 56% (62/110) of pancreatic cancers as compared to NNP that had low expression in only 9% (10/107) of specimens (P < 0.0001). All cells expressing SLC5A8 did so in the cytoplasm, whether they are neoplastic or not. Nuclear expression of SLC5A8 occurred in 38% (42/110) of cancers, but it was uncommon in NNP (7%, 8/107) (P < 0.0001). Kaplan-Meier estimates showed that survival in patients whose cancers had low SLC5A8 expression, and/or nuclear expression, was significantly worse than in patients whose cancers had none of these abnormalities (P = 0.02). For the 88 patients whose cancers had abnormal SLC5A8 expression, median survival was 1.4 years, as compared to 3.9 years in patients whose cancers both expressed high levels of SLC5A8 and lacked nuclear expression.

CONCLUSIONS

SLC5A8 nuclear translocation and loss of expression are associated with poor outcome in pancreatic ductal adenocarcinoma.

DNA methylation in promoter region as biomarkers in prostate cancer

The prostate gland is the most common site of cancer and the second leading cause of cancer death in American men. Recent emerging molecular biological technologies help us to know that epigenetic alterations such as DNA methylation within the regulatory (promoter) regions of genes are associated with transcriptional silencing in cancer. Promoter hypermethylation of critical pathway genes could be potential biomarkers and therapeutic targets for prostate cancer. In this chapter, we updated current information on methylated genes associated with the development and progression of prostate cancer. Over 40 genes have been investigated for methylation in promoter region in prostate cancer. These methylated genes are involved in critical pathways, such as DNA repair, metabolism, and invasion/metastasis. The role of hypermethylated genes in regulation of critical pathways in prostate cancer is discussed. These findings may provide new information of the pathogenesis, the exciting potential to be predictive and to provide personalized treatment of prostate cancer. Indeed, some epigenetic alterations in prostate tumors are being translated into clinical practice for therapeutic use.

Low dose irradiation of thyroid cells reveals a unique transcriptomic and epigenetic signature in RET/PTC-positive cells

The high doses of radiation received in the wake of the Chernobyl incident and the atomic bombing of Hiroshima and Nagasaki have been linked to the increased appearance of thyroid cancer in the children living in the vicinity of the site. However, the data gathered on the effect of low doses of radiation on the thyroid remain limited. We have examined the genome wide transcriptional response of a culture of TPC-1 human cell line of papillary thyroid carcinoma origin with a RET/PTC1 translocation to various doses (0.0625, 0.5, and 4Gy) of X-rays and compared it to response of thyroids with a RET/PTC3 translocation and against wild-type mouse thyroids irradiated with the same doses using Affymetrix microarrays. We have found considerable overlap at a high dose of 4Gy in both RET/PTC-positive systems but no common genes at 62.5mGy. In addition, the response of RET/PTC-positive system at all doses was distinct from the response of wild-type thyroids with both systems signaling down different pathways. Analysis of the response of microRNAs in TPC-1 cells revealed a radiation-responsive signature of microRNAs in addition to dose-responsive microRNAs. Our results point to the fact that a low dose of X-rays seems to have a significant proliferative effect on normal thyroids. This observation should be studied further as opposed to its effect on RET/PTC-positive thyroids which was subtle, anti-proliferative and system-dependent.

Nutrigenetics and nutrigenomics: viewpoints on the current status and applications in nutrition research and practice

Nutrigenetics and nutrigenomics hold much promise for providing better nutritional advice to the public generally, genetic subgroups and individuals. Because nutrigenetics and nutrigenomics require a deep understanding of nutrition, genetics and biochemistry and ever new 'omic' technologies, it is often difficult, even for educated professionals, to appreciate their relevance to the practice of preventive approaches for optimising health, delaying onset of disease and diminishing its severity. This review discusses (i) the basic concepts, technical terms and technology involved in nutrigenetics and nutrigenomics; (ii) how this emerging knowledge can be applied to optimise health, prevent and treat diseases; (iii) how to read, understand and interpret nutrigenetic and nutrigenomic research results, and (iv) how this knowledge may potentially transform nutrition and dietetic practice, and the implications of such a transformation. This is in effect an up-to-date overview of the various aspects of nutrigenetics and nutrigenomics relevant to health practitioners who are seeking a better understanding of this new frontier in nutrition research and its potential application to dietetic practice.

