Mitotic wnt signaling promotes protein stabilization and regulates cell size.

ABSTRACT

Canonical Wnt signaling is thought to regulate cell behavior mainly by inducing ß-catenin-dependent transcription of target genes. In proliferating cells Wnt signaling peaks in the G2/M phase of the cell cycle, but the significance of this "mitotic Wnt signaling" is unclear. Here we introduce Wnt-dependent stabilization of proteins (Wnt/STOP), which is independent of ß-catenin and peaks during mitosis. We show that Wnt/STOP plays a critical role in protecting proteins, including c-MYC, from GSK3-dependent polyubiquitination and degradation. Wnt/STOP signaling increases cellular protein levels and cell size. Wnt/STOP, rather than ß-catenin signaling, is the dominant mode of Wnt signaling in several cancer cell lines, where it is required for cell growth. We propose that Wnt/STOP signaling slows down protein degradation as cells prepare to divide.