Fig. 1. Overview of canonical Wnt signaling.

a In the absence of RSPO binding to LGR4/5/6, ubiquitin ligase ZNRF43/RNF43 ubiquitinates the Frizzled receptor which leads to receptor complex endocytosis, β-catenin degradation and subsequent inhibition of Wnt-driven transcriptional activity⁵. b The binding of RSPO to LGR4/5/6 potentiates Wnt signaling by removing ZNR43/RNF43 ubiquitin ligase from the cell membrane, which would otherwise mark Frizzled receptor for ubiquitination. Frizzled receptors are then able to interact with both Wnt ligand and LRP5/6 co-receptor to drive Wnt signaling cascade. β-catenin then escapes cytoplasmic proteasomal degradation, resulting in its nuclear translocation, interactions with transcription factors. TCF/LEF, and subsequent transactivation of Wnt target genes like c-MYC, CyclinD1, and Axin2⁵.