Corrigendum: Isothermal Microcalorimetry of Tumor Cells: Enhanced Thermogenesis by Metastatic Cells.

[This corrects the article DOI: 10.3389/fonc.2019.01430.].

H+-dependent inorganic phosphate transporter in breast cancer cells: Possible functions in the tumor microenvironment.

Tumor microenvironment has a high concentration of inorganic phosphate (Pi), which is actually a marker for tumor progression. Regarding Pi another class of transporter has been recently studied, an H+-dependent Pi transporter, that is stimulated at acidic pH in Caco2BBE human intestinal cells. In this study, we characterized the H+-dependent Pi transport in breast cancer cell (MDA-MB-231) and around the cancer tissue. MDA-MB-231 cell line presented higher levels of H+-dependent Pi transport as compared to other breast cell lines, such as MCF-10A, MCF-7 and T47-D. The Pi transport was linear as a function of time and exhibited a Michaelis-Menten kinetic of Km = 1.387 ±â€¯0.1674 mM Pi and Vmax = 198.6 ±â€¯10.23 Pi × h-1 × mg protein-1 hence reflecting a low affinity Pi transport. H+-dependent Pi uptake was higher at acidic pH. FCCP, Bafilomycin A1 and SCH28080, which deregulate the intracellular levels of protons, inhibited the H+-dependent Pi transport. No effect on pHi was observed in the absence of inorganic phosphate. PAA, an H+-dependent Pi transport inhibitor, reduced the Pi transport activity, cell proliferation, adhesion, and migration. Arsenate, a structural analog of Pi, inhibited the Pi transport. At high Pi conditions, the H+-dependent Pi transport was five-fold higher than the Na+-dependent Pi transport, thus reflecting a low affinity Pi transport. The occurrence of an H+-dependent Pi transporter in tumor cells may endow them with an alternative path for Pi uptake in situations in which Na+-dependent Pi transport is saturated within the tumor microenvironment, thus regulating the energetically expensive tumor processes.

Isothermal Microcalorimetry of Tumor Cells: Enhanced Thermogenesis by Metastatic Cells.

Tumor cells exhibit rewired metabolism. We carried out comparative analyses attempting to investigate whether metabolic reprograming could be measured by isothermal microcalorimetry. Intact metastatic cell lines of tongue cell carcinoma, human and murine melanoma, lung, and breast tumors consistently released more heat than non-metastatic cells or cells displaying lower metastatic potential. In tongue squamous carcinoma cells mitochondrial enriched extract reproduced the heat release pattern of intact cells. Cytochalasin D, an actin filament inhibitor, and suppression of metastasis marker Melanoma associated gene 10 (MAGEA10) decreased heat release. Uncoupling protein 2 was highly expressed in metastatic cells, but not in non-metastatic cells. Carnitine palmitoyl transferase-1 inhibitor, Etomoxir strongly inhibited heat release by metastatic cells, thus linking lipid metabolism to thermogenesis. We propose that heat release may be a quantifiable trait of the metastatic process.

Inorganic phosphate transporters in cancer: Functions, molecular mechanisms and possible clinical applications.

Inorganic phosphate is one of the most essential nutrients for the maintenance of cell life. Because of its essential role in nutrient supplementation, the study of plasma membrane inorganic phosphate transporters in cancer biology has received much attention in recent years. Several studies suggest that these transporters are up-regulated in tumor cells and thus have been considered to be important promoters of tumor progression. Altered expression levels of inorganic phosphate transporters, such as NaPi-IIb (SLC34A2) and PiT-1 (SLC20A1), have been demonstrated. The purpose of this review article was to gather the relevant experimental records on inorganic phosphate transporters in tumors and to demonstrate the importance of these proteins in clinical applications. In this work, we demonstrate that for decades, the potential use of the inorganic phosphate transporter as an antigen for the diagnosis of tumor subtypes remained unknown. With the advancement in molecular biology techniques, phosphate transporters have been identified as being associated with cancer. In addition to their altered expression in cancer, several studies have demonstrated other functions of inorganic phosphate transporters, such as transceptors, rearrangements with oncogenes and modifications in the expression of ABC transporters, aiding in the process of proliferation and drug resistance.

Metabolic Profile of Oral Squamous Carcinoma Cell Lines Relies on a Higher Demand of Lipid Metabolism in Metastatic Cells.

