Importin α phosphorylation promotes TPX2 activation by GM130 to control astral microtubules and spindle orientation

Abstract

Spindle orientation is important in multiple developmental processes as it determines cell fate and function. The orientation of the spindle depends on the assembly of a proper astral microtubule network. Here, we report that the spindle assembly factor TPX2 regulates astral microtubules. TPX2 in the spindle pole area is activated by GM130 on Golgi membranes to promote astral microtubule growth. GM130 relieves TPX2 inhibition by competing for importin α binding. Mitotic phosphorylation of importin α at Ser62 by CDK1 switches its substrate preference from TPX2 to GM130, thereby enabling competition-based activation. Importin α S62A impedes local TPX2 activation and compromises astral microtubule formation, ultimately resulting in misoriented spindles. Blocking the GM130-importin α-TPX2 pathway impairs astral microtubule growth. Our results reveal a novel role for TPX2 in the organization of astral microtubules. Furthermore, we show that the substrate preference of the important mitotic modulator importin α is regulated by CDK1-mediated phosphorylation.

Structural Organization and Function of the Golgi Ribbon During Cell Division

“…One senses unlinking and activates Src at the GC, resulting in Aurora-A activation to drive entry into mitosis and CE maturation (Barretta et al, 2016). The other is mediated by a GM130based pathway leading to the activation of TPX2, an allosteric activator of Aurora-A, to control the formation of the spindle astral fibers (Wei et al, 2015;Guo et al, 2021). Furthermore, Golgi-associated structural proteins are repurposed during mitosis to concur to the proper spindle formation (Mascanzoni et al, 2019).…”

“…A significant example is offered by GM130, which possesses a nuclear localization signal that during interphase is masked by the interaction with the matrix protein p115 (Wei et al, 2015). CDK1-mediated phosphorylation of GM130 dissociates p115, allowing the nuclear localization signal to activate a signaling axis composed of the spindle assembly factor TPX2, which binds to and activates Aurora-A to control the formation of "astral" MTs, which are necessary for correct spindle orientation (Figure 1) (Wei et al, 2015;Guo et al, 2021). Moreover, GM130 can also stabilize the spindle fibers by direct binding to MTs, thus linking Golgi membranes to the spindle (Wei et al, 2015;Wei and Seemann, 2017).…”

Annexin A1 is a polarity cue that directs planar mitotic spindle orientation during mammalian epithelial morphogenesis

“…Additionally, epithelial cell geometry and polarity have been shown to influence chromosome segregation fidelity [78]. Our cortical LGN interactome data identify several NuMA-interacting proteins that have been described to play pleotropic roles in the regulation of astral microtubule stability, mitotic spindle positioning, and kinetochore-microtubule dynamics, including the DYNC1H1/Dynein-p150 Glued /Dynactin complex [6, 32–36, 79], CLASP1 [37–39], HAUS6 [40, 41], KPNA2/Importin-α [80], PLK1 [6, 31], TUBG1/ψ-tubulin [41, 42], EIF3E/Int-6 [47], CCNB/CDK1 [36, 43], RAN [39, 44, 45]. These findings reinforce the idea that defects in astral microtubule organisation and spindle orientation upon ANXA1 depletion are likely to cause incorrect chromosome segregation.…”

The Role of GM130 in Nervous System Diseases

“…They were arrested in metaphase and then died (63). The spindle assembly factor targeting protein for xenopus kinesin-like protein 2 (TPX2) is activated by GM130 on Golgi membranes to promote the growth of astral microtubule (66). The nuclear localization signal (NLS)-like motifs of GM130 were thought to isolate Importin-α from spindle assembly factor TPX2, and then stimulated microtubule nucleation during mitosis (8).…”