Septin cooperation with tubulin polyglutamylation contributes to cancer cell adaptation to taxanes

Abstract

The mechanisms of cancer cell adaptation to the anti-microtubule agents of the taxane family are multifaceted and still poorly understood. Here, in a model of breast cancer cells which display amplified microtubule dynamics to resist Taxol®, we provide evidence that septin filaments containing high levels of SEPT9_i1 bind to microtubules in a way that requires tubulin long chain polyglutamylation. Reciprocally, septin filaments provide a scaffold for elongating and trimming polyglutamylation enzymes to finely tune the glutamate side-chain length on microtubules to an optimal level. We also demonstrate that tubulin retyrosination and/or a high level of tyrosinated tubulin is crucial to allow the interplay between septins and polyglutamylation on microtubules and that together, these modifications result in an enhanced CLIP-170 and MCAK recruitment to microtubules. Finally, the inhibition of tubulin retyrosination, septins, tubulin long chain polyglutamylation or of both CLIP-170 and MCAK allows the restoration of cell sensitivity to taxanes, providing evidence for a new integrated mechanism of resistance.

Cancer-Related Functions and Subcellular Localizations of Septins

“…The loss of TTLL3 activity, a polyglycylase required for robust primary cilium formation has been involved in colon cancer development (Rocha et al, 2014). By analogy with the finding that septin filaments recruit tubulin polyglutamylases on MTs (Froidevaux-Klipfel et al, 2015), the axonema-associated septins could perhaps function to scaffold TTLL3 on ciliary MTs, as it belongs to the same family of enzymes.…”

“…In these cells, septins are displaced from actin fibers to MTs, where they restore higher level of MT dynamics by acting as scaffolding proteins to recruit tubulin polyglutamylation enzymes. Septin recruitment to polyglutamylated MTs result in increased binding of MT modulators that play key roles in controlling catastrophe and rescue events (Froidevaux-Klipfel et al, 2015). …”

“…These findings indicate that other molecular determinants on septins or on their target organelles may play a role in septin association with either cytoskeleton element. Tubulin posttranslational modifications are one of these determinants as highlighted by the differential septin filament locations between sensitive and Taxol®-resistant breast cancer cells, which both express long SEPT9 isoforms (Froidevaux-Klipfel et al, 2015). As already observed in MDCK cells, septin filaments coalign with polyglutamylated MT tracks (Spiliotis et al, 2008).…”

“…As already observed in MDCK cells, septin filaments coalign with polyglutamylated MT tracks (Spiliotis et al, 2008). Long lateral polyglutamate chains on tubulin even enhance this association in Taxol®-resistant breast cancer cells, while septins remain associated with actin in their Taxol®-sensitive counterpart (Froidevaux-Klipfel et al, 2015). This differential septin filament localization between MTs and actin filaments correlates with a high level of SEPT9_i1 in resistant cells, while SEPT9_i3 is the main SEPT9 isoform found in the septin filaments of sensitive cells.…”

Septin Mutations in Human Cancers

“…The organization and contractile properties of actin-myosin filaments are modulated by septins, which cross-link and bend actin filaments into functional structures such as the cytokinetic contractile ring, the actin stress fibers that power cell migration, and cellular protrusions such as filopodia, pseudopodia and lamellipodia (Kinoshita et al, 1997, 2002; Joo et al, 2007; Kremer et al, 2007; Shankar et al, 2010; Hu et al, 2012; Mizutani et al, 2013; Dolat et al, 2014b; Mavrakis et al, 2014). Similarly, septins affect the organization, dynamics and post-translational modifications of the microtubule cytoskeleton, impacting the morphogenesis of epithelia and neurons (Spiliotis et al, 2008; Bowen et al, 2011; Ageta-Ishihara et al, 2013; Bai et al, 2013; Froidevaux-Klipfel et al, 2015). Moreover, microtubule-associated septins are essential for proper chromosome alignment and segregation during mitosis, and the cytoskeleton-dependent transport of membrane vesicles in interphase cells (Spiliotis et al, 2005, 2008; Bai et al, 2016).…”