Research Of Molecular Events At The Early Stage Of Colorectal Tumorigenesis

Background:Most of colorectal adenocarcinomas are believed to arise from adenomas, which are premalignant lesions. Both coding genes and non-coding genes play important roles in colorectal carcinogenesis. Sequencing the whole exome and miRNA of the adenoma will help identifying molecular biomarkers that can predict the occurrence of adenocarcinoma more precisely and help understanding the molecular pathways underlying the initial stage of colorectal tumorigenesis.Methods:1,We performed the exome capture sequencing of the normal mucosa, adenoma and adenocarcinoma tissues from the same patient. Somatic single nucleotide variations (SNVs) were identified in both the adenoma and adenocarcinoma by comparing with the normal control from the same patient.2,We validate the SNVs from first study in73adenoma and288adenocarcinoma. And we collect133colorectal cancer associated somatice mutation genes, and validate these genes in40adenomas.3,miRNA sequencing was performed on3pairs of the normal mucosa, adenoma and adenocarcinoma tissues from same patients. Differential expression and sequence variation were identified in both the adenoma and adenocarcinoma by comparing with the normal control.Results:1, We (?)tified12nonsynonymous somatic SNVs in the adenoma and42nonsynonymous somatic SNVs in the adenocarcinoma. Most of these mutations including OR6X1, SLC15A3, KRTHB4, RBFOX1, LAMA3, CDH20, BIRC6, NMBR, GLCCI1, EFR3A, and FTHL17were newly reported in colorectal adenomas. Functional annotation of these mutated genes showed that multiple cellular pathways including Wnt, cell adhesion and ubiquitin mediated proteolysis pathways were altered genetically in the adenoma and that the genetic alterations in the same pathways persist in the adenocarcinoma. CDH20and LAMA3were mutated in the adenoma while NRXN3and COL4A6were mutated in the adenocarcinoma from the same patient.2, APC was mutated in almost50%of the40adenomas. And genes associated with eel adhesion pathway were mutated in8%adenomas; genes associated with ubiquitin mediated proteolysis pathways were mutated in17.5%adenomas.Besides these pathways, DNA mismatch repair genes are mutated in10%adenomas.3, hsa-miR-135b*,hsa-miR-31and hsa-miR-503were up-regulated in both adenomas and adenocarcinomas;miR-9and miR-195were down-regulated in both adenomas and adenocarcinomas. And we found SNPs on miR-376a-2、miR-381、miR-411、 miR-503and miR-585in the3patients; we also found somatic mutation on miR-625、miR-1974、miR-376c and miR-144in adenomas or adenocarcinomas.Conclusion:Genetic alterations in the Wnt pathway, cell adhesion pathway, ubiquitin mediated proteolysis pathways and DNA mismatch repair genes occur as early as in the adenoma. miRNA also play an important role in adenomas. Thus, the comparison of genomic mutations in both coding genes and non-coding genes between adenoma and adenocarcinoma provides us a new insight into the molecular events governing the early step of colorectal tumorigenesis.