Role of SLC5A8, a plasma membrane transporter and a tumor suppressor, in the antitumor activity of dichloroacetate

There has been growing interest among the public and scientists in dichloroacetate as a potential anticancer drug. Credible evidence exists for the antitumor activity of this compound, but high concentrations are needed for significant therapeutic effect. Unfortunately, these high concentrations produce detrimental side effects involving nervous system, thereby precluding its use for cancer treatment. The mechanistic basis of the compound’s antitumor activity is its ability to activate pyruvate dehydrogenase complex through inhibition of pyruvate dehydrogenase kinase. Since the compound inhibits the kinase at micromolar concentrations, it is not known why therapeutically prohibitive high doses are needed for suppression of tumor growth. We hypothesized that lack of effective mechanisms for the entry of dichloroacetate into tumor cells may underlie this phenomenon. Here we show that SLC5A8 transports dichloroacetate very effectively with high affinity. This transporter is expressed in normal cells, but the expression is silenced in tumor cells via epigenetic mechanisms. The lack of the transporter makes tumor cells resistant to the antitumor activity of dichloroacetate. However, if the transporter is expressed in tumor cells ectopically, the cells become sensitive to the drug at low concentrations. This is evident in breast cancer cells, colon cancer cells, and prostate cancer cells. Normal cells, which constitutively express the transporter, are however not affected by the compound, indicating the tumor cell-selective therapeutic activity. The mechanism of the antitumor activity of the compound is still its ability to inhibit pyruvate dehydrogenase kinase and force mitochondrial oxidation of pyruvate. Since the silencing of SLC5A8 in tumors involves DNA methylation and its expression can be induced by treatment with DNA methylation inhibitors, our findings suggest that combining dichloroacetate with a DNA methylation inhibitor would offer a means to reduce the doses of dichloroacetate to avoid detrimental effects associated with high doses but without compromising antitumor activity.

The probiotic Lactobacillus plantarum counteracts TNF-{alpha}-induced downregulation of SMCT1 expression and function

The major short-chain fatty acid (SCFA) butyrate is produced in the colonic lumen by bacterial fermentation of dietary fiber. Butyrate serves as primary fuel for the colonocytes and also ameliorates mucosal inflammation. Disturbed energy homeostasis seen in inflamed mucosa of inflammatory bowel disease patients has been attributed to impaired absorption of butyrate. Since sodium-coupled monocarboxylate transporter 1 (SMCT1, SLC5A8) has recently been shown to play a role in Na(+)-coupled transport of monocarboxylates, including SCFA, such as luminal butyrate, we examined the effects of proinflammatory TNF-α on SMCT1 expression and function and potential anti-inflammatory role of probiotic Lactobacillus species in counteracting the TNF-α effects. Rat intestinal epithelial cell (IEC)-6 or human intestinal Caco-2 cells were treated with TNF-α in the presence or absence of Lactobacilli culture supernatants (CS). TNF-α treatments for 24 h dose-dependently inhibited SMCT1-mediated, Na(+)-dependent butyrate uptake and SMCT1 mRNA expression in IEC-6 cells and SMCT1 promoter activity in Caco-2 cells. CS of L. plantarum (LP) stimulated Na(+)-dependent butyrate uptake (2.5-fold, P < 0.05), SMCT1 mRNA expression, and promoter activity. Furthermore, preincubating the cells with LP-CS followed by coincubation with TNF-α significantly attenuated the inhibitory effects of TNF-α on SMCT1 function, expression, and promoter activity. In vivo, oral administration of live LP enhanced SMCT1 mRNA expression in the colonic and ileal tissues of C57BL/6 mice after 24 h. Efficacy of LP or their secreted soluble factors to stimulate SMCT1 expression and function and to counteract the inhibitory effects of TNF-α on butyrate absorption could have potential therapeutic value.

