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  • ATP-binding cassette (ABC) transporters  (1)
  • Human bladder carcinoma  (1)
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  • 1
    ISSN: 1573-6881
    Keywords: P-glycoprotein ; multidrug resistance ; MDR ; ATPase ; drug transport ; ATP-binding cassette (ABC) transporters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Chemotherapy, though it remains one of the front-line weapons used to treat human cancer, is often ineffective due to drug resistance mechanisms manifest in tumor cells. One common pattern of drug resistance, characterized by simultaneous resistance to multiple amphipathic, but otherwise structurally dissimilar anticancer drugs, is termed multidrug resistance. Multidrug resistance in various model systems, covering the phylogenetic range from bacteria to man, can be conferred by mammalian P-glycoproteins (PGPs), often termed multidrug transporters. PGPs are 170-kD polytopic membrane proteins, predicted to consist of two homologous halves, each with six membrane spanning regions and one ATP binding site. They are members of the ATP-binding cassette (ABC) superfamily of transporters, and are known to function biochemically as energy-dependent drug efflux pumps. However, much remains to be learned about PGP structure-function relationships, membrane topology, posttranslational regulation, and bioenergetics of drug transport. Much of the recent progress in the study of the human and mouse PGPs has come from heterologous expression systems which offer the benefits of ease of genetic selection and manipulation, and/or short generation times of the organism in which PGPs are expressed, and/or high-level expression of recombinant PGP. Here we review recent studies of PGP inE. coli, baculovirus, and yeast systems and evaluate their utility for the study of PGPs, as well as other higher eukaryotic membrane proteins.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1335
    Keywords: Pseudomonas exotoxin ; TGFα ; Rat bladder carcinoma ; Human bladder carcinoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A protein formed by fusion of transforming growth factor α withPseudomonas exotoxin (TGFα-PE40) has been shown to have the ability to kill or inhibit the growth of several carcinoma cell lines. This study was designed to evaluate thein vitro cytotoxic effects of TGFα-PE40 on rat and human bladder carcinoma cell lines with different biological potential, and normal rat urothelial cells. The rat cell lines used were D44c, LMC19, and MYU3L, which were established in our laboratory. Human cell lines used were RT4, T24, and 253J. As a normal control, we used the first-passage culture of normal rat bladder urothelium (RU-P1). We examined the number and affinity of epidermal growth factor receptors (EGFR) in these cells, the ability of TGFα-PE40 to bind EGFR, and the cytotoxic effect of TGFα-PE40 and PE40. Rat cell lines, D44c, LMC19, and MYU3L (EGFR=4.9×103–11.4×103/cell) had ED50 values (the concentration of TGFα-PE40 needed to reduce the viable cell population by 50%) of 180 pM, 540 pM and 6000 pM respectively; forc 1 (the concentration required to achieve complete inhibition of growth under continuous serum stimulation) TGFα-PE40 concentrations of 104 pM, 104 pM and higher than 104 pM respectively were required. Human cell lines, RT4, T24, and 253J (EGFR=32×103–126×103/cell) had ED50 values of 20 pM, 66 pM, and 330 pM respectively and T24 showedc 1 values of 103 pM. RU-P1 (EGFR =92.6×103/cell) had the highest ED50 value of 8000 pM. These data indicate that the susceptibility to TGFα-PE40 does not always depend on the number of EGFR, that cells having a relatively small number of EGFR respond well to TGFα-PE40, and that normal urothelial cells are more resistant to TGFα-PE40 than are cancer cells. The differential effect of TGFα-PE40 on normal and neoplastic cells provides a rational basis for its use in vivo to control tumor growth.
    Type of Medium: Electronic Resource
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