microRNA-33a prevents epithelial-mesenchymal transition, invasion and metastasis of gastric cancer cells through the Snail/Slug pathway.

Invasion and metastasis are responsible for the majority of deaths in gastric cancer (GC). microRNA-33a (miR-33a)might function as a tumor suppressor in multiple cancers. Here, we describe the regulation and function of miR-33a in GC and mechanisms involved in epithelial-mesenchymal transition (EMT) and metastasis. Firstly, GC tissues and adjacent normal tissues were collected. miR-33a up-regulation or SNAI2 depletion on GC cells were introduced in order to assess the detailed regulatory mechanism of them. We assessed the expression of miR-33a, SNAI2, Snail/Slug signaling pathway-related genes and EMT-related markers in GC tissues and cells.miR-33a distribution in GC tissues and adjacent normal tissues was measured. Cell proliferation, migration and invasion, and cell cycle distribution were assessed. In nude mice, GC tumor growth and lymph node metastasis were observed. Furthermore, the predicative value of miR-33a in prognosis of GC patients was evaluated. The obtained results indicated that lowly expressed miR-33a, highly expressed SNAI2, activated Snail/Slug and increased EMT were identified in GC tissues. miR-33a mainly located in the cytoplasm. miR-33a targeted and negatively regulated SNAI2. MKN-45 and MKN-28 cell lines were selected for in vitro experiments. Up-regulated miR-33a expression or siRNA-mediated silencing of SNAI2 suppressed the activation of Snail/Slug, whereby GC cell proliferation, invasion and migration, EMT, tumor growth and lymph node metastasis were inhibited. High expression of miR-33a was a protective factor influencing the prognosis of GC. This study suggests that miR-33a inhibited EMT, invasion and metastasis of GC through the Snail/Slug signaling pathway by modulating SNAI2 expression.