Deletion mapping of chromosome region 12q13-24 in colorectal cancer

Colorectal cancer is one of the most common cancers in the world. Colorectal cancer develops after a long and multistep process of carcinogenesis. Inactivation of tumor suppressor genes is among the most important steps in development of colorectal cancer. Analysis of loss of heterozygosity (LOH) is an effective method to determine the localization of tumor suppressor genes. In this study, we used five microsatellite markers to analyze the region 12q13-24 among 47 patients with colorectal cancer. The frequency of LOH and the clinicopathological data were compared using logistic regression and a chi-square test. In 34 of 47 tumor tissues (72%), LOH was detected at least in one marker. The highest LOH frequency was 34%, on the D12S129 locus; the lowest frequency was 23%, on the D12S78 locus. Loss of heterozygosity was detected as 32% on D12S83, 30% on D12S346, and 26% on D12S1660. No statistically significant correlation was found between the frequency of LOH and clinicopathological features (P > 0.05). Chromosome region 12q13-24 contains several known genes that may be candidate tumor suppressor genes, including RASAL1, ITGA7, STAB2, GLIPR1, and SLC5A8. Although the exact roles of these genes in colorectal cancer formation remain to be clarified, the present data point to a tumor suppressor role.

Butyrate utilization by the colonic mucosa in inflammatory bowel diseases: a transport deficiency

The short-chain fatty acid butyrate, which is mainly produced in the lumen of the large intestine by the fermentation of dietary fibers, plays a major role in the physiology of the colonic mucosa. It is also the major energy source for the colonocyte. Numerous studies have reported that butyrate metabolism is impaired in intestinal inflamed mucosa of patients with inflammatory bowel disease (IBD). The data of butyrate oxidation in normal and inflamed colonic tissues depend on several factors, such as the methodology or the models used or the intensity of inflammation. The putative mechanisms involved in butyrate oxidation impairment may include a defect in beta oxidation, luminal compounds interfering with butyrate metabolism, changes in luminal butyrate concentrations or pH, and a defect in butyrate transport. Recent data show that butyrate deficiency results from the reduction of butyrate uptake by the inflamed mucosa through downregulation of the monocarboxylate transporter MCT1. The concomitant induction of the glucose transporter GLUT1 suggests that inflammation could induce a metabolic switch from butyrate to glucose oxidation. Butyrate transport deficiency is expected to have clinical consequences. Particularly, the reduction of the intracellular availability of butyrate in colonocytes may decrease its protective effects toward cancer in IBD patients.

Colonic gene expression in conventional and germ-free mice with a focus on the butyrate receptor GPR109A and the butyrate transporter SLC5A8

INTRODUCTION

Butyrate is a bacterial fermentation product that produces its beneficial effects on colon through GPR109A, a butyrate receptor, and SLC5A8, a butyrate transporter. In this study, we compared the expression of GPR109A and SLC5A8 between conventional mice and germ-free mice to test the hypothesis that the expression of these two proteins will be decreased in germ-free mice compared to conventional mice because of the absence of bacterial fermentation products and that colonization of germ-free mouse colon with conventional bacteria will reverse these changes.

METHODS

RNA was prepared from the ileum and colon of conventional mice and germ-free mice and used for RT-PCR to determine mRNA levels. Tissue sections were used for immunohistochemical analysis to monitor the expression of GPR109A and SLC5A8 at the protein level. cDNA microarray was used to determine the differential expression of the genes in the colon between conventional mice and germ-free mice.

