STAT3 upregulates miR-92a to inhibit RECK expression and to promote invasiveness of lung cancer cells

Background: Signal transducer and activator of transcription 3 (STAT3) activation is frequently found in human lung cancer and is associated with increased metastasis and reduced survival. How STAT3 enhances invasiveness is unclear. Methods: The expression of microRNAs and target genes was measured by real-time RT-PCR. Protein level was studied by western blotting. Luciferase reporter assay was used to confirm the direct targeting of microRNAs. Gelatin zymography was used to study matrix metalloproteinase (MMP) activity. Transwell assay was used to investigate cell migration and invasion. Results: Enforced expression of STAT3 decreases the endogenous MMP inhibitor RECK protein but not mRNA level in H460 cells. Conversely, STAT3 inhibitor S3I-201 increases RECK protein in STAT3-activating H1299 cells. We demonstrate that STAT3 upregulates miR-92a to repress RECK via post-transcriptional inhibition. The RECK 3'-untranslated region (3'UTR) reporter activity assay suggests that RECK is a direct repression target of miR-92a. Delivery of pre-miR-92a reduces RECK protein level whereas transfection of anti-miR-92a restores STAT3-induced downregulation of RECK. Anti-miR-92a attenuates MMP activity, migration and invasion of H1299 cells and STAT3-overexpressing H460 cells, suggesting miR-92a is critical for STAT3-induced invasiveness. Conclusion: The STAT3-induced miR-92a promotes cancer invasion by suppressing RECK and targeting of the STAT3/miR-92a axis may be helpful for cancer treatment.