Altered expression of M beta 2, the class II beta-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 beta-tubulin, the cellular target for these drugs. Vertebrates have six classes of beta-tubulin isotypes, each displaying a distinct pattern of expression. Although the functional significance of multiple beta-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 beta-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 beta-tubulin isotypes. Two isotypes, M beta 5 and M beta 3, 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 M beta 2 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 M beta 2, the class II beta-tubulin isotype, may contribute to the development of high resistance to taxol.