Tumor cells are subjected to a broad range of selective pressures. As a result of the imposed stress, subpopulations of surviving cells exhibit individual biochemical phenotypes that reflect metabolic reprograming. The present work aimed at investigating metabolic parameters of cells displaying increasing degrees of metastatic potential. The metabolites present in cell extracts fraction of tongue fibroblasts and of cell lines derived from human tongue squamous cell carcinoma lineages displaying increasing metastatic potential (SCC9 ZsG, LN1 and LN2) were analyzed by 1H NMR (nuclear magnetic resonance) spectroscopy. Living, intact cells were also examined by the non-invasive method of fluorescence lifetime imaging microscopy (FLIM) based on the auto fluorescence of endogenous NADH. The cell lines reproducibly exhibited distinct metabolic profiles confirmed by Partial Least-Square Discriminant Analysis (PLS-DA) of the spectra. Measurement of endogenous free and bound NAD(P)H relative concentrations in the intact cell lines showed that ZsG and LN1 cells displayed high heterogeneity in the energy metabolism, indicating that the cells would oscillate between glycolysis and oxidative metabolism depending on the microenvironment's composition. However, LN2 cells appeared to have more contributions to the oxidative status, displaying a lower NAD(P)H free/bound ratio. Functional experiments of energy metabolism, mitochondrial physiology, and proliferation assays revealed that all lineages exhibited similar energy features, although resorting to different bioenergetics strategies to face metabolic demands. These differentiated functions may also promote metastasis. We propose that lipid metabolism is related to the increased invasiveness as a result of the accumulation of malonate, methyl malonic acid, n-acetyl and unsaturated fatty acids (CH2)n in parallel with the metastatic potential progression, thus suggesting that the NAD(P)H reflected the lipid catabolic/anabolic pathways.

Angiogenesis and evading immune destruction are the main related transcriptomic characteristics to the invasive process of oral tongue cancer.

Metastasis of head and neck tumors is responsible for a high mortality rate. Understanding its biochemistry may allow insights into tumorigenesis. To that end we carried out RNA-Seq analyses of 5 SCC9 derived oral cancer cell lines displaying increased invasive potential. Differentially expressed genes (DEGs) were annotated based on p-values and false discovery rate (q-values). All 292 KEGG pathways related to the human genome were compared in order to pinpoint the absolute and relative contributions to the invasive process considering the 8 hallmarks of cancer plus 2 new defined categories, as well as we made with our transcriptomic data. In terms of absolute contribution, the highest correlations were associated to the categories of evading immune destruction and energy metabolism and for relative contributions, angiogenesis and evading immune destruction. DEGs were distributed into each one of all possible modes of regulation, regarding up, down and continuum expression, along the 3 stages of metastatic progression. For p-values twenty-six genes were consistently present along the tumoral progression and 4 for q-values. Among the DEGs, we found 2 novel potentially informative metastatic markers: PIGG and SLC8B1. Furthermore, interactome analysis showed that MYH14, ANGPTL4, PPARD and ENPP1 are amenable to pharmacological interventions.

Characterization of inorganic phosphate transport in the triple-negative breast cancer cell line, MDA-MB-231.

BACKGROUND: Recent studies demonstrate that interstitial inorganic phosphate is significantly elevated in the breast cancer microenvironment as compared to normal tissue. In addition it has been shown that breast cancer cells express high levels of the NaPi-IIb carrier (SLC34A2), suggesting that this carrier may play a role in breast cancer progression. However, the biochemical behavior of inorganic phosphate (Pi) transporter in this cancer type remains elusive. METHODS: In this work, we characterize the kinetic parameters of Pi transport in the aggressive human breast cancer cell line, MDA-MB-231, and correlated Pi transport with cell migration and adhesion. RESULTS: We determined the influence of sodium concentration, pH, metabolic inhibitors, as well as the affinity for inorganic phosphate in Pi transport. We observed that the inorganic phosphate is dependent on sodium transport (K0,5 value = 21.98 mM for NaCl). Furthermore, the transport is modulated by different pH values and increasing concentrations of Pi, following the Michaelis-Menten kinetics (K0,5 = 0.08 mM Pi). PFA, monensin, furosemide and ouabain inhibited Pi transport, cell migration and adhesion. CONCLUSIONS: Taken together, these results showed that the uptake of Pi in MDA-MB-231 cells is modulated by sodium and by regulatory mechanisms of intracellular sodium gradient. General Significance: Pi transport might be regarded as a potential target for therapy against tumor progression.

Reciprocal modulation of histone deacetylase inhibitors sodium butyrate and trichostatin A on the energy metabolism of breast cancer cells.

