A three-dimensional model of the human facilitative glucose transporter Glut1

The human facilitative transporter Glut1 is the major glucose transporter present in all human cells, has a central role in metabolism, and is an archetype of the superfamily of major protein facilitators. Here we describe a three-dimensional structure of Glut1 based on helical packing schemes proposed for lactose permease and Glut1 and predictions of secondary structure, and refined using energy minimization, molecular dynamics simulations, and quality and environmental scores. The Ramachandran scores and the stereochemical quality of the structure obtained were as good as those for the known structures of the KcsA K(+) channel and aquaporin 1. We found two channels in Glut1. One of them traverses the structure completely, and is lined by many residues known to be solvent-accessible. Since it is delimited by the QLS motif and by several well conserved residues, it may serve as the substrate transport pathway. To validate our structure, we determined the distance between these channels and all the residues for which mutations are known. From the locations of sugar transporter signatures, motifs, and residues important to the transport function, we find that this Glut1 structure is consistent with mutagenesis and biochemical studies. It also accounts for functional deficits in seven pathogenic mutants.     

IL-12 prevents tolerance induction with mouse thyroglobulin by priming pathogenic T cells in experimental autoimmune thyroiditis: role of IFN-gamma and the costimulatory molecules CD40l and CD28

Deaggregated mouse thyroglobulin (dMTg) induces tolerance to experimental autoimmune thyroiditis (EAT), a Th1-cell-mediated disease. To test whether IL-12, a potent activator of Th1 cells, can overcome tolerance induction, different doses of IL-12 were given to CBA/J mice during the critical interval of 2--3 days after dMTg administration. After challenge with MTg/LPS, dMTg/IL-12-pretreated mice showed more extensive thyroiditis than immunized controls, but comparable levels of anti-MTg and T cell proliferation. Without challenge, few MTg antibodies were produced. In contrast, pretreatment with dMTg/poly A:U or dMTg/IL-1, two other T cell activators which also interfere with tolerance induction, induced antibodies before challenge, but not more severe thyroiditis. Mice pretreated with IL-12 without dMTg developed thyroiditis comparable to immunized controls, but less severe thyroiditis than dMTg/IL-12-pretreated mice. Clearly, IL-12 not only blocked tolerance induction, but also primed antigen-specific T cells during the tolerogenic period of dMTg pretreatment, resulting in stronger thyroiditis than immunization only. Neither treatment with anti-IFN-gamma nor the use of IFN-gamma knockout mice altered the capacity of IL-12 to prevent tolerance induction. However, both anti-CD28 and anti-CD40L antibodies diminished the priming effect by dMTg/IL-12. The mechanisms of IL-12 action include priming of MTg-specific T cells and the involvement of T cell costimulatory molecules.     

Modulation of endocytic traffic in polarized Madin-Darby canine kidney cells by the small GTPase RhoA

Efficient postendocytic membrane traffic in polarized epithelial cells is thought to be regulated in part by the actin cytoskeleton. RhoA modulates assemblies of actin in the cell, and it has been shown to regulate pinocytosis and phagocytosis; however, its effects on postendocytic traffic are largely unexplored. To this end, we expressed wild-type RhoA (RhoAWT), dominant active RhoA (RhoAV14), and dominant inactive RhoA (RhoAN19) in Madin-Darby canine kidney (MDCK) cells expressing the polymeric immunoglobulin receptor. RhoAV14 expression stimulated the rate of apical and basolateral endocytosis, whereas RhoAN19 expression decreased the rate from both membrane domains. Polarized basolateral recycling of transferrin was disrupted in RhoAV14-expressing cells as a result of increased ligand release at the apical pole of the cell. Degradation of basolaterally internalized epidermal growth factor was slowed in RhoAV14-expressing cells. Although apical recycling of immunoglobulin A (IgA) was largely unaffected in cells expressing RhoAV14, transcytosis of basolaterally internalized IgA was severely impaired. Morphological and biochemical analyses demonstrated that a large proportion of IgA internalized from the basolateral pole of RhoAV14-expressing cells remained within basolateral early endosomes and was slow to exit these compartments. RhoAN19 and RhoAWT expression had little effect on these postendocytic pathways. These results indicate that in polarized MDCK cells activated RhoA may modulate endocytosis from both membrane domains and postendocytic traffic at the basolateral pole of the cell.     

