Clusterin Promotes the Migration and Invasion of Highly Aggressive Breast Cancer Cells Through Molecular Mechanisms That Affect the Cell Cytoskeleton and Extracellular Matrix Dynamics

Metastatic breast cancer (BC) remains a major clinical challenge, and identifying molecular mechanisms driving tumor cell migration and invasion is critical to develop effective therapeutic strategies. Clusterin (CLU), a secreted chaperone-like protein, is upregulated in BC and metastatic tissue; however, its functional contribution to tumor aggressiveness remains unclear. Here, we silenced CLU by siRNA in two BC cell lines with distinct aggressiveness and examined its impact on migration, invasion, and associated signaling pathways. Following CLU silencing, cell migration and invasion were assessed using transwell assays. Cytoskeletal organization was evaluated by F-actin staining, while downstream signaling pathways were analyzed by RT-PCR, Western blotting, and Rho GTPase pull-down. A comparative proteomic analysis was performed in CLU-expressing and CLU-silenced MDA-MB-231 cells. CLU knockdown significantly reduced migration and invasion in MDA-MB-231, concomitantly with loss of F-actin-rich membrane protrusions, reduced expression of MMP9, COL1A1, and COL4A1, and decreased activation of Akt, NF-kappa B, and RhoA. Proteomic profiling revealed extensive remodeling of pathways involved in cell adhesion, cytoskeletal dynamics, and extracellular matrix interactions. Differently, no or very mild effects were observed in CLU-silenced MCF-7 cells. These findings identify CLU as an upstream regulator of a pro-metastatic adhesion-cytoskeleton signaling in BC, selectively operative in EMT-engaged, basal-like cells, highlighting the importance of patient stratification for CLU-targeted therapeutic strategies.