Colonic ketogenesis, a microbiota-regulated process, contributes to blood ketones and protects against colitis in mice

Ketogenesis is considered to occur primarily in liver to generate ketones as an alternative energy source for non-hepatic tissues when glucose availability/utilization is impaired. 3-Hydroxy-3-methylglutaryl-CoA synthase-2 (HMGCS2) mediates the rate-limiting step in this mitochondrial pathway. Publicly available databases show marked down-regulation of HMGCS2 in colonic tissues in Crohn's disease and ulcerative colitis. This led us to investigate the expression and function of this pathway in colon and its relevance to colonic inflammation in mice. Hmgcs2 is expressed in cecum and colon. As global deletion of Hmgcs2 showed significant postnatal mortality, we used a conditional knockout mouse with enzyme deletion restricted to intestinal tract. These mice had no postnatal mortality. Fasting blood ketones were lower in these mice, indicating contribution of colonic ketogenesis to circulating ketones. There was also evidence of gut barrier breakdown and increased susceptibility to experimental colitis with associated elevated levels of IL-6, IL-1β, and TNF-α in circulation. Interestingly, many of these phenomena were mostly evident in male mice. Hmgcs2 expression in colon is controlled by colonic microbiota as evidenced from decreased expression in germ-free mice and antibiotic-treated conventional mice and from increased expression in a human colonic epithelial cell line upon treatment with aqueous extracts of cecal contents. Transcriptomic analysis of colonic epithelia from control mice and Hmgcs2-null mice indicated an essential role for colonic ketogenesis in the maintenance of optimal mitochondrial function, cholesterol homeostasis, and cell-cell tight-junction organization. These findings demonstrate a sex-dependent obligatory role for ketogenesis in protection against colonic inflammation in mice.

Metabolic Signature of Warburg Effect in Cancer: An Effective and Obligatory Interplay between Nutrient Transporters and Catabolic/Anabolic Pathways to Promote Tumor Growth

Aerobic glycolysis in cancer cells, originally observed by Warburg 100 years ago, which involves the production of lactate as the end product of glucose breakdown even in the presence of adequate oxygen, is the foundation for the current interest in the cancer-cell-specific reprograming of metabolic pathways. The renewed interest in cancer cell metabolism has now gone well beyond the original Warburg effect related to glycolysis to other metabolic pathways that include amino acid metabolism, one-carbon metabolism, the pentose phosphate pathway, nucleotide synthesis, antioxidant machinery, etc. Since glucose and amino acids constitute the primary nutrients that fuel the altered metabolic pathways in cancer cells, the transporters that mediate the transfer of these nutrients and their metabolites not only across the plasma membrane but also across the mitochondrial and lysosomal membranes have become an integral component of the expansion of the Warburg effect. In this review, we focus on the interplay between these transporters and metabolic pathways that facilitates metabolic reprogramming, which has become a hallmark of cancer cells. The beneficial outcome of this recent understanding of the unique metabolic signature surrounding the Warburg effect is the identification of novel drug targets for the development of a new generation of therapeutics to treat cancer.

Sigma Receptors: Novel Regulators of Iron/Heme Homeostasis and Ferroptosis

Sigma receptors are non-opiate/non-phencyclidine receptors that bind progesterone and/or heme and also several unrelated xenobiotics/chemicals. They reside in the plasma membrane and in the membranes of the endoplasmic reticulum, mitochondria, and nucleus. Until recently, the biology/pharmacology of these proteins focused primarily on their role in neuronal functions in the brain/retina. However, there have been recent developments in the field with the discovery of unexpected roles for these proteins in iron/heme homeostasis. Sigma receptor 1 (S1R) regulates the oxidative stress-related transcription factor NRF2 and protects against ferroptosis, an iron-induced cell death process. Sigma receptor 2 (S2R), which is structurally unrelated to S1R, complexes with progesterone receptor membrane components PGRMC1 and PGRMC2. S2R, PGRMC1, and PGRMC2, either independently or as protein-protein complexes, elicit a multitude of effects with a profound influence on iron/heme homeostasis. This includes the regulation of the secretion of the iron-regulatory hormone hepcidin, the modulation of the activity of mitochondrial ferrochelatase, which catalyzes iron incorporation into protoporphyrin IX to form heme, chaperoning heme to specific hemoproteins thereby influencing their biological activity and stability, and protection against ferroptosis. Consequently, S1R, S2R, PGRMC1, and PGRMC2 potentiate disease progression in hemochromatosis and cancer. These new discoveries usher this intriguing group of non-traditional progesterone receptors into an unchartered territory in biology and medicine.

Abstract 3699: Involvement of p53 and KRAS in the regulation of SLC38A5 in colon cancer

Cancer-associated upregulation has been demonstrated for selective glucose transporters and amino acid transporters. The amino acid transporter SN2 (SLC38A5) represents the latest addition to this list. Transcriptomic analysis of tumor tissues has shown SLC38A5 is upregulated in breast and colon cancer. SLC38A5 is an amino acid-dependent Na+/H+ exchanger, induced in cancer, which not only supplies amino acids to cancer cells but also maintains an alkaline intracellular pH. The substrates for SLC38A5 include glutamine, asparagine, histidine, methionine, glycine, and serine, highlighting the role of SLC38A5 in glutamine addiction and one-carbon metabolism, both pathways being essential for cancer cells. In addition, SLC38A5 activates macropinocytosis, a process involved in cellular uptake of proteins in the extracellular fluid to meet amino acid demands in cancer cells. Since the transporter is upregulated in colon cancer, we hypothesized that the multiple functions of SLC38A5 fuel the growth, proliferation, and survival in colon cancer cells and that its induction involves oncogenic mutations in p53 and KRAS that are common mediators of carcinogenesis in colon. Firstly, we used a panel of colon cancer cells and analyzed SLC38A5 expression and its functional characteristics. Next, we compared SLC38A5 expression and function between two isogenic cell lines: SW48 with and without the oncogenic mutation (G12D) in KRAS and HCT116 with and without the tumor suppressor p53. Among the colon cancer cells examined, KM12L4 showed highest expression of SLC38A5; therefore, we characterized the function of the transporter in detail in this cell line. Our studies showed that KM12L4 cells were able to take up serine, one of the substrates for SLC38A5, in a Na+-dependent manner in the presence of 5 mM tryptophan, which is not a substrate for SLC38A5 but is known to block LAT1 transporter, which also transports serine. SLC38A5 exhibited an active serine-uptake when Na+ was replaced with Li+ at a higher pH. Li+ tolerance and a higher activity at an alkaline pH are two unique features of SLC38A5. The oncogenic mutation G12D in KRAS increased SLC38A5 activity in SW48 cells. In contrast, loss of p53 decreased SLC38A5 activity in HCT116 cells. These data demonstrate that SLC38A5 is induced in colon cancer cells and its activity is increased in the presence of oncogenic KRAS mutations and suppressed when p53 is inactivated, thus providing a valuable insight into the molecular mechanisms for the upregulation of the transporter in colon cancer. We conclude that SLC38A5, an amino acids transporter, is upregulated in colon cancer and its functions are uniquely suited to promote cell proliferation and tumor growth. We also conclude that KRAS and p53 functional status play a critical role in the increased SLC38A5 expression and activity in colon cancer. These data suggest that SLC38A5 could be exploited as a drug target for cancer therapy.

