MicroRNA-21 inhibits Serpini1, a gene with novel tumour suppressive effects in gastric cancer.

Background: A thorough understanding of gastric cancer at the molecular level is urgently needed. One prominent oncogenic microRNA, miR-21, was previously reported to be upregulated in gastric cancer.

Methods: We performed an unbiased search for downstream messenger RNA targets of miR-21, based on miR-21 dysregulation, by using human tissue specimens and the MKN28 human gastric carcinoma cell line. Molecular techniques include microRNA microarrays, cDNA microarrays, qRT-PCR for miR and mRNA expression, transfection of MKN28 with miR-21 inhibitor or Serpini1 followed by Western blotting, cell cycle analysis by flow cytometry and luciferase reporter assay.

Results: This search identified Serpini1 as a putative miR-21 target. Luciferase assays demonstrated direct interaction between miR-21 and Serpini1 3'UTR. miR-21 and Serpini1 expression levels were inversely correlated in a subgroup of gastric cancers, suggesting a regulatory mechanism that included both of these molecules. Furthermore, Serpini1 induced growth retardation of MKN28 and induced vigorous G1/S arrest suggesting its potential tumour-suppressive function in the stomach.

Conclusion: Taken together, these data suggest that in a subgroup of gastric cancers, miR-21 is upregulated, inducing downregulation of Serpini1, which in turn releases the G1-S transition checkpoint, with the end result being increased tumour growth.