SMAD2, SMAD3 and SMAD4 mutations in colorectal cancer
Menée sur 36 lignées cellulaires et 744 échantillons tumoraux prélevés sur des patients atteints d'un cancer colorectal, cette étude analyse la fréquence de mutations dans les gènes SMAD2, SMAD3 et SMAD4
Activation of the canonical transforming growth factor-β (TGF-β) signaling pathway provides growth inhibitory signals in the normal intestinal epithelium. Colorectal cancers (CRCs) frequently harbor somatic mutations in the pathway members, TGFBR2 and SMAD4, but to what extent mutations in SMAD2 or SMAD3 contribute to tumorigenesis is unclear. A cohort of 744 primary CRCs and 36 CRC cell lines were sequenced for SMAD4, SMAD2 and SMAD3, and analyzed for allelic loss by SNP microarray analysis. Mutation spectra were compared between the genes, the pathogenicity of mutations was assessed and relationships with clinicopathological features were examined. The prevalence of SMAD4, SMAD2 and SMAD3 mutations in sporadic CRC was 8.6% (64/744), 3.4% (25/744) and 4.3% (32/744), respectively. A significant overrepresentation of two genetic hits was detected for SMAD4 and SMAD3, consistent with these genes acting as tumor suppressors. SMAD4 mutations were associated with mucinous histology. The mutation spectra of SMAD2 and SMAD3 were highly similar to that of SMAD4, both in mutation type and location within the encoded proteins. In silico analyses suggested the majority of the mutations were pathogenic, with most missense changes predicted to reduce protein stability or hinder SMAD complex formation. The latter altered interface residues or disrupted the phosphorylation regulated Ser-Ser-X-Ser motifs within SMAD2 and SMAD3. Functional analyses of selected mutations demonstrated reductions in SMAD3 transcriptional activity and SMAD2-SMAD4 complex formation. Joint biallelic hits in SMAD2 and SMAD3 were overrepresented and mutually exclusive to SMAD4 mutation, underlining the critical roles of these three proteins within the TGF-β signaling pathway.