Citation Format: Nhi Thi Nguyen, Sathish Sivaprakasam, Vadivel Ganapathy. Involvement of p53 and KRAS in the regulation of SLC38A5 in colon cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3699.

Potent Inhibition of Macropinocytosis by Niclosamide in Cancer Cells: A Novel Mechanism for the Anticancer Efficacy for the Antihelminthic

Niclosamide, a drug used to treat tapeworm infection, possesses anticancer effects by interfering with multiple signaling pathways. Niclosamide also causes intracellular acidification. We have recently discovered that the amino acid transporter SLC38A5, an amino acid-dependent Na+/H+ exchanger, activates macropinocytosis in cancer cells via amino acid-induced intracellular alkalinization. Therefore, we asked whether niclosamide will block basal and SLC38A5-mediated macropinocytosis via intracellular acidification. We monitored macropinocytosis in pancreatic and breast cancer cells using TMR-dextran and the function of SLC38A5 by measuring Li+-stimulated serine uptake. The peptide transporter activity was measured by the uptake of glycylsarcosine. Treatment of the cancer cells with niclosamide caused intracellular acidification. The drug blocked basal and serine-induced macropinocytosis with differential potency, with an EC50 of ~5 μM for the former and ~0.4 μM for the latter. The increased potency for amino acid-mediated macropinocytosis is due to direct inhibition of SLC38A5 by niclosamide in addition to the ability of the drug to cause intracellular acidification. The drug also inhibited the activity of the H+-coupled peptide transporter. We conclude that niclosamide induces nutrient starvation in cancer cells by blocking macropinocytosis, SLC38A5 and the peptide transporter. These studies uncover novel, hitherto unknown, mechanisms for the anticancer efficacy of this antihelminthic.

Binding of Citrate-Fe3+ to Plastic Culture Dishes, an Artefact Useful as a Simple Technique to Screen for New Iron Chelators

NaCT mediates citrate uptake in the liver cell line HepG2. When these cells were exposed to iron (Fe³⁺), citrate uptake/binding as monitored by the association of [¹⁴C]-citrate with cells increased. However, there was no change in NaCT expression and function, indicating that NaCT was not responsible for this Fe³⁺-induced citrate uptake/binding. Interestingly however, the process exhibited substrate selectivity and saturability as if the process was mediated by a transporter. Notwithstanding these features, subsequent studies demonstrated that the iron-induced citrate uptake/binding did not involve citrate entry into cells; instead, the increase was due to the formation of citrate-Fe³⁺ chelate that adsorbed to the cell surface. Surprisingly, the same phenomenon was observed in culture wells without HepG2 cells, indicating the adsorption of the citrate-Fe³⁺ chelate to the plastic surface of culture wells. We used this interesting phenomenon as a simple screening technique for new iron chelators with the logic that if another iron chelator is present in the assay system, it would compete with citrate for binding to Fe³⁺ and prevent the formation and adsorption of citrate-Fe³⁺ to the culture well. This technique was validated with the known iron chelators deferiprone and deferoxamine, and with the bacterial siderophore 2,3-dihydroxybenzoic acid and the catechol carbidopa.

Unconventional Functions of Amino Acid Transporters: Role in Macropinocytosis (SLC38A5/SLC38A3) and Diet-Induced Obesity/Metabolic Syndrome (SLC6A19/SLC6A14/SLC6A6)

Amino acid transporters are expressed in mammalian cells not only in the plasma membrane but also in intracellular membranes. The conventional function of these transporters is to transfer their amino acid substrates across the lipid bilayer; the direction of the transfer is dictated by the combined gradients for the amino acid substrates and the co-transported ions (Na⁺, H⁺, K⁺ or Cl⁻) across the membrane. In cases of electrogenic transporters, the membrane potential also contributes to the direction of the amino acid transfer. In addition to this expected traditional function, several unconventional functions are known for some of these amino acid transporters. This includes their role in intracellular signaling, regulation of acid–base balance, and entry of viruses into cells. Such functions expand the biological roles of these transporters beyond the logical amino acid homeostasis. In recent years, two additional unconventional biochemical/metabolic processes regulated by certain amino acid transporters have come to be recognized: macropinocytosis and obesity. This adds to the repertoire of biological processes that are controlled and regulated by amino acid transporters in health and disease. In the present review, we highlight the unusual involvement of selective amino acid transporters in macropinocytosis (SLC38A5/SLC38A3) and diet-induced obesity/metabolic syndrome (SLC6A19/SLC6A14/SLC6A6).

Drosophila INDY and Mammalian INDY: Major Differences in Transport Mechanism and Structural Features despite Mostly Similar Biological Functions

INDY (I’m Not Dead Yet) is a plasma membrane transporter for citrate, first identified in Drosophila. Partial deficiency of INDY extends lifespan in this organism in a manner similar to that of caloric restriction. The mammalian counterpart (NaCT/SLC13A5) also transports citrate. In mice, it is the total, not partial, absence of the transporter that leads to a metabolic phenotype similar to that caloric restriction; however, there is evidence for subtle neurological dysfunction. Loss-of-function mutations in SLC13A5 (solute carrier gene family 13, member A5) occur in humans, causing a recessive disease, with severe clinical symptoms manifested by neonatal seizures and marked disruption in neurological development. Though both Drosophila INDY and mammalian INDY transport citrate, the translocation mechanism differs, the former being a dicarboxylate exchanger for the influx of citrate²⁻ in exchange for other dicarboxylates, and the latter being a Na⁺-coupled uniporter for citrate²⁻. Their structures also differ as evident from only ~35% identity in amino acid sequence and from theoretically modeled 3D structures. The varied biological consequences of INDY deficiency across species, with the beneficial effects predominating in lower organisms and detrimental effects overwhelming in higher organisms, are probably reflective of species-specific differences in tissue expression and also in relative contribution of extracellular citrate to metabolic pathways in different tissues

Modulational instability and soliton generation in chiral Bose-Einstein condensates with zero-energy nonlinearity

By means of analytical and numerical methods, we address the modulational instability (MI) in chiral condensates governed by the Gross-Pitaevskii equation including the current nonlinearity. The analysis shows that this nonlinearity partly suppresses the MI driven by the cubic self-focusing, although the current nonlinearity is not represented in the system's energy (although it modifies the momentum), hence it may be considered as zero-energy nonlinearity. Direct simulations demonstrate generation of trains of stochastically interacting chiral solitons by MI. In the ring-shaped setup, the MI creates a single traveling solitary wave. The sign of the current nonlinearity determines the direction of propagation of the emerging solitons.

