Uncovering the Role of Protein Kinase TAOK2 as an Endoplasmic Reticulum-Microtubule Tether

Abstract

Kinase signaling drives a multitude of components of neuronal development such as establishment of polarity, dendritic growth and arborization, dendritic spine formation, and synaptogenesis. Thousand And One amino acid Kinases (TAOKs) are a subfamily of sterile-20 (STE20) kinases possessing an N-terminal kinase domain and diverging C-terminal extended regulatory domains. As evolutionarily conserved kinases, TAO kinases have been shown to play important roles in neuronal development in rodents and invertebrates. Recent studies have linked de novo variants of human TAOK1/2 to neurodevelopmental diseases, thus making it imperative to understand their role in neuronal development. Despite its disease association, the molecular functions of TAO kinases remain unknown. Here, I focus on understanding the molecular and cellular function of the largest member of the TAO family, TAOK2 kinase. We find that TAOK2 is an endoplasmic reticulum (ER) resident multi-pass membrane-spanning kinase that localizes to distinct junctures of the ER through six transmembrane helices and an amphipathic helix. Additionally, we found that TAOK2 associates to microtubules directly and with high affinity through its cytoplasmic facing C-terminal tail. Furthermore, TAOK2 acts as a functional ER-microtubule tether, knockout of which leads to increased ER motility, increased microtubule growth but decreased ER tip attachment-complex movement. We determine that TAOK2 interacts with microtubule plus-end binding (EB) proteins through a distinctive SxIP motif. Finally, we determine that TAOK2 microtubule binding is regulated by its catalytic activity, loss of which leads to perturbations of ER and microtubule motility. This work identifies TAOK2 as an ER-microtubule tether and reveals a kinase-regulated mechanism for control of ER dynamics critical for cell growth and division. To further understand the context of TAOK2 signaling and determine TAOK2 interactors between the ER and microtubules, I propose the use of proximity labeling utilizing BioID2 and mass spectrometry. I lay out the blueprint for these experiments and the preliminary data from pilot experiments. Finally, I provide implications of these findings on how TAOK2 functions as an ER-microtubule tether might contribute to neurodevelopment.