Tumor cells display different bioenergetic profiles when compared to normal cells. In the present work we showed metabolic reprogramming by means of inhibitors of histone deacetylase (HDACis), sodium butyrate and trichostatin A in breast cancer cells representing different stages of aggressiveness and metabolic profile. When testing the effect of NaB and TSA on viability of cells, it was shown that non-tumorigenic MCF-10A cells were less affected by increasing doses of the drugs than the tumorigenic, hormone dependent, tightly cohesive MCF-7, T-47D and the highly metastatic triple-negative MDA-MB 231 cells. T-47D cells were the most sensitive to treatment with both, NaB and TSA. Experiments measuring anchorage- independent growth of tumor cells showed that MCF-7, T-47D, and MDA-MB-231 cells were equally sensitive to the treatment with NaB. The NaB induced an attenuation of glycolysis, reflected by a decrease in lactate release in MCF-7 and T47D lines. Pyruvate kinase activity was significantly enhanced by NaB in MDA-MB-231 cells only. In contrast, the inhibitor enhanced lactate dehydrogenase activity specifically in T-47 D cells. Glucose-6-phosphate dehydrogenase activity was shown to be differentially modulated by NaB in the cell lines investigated: the enzyme was inhibited in MCF-7 cells, whereas in T-47D and MDA-MB-231 cells, G6PDH was activated. NaB and TSA were able to significantly increase the oxygen consumption by MDA-MB-231 and T-47D cells. Collectively the results show that epigenetic changes associated to acetylation of proteins in general affect the energy metabolism in all cancer cell lines and that mitochondria may occupy a central role in metastasis.

Methyl jasmonate: putative mechanisms of action on cancer cells cycle, metabolism, and apoptosis.

Methyl jasmonate (MJ), an oxylipid that induces defense-related mechanisms in plants, has been shown to be active against cancer cells both in vitro and in vivo, without affecting normal cells. Here we review most of the described MJ activities in an attempt to get an integrated view and better understanding of its multifaceted modes of action. MJ (1) arrests cell cycle, inhibiting cell growth and proliferation, (2) causes cell death through the intrinsic/extrinsic proapoptotic, p53-independent apoptotic, and nonapoptotic (necrosis) pathways, (3) detaches hexokinase from the voltage-dependent anion channel, dissociating glycolytic and mitochondrial functions, decreasing the mitochondrial membrane potential, favoring cytochrome c release and ATP depletion, activating pro-apoptotic, and inactivating antiapoptotic proteins, (4) induces reactive oxygen species mediated responses, (5) stimulates MAPK-stress signaling and redifferentiation in leukemia cells, (6) inhibits overexpressed proinflammatory enzymes in cancer cells such as aldo-keto reductase 1 and 5-lipoxygenase, and (7) inhibits cell migration and shows antiangiogenic and antimetastatic activities. Finally, MJ may act as a chemosensitizer to some chemotherapics helping to overcome drug resistant. The complete lack of toxicity to normal cells and the rapidity by which MJ causes damage to cancer cells turn MJ into a promising anticancer agent that can be used alone or in combination with other agents.

Mitochondria: are mitochondria accessory to metastasis?

Since the nineteenth century the importance of mitochondria in cellular physiology has been growing steadily. Not only the organelle harbors the main systems for ATP generation, but also buffers the redox potential in the cytosol and is one of the protagonists of the intrinsic pathway for apoptosis. In tumor cells, mitochondria went from being dysfunctional compartments to playing a supportive or perhaps even a triggering part in metastasis. This "Organelle In Focus" article discusses the classical metabolic events that occur in mitochondria and why these pathways could be essential for the onset of the malignant phenotype. Finally, we propose that the oxidative metabolism of tumor cells in conjunction with the inactivation of anoikis may have been coopted through a non-adaptive evolutionary process.

How does the metabolism of tumour cells differ from that of normal cells.

Tumour cells thrive in environments that would be hostile to their normal cell counterparts. Survival depends on the selection of cell lines that harbour modifications of both, gene regulation that shifts the balance between the cell cycle and apoptosis and those that involve the plasticity of the metabolic machinery. With regards to metabolism, the selected phenotypes usually display enhanced anaerobic glycolysis even in the presence of oxygen, the so-called Warburg effect, and anabolic pathways that provide precursors for the synthesis of lipids, proteins and DNA. The review will discuss the original ideas of Otto Warburg and how they initially led to the notion that mitochondria of tumour cells were dysfunctional. Data will be presented to show that not only the organelles are viable and respiring, but that they are key players in tumorigenesis and metastasis. Likewise, interconnecting pathways that stand out in the tumour phenotype and that require intact mitochondria such as glutaminolysis will be addressed. Furthermore, comments will be made as to how the peculiarities of the biochemistry of tumour cells renders them amenable to new forms of treatment by highlighting possible targets for inhibitors. In this respect, a case study describing the effect of a metabolite analogue, the alkylating agent 3BP (3-bromopyruvate), on glycolytic enzyme targets will be presented.

