SMAD2,SMAD3andSMAD4Mutations in Colorectal Cancer

Abstract

Activation of the canonical TGF-b 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 single-nucleotide polymorphism (SNP) microarray analysis. Mutation spectra were compared between the genes, the pathogenicity of mutations was assessed, and relationships with clinicopathologic features were examined. The prevalence of SMAD4, SMAD2, and SMAD3 mutations in sporadic CRCs was 8.6% (64 of 744), 3.4% (25 of 744), and 4.3% (32 of 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-XSer motifs within SMAD2 and SMAD3. Functional analyses of selected mutations showed 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-b signaling pathway. Cancer Res; 73(2); 725-35. Ó2012 AACR.

Genetic alterations in Japanese extrahepatic biliary tract cancer

“…SMAD4 is a tumor suppressor gene containing two evolutionarily conserved regions as follows: Mad homology 1 and 2 domains (MH1 and MH2, respectively) (42,43). The four mutations, p.D351H, p.G352E, p.R361H and p.A532D, are located in the MH2 domain (codon 319-552), which serves an important role in heteromerization and transactivation functions (43).…”

“…The four mutations, p.D351H, p.G352E, p.R361H and p.A532D, are located in the MH2 domain (codon 319-552), which serves an important role in heteromerization and transactivation functions (43). The mutations at codons 351 and 361 are frequently reported (43). The two residues, Asp351 and Arg361, are located in the loop-helix region of SMAD4, and are involved in the interaction with Asp450 in SMAD2 (43).…”

“…The mutations at codons 351 and 361 are frequently reported (43). The two residues, Asp351 and Arg361, are located in the loop-helix region of SMAD4, and are involved in the interaction with Asp450 in SMAD2 (43). Therefore, these mutations may change the loop-helix structure, disrupting the heterodimerization between SMAD2 and SMAD4.…”

Colorectal cancer carcinogenesis: a review of mechanisms

“…The region carrying the deleted in colorectal cancer gene (a dependence factor) is more frequently lost in advanced cancers 70 . The mutations in similar to mothers against decapentaplegic (SMAD) homologproteins, namely SMAD2, SMAD3, SMAD4 and SMAD7, which are regulators of TGF β signaling, have been associated with CRC [71][72][73] . SMAD 4 loss predicts worse prognosis for fluorouracil-based therapies 74 .…”

TGFBR1*6A is a potential modifier of migration and invasion in colorectal cancer cells

“…Colorectal cancer cells evade the antiproliferative effects of TGF-β by acquiring mutations in components of this signaling pathway. Common mutations of TGF-β pathway components, including ligands, receptors, Smads and Smad-interacting transcription factors, increases the risk of developing colorectal cancer (5)(6)(7). Cross-talk between TGF-β, Smads and other cell signaling pathways is also activated by the TGF-β receptors, through either phosphorylation or direct interaction (8).…”