SLC6A14 deficiency is linked to obesity, fatty liver, and metabolic syndrome but only under conditions of a high-fat diet

SLC6A14 is a Na⁺/Cl^--coupled transporter for neutral/cationic amino acids, expressed in ileum and colon. A single-nucleotide polymorphism (SNP), rs2011162 (-22,510C > G), in SLC6A14 coding for the 3'-untranslated region (3'-UTR) is associated with obesity in humans. But the impact of this polymorphism on the transporter expression and its connection to obesity are not known. Our objective was to address these issues. The impact of rs2011162 (-22,510C > G) on SLC6A14 expression was monitored using a luciferase reporter. The link between Slc6a14 and obesity was investigated in wild type and Slc6a14^-/- mice when fed a normal diet or a high-fat diet. The obesity-associated 3'-UTR polymorphism reduced SLC6A14 expression. With a high-fat diet, Slc6a14^-/- mice gained more weight than wild type mice. With normal diet, there was no difference between the two genotypes. The gain in body weight with the high-fat diet in Slc6a14^-/- mice was accompanied with metabolic syndrome. With the high-fat diet, Slc6a14^-/- mice showed increased food intake, developed fatty liver, and altered plasma amino acid profile. The high-fat diet-associated hepatic steatosis in Slc6a14^-/- mice showed male preponderance. We conclude that the 3'-UTR SNP in SLC6A14 associated with obesity decreases the expression of SLC6A14 and that the deficiency of SLC6A14 is linked to obesity. This is supported by the findings that Slc6a14^-/- mice develop obesity, fatty liver, and metabolic syndrome. This connection is evident only with a high-fat diet. Therefore, dietary/pharmacologic interventions that induce SLC6A14 expression in the intestinal tract might have potential for obesity prevention.¹.

Hereditary hemochromatosis disrupts uric acid homeostasis and causes hyperuricemia via altered expression/activity of xanthine oxidase and ABCG2

Hereditary hemochromatosis (HH) is mostly caused by mutations in the iron-regulatory gene HFE. The disease is associated with iron overload, resulting in liver cirrhosis/cancer, cardiomegaly, kidney dysfunction, diabetes, and arthritis. Fe2+-induced oxidative damage is suspected in the etiology of these symptoms. Here we examined, using Hfe-/- mice, whether disruption of uric acid (UA) homeostasis plays any role in HH-associated arthritis. We detected elevated levels of UA in serum and intestine in Hfe-/- mice compared with controls. Though the expression of xanthine oxidase, which generates UA, was not different in liver and intestine between wild type and Hfe-/- mice, the enzymatic activity was higher in Hfe-/- mice. We then examined various transporters involved in UA absorption/excretion. Glut9 expression did not change; however, there was an increase in Mrp4 and a decrease in Abcg2 in Hfe-/- mice. As ABCG2 mediates intestinal excretion of UA and mutations in ABCG2 cause hyperuricemia, we examined the potential connection between iron and ABCG2. We found p53-responsive elements in hABCG2 promoter and confirmed with chromatin immunoprecipitation that p53 binds to this promoter. p53 protein was reduced in Hfe-/- mouse intestine. p53 is a heme-binding protein and p53-heme complex is subjected to proteasomal degradation. We conclude that iron/heme overload in HH increases xanthine oxidase activity and also promotes p53 degradation resulting in decreased ABCG2 expression. As a result, systemic UA production is increased and intestinal excretion of UA via ABCG2 is decreased, causing serum and tissue accumulation of UA, a potential factor in the etiology of HH-associated arthritis.

Chronic exposure to excess iron promotes EMT and cancer via p53 loss in pancreatic cancer

Based on the evidence that hemochromatosis, an iron-overload disease, drives hepatocellular carcinoma, we hypothesized that chronic exposure to excess iron, either due to genetic or environmental causes, predisposes an individual to cancer. Using pancreatic cancer as our primary focus, we employed cell culture studies to interrogate the connection between excess iron and cancer, and combined in vitro and in vivo studies to explore the connection further. Ferric ammonium citrate was used as an exogenous iron source. Chronic exposure to excess iron induced epithelial-mesenchymal transition (EMT) in normal and cancer cell lines, loss of p53, and suppression of p53 transcriptional activity evidenced from decreased expression of p53 target genes (p21, cyclin D1, Bax, SLC7A11). To further extrapolate our cell culture data, we generated EL-Kras^G12D (EL-Kras) mouse (pancreatic neoplastic mouse model) expressing Hfe^+/+and Hfe^−/− genetic background. p53 target gene expression decreased in EL-Kras/Hfe^−/− mouse pancreas compared to EL-Kras/Hfe^+/+ mouse pancreas. Interestingly, the incidence of acinar-to-ductal metaplasia and cystic pancreatic neoplasms (CPN) decreased in EL-Kras/Hfe^−/− mice, but the CPNs that did develop were larger in these mice than in EL-Kras/Hfe^+/+ mice. In conclusion, these in vitro and in vivo studies support a potential role for chronic exposure to excess iron as a promoter of more aggressive disease via p53 loss and SLC7A11 upregulation within pancreatic epithelial cells.

The lactate receptor GPR81 promotes breast cancer growth via a paracrine mechanism involving antigen-presenting cells in the tumor microenvironment

GPR81 is a G-protein-coupled receptor for lactate, which is upregulated in breast cancer and plays an autocrine role to promote tumor growth by tumor cell-derived lactate. Here we asked whether lactate has any paracrine role via activation of GPR81 in cells present in tumor microenvironment to help tumor growth. First, we showed that deletion of Gpr81 suppresses breast cancer growth in a constitutive breast cancer mouse model (MMTV-PyMT-Tg). We then used a syngeneic transplant model by monitoring tumor growth from a mouse breast cancer cell line (AT-3, Gpr81-negative) implanted in mammary fat pad of wild-type mice and Gpr81-null mice. Tumor growth was suppressed in Gpr81-null mice compared with wild-type mice. There were more tumor-infiltrating T cells and MHCII^hi-immune cells in tumors from Gpr81-null mice compared with tumors from wild-type mice. RNA-seq analysis of tumors indicated involvement of immune cells and antigen presentation in Gpr81-dependent tumor growth. Antigen-presenting dendritic cells expressed Gpr81 and activation of this receptor by lactate suppressed cell-surface presentation of MHCII. Activation of Gpr81 in dendritic cells was associated with decreased cAMP, IL-6 and IL-12. These findings suggest that tumor cell-derived lactate activates GPR81 in dendritic cells and prevents presentation of tumor-specific antigens to other immune cells. This paracrine mechanism is complementary to the recently discovered autocrine mechanism in which lactate induces PD-L1 in tumor cells via activation of GPR81 in tumor cells, thus providing an effective means for tumor cells to evade immune system. As such, blockade of GPR81 signaling could boost cancer immunotherapy.

