Calpain 2 Isoform‐Specific Cleavage of Filamin A Enhances HIF1α Nuclear Translocation, Promoting Metastasis in Triple‐Negative Breast Cancer

Triple-negative breast cancer (TNBC) remains a challenge due to its aggressive nature and limited therapeutic options. Calpain 2, a member of the calcium-dependent cysteine protease family, is particularly associated with poor prognosis in TNBC. This study explores the isoform-specific role of calpain 2 in TNBC, examining its correlation with prognosis and its mechanistic impact on metastasis. Bioinformatic analyses, including Kaplan-Meier survival plots, univariate Cox proportional analysis, and gene set enrichment analysis (GSEA), assessed <i>CAPN2</i> expression and its association with mesenchymal genes in TNBC. Results of cell-based experiments with <i>CAPN2</i> knockdown or overexpression indicate that elevated <i>CAPN2</i> expression correlates with poor clinical outcomes and enhanced metastatic potential in TNBC. <i>CAPN2</i> knockdown inhibited the epithelial-mesenchymal transition (EMT), reducing cancer cell proliferation, migration, and invasion. Calpain 2 downregulation reversed the EMT by reducing isoform-specific cleavage of filamin A, HIF1α nuclear localization and <i>TWIST1</i> transcription. CNa <b>29</b>, a calpain 2-specific inhibitor, reduced cancer cell proliferation, decreased filamin A cleavage, downregulated <i>TWIST1</i> expression, and significantly retarded metastasis,. In conclusion, calpain 2 plays a critical role in TNBC progression by modulating HIF1α and <i>TWIST1</i>, to promote the EMT and metastasis. Isoform-selective inhibition of calpain 2 with CNa <b>29</b> presents a promising therapeutic strategy for managing TNBC.