Abstract 2121: Microtubule-regulated mRNA translation signaling and therapeutic implications in cancer
Authors: Khade Prashant , Giannakakou Paraskevi 
Published: August 2015

Abstract
Drugs that affect microtubule dynamics and function, both those that stabilize microtubules (e.g. taxanes) and those that depolymerize them (e.g. vincas, Eribulin) are widely used in cancer chemotherapy. However, their mechanism of action at the molecular level and the signaling pathways regulated by microtubule dynamics are not fully understood, precluding chemotherapy customization to the individuals. Previously, we have reported that microtubule dynamics control the translation of HIF-1α mRNA. We showed that treatment with microtubule-targeting drugs (MTDs) shifts HIF-1α mRNA from actively translating polysomes to non-translating ribosomes resulting in inhibition of HIF-1α transcriptional activity. Using cell lines with acquired mutations at different MTD binding sites we conclusively showed that microtubule disruption was required for the inhibition of HIF translation. However, additional mRNAs susceptible to MTD treatment or the exact signaling pathway that senses microtubule disruption and leads to inhibition of translation are not known. Polysome RNA-Seq analyses of untreated and drug treated cells has identified additional mRNAs whose polysome association is shifted towards inactive translation similar to HIF-1α mRNA. We are using bioinformatics analyses to identify a common microtubule-susceptibility motif in addition to validation experiments at the protein and pathway level. The polysome analysis showed that protein synthesis is inhibited at the stage of translation initiation. In an effort to better understand the underlying mechanism of translation inhibition of HIF-1α mRNA and additional microtubule-dependent mRNAs, we assessed 4E-BP1 protein as its phosphorylation is a key regulator of cap dependent mRNA translation. We observed that taxanes or Eribulin treatment hyper-phosphorylates 4E-BP1 without affecting ribosomal protein S6 (rpS6) phosphorylation. Using the taxane-resistant breast cancer cell line MB-231/K20T which harbors an acquired mutation at the taxane binding site of β-tubulin we showed that Taxol treatment has no effect on 4E-BP1 hyper- phosphorylation, consistent with its lack of microtubule activity. In contrast, Eribulin, which has a distinct binding site on tubulin, is able to overcome taxol-resistance by fully engaging the microtubule-4E-BP1 axis. Interestingly, in renal cell carcinoma (RCC) cells, for which treatment with microtubule inhibitors has no clinical benefit, we didn't observe 4E-BP1 hyper-phosphorylation after taxane or Eribulin treatment, even though microtubules were affected. These results suggest that the microtubule-4E-BP1 axis is compromised in RCC and that there is a link between 4E-BP1 phosphorylation and MTD efficacy. Hence, we propose that identifying the link of 4E-BP1 dependent signaling with microtubules will have important therapeutic implications in MTD chemotherapy.
Citation Format: Prashant Khade, Paraskevi Giannakakou. Microtubule-regulated mRNA translation signaling and therapeutic implications in cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2121. doi:10.1158/1538-7445.AM2015-2121