Abstract 1889: Chronic exposure to excess iron promotes EMT and cancer via p53 loss in pancreatic cancer

Pancreatic cancer especially the pancreatic ductal adenocarcinoma (PDAC) is by far the most lethal of all cancers with a five year survival rate of less than 5%. Gemcitabine is currently used as a first line therapy for locally advanced and metastatic PDAC but with a very low success rate. Hence, there is an urgent need to better understand what actually drives this cancer so as to come up with a better diagnostic and therapeutic strategies. Excess heme and iron are known to be pro-tumorigenic. When present in excess, these molecules become toxic. Fe2+ in free form is a potent oxidant; it catalyzes the Fenton reaction to generate hydroxyl radicals (Fe2++ H2O2 → Fe3+ + HO• + OH-), a potent reactive oxygen species. Free heme is also toxic as it catalyzes free radical reaction and induces oxidative damage. Accumulation of iron and heme to toxic levels occurs in genetic diseases (hemochromatosis, sickle cell disease), pathological conditions (hemolytic anemia, ischemia reperfusion), infections, and clinical/therapeutic conditions (repeated blood transfusion). Excess intake of iron and heme from dietary sources could also lead to iron/heme overload, particularly in the colon. In this regard, red meat with its ~10-fold higher heme content than white meat is specifically relevant. Among these conditions however, hemochromatosis deserves special mention. Based on the evidence that hemochromatosis, an iron-overload disease, drives hepatocellular carcinoma, we hypothesized that chronic exposure to excess iron, either due to genetic or epigenetic causes, predisposes an individual to cancer. We employed cell culture studies to interrogate the connection between excess iron and cancer in multiple tissues and combined in vitro and in vivo studies to explore the connection in pancreas further. Ferric ammonium citrate was used as an exogenous iron source. Chronic exposure to excess iron induced epithelial-mesenchymal transition (EMT) in normal and cancer cell lines, loss of p53, and suppression of p53 transcriptional activity. In order to further extrapolate our cell culture data, we generated EL-KRASG12D or EL-Kras mouse (pancreatic neoplastic mouse model) expressing Hfe+/+ and Hfe-/- genetic background. p53 target gene expression decreased in EL-Kras/Hfe-/- mouse pancreas compared to EL-Kras/Hfe+/+ mouse pancreas. Interestingly, the incidence of acinar-to-ductal metaplasia and cystic pancreatic neoplasms (CPN) decreased in EL-Kras/Hfe-/- mice, but the CPNs that did develop were larger in these mice than in EL-Kras/Hfe+/+ mice. In conclusion, these in vitro and in vivo studies support a potential role for chronic exposure to excess iron as a promoter of more aggressive disease via p53 loss within pancreatic epithelial cells.

Citation Format: Devaraja Rajasekaran, Jiro Ogura, Mitchell Wachtel, Sabarish Ramachandran, Ellappan Babu, Sathish Sivaprakasam, Paul J. Grippo, Carolina Torres, Thangaraju Muthusamy, Jaya P. Gnana-Prakasam, Yangzom D. Bhutia. Chronic exposure to excess iron promotes EMT and cancer via p53 loss in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1889.

Abstract 3585: Amino acid transporter SLC6A14: A novel drug target for colorectal cancer

SLC6A14 is a Na+/Cl− -dependent amino acid transporter capable of transporting 18 of the 20 proteinogenic amino acids, including arginine, leucine (mTOR activators) and glutamine (necessary for nucleotide biosynthesis). This transporter is expressed at basal levels in normal colon but significantly upregulated in colorectal cancer (CRC). However, the relevance of this upregulation to disease progression remains unknown. We postulated that deletion of SLC6A14 or pharmacological blockade of its function would suppress CRC by depleting amino acids and interfering with mTOR signaling selectively in tumor cells. To test this postulate, we first used Slc6a14-null mice. With two different models of spontaneous CRC (Apcmin/- and DSS/AOM), we found the tumor incidence and tumor growth were much lower in mice with Slc6a14-null background than in mice with Slc6a14. To evaluate the impact of pharmacologic blockade of the transporter on tumor growth we used a syngeneic tumor mouse model with MC-38 cells (a mouse CRC cell line); blockade of Slc6a14 with alpha-methyl tryptophan (α-MT) markedly reduced tumor growth. We then determined the transcriptome profiles of colonic epithelial cells and colonic non-epithelial cells from wild type mice and Slc6a14-null mice by RNAseq. There were hundreds of genes that were either upregulated or downregulated in the null mice. Ingenuity pathway analysis (IPA) of these data revealed predictive activation of canonical AMPK signaling pathway in colonic epithelial of Slc6a14-null mice. AMPK has anticancer activities by modulating multiple pathways including negatively regulating mTOR signaling. Moreover, upstream analysis showed predictive inactivation of two important tumor growth and survival signaling pathways ERK and EGF in the colon of the null mice. Likewise, significant upregulation of APC downregulated 1 (APCDD1) in epithelial cells in null mice implies predictive suppression of canonical Wnt signaling pathway. We also found marked differences in fecal microbiota as a result of Slc6a14 deletion. There was an increase in the relative abundance of beneficial microbiota including those capable of generating short chain fatty acids and lactic acid in null mice. We conclude that deletion of Slc6a14 or its pharmacological blockade protects against CRC by inducing amino acid starvation in tumor cells, thereby causing changes in multiple signaling pathways and in colonic microbiome. These studies identify SLC6A14 as a novel drug target for the treatment of colorectal cancer.

Citation Format: Mohd Omar Faruk Sikder, Sathish Sivaprakasam, Vadivel Ganapathy. Amino acid transporter SLC6A14: A novel drug target for colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3585.

