Kinesin-4 KIF21B limits microtubule growth to allow rapid centrosome polarization in T cells

Abstract

When a T cell and an antigen-presenting cell form an immunological synapse, rapid dynein-driven translocation of the centrosome towards the contact site leads to reorganization of microtubules and associated organelles. Currently, little is known about how the regulation of microtubule dynamics contributes to this process. Here, we show that the knockout of KIF21B, a kinesin-4 linked to autoimmune disorders, causes microtubule overgrowth and perturbs centrosome translocation. KIF21B restricts microtubule length by inducing microtubule pausing typically followed by catastrophe. Catastrophe induction with vinblastine prevented microtubule overgrowth and was sufficient to rescue centrosome polarization in KIF21B-knockout cells. Biophysical simulations showed that a relatively small number of KIF21B molecules can restrict microtubule length and promote an imbalance of dynein-mediated pulling forces that allows the centrosome to translocate past the nucleus. We conclude that proper control of microtubule length is important for allowing rapid remodeling of the cytoskeleton and efficient T cell polarization.

Dynein self-organizes while translocating the centrosome in T-cells

“…A different parametrization leading to longer MTs would add a lot of computational complexity. However, a more dense MT network will probably lead to more MTs contributing to stalks and more efficient capture, while it may also induce a force-balanced system that is unable to translocate the centrosome (Kim and Maly, 2009;Hooikaas et al, 2020;Hornak and Rieger, 2020).…”

“…The Cytosim framework allows for modular agent-based simulations of cytoskeletal systems using overdamped Langevin equations. Our previous T-cell model (Hooikaas et al, 2020) was extended to three spatial dimensions and to include mobile dynein in the immunological synapse.…”

“…The centrosome is confined to a spherical cap. The numerical values of the parameters describing the MT dynamics were estimated from TIRF microscopy data of EB3-GFP comets in polarized T cells (Hooikaas et al, 2020), using a classic two-state MT dynamics model, in which the MT can be in a growing state and in a shrinking state. In the growing state, the MT polymerization rate decays exponentially with the force.…”

“…The transition from the growing state to the shrinking state is characterized by a catastrophe rate, which is different for a freely growing end and for an end exposed to a large force (see Methods). We use 150 MTs which is in the range of the number of MTs previously estimated in these cells (Hooikaas et al, 2020). Other numerical parameters were chosen according to literature values and are listed in Table 1. In the transitory phase II, we take the shape change of the T cell by actin reorganization into account.…”

“…However, their precise coordination and molecular mechanisms are mostly unknown. Although it is known that centrosome translocation is mediated by dynein motors, it is still elusive how this is precisely organized and what role the MT network and associated proteins play (Kuhn and Poenie, 2002;Combs et al, 2006;Hooikaas et al, 2020). A recent study showed that T-cell centrosome translocation displayed a defining phenomenon, where a MT bundle formed perpendicular to the IS and this structure shrank during centrosome translocation (Yi et al, 2013).…”