Posttranslationale Tubulin-Modifikationen in der Zellmorphogenese und -migration

The epithelial tissue is essential for the physiological function of the organism. In order to fulfill their organspecific functions, the epithelial cell needs a directed transport machinery. Proteins and other relevant intracellular components are bidirectionally transported between the apical and basal cell poles along a complex organized cytoskeletal network. Epithelial monolayer formation depends on the composition of the microtubule cytoskeleton. Tubulin tyrosination and detyrosination, one of the best characterized post-translational modifications, influence epithelial cell shape and motility. Tubulin tyrosine ligase (TTL), an en- zyme that posttranslationally adds tyrosine to the carboxy terminus of detyrosinated α-tubulin, was depleted as well as overexpressed in 2D epithelial monolayers and in 3D cell culture models. The absence of TTL results in high levels of detyrosinated tubulin and cellular shape changes into an initial flat morphology and retardedly columnar epithelial cell shape. Enhanced cell adhesion to extracellular matrices and accelerated migration patterns of TTL-knockout cells combined with reverse effects in TTL-overexpressing cells indicate that the expression of TTL affects the organization of cell adhesion foci. Co-precipitation of detyrosinated and acetylated tubulin with Vinculin, one of the most important focal adhesion scaffold components, coincides with increased quantities and persistence of focal adhesion plaques in TTL-knockout cells. Conjunction of epithelial cells into monolayer sheets implies the ability to migrate and to undergo cellular polarization. Monolayer formation and cell polarization comprise reorganizati- on of cytoskeletal elements and rearrangements of structural protein interactions. Oriented cell migration and the organization of focal adhesions significantly lose directionality with diminishing amounts of microtubules enriched in detyrosinated tubulin. On the other hand, increasing quantities of detyrosinated tubulin results in faster plus end elongation of microtubules in migrating and in polarized epithelial cells. These plus ends are decorated by the plus end binding protein 1 (EB1), which mediates interactions between microtubules enriched in detyrosinated tubulin and the integrin-ILK complex at focal adhesions. EB1 accumulates at the apical cell pole at the base of the primary cilium following cell polarization. Polarized cells almost devo- id of detyrosinated tubulin form stunted primary cilia and multiluminal cysts in 3D-matrices. The balance between detyrosinated and tyrosinated tubulin influences microtubule dynamics, affects the orientation of focal adhesions and determines the organization of primary cilia on epithelial cells. The findings expand the knowledge about microtubules posttranslational modifications and indicate their relevance for the physiological functions of the epithelial cell. The modulation of TTL expression affects cellular processes like cellular migration and adhesion. Furthermore, the dynamics of focal adhesions as well as microtubule-associated proteins were influenced by TTL expression. The new insights offer connecting points for future research into oncological and biomedical therapy approaches.