Abstract 1479: Bacterial dysbiosis in the mouse model of hemochromatosis: Increased risk of colitis and colitis-associated colon cancer

Hemochromatosis, an inherited iron-overload disease, causes tissue damage due to deposition of iron in toxic levels in most tissues including the liver, heart, kidney, pancreas and colon. Free iron, both in the inorganic form (i.e, non-transferrin-bound and non-ferritin-bound) and organic form (i.e. heme), facilitates Fenton reaction to generate hydroxyl radicals and to induce cellular oxidative damage that is observed in carcinogenesis. The primary site of iron deposition in hemochromatosis patients is liver, and therefore, liver cancer formation in these patients has been studied extensively. However, little is known about the iron-elicited colonic pathologies, mainly colonic inflammation and colon cancer. Here we postulate that iron overload as observed in hemochromatosis disrupts healthy colonic homeostasis and exacerbates the development of colon inflammation and colon cancer. To test our hypothesis, we examined the progression and severity of colitis and colon cancer in Hfe-/- mouse and the wild type control. Hfe-/- mouse is a model for classical hemochromatosis. Besides serum and liver, high concentrations of iron and heme deposits are found in the colon of Hfe-/- mouse. Experimental colitis was induced by administration of Dextran Sodium Sulfate (DSS) in drinking water. Colitis-associated colon cancer was initiated by the intraperitoneal injection of carcinogen, azoxymethane (AOM) and the carcinogenesis was driven by DSS administration. Colonic inflammation was more severe in the Hfe-/- mouse than in control. In addition, hemochromatosis mouse developed more and larger colonic polyps than the control group. We observed that this high susceptibility to colitis and colon cancer in Hfe-/- but not wild type mouse, lies in the differences in strains regarding the bacterial composition and colonic defense machinery. 16S ribosomal RNA sequencing of fecal bacteria revealed that the microbiota composition of Hfe-/- mouse altered to favor the pathogenic bacteria that belong to phyla Proteobacteria and TM7. In addition, the Hfe-/- proinflammatory bacteria adhered to colon and thus increased the colonic bacterial load. This phenomenon, addressed as bacterial dysbiosis, is considered a hallmark of colon inflammation and colon cancer. Furthermore, we observed that the colonic epithelial cells of Hfe-/- mouse had a lower expression of antimicrobial peptides and thus a defective first line defense against the pathogens. Finally, hemochromatosis mouse colon under inflammation released higher concentration of the pro-inflammatory cytokines that contributed to the creation of the hostile colonic environment. In summary, iron overload as seen in hemochromatosis, impairs the colonic defense machinery and it causes bacterial dysbiosis, thus providing the ideal environment for the colitis and colon cancer development.

Citation Format: Bojana Ristic, Sathish Sivaprakasam, Rao Kottapalli, Abdul Hamood, Vadivel Ganapathy. Bacterial dysbiosis in the mouse model of hemochromatosis: Increased risk of colitis and colitis-associated colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1479.

High level extracellular production of recombinant human interferon alpha 2b in glycoengineered Pichia pastoris: culture medium optimization, high cell density cultivation and biological characterization

AIMS

The present study was aimed at design of experiments (DoE)- and artificial intelligence-based culture medium optimization for high level extracellular production of a novel recombinant human interferon alpha 2b (huIFNα2b) in glycoengineered Pichia pastoris and its characterization.

METHODS AND RESULTS

The artificial neural network-genetic algorithm model exhibited improved huIFNα2b production and better predictability compared to response surface methodology. The optimized medium exhibited a fivefold increase in huIFNα2b titre compared to the complex medium. A maximum titre of huIFNα2b (436 mg l^-1 ) was achieved using the optimized medium in the bioreactor. Real-time capacitance data from dielectric spectroscopy were utilized to model the growth kinetics with unstructured models. Biological characterization by antiproliferative assay proved that the purified recombinant huIFNα2b was biologically active, exhibiting growth inhibition on breast cancer cell line.

CONCLUSIONS

Culture medium optimization resulted in enhanced production of huIFNα2b in glycoengineered P. pastoris at both shake flask and bioreactor level. The purified huIFNα2b was found to be N-glycosylated and biologically active.

SIGNIFICANCE AND IMPACT OF THE STUDY

DoE-based medium optimization strategy significantly improved huIFNα2b production. The antiproliferative activity of huIFNα2b substantiates its potential scope for application in cancer therapy.

Abstract 5735: Amino acid transporter SLC6A14: A novel drug target for colorectal cancer and colitis and its transcriptional regulation by TCF4/beta-catenin pathway

Amino Acid Transporter SLC6A14: A Novel Drug Target for Colorectal Cancer & Colitis and Its Transcriptional Regulation by TCF4/β-catenin Pathway

Mohd Omar Faruk Sikder, Sathish Sivaprakasam, Vadivel Ganapathy

Texas Tech University Health Sciences Center

SLC6A14 is a Na+/Cl− -dependent amino acid transporter capable of transporting 18 of the 20 proteinogenic amino acids, including leucine (mTOR activator), glutamine (necessary for nucleotide biosynthesis), and arginine (substrate for iNOS). This transporter is expressed at basal levels in normal colon but significantly upregulated in colorectal cancer (CRC) and colitis. However, the relevance of this upregulation to disease progression and the mechanisms involved in the upregulation remain unknown. We postulated that deletion of SLC6A14 or pharmacological blockade of its function may suppress CRC by depleting amino acids and interfering with mTOR signaling selectively in tumor cells. It may also ameliorate the severity of colitis by diminishing NO synthesis by iNOS in colonic epithelial cells. Since TCF4/β-catenin/Wnt signaling is activated in CRC and colitis, we postulated that TCF4/β-catenin might control the expression of SLC6A14. We tested these hypotheses in the present study. CRC cells treated in vitro with α-methyl tryptophan, a selective blocker of SLC6A14, showed evidence of amino acid deprivation, decreased mTOR activity, and increased autophagy and apoptosis. In nude mouse xenografts with LS174T cells (a CRC cell line), silencing of SLC6A14 by shRNA markedly reduced tumor growth. Accordingly, Slc6a14-/- mice showed reduced tumor incident and tumor size compared to the wild type mice in AOM/DSS-induced colitis-associated colon cancer mouse model. Furthermore, Slc6a14-null mice showed decreased disease progression in an experimental colitis model (Dextran sulfate sodium-induced colitis) compared to wild type mice. In vitro treatment of LS174T cells with calphostin-C, a potent inhibitor of TCF4/β-catenin, dramatically reduced the expression of SLC6A14 mRNA and protein levels, whereas treatment of KM12L4 and KM12C cells with Wnt agonist AMBMP showed the opposite trend. Finally, ChIP assay demonstrated that TCF4/β-catenin complex directly regulates the expression of SLC6A14 in human CRC cells by binding with its promoter. We conclude that the increased β-catenin/Wnt signaling in CRC and colitis is responsible for the upregulation of SLC6A14 under these pathological conditions and that deletion of the transporter or its pharmacological blockade

protects against colitis and CRC. These studies identify SLC6A14 as a novel drug target for the treatment of colonic inflammation and CRC.

Citation Format: Mohd Omar Sikder, Sathish Sivaprakasam, Ganapathy Vadivel. Amino acid transporter SLC6A14: A novel drug target for colorectal cancer and colitis and its transcriptional regulation by TCF4/beta-catenin pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5735.

