Nucleation of the destruction complex on the centrosome accelerates degradation of β-catenin and regulates Wnt signal transmission

Abstract

Wnt signal transduction is controlled by the destruction complex (DC), a condensate comprising scaffold proteins and kinases that regulate β-catenin stability. Overexpressed DC scaffolds undergo liquid–liquid phase separation (LLPS), but DC mesoscale organization at endogenous expression levels and its role in β-catenin processing were previously unknown. Here, we find that DC LLPS is nucleated by the centrosome. Through a combination of CRISPR-engineered custom fluorescent tags, finite element simulations, and optogenetic tools that allow for manipulation of DC concentration and multivalency, we find that centrosomal nucleation drives processing of β-catenin by colocalizing DC components to a single reaction crucible. Enriching GSK3β partitioning on the centrosome controls β-catenin processing and prevents Wnt-driven embryonic stem cell differentiation to mesoderm. Our findings demonstrate the role of nucleators in controlling biomolecular condensates and suggest tight integration between Wnt signal transduction and the cell cycle.

To condense or not to condense: Wnt regulation by centrosome-nucleated biomolecular condensates

“…Together, this work provides key insights into Wnt signaling, helping reconcile earlier in vitro, cell culture and in vivo experiments concerning the DC assembly state ( 2 ). These data reveal that, at least in cultured mammalian cells, DCs form phase-separated biomolecular condensates even when proteins are all expressed at endogenous levels.…”

“…Lach et al. ( 2 ) take this on via a highly multidisciplinary approach. They note that phase-separating systems can exhibit switch-like responses to changes in concentration, potentially explaining differences in DC assembly in vitro and in vivo.…”

“…What was less expected was that, in the absence of Wnt signals, βcat also accumulated in one or two bright, spherical puncta near the nuclei ( 2 ). These resembled liquid-like biomolecular condensates, fusing and splitting.…”

“…Most intriguing, the one or two puncta per cell colocalized with centrosomes, the cell’s major microtubule organizing center ( 2 ). Lach et al.…”

“…Lach et al. ( 2 ) then created a tool to test whether condensation elevates Wnt regulatory activity in vivo: a version of the DC kinase GSK3 that oligomerizes in response to light. Strikingly, inducing GSK3 oligomerization rapidly increased GSK3 concentration specifically in centrosomal puncta, without triggering assembly of extracentrosomal puncta.…”