Comparison of β-tubulin mRNA and protein levels in 12 human cancer cell lines

Antimitotic drugs are chemotherapeutic agents that bind tubulin and microtubules. Resistance to these drugs is a major clinical problem. One hypothesis is that the cellular composition of tubulin isotypes may predict the sensitivity of a tumor to antimitotics. Reliable and sensitive methods for measuring tubulin isotype levels in cells and tissues are needed to address this hypothesis. Quantitative measurements of tubulin isotypes have frequently relied upon inferring protein amounts from mRNA levels. To determine whether this approach is justified, protein and mRNA levels of β‐tubulin isotypes from 12 human cancer cell lines were measured. This work focused on only β‐tubulin isotypes because we had readily available monoclonal antibodies for quantitative immunoblots. The percentage of β‐tubulin isotype classes I, II, III, and IVa + IVb mRNA and protein were compared. For β‐tubulin class I that comprises >50% of the β‐tubulin protein in 10 of the 12 cell lines, there was good agreement between mRNA and protein percentages. Agreement between mRNA and protein was also found for β‐tubulin class III. For β‐tubulin classes IVa + IVb, we observed higher protein levels compared to mRNA levels. β‐Tubulin class II protein was found in only four cell lines and in very low abundance. We conclude that quantitative Western blotting is a reliable method for measuring tubulin isotype levels in human cancer cell lines. Inferring protein amounts from mRNA levels should be done with caution, since the correspondence is not one‐to‐one for all tubulin isotypes. Cell Motil. Cytoskeleton 2006. © 2005 Wiley‐Liss, Inc.