Coordinated Regulation of β-Tubulin Isotypes and Epithelial-to-Mesenchymal Transition Protein ZEB1 in Breast Cancer Cells

The regulation of beta-tubulin isotypes, the primary targets for antimitotic chemotherapeutic drugs like taxanes, has implications for drug response and drug resistance. Over the past 15 years, micro-RNAs have been studied widely as regulators of mRNA levels. For example, the tumor suppressor miR-200c was shown in cell culture to target mesenchymal genes, including ZEB1 [Cochrane et al. (2009) Mol. Cancer Ther. 8 (5), 1055-1066]. In that work, exogenous miR-200c was also shown to reduce beta-tubulin class III, one of its predicted targets. Furthermore, decreased miR-200c and increased beta-tubulin class III were associated with poor outcomes for ovarian cancer patients [Cittelly, D.M. et al. (2012) Mol. Cancer Ther. 11 (12), 2556-2565]. Because miR-200c targets the epithelial-to-mesenchymal inducer ZEB1, we wanted to know whether changes in ZEB1 parallel beta-tubulin isotype changes, implicating beta-tubulin isotypes in ZEB1-associated cell survival pathways. We found coordinated positive feedback regulation of mRNA for ZEB1 and beta-tubulin isotype classes I, III, and IVB in MDA-MB-231 breast cancer cells, commonly used as a model for triple-negative breast cancers. Low levels of paclitaxel (40 nM) were found to significantly reduce mRNA levels for these tubulin genes along with a 2-3-fold increase in rniR-200c. ZEB1 silencing also reduced beta-tubulin isotype classes I, III, and IVB mRNA, whereas upregulation of ZEB1 was associated with increases in these isotype classes. Our work indicates that paclitaxel-induced reduction of ZEB1 and beta-tubulin isotypes are, in part, due to increased activity of miR-200c. These results suggest that in aggressive breast cancers, as modeled by MDA-MB-231 cells, beta-tubulin class HI is a biomarker for cell survival mediated through ZEB1-induced tumor progression pathways.