Abstract

Background: Gastric cancer (GC) is the third cause of cancer death in the world. In Latin America, GC is one of the leading causes of death, particularly in Chile. E-cadherin has been classified as a tumor suppressor gene that participates in cell adhesion. Reduction or loss of E-cadherin expression could promote tumor progression particularly in the sporadic diffuse subtype of GC (SDGC). In addition, inactivation germline mutations of CDH1 (E-cadherin gene) have been linked to the hereditary diffuse gastric cancer (HDGC) syndrome. Methods: We evaluated the expression of E-cadherin by Immunohistochemistry (IHC) in SDGC (n=27) and HDGC (n=22) cohorts. We also analyzed, by Sanger sequencing the full coding region of CDH1 in both cohorts. To identified miRNA-CDH1 interactions, an in silico analysis by mirWalk 2.0 software (5 or more algorithms) was performed. To validated in silico findings, 10 paired tumor and normal matched fresh gastric tissues were analyzed by miQ-PCR (miRNA) and qRT-PCR assay (CDH1 transcript) were performed. Results: The expression analysis of E-cadherin showed loss of expression in 13/27 (48%) SDGC and in 19/22 (90%) HDGC cases, respectively. The decrease of E-cadherin expression was significantly higher in the hereditary cohort (p=0.002, χ2: 9.12, 95%CI:13.0-63.3). Exome sequence analysis of the full coding region of CDH1 identified 3 and 9 mutations in SDGC and HDGC, respectively. Correlation between loss of protein expression by IHC and mutations was not found. Next, we explore the role of miRNA, as an alternative mechanism of the loss of E-cadherin protein expression. In silico analysis identified 417 miRNAs candidates with predicted binding sites. Among these candidates, all members of the polycistronic cluster miR-17/92 have seed regions against the 3'-UTR of the CDH1 transcript. Levels of expression of all 6 members of the polycistronic cluster were validated against CDH1 expression in paired normal and tumor fresh tissues of SDGC. A strong inverse correlation between the overexpression of miR-20a and downregulation of CDH1 transcript was found exclusively in tumor tissue (p= 0.0267) but not in normal counterparts. These results were validated in the STAD-TCGA cohort. Conclusions: Our results might explain the loss of expression of CDH1 in GC due to overexpression miR-20, a member of the polycistronic cluster miR-17/92. Future experimental validation of the predicted seed region will be necessary to confirm these findings.