RESULTS

In conventional mice with normal bacterial colonization of the intestinal tract, GPR109A and SLC5A8 are expressed on the apical membrane of epithelial cells lining the ileum and colon. In germ-free mice, the expression of GPR109A and SLC5A8 is reduced markedly in the ileum and colon. The expression returns to normal levels when the intestinal tract of germ-free mice is colonized with bacteria. The expression of the Na(+)-coupled glucose transporter, SGLT1, follows a similar pattern. Microarray analysis identifies approximately 700 genes whose expression is altered more than twofold in germ-free mice compared to conventional mice. Among these genes are the chloride/bicarbonate exchanger SLC26A3 and the water channel aquaporin 4. The expression of SLC26A3 and AQP4 in ileum and colon is reduced in germ-free mice, but the levels return to normal upon bacterial colonization.

CONCLUSION

Gut bacteria play an active role in the control of gene expression in the host intestinal tract, promoting the expression of the genes that are obligatory for the biological actions of the bacterial fermentation product butyrate and also the genes that are related to electrolyte and water absorption.

Diclofenac-induced stimulation of SMCT1 (SLC5A8) in a heterologous expression system: a RPE specific phenomenon

SMCT1 is a Na(+)-coupled monocarboxylate transporter expressed in a variety of tissues including kidney, thyroid, small intestine, colon, brain, and retina. We found recently that several non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the activity of SMCT1. Here we evaluated the effect of diclofenac, also a NSAID, on SMCT1. SMCT1 cDNA was expressed heterologously in the human retinal pigment epithelial cell lines HRPE and ARPE-19, the human mammary epithelial cell line MCF7, and in Xenopus laevis oocytes. Transport was monitored by substrate uptake and substrate-induced currents. Na(+)-dependent uptake/current was considered as SMCT1 activity. The effect of diclofenac was evaluated for specificity, dose-response, and influence on transport kinetics. To study the specificity of the diclofenac effect, we evaluated the influence of this NSAID on the activity of several other cloned transporters in mammalian cells under identical conditions. In contrast to several NSAIDs that inhibited SMCT1, diclofenac stimulated SMCT1 when expressed in HRPE and ARPE-19 cells. The stimulation was marked, ranging from 2- to 5-fold depending on the concentration of diclofenac. The stimulation was associated with an increase in the maximal velocity of the transport system as well as with an increase in substrate affinity. The observed effect on SMCT1 was selective because the activity of several other cloned transporters, when expressed in HRPE cells and studied under identical conditions, was not affected by diclofenac. Interestingly, the stimulatory effect on SMCT1 observed in HRPE and ARPE-19 cells was not evident in MCF7 cells nor in the X. laevis expression system, indicating that SMCT1 was not the direct target for diclofenac. The RPE-specific effect suggests that the target of diclofenac that mediates the stimulatory effect is expressed in RPE cells but not in MCF7 cells or in X. laevis oocytes. Since SMCT1 is a concentrative transporter for metabolically important compounds such as pyruvate, lactate, beta-hydroxybutyrate, and nicotinate, the stimulation of its activity by diclofenac in RPE cells has biological and clinical significance.

Identification and characterization of the human SLC5A8 gene promoter

The human SLC5A8 gene is a tumor suppressor. Its silencing may contribute to the carcinogenesis and progression of various tumors, which makes this gene an attractive molecular marker and a potential target for diagnosis and therapy. Little is known about transcriptional mechanisms controlling SLC5A8 gene expression. To better understand the molecular mechanisms regulating SLC5A8 expression, we characterized the 5'-regulatory region and a part of exon 1. Luciferase reporter assays of deletion mutants of SLC5A8 promoter demonstrated that a 295-bp region is essential for the basal promoter activity of the SLC5A8 gene. Further analysis indicated that the CCAAT boxes and GC boxes were involved in positive regulation of SLC5A8 promoter. Overexpression of two transcription factors, CCAAT/enhancer binding protein beta (C/EBPbeta) and specific transcription factor 1 (Sp1), upregulated the activities of the human SLC5A8 promoter and protein expression, suggesting that both C/EBPbeta and Sp1 transcription factors might have functions in SLC5A8 transcription. Taken together, our results elucidate the mechanism underlying the regulation of SLC5A8 gene transcription and also define a novel regulatory sequence that may be used to increase expression of the SLC5A8 gene in cancer gene therapy.