G1 cell cycle progression and the expression of G1 cyclins are regulated by PI3K/AKT/mTOR/p70S6K1 signaling in human ovarian cancer cells

Ovarian cancer is one of the most common cancers among women. Recent studies demonstrated that the gene encoding the p110alpha catalytic subunit of phosphatidylinositol 3-kinase (PI3K) is frequently amplified in ovarian cancer cells. PI3K is involved in multiple cellular functions, including proliferation, differentiation, antiapoptosis, tumorigenesis, and angiogenesis. In this study, we demonstrate that the inhibition of PI3K activity by LY-294002 inhibited ovarian cancer cell proliferation and induced G(1) cell cycle arrest. This effect was accompanied by the decreased expression of G(1)-associated proteins, including cyclin D1, cyclin-dependent kinase (CDK) 4, CDC25A, and retinoblastoma phosphorylation at Ser(780), Ser(795), and Ser(807/811). Expression of CDK6 and beta-actin was not affected by LY-294002. Expression of the cyclin kinase inhibitor p16(INK4a) was induced by the PI3K inhibitor, whereas steady-state levels of p21(CIP1/WAF1) were decreased in the same experiment. The inhibition of PI3K activity also inhibited the phosphorylation of AKT and p70S6K1, but not extracellular regulated kinase 1/2. The G(1) cell cycle arrest induced by LY-294002 was restored by the expression of active forms of AKT and p70S6K1 in the cells. Our study shows that PI3K transmits a mitogenic signal through AKT and mammalian target of rapamycin (mTOR) to p70S6K1. The mTOR inhibitor rapamycin had similar inhibitory effects on G(1) cell cycle progression and on the expression of cyclin D1, CDK4, CDC25A, and retinoblastoma phosphorylation. These results indicate that PI3K mediates G(1) progression and cyclin expression through activation of an AKT/mTOR/p70S6K1 signaling pathway in the ovarian cancer cells.     

Cardioprotective effects of ingliforib, a novel glycogen phosphorylase inhibitor

Interventions such as glycogen depletion, which limit myocardial anaerobic glycolysis and the associated proton production, can reduce myocardial ischemic injury; thus it follows that inhibition of glycogenolysis should also be cardioprotective. Therefore, we examined whether the novel glycogen phosphorylase inhibitor 5-Chloro-N-[(1S,2R)-3-[(3R,4S)-3,4-dihydroxy-1-pyrrolidinyl)]-2-hydroxy-3-oxo-1-(phenylmethyl)propyl]-1H-indole-2-carboxamide (ingliforib; CP-368,296) could reduce infarct size in both in vitro and in vivo rabbit models of ischemia-reperfusion injury (30 min of regional ischemia, followed by 120 min of reperfusion). In Langendorff-perfused hearts, constant perfusion of ingliforib started 30 min before regional ischemia and elicited a concentration-dependent reduction in infarct size; infarct size was reduced by 69% with 10 microM ingliforib. No significant drug-induced changes were observed in either cardiac function (heart rate, left ventricular developed pressure) or coronary flow. In open-chest anesthetized rabbits, a dose of ingliforib (15 mg/kg loading dose; 23 mg.kg(-1).h(-1) infusion) selected to achieve a free plasma concentration equivalent to an estimated EC(50) in the isolated hearts (1.2 microM, 0.55 microg/ml) significantly reduced infarct size by 52%, and reduced plasma glucose and lactate concentrations. Furthermore, myocardial glycogen phosphorylase a and total glycogen phosphorylase activity were reduced by 65% and 40%, respectively, and glycogen stores were preserved in ingliforib-treated hearts. No significant change was observed in mean arterial pressure or rate-pressure product in the ingliforib group, although heart rate was modestly decreased postischemia. In conclusion, glycogen phosphorylase inhibition with ingliforib markedly reduces myocardial ischemic injury in vitro and in vivo; this may represent a viable approach for both achieving clinical cardioprotection and treating diabetic patients at increased risk of cardiovascular disease.     

