The loss of CDH1 expression is a frequent event in gastric cancer (GC), in sporadic and hereditary manifestation, important in the invasion and metastasis process. Approximately, 15-50% of families affected by hereditary diffuse gastric cancer syndrome (HDGC) have germline mutations in the CDH1 gene. Evidences established that hsa-miR-9 participates of this protein downregulation in breast cancer and hepatocellular carcinoma. In the present study, we investigated the possibility of hsa-miR-9 is involved in CDH1 negative regulation in HDGC and sporadic GC. For the relative quantification of hsa-miR-9 expression by real-time PCR, was used samples from 9 patients with HDGC and paired samples of sporadic GC and adjacent non-neoplasic gastric tissue of 138 patients. Additionally, was performed copy number variation analysis of the MYC gene, a positive regulator of has-miR-9, in HDGC samples. The expression of CDH1 mRNA and its protein in sporadic GC samples were performed by real time PCR and Western Blot, respectively. All HDGC samples, exhibited increased of hsa-miR-9 expression and copies number of MYC (≥3 copies) independent of the presence of germline mutation in CDH1 gene. In sporadic GC it was detected a reduction of CDH1 mRNA expression, CDH1 and hsa-miR-9. Moreover, was found a significant association of CDH1 reduced expression in diffuse-type tumors and advanced. The reduction of CDH1 mRNA expression, CDH1 and hsa-miR-9 was significantly associated with lymph node metastasis and tumor stage III-IV. In correlation analysis, was identified a very strong correlation between the expression of mRNA and protein of CDH1, and a strong correlation between the CDH1 mRNA expression and hsa-miR-9, and the protein expression of CDH1 and hsa-miR-9. The hsa-miR-9 takes a controversial role in CG according to the type of manifestation, playing oncomiR paper in HDGC, occasionally behaving like tsmiR in sporadic. In HDGC, we suggest that hsa-miR-9 overexpression could be influenced by MYC amplification and that it functions as a second event mechanism in patients with germline mutation in the gene CDH1. Regarding sporadic GC, as an alternative hypothesis based on the theory of field cancerization, we suggest that there is an increased expression of hsa-miR-9 in the adjacent stomach tissue compared to the gastric tissue without cancer. This overexpression would be higher in adjacent tissue than in the tumor, leading to downregulation of CDH1, important for epithelial-mesenchymal transition and tumor initiation.
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