VPS28, an ESCRT-I protein, regulates mitotic spindle organization via Gβγ, EG5 and TPX2

The mitotic spindle is a dynamic macromolecular complex essential for chromosome segregation. ESCRT (gndosomal sorting complexes required for transport) proteins are emerging as relevant mitotic players putatively recruiting spindle organizers. Here, we describe that VPS28, an ESCRT-1 component, directly interacts with G beta gamma, a signaling heterodimer with documented impact on microtubule dynamics, composing a novel organizer of the mitotic spindle aster. We found that VPS28 localizes to mitotic microtubules where it recruits G beta gamma. Reducing VPS28 expression impairs kinesin Eg5 and TPX2 localization to the mitotic spindle. The interaction between VPS28 and GI37 involves the carboxyl-terminal region of VPS28, which usually interacts with VPS36, its regular partner at multivesicular bodies. The VPS28-G beta gamma complex is better constituted in the presence of Ga independently of G protein coupled receptor-stimulation, suggesting an intrinsic mechanism of regulation by which this novel complex contributes to mitotic spindle organization in mammalian cells.