Germline mutations in FAF1 are associated with hereditary colorectal cancer

Laia Bonjoch1, Sebastià Franch-Expósito1, Pilar Garre2, Jenifer Muñoz1, Coral Arnau-Collell1, Marcos Díaz-Gay 1, Clara Esteban-Jurado 1, Anna Gratacós 1, Giulia Raimondi3, Miriam Cuatrecasas4, Teresa Ocaña1, Antoni Castells1, Cristina Fillat3, Francesc Balaguer1, Trinidad Caldés2, Laura Valle5, Sergi Castellví-Bel 1

1Gastroenterology Department, Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBEREHD), Hospital Clínic, IDIBAPS, Barcelona, Spain. 2Molecular Oncology Laboratory, Hospital Clínico San Carlos, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Madrid, Spain. 3Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Gastrointestinal and Pancreatic Oncology, IDIBAPS, Barcelona, Spain. 4Department of Pathology, Hospital Clinic, IDIBAPS, Barcelona, Spain. 5Hereditary Cancer Program, Catalan Institute of Oncology, IDIBELL, Hospitalet de Llobregat, Spain

Abstract

Objectives

Colorectal cancer (CRC) represents the third most common cancer worldwide. Besides hereditary forms, ~30% of cases present familial aggregation mostly with an unknown inherited cause. Our aim is to identify new genes involved in the germline predisposition to CRC, by means of an exhaustive functional characterisation of candidate variants previously prioritised by our research group.

Methods

We analysed 75 patients with non-filiated familial CRC from 40 families by whole-exome sequencing. An external replication cohort of 529 families was also examined by targeted-gene sequencing. We developed a knockout cellular model by CRISPR/Cas gene editing for the candidate gene FAF1. FAF1 genetic variants were generated by site-directed mutagenesis and ectopically expressed by transfection. We carried out apoptosis, proliferation and protein-specific functional assays to test the role of the identified variants.

Results

A first possibly pathogenic FAF1 variant (c.1111G>A; p.D371N) was detected in the initial cohort in 3 CRC patients from the same family. A second genetic variant was detected in the replication cohort (c.254G>C; p.R85P). Both variants showed protein instability and, once transfected, produced an abnormal cellular phenotype by promoting apoptosis resistance and sustaining NF-kB signalling and proliferation pathways.

Conclusions

Our findings support the tumor suppressor profile of FAF1 and the pathogenicity of the identified variants. Therefore, FAF1 could be hypothesised to be a newly identified gene for inherited predisposition to CRC, although additional CRC cohorts should be explored in order to identify additional carriers and mutations.

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