Class III β-tubulin and the cytoskeletal gateway for drug resistance in ovarian cancer

The Class III beta-tubulin isotype (beta III-tubulin) is a predictive biomarker in ovarian cancer and other solid tumor malignancies. We discovered that beta III-tubulin function is linked to two GTPases: guanylate-binding protein 1 (GBP1), which activates its function, and GNAI1, which inhibits it. This finding was demonstrated in a panel of ovarian cancer cells resistant to several chemotherapeutic agents. Using a protein microarray, we identified PIM1 as the downstream partner of GBP1, recruited into the cytoskeleton under hypoxic conditions. The clinical value of these observations was tested by performing an archive study of 98 ovarian cancer patients, which demonstrated that the beta III-tubulin -/PIM1- cohort responded to treatment, exhibiting long overall survival (OS), while beta III-tubulin +/PIM+ patients experienced poor outcomes and OS times similar to patients receiving palliation alone. beta III-tubulin expression is commonly believed responsible for paclitaxel resistance due to its enhancement of the dynamic instability of microtubules, which counteracts the activity of taxanes. In contrast, our research reveals that beta III-tubulin behaves as a gateway for prosurvival signals, such as PIM1, to move into the cytoskeleton. When cells are exposed to microenvironmental stressors, they activate this pathway by telling the cytoskeleton to incorporate PIM1 through GBP1 and beta III-tubulin, which ultimately leads to drug resistance. This discovery reveals that beta III-tubulin does not act alone but requires partners to play its role. The discovery of such protein:protein interactions underlying this prosurvival cascade makes feasible the development of therapeutic approaches using novel compounds that are capable of inhibiting the transmission of prosurvival signals into the cytoskeleton. J. Cell. Physiol. 227: 10341041, 2012. (C) 2011 Wiley Periodicals, Inc.