Measuring the combinatorial expression of solute transporters and metalloproteinases transcripts in colorectal cancer

Background

It was hypothesised that colorectal cancer (CRC) could be diagnosed in biopsies by measuring the combined expression of a small set of well known genes. Genes were chosen based on their role in either the breakdown of the extracellular matrix or with changes in cellular metabolism both of which are associated with CRC progression

Findings

Gene expression data derived from quantitative real-time PCR for the solute transporter carriers (SLCs) and the invasion-mediating matrix metalloproteinases (MMPs) were examined using a Linear Descriminant Analysis (LDA). The combination of MMP-7 and SLC5A8 was found to be the most predictive of CRC.

Conclusion

A combinatorial analysis technique is an effective method for both furthering our understanding on the molecular basis of some aspects of CRC, as well as for leveraging well defined cancer-related gene sets to identify cancer. In this instance, the combination of MMP-7 and SLC5A8 were optimal for identifying CRC.

A metabolic switch in brain: glucose and lactate metabolism modulation by ascorbic acid

In this review, we discuss a novel function of ascorbic acid in brain energetics. It has been proposed that during glutamatergic synaptic activity neurons preferably consume lactate released from glia. The key to this energetic coupling is the metabolic activation that occurs in astrocytes by glutamate and an increase in extracellular [K(+)]. Neurons are cells well equipped to consume glucose because they express glucose transporters and glycolytic and tricarboxylic acid cycle enzymes. Moreover, neuronal cells express monocarboxylate transporters and lactate dehydrogenase isoenzyme 1, which is inhibited by pyruvate. As glycolysis produces an increase in pyruvate concentration and a decrease in NAD(+)/NADH, lactate and glucose consumption are not viable at the same time. In this context, we discuss ascorbic acid participation as a metabolic switch modulating neuronal metabolism between rest and activation periods. Ascorbic acid is highly concentrated in CNS. Glutamate stimulates ascorbic acid release from astrocytes. Ascorbic acid entry into neurons and within the cell can inhibit glucose consumption and stimulate lactate transport. For this switch to occur, an ascorbic acid flow is necessary between astrocytes and neurons, which is driven by neural activity and is part of vitamin C recycling. Here, we review the role of glucose and lactate as metabolic substrates and the modulation of neuronal metabolism by ascorbic acid.

GPR109A is a G-protein-coupled receptor for the bacterial fermentation product butyrate and functions as a tumor suppressor in colon

Short-chain fatty acids, generated in colon by bacterial fermentation of dietary fiber, protect against colorectal cancer and inflammatory bowel disease. Among these bacterial metabolites, butyrate is biologically most relevant. GPR109A is a G-protein-coupled receptor for nicotinate but recognizes butyrate with low affinity. Millimolar concentrations of butyrate are needed to activate the receptor. Although concentrations of butyrate in colonic lumen are sufficient to activate the receptor maximally, there have been no reports on the expression/function of GPR109A in this tissue. Here we show that GPR109A is expressed in the lumen-facing apical membrane of colonic and intestinal epithelial cells and that the receptor recognizes butyrate as a ligand. The expression of GPR109A is silenced in colon cancer in humans, in a mouse model of intestinal/colon cancer, and in colon cancer cell lines. The tumor-associated silencing of GPR109A involves DNA methylation directly or indirectly. Reexpression of GPR109A in colon cancer cells induces apoptosis, but only in the presence of its ligands butyrate and nicotinate. Butyrate is an inhibitor of histone deacetylases, but apoptosis induced by activation of GPR109A with its ligands in colon cancer cells does not involve inhibition of histone deacetylation. The primary changes in this apoptotic process include down-regulation of Bcl-2, Bcl-xL, and cyclin D1 and up-regulation of death receptor pathway. In addition, GPR109A/butyrate suppresses nuclear factor-kappaB activation in normal and cancer colon cell lines as well as in normal mouse colon. These studies show that GPR109A mediates the tumor-suppressive effects of the bacterial fermentation product butyrate in colon.