Genomic instability at the 13q31 locus and somatic mtDNA mutation in the D-loop site correlate with tumor aggressiveness in sporadic Brazilian breast cancer cases.

OBJECTIVE: Genomic instability is a hallmark of malignant tissues. In this work, we aimed to characterize nuclear and mitochondrial instabilities by determining short tandem repeats and somatic mitochondrial mutations, respectively, in a cohort of Brazilian sporadic breast cancer cases. Furthermore, we performed an association analysis of the molecular findings and the clinical pathological data. METHODS: We analyzed 64 matched pairs of breast cancer and adjacent non-cancerous breast samples by genotyping 13 nuclear short tandem repeat loci (namely, D2S123, TPOX, D3S1358, D3S1611, FGA, D7S820, TH01, D13S317, D13S790, D16S539, D17S796, intron 12 BRCA1 and intron 1 TP53) that were amplified with the fluorescent AmpFlSTR Identifiler Genotyping system (Applied Biosystems, USA) and by silver nitrate staining following 6% denaturing polyacrylamide gel electrophoresis. Somatic mtDNA mutations in the D-loop site were assessed with direct sequencing of the hypervariable HVI and HVII mitochondrial regions. RESULTS: Half of the cancer tissues presented some nuclear instability. Interestingly, the D13S790 locus was the most frequently affected (36%), while the D2S123 locus presented no alterations. Forty-two percent of the cases showed somatic mitochondrial mutations, the majority at region 303-315 poly-C. We identified associations between Elston grade III, instabilities at 13q31 region (p = 0.0264) and mtDNA mutations (p = 0.0041). Furthermore, instabilities at 13q31 region were also associated with TP53 mutations in the invasive ductal carcinoma cases (p= 0.0207). CONCLUSION: Instabilities at 13q31 region and the presence of somatic mtDNA mutations in a D-loop site correlated with tumor aggressiveness.

Genomic instability at the 13q31 locus and somatic mtDNA mutation in the D-loop site correlate with tumor aggressiveness in sporadic Brazilian breast cancer cases

OBJECTIVE: Genomic instability is a hallmark of malignant tissues. In this work, we aimed to characterize nuclear and mitochondrial instabilities by determining short tandem repeats and somatic mitochondrial mutations, respectively, in a cohort of Brazilian sporadic breast cancer cases. Furthermore, we performed an association analysis of the molecular findings and the clinical pathological data. METHODS: We analyzed 64 matched pairs of breast cancer and adjacent non-cancerous breast samples by genotyping 13 nuclear short tandem repeat loci (namely, D2S123, TPOX, D3S1358, D3S1611, FGA, D7S820, TH01, D13S317, D13S790, D16S539, D17S796, intron 12 BRCA1 and intron 1 TP53) that were amplified with the fluorescent AmpFlSTR Identifiler Genotyping system (Applied Biosystems, USA) and by silver nitrate staining following 6% denaturing polyacrylamide gel electrophoresis. Somatic mtDNA mutations in the D-loop site were assessed with direct sequencing of the hypervariable HVI and HVII mitochondrial regions. RESULTS: Half of the cancer tissues presented some nuclear instability. Interestingly, the D13S790 locus was the most frequently affected (36%), while the D2S123 locus presented no alterations. Forty-two percent of the cases showed somatic mitochondrial mutations, the majority at region 303-315 poly-C. We identified associations between Elston grade III, instabilities at 13q31 region (p = 0.0264) and mtDNA mutations (p = 0.0041). Furthermore, instabilities at 13q31 region were also associated with TP53 mutations in the invasive ductal carcinoma cases (p= 0.0207). CONCLUSION: Instabilities at 13q31 region and the presence of somatic mtDNA mutations in a D-loop site correlated with tumor aggressiveness.

Energy and redox homeostasis in tumor cells.