Abstract 4477: Downregulation of ABCG2 expression in colitis and colon cancer: Relevance to iron overload, hemochromatosis and p53, and therapeutic use of carbidopa to reverse the downregulation

The efflux pump ABCG2 is a part of cellular defense. In intestine it is located at the luminal side, and effluxes exogenous/endogenous dysplasia-promoting agents. Since cancer cells exposed to chemotherapeutics overexpress ABCG2 to remove these drugs, ABCG2 is considered a multidrug-resistance protein. However, its physiologic protective role in cancer initiation/progression has not received much attention. In numerous studies, ABCG2 is present in colon at lower levels in patients with colitis and chemotherapy-naïve colon cancer than in controls. We therefore hypothesized that the physiologic role of ABCG2 is to suppress colonic inflammation and colon cancer. To test this, we monitored Abcg2 expression in the intestinal tract in experimental and genetic mouse models of colon cancer and colitis. In normal mice, Abcg2 was expressed throughout the intestinal tract, jejunum being the site with maximal expression. Colon was positive for expression, but the expression was lower than in jejunum. Compared to control colon, Abcg2 was present at lower levels in colonic polyps from experimental and genetic models of colon cancer; the same trend was seen in normal and cancer cell lines of colonic origin. In line with human colitis studies, colons from colitis mouse models had lower expression of Abcg2 compared to control colon. The association of excess iron to colon cancer is well known, but it is not known if excess iron has any role in tumor-associated downregulation of ABCG2 in colon. We used Hfe-/- mice as a model for hemochromatosis, a genetic iron-overload disease, and exploited the ability of Abcg2 to export uric acid as a measure of Abcg2 function. Colons from Hfe-/- mice had lower expression of Abcg2 and higher accumulation of uric acid. This decrease in Abcg2 function indicated that excess iron, directly or indirectly, dictates Abcg2 expression in colon. To better understand this phenomenon, colon cells were treated with ferric ammonium citrate as an iron source. This in vitro iron-overload model demonstrated nuclear depletion of the tumor suppressor p53, and at the same time a decrease in Abcg2 expression. In addition, Abcg2 mRNA was undetectable in p53-null mouse embryonic mouse fibroblasts, suggesting that Abcg2 is a p53 target. Additional in vitro studies included treatment of normal and cancer colon cells with Carbidopa, a drug which was recently shown as an aryl hydrocarbon receptor agonist. Our studies showed that Carbidopa is a potent iron chelator and an inducer of ABCG2 expression. In summary, ABCG2 is silenced in colon cancer and colitis, and the decreased expression of p53 under these conditions might be responsible for the decreased ABCG2 expression. Carbidopa could be used to reduce cellular levels of iron and to reverse iron-induced downregulation of ABCG2 as a prevention/treatment strategy for colitis and colon cancer.

Citation Format: Bojana Ristic, Sathish Sivaprakasam, Jiro Ogura, Vadivel Ganapathy. Downregulation of ABCG2 expression in colitis and colon cancer: Relevance to iron overload, hemochromatosis and p53, and therapeutic use of carbidopa to reverse the downregulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4477.

Gpr109a limits microbiota-induced IL-23 production to constrain ILC3-mediated colonic inflammation and carcinogenesis

A set of coordinated interactions between gut microbiota and the immune cells surveilling the intestine play a key role in shaping local immune responses and intestinal health. There are several immunoregulatory mechanisms in place that prevent the needless activation of immune cells against harmless gut bacteria. The dysregulation of interleukin-23 (IL-23) plays a critical role in the induction of several inflammatory diseases including inflammatory bowel disease (IBD). However, the molecular mechanisms regulating IL-23 production are poorly characterized. Gpr109a is a G-protein coupled receptor that is expressed at a very high level on innate immune cells and has been previously shown to play a key role in the induction of colonic Tregs. We show that Gpr109a−/−Rag1−/− mice exhibit spontaneous rectal prolapse and colonic inflammation, as characterized by the presence of an elevated number of IL-17-producing Rorγt+ innate lymphoid cells (ILC3). The genetic deletion of Rorγt ameliorated the spontaneous colonic inflammation in Gpr109a−/−Rag1−/− mice. Gpr109a-deficient colonic dendritic cells promote ILC3 by producing higher amounts of IL-23. Antibiotics treatment to deplete gut microbiota decreased IL-23 production, ILC3, and colonic inflammation in Gpr109a−/−Rag1−/− mice. Administration of niacin, a Gpr109a agonist, suppressed both IL-23 production by colonic DCs and ILC3 count in a Gpr109a-dependent manner. Collectively, our data presents a model suggesting that targeting Gpr109a will be potentially beneficial in the suppression of IL-23 mediated immunopathologies.

Gpr109a Limits Microbiota-Induced IL-23 Production To Constrain ILC3-Mediated Colonic Inflammation

A set of coordinated interactions between gut microbiota and the immune cells surveilling the intestine play a key role in shaping local immune responses and intestinal health. Gpr109a is a G protein-coupled receptor expressed at a very high level on innate immune cells and previously shown to play a key role in the induction of colonic regulatory T cells. In this study, we show that Gpr109a^-/-Rag1^-/- mice exhibit spontaneous rectal prolapse and colonic inflammation, characterized by the presence of an elevated number of IL-17-producing Rorγt⁺ innate lymphoid cells (ILCs; ILC3). Genetic deletion of Rorγt alleviated the spontaneous colonic inflammation in Gpr109a^-/-Rag1^-/- mice. Gpr109a-deficient colonic dendritic cells produce higher amounts of IL-23 and thereby promote ILC3. Moreover, the depletion of gut microbiota by antibiotics treatment decreased IL-23 production, ILC3, and colonic inflammation in Gpr109a^-/-Rag1^-/- mice. The ceca of Gpr109a^-/-Rag1^-/- mice showed significantly increased colonization by members of Bacteroidaceae, Porphyromonadaceae, Prevotellaceae, Streptococcaceae, Christensenellaceae, and Mogibacteriaceae, as well as IBD-associated microbiota such as Enterobacteriaceae and Mycoplasmataceae, compared with Rag1^-/- mice, housed in a facility positive for Helicobacter and murine norovirus. Niacin, a Gpr109a agonist, suppressed both IL-23 production by colonic DCs and ILC3 number in a Gpr109a-dependent manner. Collectively, our data present a model suggesting that targeting Gpr109a will be potentially beneficial in the suppression of IL-23-mediated immunopathologies.

