Secreted clusterin promotes the migration and invasion of triple-negative breast cancer cells

Introduction. Treatment of metastatic breast cancer (BC) remains a major problem. Thus, understanding the molecular processes that favor the acquisition of a motile phenotype, may help to find new “druggable” targets to block BC cells escape. Clusterin (CLU) is a secreted glycoprotein up regulated in BC that plays a role in cell adhesion, lipid metabolism, and membrane transporter recycling. We investigated the effects of CLU silencing on the migratory and invasive capacity of BC cells focusing our attention on the mechanisms that support extracellular matrix (ECM) remodeling and cytoskeleton fibers rearrangements. Materials and methods. We abrogated CLU expression (siRNA transfection) in two BC cell lines at different stages of malignancy, MCF-7 and MDA-MB-231. We used transwell migration and invasion assays to study cell motility, and molecular biology techniques i.e., RT-PCR, Western Blot, immunocytochemistry, Rho/GTP pull down assay, to explore the mechanisms underlying the observed phenotypes. Results and discussion. In the aggressive triple-negative breast cancer (TNBC) cell line, MDA-MB-231, CLU knock-down reduced both the migration and invasion. This phenotype was accompanied by a dramatic change in the cell shape, an impressive reduction of F-actin-enriched (filopodia-like) cell membrane protrusions, MMP9 down-regulation, and decreased activation of AKT, NF-KB and RhoA GTPase. Conversely, CLU silencing had no effects in luminal-like MCF-7 cells. We also found that CD44 and LRP1 receptors, which are involved in lamellipodia formation and cell motility, are more expressed in MDA-MB-231 than MCF-7 cells. Conclusions. Our work suggests that CLU contributes to the migratory phenotype of TNBC cells affecting the transduction of cell signalings that modulate the dynamics of the cytoskeleton and promote the ECM degradation through a mechanism that may involve the CD44/LRP1 axis. Of note, CLU is a known ligand of LRP1. Although our study needs to be extended in vivo, we are confident that it may have relevant translational implications, including the possibility to limit the disease progression towards a metastatic stage in specific subpopulations of BC patients that may benefit of CLU antisense oligonucleotides (already available) in combination with chemotherapy.