A cryptic tubulin-binding domain links MEKK1 to microtubule remodelling

ABSTRACT The MEKK1 protein is a pivotal kinase activator of responses to cellular stress. Activation of MEKK1 can trigger various responses, including mitogen activated protein (MAP) kinases, NF-κB signalling, or cell migration. Notably, MEKK1 activity is triggered by microtubule-targeting chemotherapies, amongst other stressors. Here we show that MEKK1 contains a previously unidentified tumour overexpressed gene (TOG) domain. The MEKK1 TOG domain binds to tubulin heterodimers—a canonical function of TOG domains—but is unusual in that it appears alone rather than as part of a multi-TOG array, and has structural features distinct from previously characterised TOG domains. MEKK1 TOG demonstrates a clear preference for binding curved tubulin heterodimers, which exist in soluble tubulin and at sites of microtubule polymerisation and depolymerisation. Mutations disrupting tubulin-binding lead to destabilisation of the MEKK1 protein in cells, and ultimately a decrease in microtubule density at the leading edge of polarised cells. We also show that MEKK1 mutations at the tubulin-binding interface of the TOG domain recur in patient derived tumour sequences, suggesting selective enrichment of tumour cells with disrupted MEKK1–microtubule association. Together, these findings provide a direct link between the MEKK1 protein and tubulin, which is likely to be relevant to cancer cell migration and response to microtubule-modulating therapies. SIGNIFICANCE STATEMENT The protein kinase MEKK1 activates stress response pathways in response to various cellular stressors, including chemotherapies that disrupt dynamics of the tubulin cytoskeleton. Filipčík et al., show that MEKK1 contains a previously uncharacterised domain that can preferentially bind to the curved tubulin heterodimer—which is found at sites of microtubule assembly and disassembly. Mutations that interfere with MEKK1-tubulin binding disrupt microtubule networks in migrating cells and are enriched in patient-derived tumour sequences. These results suggest that MEKK1-tubulin binding may be relevant to cancer progression, and the efficacy of microtubule-disrupting chemotherapies that require the activity of MEKK1.