Colon cancer cells maintain low levels of pyruvate to avoid cell death caused by inhibition of HDAC1/HDAC3

Human colon cancer cells and primary colon cancer silence the gene coding for LDH (lactate dehydrogenase)-B and up-regulate the gene coding for LDH-A, resulting in effective conversion of pyruvate into lactate. This is associated with markedly reduced levels of pyruvate in cancer cells compared with non-malignant cells. The silencing of LDH-B in cancer cells occurs via DNA methylation, with involvement of the DNMTs (DNA methyltransferases) DNMT1 and DNMT3b. Colon cancer is also associated with the expression of pyruvate kinase M2, a splice variant with low catalytic activity. We have shown recently that pyruvate is an inhibitor of HDACs (histone deacetylases). Here we show that pyruvate is a specific inhibitor of HDAC1 and HDAC3. Lactate has no effect on any of the HDACs examined. Colon cancer cells exhibit increased HDAC activity compared with non-malignant cells. HDAC1 and HDAC3 are up-regulated in colon cancer cells and in primary colon cancer, and siRNA (small interfering RNA)-mediated silencing of HDAC1 and HDAC3 in colon cancer cells induces apoptosis. Colon cancer cells silence SLC5A8, the gene coding for a Na(+)-coupled pyruvate transporter. Heterologous expression of SLC5A8 in the human colon cancer cell line SW480 leads to inhibition of HDAC activity when cultured in the presence of pyruvate. This process is associated with an increase in intracellular levels of pyruvate, increase in the acetylation status of histone H4, and enhanced cell death. These studies show that cancer cells effectively maintain low levels of pyruvate to prevent inhibition of HDAC1/HDAC3 and thereby to evade cell death.

Modulation of butyrate transport in Caco-2 cells

The aim of this study was to investigate the putative influence of some pharmacological agents and drugs of abuse upon the apical uptake of butyrate (BT) into Caco-2 cells. The apical uptake of (14)C-BT by Caco-2 cells was (1) time and concentration dependent, (2) pH dependent, (3) Na(+) independent and Cl(-) dependent, (4) energy dependent, (5) inhibited by several BT structural analogues (acetate, propionate, alpha-ketobutyrate, pyruvate, lactate), (6) insensitive to the anion exchange inhibitors DIDS and SITS and (7) inhibited by the monocarboxylate transport (MCT) inhibitors NPPB and pCMB. These characteristics are compatible with an involvement of MCT1-mediated transport. Acutely, uptake of a low concentration of (14)C-BT (10 microM) was reduced by acetaldehyde, acetylsalicylic acid, indomethacin, caffeine and theophylline and increased by MDMA. Chronically, uptake was increased by caffeine and decreased by tetrahydrocannabinol and MDMA; reverse transcription quantitative real-time PCR analysis showed that these three compounds decreased the mRNA levels of MCT1. Acutely, acetaldehyde, indomethacin and MDMA reduced the uptake of a high concentration of (14)C-BT (20 mM), and acetylsalicylic acid increased it. Chronically, none of the compounds affected uptake. Acetaldehyde, indomethacin and propionate seem to be competitive inhibitors of (14)C-BT uptake. Acetylsalicylic acid simultaneously increased the K (m) and the V (max) of (14)C-BT uptake. In conclusion, MCT1-mediated transport of (14)C-BT in Caco-2 cells is modulated by either acute or chronic exposure to some pharmacological agents and drugs of abuse (acetaldehyde, acetylsalicylic acid, indomethacin, caffeine, theophylline and the drugs of abuse tetrahydrocannabinol and MDMA).

