Volume-sensitive chloride currents in four epithelial cell lines are not directly correlated to the expression of the MDR-1 gene.
It has been shown recently that heterologous expression of human MDR-1 gene, which is responsible for multidrug resistance during cancer therapy, causes appearance of volume-sensitive Cl- currents, thus suggesting that the product of the MDR-1 gene (the P-glycoprotein) has a Cl- channel activity (Valverde, M. A., Diaz, M., Sepulveda, M. A., Gill, D. R., Hyde, S. C., and Higgins, C. F. (1992) Nature 355, 830-833). In the present work, we have tested four epithelial cell lines both for the expression of MDR-1 gene and for the presence of volume-sensitive Cl- currents. LoVo/H and LoVo/Dx cells derive from a human colon adenocarcinoma, the latter cell line being resistant to high concentrations of the antitumoral drug doxorubicin. 9HTEo- cells were obtained by transformation of human tracheal epithelium. The 9HTEo-/Dx cell line was established from these cells by selection in doxorubicin. As expected, higher levels of P-glycoprotein expression were detected in LoVo/Dx and 9HTEo-/Dx by means of reverse transcriptase polymerase chain reaction technique, indirect immunofluorescence, and Western immunoblot assays. In contrast with these data, the size of swelling-induced Cl- current was the same in the sensitive cell line and in its drug-resistant counterpart. Actually, the Cl- conductance of 9HTEo- and 9HTEo-/Dx was 4-fold higher than that of either LoVo/H or LoVo/Dx cells. This indicates that the amplitude of this conductance is not directly related to the expression of the MDR-1 gene.
Rasola
A
A
Laboratorio di Genetica Molecolare, Istituto Giannina Gaslini, Genova, Italy.
Galietta
L J
LJ
Gruenert
D C
DC
Romeo
G
G
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D048429:Cell Size; D018118:Chloride Channels / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism*; D004317:Doxorubicin / Q000494:pharmacology; D004351:Drug Resistance; D004553:Electric Conductivity / Q000187:drug effects; D004848:Epithelium / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D008562:Membrane Glycoproteins / Q000378:metabolism*; D014882:Water-Electrolyte Balance
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002352:Carrier Proteins; D018118:Chloride Channels; D002712:Chlorides; D008562:Membrane Glycoproteins; D004317:Doxorubicin