Expression and function of iron-regulatory proteins in retina.

Iron is essential for cell survival and function; yet excess iron is toxic to cells. Therefore, the cellular and whole-body levels of iron are regulated exquisitely. At least a dozen proteins participate in the regulation of iron homeostasis.

Localization of members of MCT monocarboxylate transporter family Slc16 in the kidney and regulation during metabolic acidosis.

The monocarboxylate transporter family (MCT) comprises 14 members with distinct transport properties and tissue distribution. The kidney expresses several members of the MCT family, but only little is known about their exact distribution and function. Here, we investigated selected members of the MCT family in the mouse kidney.

PKG inhibits TCF signaling in colon cancer cells by blocking beta-catenin expression and activating FOXO4.

Activation of cGMP-dependent protein kinase (PKG) has anti-tumor effects in colon cancer cells but the mechanisms are not fully understood. This study has examined the regulation of beta-catenin/TCF signaling, as this pathway has been highlighted as central to the anti-tumor effects of PKG. We show that PKG activation in SW620 cells results in reduced beta-catenin expression and a dramatic inhibition of TCF-dependent transcription.

Sodium-coupled electrogenic transport of pyroglutamate (5-oxoproline) via SLC5A8, a monocarboxylate transporter.

Pyroglutamate, also known as 5-oxoproline, is a structural analog of proline. This amino acid derivative is a byproduct of glutathione metabolism, and is reabsorbed efficiently in kidney by Na(+)-coupled transport mechanisms. Previous studies have focused on potential participation of amino acid transport systems in renal reabsorption of this compound.

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

SMCT1 is a Na(+)-coupled monocarboxylate transporter expressed in a variety of tissues including kidney, thyroid, small intestine, colon, brain, and retina. We found recently that several non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the activity of SMCT1. Here we evaluated the effect of diclofenac, also a NSAID, on SMCT1.

Bortezomib blocks the catabolic process of autophagy via a cathepsin-dependent mechanism, affects endoplasmic reticulum stress and induces caspase-dependent cell death in antiestrogen-sensitive and resistant ER+ breast cancer cells.

In recent studies, we and others showed that autophagy is critical to estrogen receptor positive (ER+) breast cancer cell survival and the development of antiestrogen resistance. Consequently, new approaches are warranted for targeting autophagy in breast cancer cells undergoing antiestrogen therapy. Because crosstalk has been demonstrated between the autophagy- and proteasome-mediated pathways of protein degradation, this study investigated how the proteasome inhibitor bortezomib affects autophagy and cell survival in antiestrogen-treated ER+ breast cancer cells.

Molecular and biochemical characterization of folate transport proteins in retinal Müller cells.

Purpose: To analyze the mechanisms of folate uptake in retinal Müller cells.

Methods: RT-PCR and Western blot analysis were performed in freshly isolated neural retina and RPE/eyecup, primary mouse Müller cells, and rMC-1 cells for the three known folate transport proteins folate receptor alpha (FRalpha), proton-coupled folate transporter (PCFT), and reduced folate carrier (RFC). Laser scanning confocal microscopy (LSCM) and immunoelectron microscopy were used to determine the subcellular location of FRalpha and PCFT in primary Müller cells.

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

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

Methods: RNA was prepared from the ileum and colon of conventional mice and germ-free mice and used for RT-PCR to determine mRNA levels.

Evidence-based indications for ankle arthroscopy.

Purpose: The purpose of this study was to review the literature to provide a comprehensive description of the Level of Evidence available to support the surgical technique of ankle arthroscopy for the current generally accepted indications and assign a grade of recommendation for each of them.

Methods: A comprehensive review of the literature was performed (in August 2008) by use of the PubMed database. The abstracts from these searches were reviewed to isolate literature that described therapeutic studies investigating the results of different ankle arthroscopic treatment techniques.

