title: Mutations in alpha- and beta-tubulin that stabilize microtubules and confer resistance to colcemid and vinblastine.
abstract: 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.
authors.affiliation: Department of Integrative Biology and Pharmacology, University of Texas-Houston Medical School, Houston, Texas 77030, USA.
authors.forename: Malathi
authors.initials: M
authors.lastname: Hari
authors.forename: Yaqing
authors.initials: Y
authors.lastname: Wang
authors.forename: Sudha
authors.initials: S
authors.lastname: Veeraraghavan
authors.forename: Fernando
authors.initials: F
authors.lastname: Cabral
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D016466:CHO Cells / Q000187:drug effects / Q000378:metabolism; D006224:Cricetinae; D003703:Demecolcine / Q000494:pharmacology; D004351:Drug Resistance; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics*; D017239:Paclitaxel / Q000494:pharmacology; D014404:Tubulin / Q000235:genetics* / Q000378:metabolism; D014747:Vinblastine / Q000494:pharmacology
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D014404:Tubulin; D014747:Vinblastine; D017239:Paclitaxel; D003703:Demecolcine