GLUT8 is a novel glucose transporter-like protein that exhibits significant sequence similarity with the members of the sugar transport facilitator family (29.4% of amino acids identical with GLUT1). Human and mouse sequence (86.2% identical amino acids) comprise 12 putative membrane-spanning helices and several conserved motifs (sugar transporter signatures), which have previously been shown to be essential for transport activity, e.g. GRK in loop 2, PETPR in loop 6, QQLSGVN in helix 7, DRAGRR in loop 8, GWGPIPW in helix 10, and PETKG in the C-terminal tail. An expressed sequence tag (STS A005N15) corresponding with the 3 -untranslated region of GLUT8 has previously been mapped to human chromosome 9. COS-7 cells transfected with GLUT8 cDNA expressed a 42-kDa protein exhibiting specific, glucose-inhibitable cytochalasin B binding (K D ‫؍‬ 56.6 ؎ 18 nM) and reconstitutable glucose transport activity (8.1 ؎ 1.4 nmol/(mg protein ؋ 10 s) versus 1.1 ؎ 0.1 in control transfections). In human tissues, a 2.4-kilobase pair transcript was predominantly found in testis, but not in testicular carcinoma. Lower amounts of the mRNA were detected in most other tissues including skeletal muscle, heart, small intestine, and brain. GLUT8 mRNA was found in testis from adult, but not from prepubertal rats; its expression in human testis was suppressed by estrogen treatment. It is concluded that GLUT8 is a sugar transport facilitator with glucose transport activity and a hormonally regulated testicular function.Hexose transport into mammalian cells is catalyzed by the members of a small family of 45-55-kDa membrane proteins, GLUT1-GLUT5 (1-4). These hexose transporters belong to the larger family of transport facilitators, which comprises yeast hexose transporters, plant hexose-proton symporters, bacterial sugar-proton symporters (5, 6), and organic anion as well as organic cation transporters (7,8). Defining characteristics in the family of hexose transporters are the presence of 12 membrane-spanning helices and a number of conserved residues and motifs (see Fig. 3). These sugar transporter signatures have been characterized by sequence comparisons as well as by mutagenesis. Substitutions, e.g. of the conserved arginine and glutamate residues on the cytoplasmic surface (9), of tryptophan residues 388 and 412 in helix 10 and 11 (10, 11), tyrosines 146 and 292/293 in helix 4 and 7 (12, 13), glutamine 161 in helix 5 (14), and glutamine 282 (15), have been shown to markedly affect transporter function. In addition, mutagenesis experiments have implicated a motif (QLS) in helix 7 in determining the sugar recognition of GLUT1-GLUT5 (16).The known glucose transporter (GLUT) 1 isoforms differ in their expression in different tissues, in their kinetic characteristics, i.e. K m values (2), and in their substrate specificity. GLUT1 mediates glucose transport into erythrocytes and through the blood-brain barrier, and appears to provide a basal supply of glucose for most cells. GLUT2 catalyzes glucose uptake into the liver (17), and is an essent...

cDNA clones of two novel Ras-related GTP-binding proteins (RagA and RagB) were isolated from rat and human cDNA libraries. Their deduced amino acid sequences comprise four of the six known conserved GTPbinding motifs (PM1, -2, -3, G1), the remaining two (G2, G3) being strikingly different from those of the Ras family, and an unusually large C-terminal domain (100 amino acids) presumably unrelated to GTP binding. RagA and RagB differ by seven conservative amino acid substitutions (98% identity), and by 33 additional residues at the N terminus of RagB. In addition, two isoforms of RagB (RagB s and RagB l ) were found that differed only by an insertion of 28 codons between the GTP-binding motifs PM2 and PM3, apparently generated by alternative mRNA splicing. Polymerase chain reaction amplification with specific primers indicated that both long and short form of RagB transcripts were present in adrenal gland, thymus, spleen, and kidney, whereas in brain, only the long form RagB l was detected. A long splicing variant of RagA was not detected. Recombinant glutathione S-transferase (GST) fusion proteins of RagA and RagB s bound large amounts of radiolabeled GTP␥S in a specific and saturable manner. In contrast, GTP␥S binding of GST-RagB l hardly exceeded that of recombinant GST. GTP␥S bound to recombinant RagA, and RagB s was rapidly exchangeable for GTP, whereas no intrinsic GTPase activity was detected. A multiple sequence alignment indicated that RagA and RagB cannot be assigned to any of the known subfamilies of Ras-related GTPases but exhibit a 52% identity with a yeast protein (Gtr1) presumably involved in phosphate transport and/or cell growth. It is suggested that RagA and RagB are the mammalian homologues of Gtr1 and that they represent a novel subfamily of Ras-homologous GTP binding proteins.Ras-homologous GTPases constitute a large family of signal transducers that alternate between an activated, GTP-binding, and an inactivated, GDP-binding state (Hall, 1990;Bourne et al., 1990;Boguski and McCormick, 1993). These proteins represent cellular switches that are operated by GTP-exchange factors and factors stimulating their intrinsic GTPase activity. To date, five subfamilies of the Ras superfamily are known: Ras, Rho, Rab, Ran, and ARF 1 proteins. These subfamilies are not only characterized by common structural features but also by a similar function, e.g. regulation of growth (Ras) (Egan and Weinberg, 1993), cytoskeleton organization (Rho) (Aktories et al., 1992), or vesicle transport (Rab and ARF) (Novick and Brennwald, 1993;Kahn et al., 1993). All GTPases of the Ras superfamily have in common the presence of six conserved motifs involved in GTP/GDP binding, three of them as phosphate/magnesium binding sites (PM1-PM3), and the other three as guanine nucleotide binding sites (G1-G3) (Valencia et al., 1991). Therefore, the sequences of the least related GTPases comprise approximately 20 -30% identical amino acids, whereas the sequence similarity is considerably higher within subfamilies (e.g. Ͼ40% identity in...

No abstract

To our knowledge residual tumor after the first transurethral resection is a fact in bladder cancer treatment. The second transurethral resection offers the possibility to preserve the bladder. Furthermore, residual disease can be detected and removed in due time. In case of up staging to muscle infiltrating tumor, cystectomy is the next therapeutic step.

To our knowledge residual tumor after the first transurethral resection is a fact in bladder cancer treatment. The second transurethral resection offers the possibility to preserve the bladder. Furthermore, residual disease can be detected and removed in due time. In case of up staging to muscle infiltrating tumor, cystectomy is the next therapeutic step.