Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mammalian cell lines often become multidrug-resistant to cytotoxic drugs by amplification and/or overexpression of the P-glycoprotein (Pgy) genes. However, several malignant cell lines seem to acquire low levels of drug resistance by non-P-glycoprotein mediated mechanisms. We report here on cytogenetical signs of non-Pgy gene amplification in murine SEWA cells during the early steps of selection in Colcemid (COL). In line TC13COL0.01, rare cells exhibited a homogeneously staining region (HSR) distally in chromosome 16. As the COL-concentration was raised the HSR-chromosome was retained and, in addition, the cells developed numerous double minutes (DMs). The DMs, but not the HSR, contained amplified Pgy genes. The HSR may correspond to amplified heat shock protein 70 (Hsp70) genes, detected by Southern analysis. A second low-level COL-resistant line, TC13D70.01, contained DMs but showed no amplification of Pgy, Hsp70, Hsp90, alpha- or beta-tubulin genes. In higher COL-concentration, P-glycoprotein mediated drug resistance was induced. In contrast to actinomycin D-resistant SEWA cells, in which higher amplification levels of Pgy1 than of Pgy2 are regularly present, the COL-resistant lines showed a preference for Pgy2 gene amplification. These results are in line with the suggestion that the murine Pgy1 and Pgy2 genes have overlapping but distinct drug specificities.
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PMID:Colcemid resistance in murine SEWA cells: non-Pgy gene amplification at low levels of resistance and preferential Pgy2 gene amplification at high levels of resistance. 755 81

Single-step selections were used to obtain Chinese hamster ovary cell lines resistant to Colcemid and vinblastine. Verapamil was included in the selections to circumvent the isolation of cells with P-glycoprotein-mediated multidrug resistance and thereby enrich for cells with tubulin alterations. The isolated cell lines were 2-fold resistant to the selecting drug, exhibited cross-resistance to other drugs that inhibit microtubule assembly, and had enhanced sensitivity to the microtubule-stabilizing drug paclitaxel. The concomitant resistance to microtubule-destabilizing drugs and enhanced sensitivity to paclitaxel suggested that these cell lines have changes in microtubule assembly. Consistent with this interpretation, drug-resistant cell lines exhibited altered alpha- or beta-tubulin mobility on two-dimensional gels and higher levels (47-54%) of assembled tubulin compared with wild-type (39%) or paclitaxel-resistant cells (25%). Some drug-resistant cells also had bundled microtubules as judged by immunofluorescence. Genomic sequencing of 11 drug-resistant cell lines predicted five different alterations (D45Y, C211F, D224N, S234N, and K350N) in beta-tubulin and four different alterations (H283Y, E55K, A383V, and R390C) in alpha-tubulin. The amino acid substitutions are dispersed on the primary and tertiary structures of tubulin and, together with the other mutant properties, argue against a mechanism involving changes in drug binding. Rather, we propose that the alterations in alpha- and beta-tubulin increase microtubule stability by promoting longitudinal interdimer and intradimer interactions and/or lateral interactions between protofilaments. This enhanced stability of microtubules increases their resistance to drugs that inhibit assembly.
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PMID:Mutations in alpha- and beta-tubulin that stabilize microtubules and confer resistance to colcemid and vinblastine. 1288 31