Interactions of ATP, oestradiol, genistein and the anti-oestrogens, faslodex (ICI 182780) and tamoxifen, with the human erythrocyte glucose transporter, GLUT1.
17 beta-Oestradiol (ED when subscript to K) and the phytoestrogen isoflavone genistein (GEN) inhibit glucose transport in human erythrocytes and erythrocyte ghosts. The selective oestrogen receptor modulators or anti-oestrogens, faslodex (ICI 182780) (FAS) and tamoxifen (TAM), competitively antagonize oestradiol inhibition of glucose exit from erythrocytes (K(i(ED/FAS))=2.84+/-0.16 microM and K(i(ED/TAM))=100+/-2 nM). Faslodex has no significant inhibitory effect on glucose exit, but tamoxifen alone inhibits glucose exit (K(i(TAM))=300+/-100 nM). In ghosts, ATP (1-4 mM) competitively antagonizes oestradiol, genistein and cytochalasin B (CB)-dependent inhibitions of glucose exit, (K(i(ATP/ED))=2.5+/-0.23 mM, K(i(ATP/GEN))=0.99+/-0.17 mM and K(i(ATP/CB))=0.76+/-0.08 mM). Tamoxifen and faslodex reverse oestradiol-dependent inhibition of glucose exit with ATP>1 mM (K(i(ED/TAM))=130+/-5 nM and K(i(ED/FAS))=2.7+/-0.9 microM). The cytoplasmic surface of the glucose transporter (GLUT)1 contains four sequences with close homologies to sequences in the ligand-binding domain of human oestrogen receptor beta (hesr-2). One homology is adjacent to the Walker ATP-binding motif II (GLUT1, residues 225-229) in the large cytoplasmic segment linking transmembrane helices 6 and 7; another GLUT (residues 421-423) contains the Walker ATP-binding motif III. Mapping of these regions on to a three-dimensional template of GLUT indicates that a possible oestrogen-binding site lies between His(337), Arg(349) and Glu(249) at the cytoplasmic entrance to the hydrophilic pore spanning GLUT, which have a similar topology to His(475), Glu(305) and Arg(346) in hesr-2 that anchor the head and tail hydroxy groups of oestradiol and genistein, and thus are suitably placed to provide an ATP-sensitive oestrogen binding site that could modulate glucose export.
Afzal
Iram
I
Physiology Group, Centre for Vascular Biology, New Hunt's House, King's College London, Guy's Campus, London SE1 1UL, U.K.
Cunningham
Philip
P
Naftalin
Richard J
RJ
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D003571:Cytochalasin B / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000187:drug effects* / Q000378:metabolism; D004958:Estradiol / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology*; D004965:Estrogen Antagonists / Q000378:metabolism / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000378:metabolism / Q000494:pharmacology; D000077267:Fulvestrant; D019833:Genistein / Q000378:metabolism / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism; D051272:Glucose Transporter Type 1; D006801:Humans; D008024:Ligands; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010693:Phloretin / Q000494:pharmacology; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013629:Tamoxifen / Q000378:metabolism / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D004965:Estrogen Antagonists; D020847:Estrogen Receptor Modulators; D051272:Glucose Transporter Type 1; D008024:Ligands; D009004:Monosaccharide Transport Proteins; C495677:SLC2A1 protein, human; D013629:Tamoxifen; D000077267:Fulvestrant; D003571:Cytochalasin B; D004958:Estradiol; D000255:Adenosine Triphosphate; D019833:Genistein; D005947:Glucose; D010693:Phloretin