Identification of miRNomes in human stomach and gastric carcinoma reveals miR-133b/a-3p as therapeutic target for gastric cancer

Gastric cancer (GC) is the fourth most frequent malignant disease and the second leading cause of cancer mortality worldwide, but the molecular mechanisms underlying this clinically heterogeneous disease are complex and remain far from completely understood. Accumulating evidence suggests that abnormal microRNA (miRNA) expression is involved in tumorigenesis. However, their accurate expression pattern, function, and mechanism in GC remain unclear. Here, a heatmap analysis of the miRNomes was performed across TCGA datasets and the expression of miR-133 family was found to be consistently downregulated in GC. This result was confirmed in two GC cell lines and 20 pairs of primary GC tissues, and further study demonstrated that the downregulation of miR-133 was mainly mediated by histone modification within its promoter region. Importantly, restoration of miR-133b/a-3p expression could suppress GC cell proliferation and promote cell apoptosis by targeting anti-apoptotic molecules Mcl-1 and Bcl-xL. Consistent with in vitro results, reintroducing of miR-133b/a-3p expression significantly delayed tumor formation and reduced tumor size of GC cells in xenograft nude mice. And the inverse relationship between miR-133b/a-3p and its targets was verified in xenograft mice. Taken together, our findings suggest that miR-133b/a-3p acts as a tumor suppressor in GC by directly targeting Mcl-1 and Bcl-xL. Revealing novel mechanism for oncogene inhibition by miRNA-mediated pathways offers new avenues for GC treatment.