TOG Proteins are spatially regulated by Rac-GSK3β to control interphase microtubule dynamics

Trogden, Kathryn

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March 19, 2019

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Trogden, Kathryn
- Affiliation: College of Arts and Sciences, Department of Biology

Abstract

Within a cell, the ends of individual microtubules switch between three different phases: growth, shrinkage and pause without affecting the total mass of microtubule polymer. This inherent property of microtubules is termed dynamic instability. During interphase, microtubule dynamics are regulated by a class of proteins that interact primarily with the plus end of the microtubule (+TIPs). How these proteins are regulated, either through interactions with each other or through signaling pathways in the cell are poorly understood. Two +TIP protein families, the XMAP215 family, known as Mini spindles (Msps) in Drosophila and the CLASP family, known as Orbit, contain arrays of tubulin binding TOG domains. We show that in Drosophila S2 cells Orbit is phosphorylated by the kinase GSK3β, similar to what has been reported for mammalian CLASPs. At the periphery of the cell, GSK3β is inhibited by the Rho GTPase Rac and Orbit is no longer phosphorylated. Orbit is then able to interact with Msps through their C-termini, allowing Msps to bind to the lattice. Msps lattice binding is important for proper microtubule dynamics as mutations that disrupt this interaction lead to aberrant dynamics. This interaction requires the scaffolding protein Sentin to bring the two proteins into contact at the periphery of the cell. Further work has shown a role for another Rac effector kinase, PAK, in this pathway. This interaction may also be important for migration in Drosophila cells. Depletion of +TIPs leads to changes in cell movement, indicating that microtubule dynamics may play a role in motility.

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