Transport of the photodynamic therapy agent 5-aminolevulinic acid by distinct H+-coupled nutrient carriers coexpressed in the small intestine.

5-Aminolevulinic acid (ALA) is a prodrug used in photodynamic therapy, fluorescent diagnosis, and fluorescent-guided resection because it leads to accumulation of the photosensitizer protoporphyrin IX (PpIX) in tumor tissues. ALA has good oral bioavailability, but high oral doses are required to obtain selective PpIX accumulation in colonic tumors because accumulation is also observed in normal gut mucosa. Structural similarities between ALA and GABA led us to test the hypothesis that the H(+)-coupled amino acid transporter PAT1 (SLC36A1) will contribute to luminal ALA uptake.

Absence of iron-regulatory protein Hfe results in hyperproliferation of retinal pigment epithelium: role of cystine/glutamate exchanger.

Haemochromatosis is an iron-overload disorder with age-dependent oxidative stress and dysfunction in a variety of tissues. Mutations in HFE (histocompatability leucocyte antigen class I-like protein involved in iron homoeostasis) are responsible for most cases of haemochromatosis. We demonstrated recently that HFE is expressed exclusively in the basal membrane of RPE (retinal pigment epithelium).

The blood-brain barrier transport and cerebral distribution of guanidinoacetate in rats: involvement of creatine and taurine transporters.

Although the cerebral accumulation of guanidinoacetate (GAA) contributes to neurological complications in S-adenosylmethionine:guanidinoacetate N-methyltransferase (GAMT) deficiency, how GAA is abnormally distributed in the brain remains unknown. The purpose of this study was to investigate the transport of GAA across the blood-brain barrier (BBB) and in brain parenchymal cells in rats. [(14)C]GAA microinjected into the rat cerebrum was not eliminated from the brain, implying the negligible contribution of GAA efflux transport across the BBB.

Identification of a novel sodium-coupled oligopeptide transporter (SOPT2) in mouse and human retinal pigment epithelial cells.

Purpose: A sodium-coupled oligopeptide transporter (SOPT1) was described originally in ARPE-19 cells. The transporter is inducible by HIV-1 Tat. Recent studies of conjunctival epithelial cells have identified a second oligopeptide transporter (SOPT2).

Transport by SLC5A8 with subsequent inhibition of histone deacetylase 1 (HDAC1) and HDAC3 underlies the antitumor activity of 3-bromopyruvate.

Background: 3-bromopyruvate is an alkylating agent with antitumor activity. It is currently believed that blockade of adenosine triphosphate production from glycolysis and mitochondria is the primary mechanism responsible for this antitumor effect. The current studies uncovered a new and novel mechanism for the antitumor activity of 3-bromopyruvate.

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

Short-chain fatty acids, generated in colon by bacterial fermentation of dietary fiber, protect against colorectal cancer and inflammatory bowel disease. Among these bacterial metabolites, butyrate is biologically most relevant. GPR109A is a G-protein-coupled receptor for nicotinate but recognizes butyrate with low affinity.

Expression and localization of GPR109A (PUMA-G/HM74A) mRNA and protein in mammalian retinal pigment epithelium.

Purpose: GPR109A has been identified as a G-protein-coupled receptor for niacin. beta-hydroxybutyrate (beta-HB) is a physiologic ligand for the receptor. beta-HB, the predominate ketone body in circulation, is an important energy source for neurons, including retinal neurons, under various physiologic and pathologic conditions.

TGFbeta prevents proteasomal degradation of the cyclin-dependent kinase inhibitor p27kip1 for cell cycle arrest.

TGFbeta mediates cell cycle arrest in late G(1) phase of the cell cycle with a simultaneous peak in the levels of the cyclin-dependent kinase inhibitor, p27(kip1) (p27). In this report, we show that whereas p27 resides in the cytoplasm in the endometrial carcinoma (ECA) cell line HEC-1A, TGFbeta increases the total levels and translocation of p27 into the nucleus. Concomitantly, TGFbeta activates the transcription factors Smad2 and Smad3, inhibits proliferation, and blocks Cdk2 activity; all these events are blocked by an inhibitor of TbetaRI serine kinase activity (SD208).

