MicroRNA Signatures in Lung Adenocarcinoma Metastases: Exploring the Oncogenic Targets of Tumor-Suppressive...

Background: To improve the prognosis of patients with lung adenocarcinoma (LUAD), revolutionary treatments for metastatic lesions are essential. Methods: To identify genes closely involved in LUAD-cell-derived metastasis, we used RNA sequencing to generate microRNA (miRNA) expression signatures of brain metastatic lesions. Once tumor-suppressive miRNAs are identified, it will be possible to explore the numerous tumor-promoting genes that are regulated by miRNAs. Results: By comparison with a previously created LUAD signature, we identified several miRNAs whose expression was significantly suppressed in brain metastases. We focused on both strands of pre-miR-195 (miR-195-5p and miR-195-3p), which were significantly downregulated in brain metastatic tissues, and confirmed by ectopic expression assays that both strands of pre-miR-195 attenuated the aggressive phenotypes (cell proliferation, migration, and invasion) of LUAD cells. These data suggest that both strands of pre-miR-195 have tumor-suppressive functions in LUAD cells. Next, we explored the target molecules that each miRNA strand regulates in LUAD cells. We identified 159 target genes regulated by miR-195-5p and miR-195-3p, of which 12 genes (ANLN, CDC6, CDCA2, CDK1, CEP55, CHEK1, CLSPN, GINS1, KIF23, MAD2L1, OIP5, and TIMELESS) affect cell cycle/cell division and the prognosis of LUAD patients. Finally, we focused on two genes, ANLN (miR-195-5p target) and MAD2L1 (miR-195-3p target), and demonstrated their oncogenic functions and the molecular pathways they regulate in LUAD cells. Conclusions: The miRNA signature derived from lung cancer brain metastasis will be a landmark in the field, and analysis of this miRNA signature will accelerate the identification of genes involved in lung cancer brain metastasis.