Nutrient transporters in cancer: relevance to Warburg hypothesis and beyond

Tumor cells have an increased demand for nutrients; this demand is met by increased availability of nutrients through vasculogenesis and by enhanced cellular entry of nutrients through upregulation of specific transporters. This review focuses on three groups of nutrient transporters relevant to cancer: glucose transporters, lactate transporters, and amino acid transporters. Tumor cells enhance glucose uptake via induction of GLUT1 and SGLT1, and coordinate the increased entry of glucose with increased glycolysis. Since enhanced glycolysis in cancer is associated with lactate production, tumor cells must find a way to eliminate lactic acid to prevent cellular acidification. This is achieved by the upregulation of MCT4, a H+-coupled lactate transporter. In addition, the Na+-coupled lactate transporter SMCT1 is silenced in cancer. SMCT1 also transports butyrate and pyruvate, which are inhibitors of histone deacetylases. The silencing of SMCT1 occurs in cancers of a variety of tissues. Re-expression of SMCT1 in cancer cell lines leads to growth arrest and apoptosis in the presence of butyrate or pyruvate, suggesting that the transporter may function as a tumor suppressor. Tumor cells meet their amino acid demands by inducing xCT/4F2hc, LAT1/4F2hc, ASCT2, and ATB0,+. xCT/4F2hc is related primarily to glutathione status, protection against oxidative stress, and cell cycle progression, whereas the other three transporters are related to amino acid nutrition. Pharmacologic blockade of LAT1/4F2hc, xCT/4F2hc, or ATB0,+ leads to inhibition of cancer cell growth. Since tumor cells selectively regulate these nutrient transporters to support their rapid growth, these transporters have potential as drug targets for cancer therapy.

Sodium-coupled transport of the short chain fatty acid butyrate by SLC5A8 and its relevance to colon cancer

INTRODUCTION

SLC5A8, expressed predominantly in the colon, is a Na(+)-coupled transporter for short-chain fatty acids. In this paper, we report on the characterization of butyrate transport by SLC5A8 and the relevance of SLC5A8-mediated butyrate transport to colon cancer.

RESULTS

SLC5A8 transports butyrate via a Na(+)-dependent electrogenic process. Na(+) activation of the transport process exhibits sigmoidal kinetics, indicating involvement of more than one Na(+) in the activation process. SLC5A8 is silenced in colon cancer in humans, in a mouse model of intestinal/colon cancer, and in colon cancer cell lines. The tumor-associated silencing of SLC5A8 involves DNA methylation by DNA methyltransferase 1. Reexpression of SLC5A8 in colon cancer cells leads to apoptosis but only in the presence of butyrate. SLC5A8-mediated entry of butyrate into cancer cells is associated with inhibition of histone deacetylation. The changes in gene expression in SLC5A8/butyrate-induced apoptosis include upregulation of pro-apoptotic genes and downregulation of anti-apoptotic genes. In addition, the expression of phosphatidylinositol-3-kinase subunits is affected differentially, with downregulation of p85alpha and upregulation of p55alpha and p50alpha.

CONCLUSION

These studies show that SLC5A8 mediates the tumor-suppressive effects of the bacterial fermentation product butyrate in the colon.

DNA hypermethylation and epigenetic silencing of the tumor suppressor gene, SLC5A8, in acute myeloid leukemia with the MLL partial tandem duplication

Posttranslationally modified histones and DNA hypermethylation frequently interplay to deregulate gene expression in cancer. We report that acute myeloid leukemia (AML) with an aberrant histone methyltransferase, the mixed lineage leukemia partial tandem duplication (MLL-PTD), exhibits increased global DNA methylation versus AML with MLL-wildtype (MLL-WT; P = .02). Among the differentially methylated genes, the SLC5A8 tumor suppressor gene (TSG) was more frequently hypermethylated (P = .003). In MLL-PTD(+) cell lines having SLC5A8 promoter hypermethylation, incubation with decitabine activated SLC5A8 expression. Ectopic SLC5A8 expression enhanced histones H3 and H4 acetylation in response to the histone deacetylase inhibitor, valproate, consistent with the encoded protein-SMCT1-short-chain fatty acid transport function. In addition, enhanced cell death was observed in SMCT1-expressing MLL-PTD(+) AML cells treated with valproate. Within the majority of MLL-PTD AML is a mechanism in which DNA hypermethylation silences a TSG that, together with MLL-PTD, can contribute further to aberrant chromatin remodeling and altered gene expression.