Cancer cells display abnormal morphology, chromosomes, and metabolism. This review will focus on the metabolism of tumor cells integrating the available data by way of a functional approach. The first part contains a comprehensive introduction to bioenergetics, mitochondria, and the mechanisms of production and degradation of reactive oxygen species. This will be followed by a discussion on the oxidative metabolism of tumor cells including the morphology, biogenesis, and networking of mitochondria. Tumor cells overexpress proteins that favor fission, such as GTPase dynamin-related protein 1 (Drp1). The interplay between proapoptotic members of the Bcl-2 family that promotes Drp 1-dependent mitochondrial fragmentation and fusogenic antiapoptotic proteins such as Opa-1 will be presented. It will be argued that contrary to the widespread belief that in cancer cells, aerobic glycolysis completely replaces oxidative metabolism, a misrepresentation of Warburg's original results, mitochondria of tumor cells are fully viable and functional. Cancer cells also carry out oxidative metabolism and generally conform to the orthodox model of ATP production maintaining as well an intact electron transport system. Finally, data will be presented indicating that the key to tumor cell survival in an ROS rich environment depends on the overexpression of antioxidant enzymes and high levels of the nonenzymatic antioxidant scavengers.

CK2 phosphorylation of Schistosoma mansoni HMGB1 protein regulates its cellular traffic and secretion but not its DNA transactions.

BACKGROUND: The helminth Schistosoma mansoni parasite resides in mesenteric veins where fecundated female worms lay hundred of eggs daily. Some of the egg antigens are trapped in the liver and induce a vigorous granulomatous response. High Mobility Group Box 1 (HMGB1), a nuclear factor, can also be secreted and act as a cytokine. Schistosome HMGB1 (SmHMGB1) is secreted by the eggs and stimulate the production of key cytokines involved in the pathology of schistosomiasis. Thus, understanding the mechanism of SmHMGB1 release becomes mandatory. Here, we addressed the question of how the nuclear SmHMGB1 can reach the extracellular space. PRINCIPAL FINDINGS: We showed in vitro and in vivo that CK2 phosphorylation was involved in the nucleocytoplasmic shuttling of SmHMGB1. By site-directed mutagenesis we mapped the two serine residues of SmHMGB1 that were phosphorylated by CK2. By DNA bending and supercoiling assays we showed that CK2 phosphorylation of SmHMGB1 had no effect in the DNA binding activities of the protein. We showed by electron microscopy, as well as by cell transfection and fluorescence microscopy that SmHMGB1 was present in the nucleus and cytoplasm of adult schistosomes and mammalian cells. In addition, we showed that treatments of the cells with either a phosphatase or a CK2 inhibitor were able to enhance or block, respectively, the cellular traffic of SmHMGB1. Importantly, we showed by confocal microscopy and biochemically that SmHMGB1 is significantly secreted by S. mansoni eggs of infected animals and that SmHMGB1 that were localized in the periovular schistosomotic granuloma were phosphorylated. CONCLUSIONS: We showed that secretion of SmHMGB1 is regulated by phosphorylation. Moreover, our results suggest that egg-secreted SmHMGB1 may represent a new egg antigen. Therefore, the identification of drugs that specifically target phosphorylation of SmHMGB1 might block its secretion and interfere with the pathogenesis of schistosomiasis.

Energy metabolism in H460 lung cancer cells: effects of histone deacetylase inhibitors.

BACKGROUND: Tumor cells are characterized by accelerated growth usually accompanied by up-regulated pathways that ultimately increase the rate of ATP production. These cells can suffer metabolic reprogramming, resulting in distinct bioenergetic phenotypes, generally enhancing glycolysis channeled to lactate production. In the present work we showed metabolic reprogramming by means of inhibitors of histone deacetylase (HDACis), sodium butyrate and trichostatin. This treatment was able to shift energy metabolism by activating mitochondrial systems such as the respiratory chain and oxidative phosphorylation that were largely repressed in the untreated controls. METHODOLOGY/PRINCIPAL FINDINGS: Various cellular and biochemical parameters were evaluated in lung cancer H460 cells treated with the histone deacetylase inhibitors (HDACis), sodium butyrate (NaB) and trichostatin A (TSA). NaB and TSA reduced glycolytic flux, assayed by lactate release by H460 cells in a concentration dependent manner. NaB inhibited the expression of glucose transporter type 1 (GLUT 1), but substantially increased mitochondria bound hexokinase (HK) activity. NaB induced increase in HK activity was associated to isoform HK I and was accompanied by 1.5 fold increase in HK I mRNA expression and cognate protein biosynthesis. Lactate dehydrogenase (LDH) and pyruvate kinase (PYK) activities were unchanged by HDACis suggesting that the increase in the HK activity was not coupled to glycolytic flux. High resolution respirometry of H460 cells revealed NaB-dependent increased rates of oxygen consumption coupled to ATP synthesis. Metabolomic analysis showed that NaB altered the glycolytic metabolite profile of intact H460 cells. Concomitantly we detected an activation of the pentose phosphate pathway (PPP). The high O(2) consumption in NaB-treated cells was shown to be unrelated to mitochondrial biogenesis since citrate synthase (CS) activity and the amount of mitochondrial DNA remained unchanged. CONCLUSION: NaB and TSA induced an increase in mitochondrial function and oxidative metabolism in H460 lung tumor cells concomitant with a less proliferative cellular phenotype.

