RNF43 and ZNRF3 are commonly altered in serrated pathway colorectal tumorigenesis

// Catherine E. Bond 1 , Diane M. McKeone 1 , Murugan Kalimutho 2 , Mark L. Bettington 1, 3, 4 , Sally-Ann Pearson 1 , Troy D. Dumenil 1 , Leesa F. Wockner 5 , Matthew Burge 6 , Barbara A. Leggett 1, 4, 7 , Vicki L.J. Whitehall 1, 4, 8 1 Conjoint Gastroenterology Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia 2 Signal Transduction Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia 3 Envoi Specialist Pathologists, Brisbane, Queensland, Australia 4 School of Medicine, University of Queensland, Brisbane, Queensland, Australia 5 Cancer and Population Studies, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia 6 Department of Oncology, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia 7 Department of Gastroenterology and Hepatology, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia 8 Pathology Queensland, Brisbane, Queensland, Australia Correspondence to: Catherine E. Bond, email: Catherine.Bond@qimrberghofer.edu.au Keywords: RNF43, colorectal cancer, BRAF, MSI, Wnt signalling Received: April 07, 2016     Accepted: September 02, 2016     Published: September 20, 2016 ABSTRACT Serrated pathway colorectal cancers (CRCs) are characterised by a BRAF mutation and half display microsatellite instability (MSI). The Wnt pathway is commonly upregulated in conventional CRC through APC mutation. By contrast, serrated cancers do not mutate APC . We investigated mutation of the ubiquitin ligases RNF43 and ZNRF3 as alternate mechanism of altering the Wnt signal in serrated colorectal neoplasia. RNF43 was mutated in 47/54(87%) BRAF mutant/MSI and 8/33(24%) BRAF mutant/microsatellite stable cancers compared to only 3/79(4%) BRAF wildtype cancers (p<0.0001). ZNRF3 was mutated in 16/54(30%) BRAF mutant/MSI and 5/33(15%) BRAF mutant/microsatellite stable compared to 0/27 BRAF wild type cancers (p=0.004). An RNF43 frameshift mutation (X659fs) occurred in 80% BRAF mutant/MSI cancers. This high rate was verified in a second series of 25/35(71%) BRAF mutant/MSI cancers. RNF43 and ZNRF3 had lower transcript expression in BRAF mutant compared to BRAF wildtype cancers and less cytoplasmic protein expression in BRAF mutant/MSI compared to other subtypes. Treatment with a porcupine inhibitor reduced RNF43 / ZNRF3 mutant colony growth by 50% and synergised with a MEK inhibitor to dramatically reduce growth. This study suggests inactivation of RNF43 and ZNRF3 is important in serrated tumorigenesis and has identified a potential therapeutic strategy for this cancer subtype.