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 CAPN2 expression and its association with mesenchymal genes in TNBC. Results of cell-based experiments with CAPN2 knockdown or overexpression indicate that elevated CAPN2 expression correlates with poor clinical outcomes and enhanced metastatic potential in TNBC. CAPN2 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 TWIST1 transcription. CNa 29, a calpain 2-specific inhibitor, reduced cancer cell proliferation, decreased filamin A cleavage, downregulated TWIST1 expression, and significantly retarded metastasis,. In conclusion, calpain 2 plays a critical role in TNBC progression by modulating HIF1α and TWIST1, to promote the EMT and metastasis. Isoform-selective inhibition of calpain 2 with CNa 29 presents a promising therapeutic strategy for managing TNBC.