Conservation of the Class I β-Tubulin Gene in Human Populations and Lack of Mutations in Lung Cancers and Paclitaxel-resistant Ovarian Cancers¹

Abstract

The goal of this study was to determine the prevalence of sequence variants in the class I β-tubulin (clone m40) gene and their occurrence in human tumors and cancer cell lines. DNA was isolated from 93 control individuals representing a wide variety of ethnicities, 49 paclitaxel-naive specimens (16 ovarian cancers, 17 non-small cell lung cancers, and 16 ovarian cancer cell lines), and 30 paclitaxel-resistant specimens (9 ovarian cancers, 9 ovarian cancer cell lines, and 12 ovarian cancer xenografts in nude mice). Denaturing high-performance liquid chromatography and direct sequence analysis detected two silent polymorphisms in exon 4, Leu217Leu (CTG/CTA) and Gly400Gly (GGC/GGT), with minor allele frequencies of 17 and 0.5%, respectively. Five nucleotide substitutions and one single-base deletion were detected in introns 1, 2, and 3 and in the 3′ untranslated region. Analysis of 49 paclitaxel-naive and 30 paclitaxel-resistant specimens revealed no additional polymorphisms in the coding region. In addition, no amino acid replacements were found in chimpanzee, gorilla, and orangutan in comparison to human. Our data demonstrate a very high degree of sequence conservation in class I β-tubulin, suggesting that all residues are important in tubulin structure and function. Individual variation in response to treatment with paclitaxel is not likely to be caused by genetic variations in the β-tubulin drug target. Moreover, acquired mutations in class I β-tubulin are unlikely to be a clinically relevant cause of drug resistance.