TGF-β regulates the ERK/MAPK pathway independent of the SMAD pathway by repressing miRNA-124 to increase MALAT1 expression in nasopharyngeal carcinoma

Transforming growth factor beta (TGF-β), a pleiotropic cytokine, promotes cell proliferation and migration in multiple cancers, including nasopharyngeal carcinoma (NPC). microRNA-124 (miR-124) becomes downregulated in NPC and inhibits the tumorigenesis of this disease. However, the role of miR-124 in TGF-β-induced NPC development remains unknown. In this study, constant TGF-β stimulation repressed miR-124 expression, whereas miR-124 overexpression antagonized TGF-β-promoted NPC cell growth and migration. miR-124 overexpression decreased p-SMAD2/3, SMAD4, and p-ERK levels, indicating that ectopic miR-124 overexpression inhibited SMAD and non-SMAD pathways. Pro-oncogenic lncRNA MALAT1 was targeted by miR-124 that regulated ERK/MAPK by targeting MALAT1 independent of the SMAD signaling pathway. In conclusion, our work clarified the significant role of miR-124 in TGF-β signaling pathways independent of the SMAD signaling pathway and showed the potential of miR-124 as a new therapeutic target against NPC.