Dual targeting of l-carnitine-conjugated nanoparticles to OCTN2 and ATB0,+ to deliver chemotherapeutic agents for colon cancer therapy

l-Carnitine, obligatory for oxidation of fatty acids, is transported into cells by the Na⁺-coupled transporter OCTN2 and the Na⁺/Cl^–-coupled transporter ATB^0,+. Here we investigated the potential of L-carnitine-conjugated poly(lactic-co-glycolic acid) (PLGA) nanoparticles (LC-PLGA NPs) to deliver chemotherapeutic drugs into cancer cells by targeting the nanoparticles to both OCTN2 and ATB^0,+. The cellular uptake of LC-PLGA NPs in the breast cancer cell line MCF7 and the colon cancer cell line Caco-2 was increased compared to unmodified nanoparticles, but decreased in the absence of co-transporting ions (Na⁺ and/or Cl^–) or in the presence of competitive substrates for the two transporters. Studies with fluorescently labeled nanoparticles showed their colocalization with both OCTN2 and ATB^0,+, confirming the involvement of both transporters in the cellular uptake of LC-PLGA NPs. As the expression levels of OCTN2 and ATB^0,+ are higher in colon cancer cells than in normal colon cells, LC-PLGA NPs can be used to deliver chemotherapeutic drugs selectively into cancer cells for colon cancer therapy. With 5-fluorouracil-loaded LC-PLGA NPs, we were able to demonstrate significant increases in the uptake efficiency and cytotoxicity in colon cancer cells that were positive for OCTN2 and ATB^0,+. In a 3D spheroid model of tumor growth, LC-PLGA NPs showed increased uptake and enhanced antitumor efficacy. These findings indicate that dual-targeting LC-PLGA NPs to OCTN2 and ATB^0,+ has great potential to deliver chemotherapeutic drugs for colon cancer therapy.

Dual targeting LC-PLGA NPs to OCTN2 and ATB0,+ can selectively deliver chemotherapeutics to colon cancer cells where both transporters are overexpressed, preventing targeting to normal cells and thus avoiding off-target side effects.

Short-Chain Fatty Acid Transporters: Role in Colonic Homeostasis

Short-chain fatty acids (SCFA; acetate, propionate, and butyrate) are generated in colon by bacterial fermentation of dietary fiber. Though diffusion in protonated form is a significant route, carrier-mediated mechanisms constitute the major route for the entry of SCFA in their anionic form into colonic epithelium. Several transport systems operate in cellular uptake of SCFA. MCT1 (SLC16A1) and MCT4 (SLC16A3) are H+-coupled and mediate electroneutral transport of SCFA (H+: SCFA stoichiometry; 1:1). MCT1 is expressed both in the apical membrane and basolateral membrane of colonic epithelium whereas MCT4 specifically in the basolateral membrane. SMCT1 (SLC5A8) and SMCT2 (SLC5A12) are Na+-coupled; SMCT1-mediated transport is electrogenic (Na+: SCFA stoichiometry; 2:1) whereas SMCT2-mediated transport is electroneutral (Na+: SCFA stoichiometry; 1:1). SMCT1 and SMCT2 are expressed exclusively in the apical membrane. An anion-exchange mechanism also operates in the apical membrane in which SCFA entry in anionic form is coupled to bicarbonate efflux; the molecular identity of this exchanger however remains unknown. All these transporters are subject to regulation, notably by their substrates themselves; this process involves cell-surface receptors with SCFA as signaling molecules. There are significant alterations in the expression of these transporters in ulcerative colitis and colon cancer. The tumor-associated changes occur via transcriptional regulation by p53 and HIF1α and by promoter methylation. As SCFA are obligatory for optimal colonic health, the transporters responsible for the entry and transcellular transfer of these bacterial products in colonic epithelium are critical determinants of colonic function under physiological conditions and in disease states. © 2018 American Physiological Society. Compr Physiol 8:299-314, 2018.

Gut Microbiome and Colon Cancer: Role of Bacterial Metabolites and Their Molecular Targets in the Host

Purpose of review

The relationship between colonic bacteria and the host is symbiotic, but how communication between the two partners occurs is just beginning to be understood at the molecular level. Here, we highlight specific products of bacterial metabolism that are present in the colonic lumen and their molecular targets in the host that facilitate this communication.

Recent findings

Colonic epithelial cells and mucosal immune cells express several cell-surface receptors and nuclear receptors that are activated by specific bacterial metabolites, which impact multiple signaling pathways and expression of many genes. In addition, some bacterial metabolites also possess the ability to cause epigenetic changes in these cells via inhibition of selective enzymes involved in the maintenance of histone acetylation and DNA methylation patterns.

Summary

Colonic bacteria communicate with their host with selective metabolites that interact with host molecular targets. This chemical communication underlies a broad range of the biology and function of colonic epithelial cells and mucosal immune cells, which protect against inflammation and carcinogenesis in the colon under normal physiological conditions.

An essential role of Ffar2 (Gpr43) in dietary fibre-mediated promotion of healthy composition of gut microbiota and suppression of intestinal carcinogenesis

Composition of the gut microbiota has profound effects on intestinal carcinogenesis. Diet and host genetics play critical roles in shaping the composition of gut microbiota. Whether diet and host genes interact with each other to bring specific changes in gut microbiota that affect intestinal carcinogenesis is unknown. Ability of dietary fibre to specifically increase beneficial gut microbiota at the expense of pathogenic bacteria in vivo via unknown mechanism is an important process that suppresses intestinal inflammation and carcinogenesis. Free fatty acid receptor 2 (FFAR2 or GPR43) is a receptor for short-chain fatty acids (acetate, propionate and butyrate), metabolites of dietary fibre fermentation by gut microbiota. Here, we show FFAR2 is down modulated in human colon cancers than matched adjacent healthy tissue. Consistent with this, Ffar2(-/-) mice are hypersusceptible to development of intestinal carcinogenesis. Dietary fibre suppressed colon carcinogenesis in an Ffar2-dependent manner. Ffar2 played an essential role in dietary fibre-mediated promotion of beneficial gut microbiota, Bifidobacterium species (spp) and suppression of Helicobacter hepaticus and Prevotellaceae. Moreover, numbers of Bifidobacterium is reduced, whereas those of Prevotellaceae are increased in human colon cancers than matched adjacent normal tissue. Administration of Bifidobacterium mitigated intestinal inflammation and carcinogenesis in Ffar2(-/-) mice. Taken together, these findings suggest that interplay between dietary fibre and Ffar2 play a key role in promoting healthy composition of gut microbiota that stimulates intestinal health.

Gpr43, dietary fiber and composition of gut microbiota in colonic inflammation and carcinogenesis

Being a primary driver of gut microbiota metabolism, diet has overwhelming affect on promoting or suppressing growth of specific members of gut microbiota. Abundance of certain gut mcirobiota is also shaped by host genetics. Numerous human and animals studies show that dietary fiber consistently increase only one group of gut bacteria, which are Bifidobacterium species (spp), the primary fermenters of dietary fiber. It is unknown whether genetic make up of host influences dietary fiber mediated promotion of Bifidobacterium spp in vivo and its impact on colonic inflammation and carcinogenesis. Gpr43 is a receptor for short chain fatty acids, acetate, propionate and butyrate. Our results demonstrate that dietary fiber mediated promotion of Bifidobacterium spp and suppression of Prevotellaceae is dependent on Gpr43. Similarly, dietary fiber mediated suppression of colonic inflammation and carcinogenesis is Gpr43-dependent. Dietary fiber mediated increase in Bifidobacterium spp is relevant to suppression of colonic inflammation and carcinogenesis because administration of Bifidobacterium spp decreased susceptibility of Gpr43−/− animal to colonic inflammation and carcinogenesis. Consistent with these findings, we found that Gpr43 is down regulated and number of Bififdobacterium is decreased whereas that of Prevotellaceae is increased in human colon cancers. These findings suggest that interplay between dietary fiber and Gpr43 play a key role in promoting healthy composition of gut microbiota leading to suppression of colonic inflammation and carcinogenesis.

