Content area
Full Text
We report somatic mutations of RNF43 in over 18% of colorectal adenocarcinomas and endometrial carcinomas. RNF43 encodes an E3 ubiquitin ligase that negatively regulates Wnt signaling. Truncating mutations of RNF43 are more prevalent in microsatellite-unstable tumors and show mutual exclusivity with inactivating APC mutations in colorectal adenocarcinomas. These results indicate that RNF43 is one of the most commonly mutated genes in colorectal and endometrial cancers.
The E3 ubiquitin-protein ligase RNF43 negatively regulates the Wnt signaling pathway1. Somatic mutations in RNF43 have been associated with heightened sensitivity to compounds that target the Wnt- specific acyltransferase porcupine (PORCN) in preclinical models2. In parallel, clinical trials of small-molecule porcupine inhibitors (for example, LGK974) are ongoing in Wnt ligand-dependent malignancies (melanoma, pancreatic, breast, head and neck, and colorectal cancers). RNF43 is frequently mutated in pancreatic cystic neoplasms3 and in <5% of pancreatic carcinomas with acinar differentiation4; however, RNF43 mutations have not been reported in melanoma5, breast cancer6, or head and neck malignancies7. In colorectal cancer, Wnt signaling is more commonly dysregulated through loss-of- function APC mutations8, whereas RNF43 has not been reported to be significantly mutated in previous sequencing studies9,10.
Unexpectedly, our whole-exome sequencing of colorectal cancers identified a large number of non-silent somatic mutations in RNF43. DNA isolated from a discovery set of 185 formalin-fixed, paraffin-embedded colorectal tumor and matched normal samples collected from participants in 2 prospective cohort studies, the Nurses' Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS)11, showed RNF43 mutations in 35 (18.9%) cases (median allelic fraction of 0.23, range of 0.01-0.68) (Supplementary Table 1). Frameshiftmutations encoding p.Gly659fs and p.Arg117fs constituting insertions or deletions of 1 bp in homopolymeric tracts (microsatellite instability (MSI) loci) of seven and six C*G pairs, respectively, accounted for 41.7% (p.Gly659fs) and 8.3% (p.Arg117fs) of the RNF43 mutations identified (Fig. 1a). To exclude the possibility that these mutations represented technical artifacts, we validated 31 of the RNF43 mutations (97% of the 32 reactions that had leftover DNA available and achieved coverage of >50× in resequencing or successfully underwent Sanger sequencing) in the mutant tumors and their matched normal tissue (Supplementary Fig. 1 and Supplementary Table 1).
The unexpectedly high frequency of truncating RNF43 mutations in our colorectal tumor cohort contrasted with the paucity of RNF43 mutations reported by...