Expression of the iron-regulatory protein haemojuvelin in retina and its regulation during cytomegalovirus infection.

Haemochromatosis is a genetic disorder of iron overload resulting from loss-of-function mutations in genes coding for the iron-regulatory proteins HFE [HLA-like protein involved in iron (Fe) homoeostasis], transferrin receptor 2, ferroportin, hepcidin and HJV (haemojuvelin). Expression of the first four genes coding for these proteins in retina has been established. Here we report on the expression of HJV.

Effects of hyperglycemia and oxidative stress on the glutamate transporters GLAST and system xc- in mouse retinal Müller glial cells.

Elevated glutamate levels have been reported in humans with diabetic retinopathy. Retinal Müller glial cells regulate glutamate levels via the GLAST transporter and system x(c)(-) (cystine-glutamate exchanger). We have investigated whether transporter function and gene and/or protein expression are altered in mouse Müller cells cultured under conditions of hyperglycemia or oxidative stress (two factors implicated in diabetic retinopathy).

Citrate transport and metabolism in mammalian cells: prostate epithelial cells and prostate cancer.

Citrate, an organic trivalent anion, is a major substrate for generation of energy in most cells. It is produced in mitochondria and used either in the Krebs' cycle or released into cytoplasm through a specific mitochondrial carriers. Citrate can also be taken up from blood through different plasma membrane transporters.

A traffic signal for heterodimeric amino acid transporters to transfer from the ER to the Golgi.

Heterodimeric amino acid transporters represent a unique class of transport systems that consist of a light chain that serves as the 'transporter proper' and a heavy chain that is necessary for targeting the complex to the plasma membrane. The currently prevailing paradigm assigns no role for the light chains in the cellular processing of these transporters. In this issue of the Biochemical Journal, Sakamoto et al.

Taurine uptake across the human intestinal brush-border membrane is via two transporters: H+-coupled PAT1 (SLC36A1) and Na+- and Cl(-)-dependent TauT (SLC6A6).

Taurine is an essential amino acid in some mammals and is conditionally essential in humans. Taurine is an abundant component of meat and fish-based foods and has been used as an oral supplement in the treatment of disorders such as cystic fibrosis and hypertension. The purpose of this investigation was to identity the relative contributions of the solute transporters involved in taurine uptake across the luminal membrane of human enterocytes.

Nutrient transporters in cancer: relevance to Warburg hypothesis and beyond.

Tumor cells have an increased demand for nutrients; this demand is met by increased availability of nutrients through vasculogenesis and by enhanced cellular entry of nutrients through upregulation of specific transporters. This review focuses on three groups of nutrient transporters relevant to cancer: glucose transporters, lactate transporters, and amino acid transporters. Tumor cells enhance glucose uptake via induction of GLUT1 and SGLT1, and coordinate the increased entry of glucose with increased glycolysis.

Farnesoid X receptor deficiency in mice leads to increased intestinal epithelial cell proliferation and tumor development.

Increased dietary fat consumption is associated with colon cancer development. The exact mechanism by which fat induces colon cancer is not clear, however, increased bile acid excretion in response to high-fat diet may promote colon carcinogenesis. The farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily, and bile acids are endogenous ligands of FXR.

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

Human colon cancer cells and primary colon cancer silence the gene coding for LDH (lactate dehydrogenase)-B and up-regulate the gene coding for LDH-A, resulting in effective conversion of pyruvate into lactate. This is associated with markedly reduced levels of pyruvate in cancer cells compared with non-malignant cells. The silencing of LDH-B in cancer cells occurs via DNA methylation, with involvement of the DNMTs (DNA methyltransferases) DNMT1 and DNMT3b.