Importin α/β Promote Kif18B Microtubule Association to Spatially Control Microtubule Destabilization

Abstract

Tight regulation of microtubule dynamics and microtubule organization is necessary for proper spindle assembly and chromosome segregation. The microtubule destabilizing Kinesin-8, Kif18B, controls astral microtubule dynamics and spindle positioning. Kif18B interacts with importin alpha/beta as well as with the plus-tip tracking protein EB1, but how these associations modulate Kif18B activity or function is not known. We mapped the key binding sites on Kif18B, made residue-specific mutations, and assessed their impact on Kif18B function. Blocking EB1 interaction disrupted Kif18B MT plus-end accumulation and inhibited its ability to control astral microtubule length in cells. Blocking importin alpha/beta interaction reduced Kif18B plus-end accumulation on astral MTs but did not inhibit its ability to control astral MT length. In vitro, importin alpha/beta increased Kif18B binding to the microtubule lattice, which enhanced Kif18B accumulation at microtubule plus ends, and stimulated microtubule destabilization, suggesting that the importins spatially regulate Kif18B. In contrast, EB1 promoted microtubule destabilization without increasing lattice binding in vitro, which suggests that EB1 and importin alpha/beta have distinct roles in the regulation of astral microtubule dynamics. We propose that Ran-regulation is important not only to control motor function near chromatin but also provides a spatial control mechanism to modulate microtubule binding of NLS-containing spindle assembly factors.

Stu2 has an essential kinetochore role independent of regulating microtubule dynamics

“…Additionally, a recent study by Shrestha et al . found that importin α/β binding to the microtubule destabilizing Kinesin-8, Kif18B, directly regulates its ability to control microtubule dynamics and spindle positioning by altering its binding to the microtubule lattice (Shrestha et al, 2022). An importin complex association may even regulate MAP function upon nuclear envelope breakdown (i.e.…”

“…For example, importin binding controls the efficiency of microtubule nucleation by TPX2 via selectively blocking the interaction with microtubule nucleation intermediates (Roostalu et al, 2015). Additionally, a recent study by Shrestha et al found that importin α/β binding to the microtubule destabilizing Kinesin-8, Kif18B, directly regulates its ability to control microtubule dynamics and spindle positioning by altering its binding to the microtubule lattice (Shrestha et al, 2022). An importin complex association may even regulate MAP function upon nuclear envelope breakdown (i.e.…”