Altered expression of Mβ2, the class II β-tubulin isotype, in a murine J774.2 cell line with a high level of taxol resistance

A series of taxol- and taxotere-resistant J774.2 cell lines has been characterized with respect to altered expression of β-tubulin, the cellular target for these drugs. Vertebrates have six classes of β-tubulin isotypes, each displaying a distinct pattern of expression. Although the functional significance of multiple β-tubulins has not been fully defined, there is evidence that the individual isotypes contribute to differences in microtubule dynamics and drug binding. To determine if alterations in the expression of β-tubulin isotypes play a role in taxol resistance, a PCR- based methodology was developed that permits highly specific amplification of each of the six known murine β-tubulin isotypes. Two isotypes, Mβ5 and Mβ3, were expressed abundantly in the drug-sensitive parental J774.2 cells. Although expressed at an extremely low level in the parental cells, expression of the Mβ2 isotype was increased 21-fold (<0.005) in the cell line most resistant to taxol. These findings suggest that a cell can alter its relative tubulin isotype composition in response to an external stress and specifically imply that altered expression of Mβ2, the class II β- tubulin isotype, may contribute to the development of high resistance to taxol.