Abstract 986: Role of Gpr43 in intestinal inflammation and carcinogenesis

Consumption of dietary fiber is positively correlated with lower incidence of inflammation and carcinogenesis in intestine. In colon dietary fibers are fermented by gut microbiota into short chain fatty acids (SCFA, acetate, propionate and butyrate). Several studies demonstrate that SCFA play a key role in protection of intestine from inflammation and carcinogenesis. However, detail molecular mechanisms underlying the biological effects of SCFA on intestine health are not fully understood. Gpr43 is cell surface receptor for SCFA and recent evidences suggest that it regulates colonic inflammation in a context dependent manner. Intestinal inflammation is one of the risk factor for development of cancer in gut. Based on these findings, role of Gpr43 in regulation of colon carcinogenesis was evaluated. Colitis associated colon cancer in wild type (WT) and Gpr43-/- mice was induced by single intraperitoneal injection of azoxymethane (AOM) and repeated cycles of dextran sulfate sodium (DSS) in drinking water. Gpr43-/- mice showed drastically reduced survival, severe weight loss and increased diarrhea and rectal bleeding than WT mice. At the end of treatment, colons of Gpr43-/- mice exhibited increased number of polyps than that of WT mice. Reciprocal bone marrow chimera experiments revealed that Gpr43 expression in non-hematopoietic cells play a major role in suppression of colonic inflammation and carcinogenesis. The data presented here suggest a model in which Gpr43 plays a critical role in facilitating positive effects of dietary fiber and gut microbiota on intestinal health.

Citation Format: Sathish Sivaprakasam, Ashish Gurav, Ganapathy Vadivel, Nagendra Singh. Role of Gpr43 in intestinal inflammation and carcinogenesis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 986. doi:10.1158/1538-7445.AM2015-986

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.

Nullified time-of-flight lead-lag in synchronization of chaotic external-cavity laser diodes

Synchronization of three chaotic diode lasers is effected in a transmitter-mediator-receiver configuration. The transmitter laser's output is bidirectionally coupled to the mediator laser to achieve anticipating synchronization in their output intensities. The mediator laser's output is unidirectionally coupled to the receiver laser to achieve lag synchronization in their output intensities. This combination of lead and lag synchronization nullifies the time-of-flight lead-lag in synchronization between the transmitter and receiver lasers. This approach provides a means of eliminating time-of-flight delays in the synchronization of remote transmitters and receivers.

Lag times and parameter mismatches in synchronization of unidirectionally coupled chaotic external cavity semiconductor lasers

We report an analysis of synchronization between two unidirectionally coupled chaotic external cavity master and slave semiconductor lasers with two characteristic delay times, where the delay time in the coupling is different from the delay time in the coupled systems themselves. We demonstrate that parameter mismatches in photon decay rates for the master and slave lasers can explain the experimental observation that the lag time is equal to the coupling delay time.

Transition between anticipating and lag synchronization in chaotic external-cavity laser diodes

Chaotic synchronization is investigated by use of two diode lasers as transmitter and receiver. The transmitter laser is rendered chaotic by application of optical feedback in an external-cavity configuration. Changes in the spectrum of the synchronized system are shown to be associated with the transition between anticipating and lag synchronization.

Inverse anticipating chaos synchronization

We derive conditions for achieving inverse anticipating synchronization where a driven time-delay chaotic system synchronizes to the inverse future state of the driver. The significance of inverse anticipating chaos in delineating synchronization regimes in time-delay systems is elucidated. The concept is extended to cascaded time-delay systems.

Parameter mismatches and perfect anticipating synchronization in bidirectionally coupled external cavity laser diodes

We study perfect chaos synchronization between two bidirectionally coupled external cavity semiconductor lasers and demonstrate that mismatches in laser photon decay rates can explain the experimentally observed anticipating time in synchronization.

Experimental demonstration of anticipating synchronization in chaotic semiconductor lasers with optical feedback

We report the first experimental observation of anticipating chaotic synchronization in an optical system using two diode lasers as transmitter and receiver. The transmitter laser is rendered chaotic by application of an optical feedback in an external-cavity configuration. It is found that the anticipation time does not depend on the external-cavity round trip time of the transmitter.

Cascaded synchronization of external-cavity laser diodes

An experimental demonstration of optical synchronization of a chain of chaotic external-cavity laser diodes is reported for what is believed to be the first time. The experiment is performed in the low-frequency-fluctuation regime.

Integrity of semiconductor laser chaotic communications to naïve eavesdroppers

The integrity of a chaotic encoding technique based on an external-cavity semiconductor laser transmitter-receiver system is experimentally examined. A semiconductor laser placed in the transmission path of the system is used to represent an eavesdropper intercepting a chaotic communication. The eavesdropper is able to obtain a copy of the transmission but is unable to decode the message. A chaotic communication system based on external-cavity semiconductor lasers is seen therefore to be secure against this form of interception.

Experimental verification of the synchronization condition for chaotic external cavity diode lasers

The synchronization condition obtained numerically by Ahlers, Parlitz, and Lauterborn [Phys. Rev. E 58, 7208 (1998)] is verified experimentally.

Critical signal strength for effective decoding in diode laser chaotic optical communications

Synchronized external-cavity diode lasers are used for chaotic optical encryption and decryption. It is shown that effective decoding requires the signal strength to exceed a certain value determined by the precise operating conditions.

Signal masking for chaotic optical communication using external-cavity diode lasers

Amplitude modulation is used to encode a message into the output of a chaotic laser-diode optical transmitter, and decoding of the message by use of a synchronized chaotic laser-diode receiver is demonstrated experimentally. The chaotic carrier is shown to effectively mask the transmitted message.

Demonstration of optical synchronization of chaotic external-cavity laser diodes

An experimental demonstration of optical synchronization of chaotic external-cavity semiconductor laser diodes is reported for what is believed to be the first time. It is shown that at an optimum coupling strength between the master and the slave lasers high-quality synchronization can be obtained.

Mode hopping in external-cavity diode lasers

Mode hopping in external-cavity AlGaAs diode lasers has been studied experimentally. Its dependence on the amount of feedback and the external-cavity round-trip phase has been studied. The results are compared with the predictions of potential well models. As the feedback is increased the results differ considerably from this theory. A qualitative treatment is also presented.