Azaadamantane benzamide 5-HT4 agonists: gastrointestinal prokinetic SC-54750

Azaadamantanone 1 was converted to a series of aminoazaadamantane benzamides 9a-d, which were profiled for serotonin receptor activity. Aminomethylazaadamantane SC-54750 is a potent 5-HT(4) agonist and 5-HT(3) antagonist with in vivo efficacy in gastroparesis models and also inhibits cisplatin-induced emesis.     

Hydrogen peroxide formation and actin filament reorganization by Cdc42 are essential for ethanol-induced in vitro angiogenesis

This report focuses on the identification of the molecular mechanisms of ethanol-induced in vitro angiogenesis. The manipulation of angiogenesis is an important therapeutic approach for the treatment of cancer, cardiovascular diseases, and chronic inflammation. Our results showed that ethanol stimulation altered the integrity of actin filaments and increased the formation of lamellipodia and filopodia in SVEC4-10 cells. Further experiments demonstrated that ethanol stimulation increased cell migration and invasion and induced in vitro angiogenesis in SVEC4-10 cells. Mechanistically, ethanol stimulation activated Cdc42 and produced H(2)O(2) a reactive oxygen species intermediate in SVEC4-10 cells. Measuring the time course of Cdc42 activation and H(2)O(2) production upon ethanol stimulation revealed that the Cdc42 activation and the increase of H(2)O(2) lasted more than 3 h, which indicates the mechanisms of the long duration effects of ethanol on the cells. Furthermore, either overexpression of a constitutive dominant negative Cdc42 or inhibition of H(2)O(2) production abrogated the effects of ethanol on SVEC4-10 cells, indicating that both the activation of Cdc42 and the production of H(2)O(2) are essential for the actions of ethanol. Interestingly, we also found that overexpression of a constitutive dominant positive Cdc42 itself was sufficient to produce H(2)O(2) and to induce in vitro angiogenesis. Taken together, our results suggest that ethanol stimulation can induce H(2)O(2) production through the activation of Cdc42, which results in reorganizing actin filaments and increasing cell motility and in vitro angiogenesis.     

Stable and transient expression of chimeric peroxisomal membrane proteins induces an independent "zippering" of peroxisomes and an endoplasmic reticulum subdomain

Peroxisomal ascorbate peroxidase (APX) (EC 1.11.1.11) was shown recently to sort through a subdomain of the ER (peroxisomal endoplasmic reticulum; pER), and in certain cases, alter the distribution and/or morphology of peroxisomes and pER when overexpressed transiently in Nicotiana tabacum L. cv. Bright Yellow 2 (BY-2) cells. Our goal was to gain insight into the dynamics of peroxisomal membrane protein sorting by characterizing the structure and formation of reorganized peroxisomes and pER. Specifically, we test directly the hypothesis that the observed phenomenon is due to the oligomerization of cytosol-facing, membrane-bound polypeptides. a process referred to as membrane "zippering". Results from differential detergent permeabilization experiments confirmed that peroxisomal APX is a C-terminal "tail-anchored" (Cmatrix-Ncytosol) membrane protein with a majority of the polypeptide facing the cytosol. Transient expression of several APX chimeras whose passenger polypeptides can form dimers or trimers resulted in the progressive formation of "globular" peroxisomes and circular pER membranes. Stable expression of the trimer-capable fusion protein yielded suspension cultures that reproducibly maintained a high degree of peroxisomal globules but relatively few detectable pER membranes. Electron micrographs revealed that the globules consisted of numerous individual peroxisomes, seemingly in direct contact with other peroxisomes and/or mitochondria. These peroxisomal clusters or aggregates were not observed in cells transiently expressing monomeric versions of APX. These findings indicate that the progressive, independent "zippering" of peroxisomes and pER is due to the post-sorting oligomerization of monomeric, cytosol-facing polypeptides that are integrally inserted into the membranes of "like" organelles. The dynamics of this process are discussed, especially with respect to the involvement of the microtubule cytoskeleton.