# Mutational scanning reveals oncogenic CTNNB1 mutations have diverse effects on signaling

## TL;DR

This study uses genome editing to explore how different mutations in the CTNNB1 gene affect Wnt signaling and cancer development.

## Contribution

The study provides a comprehensive analysis of all possible missense mutations in a key cancer-related gene hotspot.

## Key findings

- Mutation effect scores distinguish tumor subclasses in hepatocellular carcinoma based on β-catenin signaling levels.
- Weaker CTNNB1 mutations correlate with increased immune cell infiltration in the tumor microenvironment.
- The research defines genetic requirements for β-catenin degron function and substrate recognition by β-TRCP.

## Abstract

CTNNB1, the gene encoding β-catenin, is a frequent target for oncogenic mutations activating the canonical Wnt signaling pathway, typically through missense mutations within a degron hotspot motif in exon 3. Here, we combine saturation genome editing with a fluorescent reporter assay to quantify signaling phenotypes for all 342 possible missense mutations in the mutation hotspot. Our data define the genetic requirements for β-catenin degron function, refine the consensus motif for substrate recognition by β-TRCP and reveal diverse levels of signal activation among known driver mutations. Tumorigenesis in different human tissues involves selection for CTNNB1 mutations spanning distinct ranges of predicted activity. In hepatocellular carcinoma, mutation effect scores distinguish two tumor subclasses with different levels of β-catenin signaling, and weaker mutations predict greater immune cell infiltration in the tumor microenvironment. Our work provides a resource to understand mutational diversity within a pan-cancer mutation hotspot, with potential implications for targeted therapy.

Saturation genome editing of a cancer mutation hotspot in CTNNB1, the gene encoding β-catenin, reveals a gradient of effects of missense mutations on Wnt signaling.