Galectin-3 Negatively Regulates miR-31 Processing in Breast Cancer Cells

MicroRNA-31 (miR-31) acts as a tumor suppressor and is downregulated in breast cancer, but the mechanism responsible for its reduced maturation remains unclear. To investigate this, we examined the expression patterns of pri- and mature miR-31 across multiple human tumor cell lines. Quantitative PCR revealed that while pri-miR-31 was abundantly expressed, mature miR-31 levels were selectively decreased in breast cancer cells, indicating a block at the post-transcriptional processing step. Treatment with the histone deacetylase inhibitor trichostatin A (TSA) restored miR-31 expression while concurrently suppressing Galectin-3, suggesting a potential regulatory link between the two molecules. RNA electrophoretic mobility shift assays (EMSA) demonstrated direct binding of recombinant Galectin-3 to in vitro-transcribed pre-miR-31. Protein-RNA docking analysis further supported this interaction, identifying the CUGGG motif (C35-G39) within pre-miR-31 as the key contact region interacting with the carbohydrate recognition domain (CRD) of Galectin-3. Functional analyses in MCF7 cells, which exhibit the highest endogenous Galectin-3 levels, showed that Galectin-3 knockdown markedly increased mature miR-31 expression without altering pri-miR-31 levels, confirming regulation at the processing stage. TaqMan™ microRNA profiling revealed that Galectin-3 depletion selectively altered a subset of miRNAs, including miR-31, suggesting partial remodeling of the cellular miRNA landscape. Collectively, our findings identify Galectin-3 as a negative regulator of miR-31 maturation in breast cancer cells and suggest a novel role for this lectin in post-transcriptional control of microRNA biogenesis.