Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.49 (reverse transcriptase)
 31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Volume-sensitive chloride currents in four epithelial cell lines are not directly correlated to the expression of the MDR-1 gene. 790

The two COX (cyclo-oxygenase) isoenzymes COX-1 and -2 catalyse the initial step in the conversion of arachidonic acid into PG (prostaglandin) hormones. The identification of an mRNA transcript encoding a splice variant of human COX-1 was reported more than a decade ago [Diaz, Reginato and Jimenez (1992) J. Biol. Chem. 267, 10816-10822], yet catalytic activity and tissue expression of the corresponding spliced protein remained uncharacterized. The splice variant lacks amino acids 396-432, corresponding to the last 37 amino acids of exon 9 of the gene encoding COX-1. These amino acids form a loop at one side of the peroxidase active site of the protein. We expressed the full-length and spliced COX-1 cDNAs in COS-7 and Sf9 insect cells, and determined the PG-forming activity using incubations with radiolabelled arachidonic acid and HPLC analyses. When expressed in either system, abundant PG formation was observed with the full-length COX-1, whereas the spliced protein did not form any detectable product. Peroxidase activity was readily detected in microsomes prepared from COS-7 cells transfected with COX-1 but not with the splice variant. In reverse transcriptase-PCR experiments, we detected the mRNA for the alternatively spliced and full-length COX-1 in human brain, tonsil and colon tissue, yet we were unable to detect expression of the spliced protein in the same tissues using immunoprecipitation and Western-blot analyses. We conclude that, whereas the mRNA transcript for the spliced COX-1 is present in various human tissues, the corresponding protein is either not formed or subject to rapid proteolytic degradation.
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PMID:Human cyclo-oxygenase-1 and an alternative splice variant: contrasts in expression of mRNA, protein and catalytic activities. 1536 Oct 66