Expression of ABC transporters, p53, Bax, Bcl-2 in an archival sample of non-small cell lung cancer bearing a deletion in the EGFR gene.

EGFR mutations have been correlated to responsiveness to treatment with tyrosine kinase inhibitors. These drugs are themselves substrates for ABC transporters. In the present work we describe the immunohistochemical profile of an archival sample from a male Brazilian patient with no Asian ancestry and never smoker, diagnosed with non-small cell lung cancer. This tumor was found to contain an in-frame hemi- or homozygous deletion, E746-A750 in exon 19 of the EGFR gene. Immunohistochemistry revealed a relatively weak staining for the ABC transporter subfamily ABCC1 and strongly for ABCB1. The cytoplasm stained positively for Bax and the nucleus stained for p53, but was negative for Bcl-2. Antibody against acetylated lysine revealed staining in both, cytoplasm and nucleus of tumor cells in contrast to normal cells which were essentially negative. The overall immunohistochemistry pattern obtained for this sample indicates that the del E746-A750 mutation may have down-regulated the expression of ABCC1. The results also suggest that the NSCLC analyzed displayed a transcriptionally active chromatin as judged by the results obtained with the anti-acetylated lysine antibody.

Plasma Epstein-Barr viral load predicting response after chemotherapy for post-transplant lymphoproliferative disease.

Transplant patients are particularly at risk of developing B post-transplant lymphoproliferative disease (PTLD) related to intensive immunosuppressive treatment to prevent graft rejection. In EBV-positive PTLDs, EBV-DNA can be found in the patients' peripheral blood. Several methods have been described to assess peripheral blood EBV viral load. We report a case of a 13-year-old child who developed EBV-positive PTLD after renal transplantation. We assessed EBV plasma viral load by quantitative PCR and we found that the clearance of EBV-DNA correlated well with response to treatment.

Schistosoma mansoni: SmLIMPETin, a member of a novel family of invertebrate-only regulatory proteins.

Eukaryotic LIM domain proteins contain zinc finger forming motifs rich in cysteine and histidine that enable them to interact with other proteins. A cDNA clone isolated from an adult schistosome cDNA library revealed a sequence that coded for a novel class of proteins bearing 6 LIM domains and an N-terminal PET domain, SmLIMPETin. Phylogeny reconstruction of SmLIMPETin and comparison of its sequence to invertebrate homologues and to the vertebrate four-and-a-half LIM domains protein family (FHLs), uncovered a novel LIM domain protein family, the invertebrate LIM and PET domain protein family (LIMPETin). Northern blots, RT-PCR and Western blot showed that SmLIMPETin gene was less expressed in sexually mature adult females compared to sexually immature adult females and sexually mature and immature adult males, and not expressed in schistosomula.

A unique nuclear receptor direct repeat 17 (DR17) is present within the upstream region of Schistosoma mansoni female-specific p14 gene.

The eggs produced by sexually mature female Schistosma mansoni are responsible for the pathogenesis of the disease. The eggshell precursor gene p14 is expressed only in the vitelline cells of sexually mature female worms in response to a yet unidentified male stimulus. Herein, we report the identification of a novel nuclear receptor response element in the upstream region of the p14 gene. This element contains the canonical hexameric DNA core motif, 5'-PuGGTCA, composed of an atypically spaced direct repeat (DR17). Schistosome nuclear receptors SmRXR1 and SmNR1 specifically bound to the p14-DR17 element as a heterodimer. SmRXR1, but not SmNR1, bound to the motif as a monomer. Introduction of mutations in the TCA core sequence completely abolished the binding by SmRXR1/SmNR1 heterodimer. This finding supports our hypothesis that the expression of Schistosoma mansonip14 gene is regulated through the nuclear receptor signaling pathway.