RT Journal Article
SR Electronic
T1 RNF43 germline and somatic mutation in serrated neoplasia pathway and its association with BRAF mutation
JF Gut
JO Gut
FD BMJ Publishing Group Ltd and British Society of Gastroenterology
SP 1645
OP 1656
DO 10.1136/gutjnl-2016-311849
VO 66
IS 9
A1 Helen H N Yan
A1 Jeffrey C W Lai
A1 Siu Lun Ho
A1 Wai Keung Leung
A1 Wai Lun Law
A1 Janet F Y Lee
A1 Anthony K W Chan
A1 Wai Yin Tsui
A1 Annie S Y Chan
A1 Bernard C H Lee
A1 Sarah S K Yue
A1 Alice H Y Man
A1 Hans Clevers
A1 Siu Tsan Yuen
A1 Suet Yi Leung
YR 2017
UL http://gut.bmj.com/content/66/9/1645.abstract
AB Objective Serrated polyps (hyperplastic polyps, sessile or traditional serrated adenomas), which can arise in a sporadic or polyposis setting, predispose to colorectal cancer (CRC), especially those with microsatellite instability (MSI) due to MLH1 promoter methylation (MLH1me+). We investigate genetic alterations in the serrated polyposis pathway.Design We used a combination of exome sequencing and target gene Sanger sequencing to study serrated polyposis families, sporadic serrated polyps and CRCs, with validation by analysis of The Cancer Genome Atlas (TCGA) cohort, followed by organoid-based functional studies.Results In one out of four serrated polyposis families, we identified a germline RNF43 mutation that displayed autosomal dominant cosegregation with the serrated polyposis phenotype, along with second-hit inactivation through loss of heterozygosity or somatic mutations in all serrated polyps (16), adenomas (5) and cancer (1) examined, as well as coincidental BRAF mutation in 62.5% of the serrated polyps. Concurrently, somatic RNF43 mutations were identified in 34% of sporadic sessile/traditional serrated adenomas, but 0% of hyperplastic polyps (p=0.013). Lastly, in MSI CRCs, we found significantly more frequent RNF43 mutations in the MLH1me+ (85%) versus MLH1me− (33.3%) group (p<0.001). These findings were validated in the TCGA MSI CRCs (p=0.005), which further delineated a significant differential involvement of three Wnt pathway genes between these two groups (RNF43 in MLH1me+; APC and CTNNB1 in MLH1me−); and identified significant co-occurrence of BRAF and RNF43 mutations in the MSI (p<0.001), microsatellite stable (MSS) (p=0.002) and MLH1me+ MSI CRCs (p=0.042). Functionally, organoid culture of serrated adenoma or mouse colon with CRISPR-induced RNF43 mutations had reduced dependency on R-spondin1.Conclusions These results illustrate the importance of RNF43, along with BRAF mutation in the serrated neoplasia pathway (both the sporadic and familial forms), inform genetic diagnosis protocol and raise therapeutic opportunities through Wnt inhibition in different stages of evolution of serrated polyps.