MiR-199a-5p Decreases Esophageal Cancer Cell Proliferation Partially through Repression of Jun-B

SIMPLE SUMMARY: The expression of specific microRNAs may be significantly altered in different kinds of cancers. MiR-199a-5p has been shown to be downregulated in multiple malignancies and function as a tumor suppressor. We have previously shown that miR-199a-5p is markedly downregulated in esophageal squamous cancer cell lines compared to esophageal epithelial cells. MiR-199a-5p is predicted to interact directly with Jun-B mRNA, an important component of the AP1 transcription factor, with high affinity. The aim of our study was to determine expression of Jun-B in esophageal cancer cells as well as to investigate the interaction between miR-199a-5p and Jun-B in these cells and to characterize the functional implications of this interaction. ABSTRACT: MicroRNA (miR)-199a-5p has been shown to function as a tumor suppressor in some malignancies but its role in esophageal cancer is poorly understood. To further explore its role in esophageal cancer, we sought to investigate the interaction between miR-199a-5p and Jun-B, an important component of the AP1 transcription factor, which contains a potential binding site for miR-199a-5p in its mRNA. We found that levels of miR-199a-5p are reduced in both human esophageal cancer specimens and in multiple esophageal cancer cell lines compared to esophageal epithelial cells. Jun-B expression is correspondingly elevated in these tumor specimens and in several cell lines compared to esophageal epithelial cells. Jun-B mRNA expression and stability, as well as protein expression, are markedly decreased following miR-199a-5p overexpression. A direct interaction between miR-199a-5p and Jun-B mRNA was confirmed by a biotinylated RNA-pull down assay and luciferase reporter constructs. Either forced expression of miR-199a-5p or Jun-B silencing led to a significant decrease in cellular proliferation as well as in AP-1 promoter activity. Our results provide evidence that miR-199a-5p functions as a tumor suppressor in esophageal cancer cells by regulating cellular proliferation, partially through repression of Jun B.