Clusterin promotes cell motility via ECM degradation and cytoskeleton reorganization in triple-negative breast cancer cells

Literature provides a rather complex scenario in which role of Clusterin (CLU) in the onset and progression of tumors may seem contradictory. However, given the chaperone-like function of this protein, we hypothesized that in breast cancer it may play a role in intercellular communication by interacting with components of the extracellular matrix (ECM) and participating in its remodeling processes. Our hypothesis was evaluated by loss-of-function assays using a siRNA sequence (CLU-siRNA) to abrogate CLU expression in two breast adenocarcinoma cell lines at different stages of differentiation, MCF-7 and MDA-MB-231. We demonstrated through transwell migration and invasion assays that CLU knock-down led to a significant reduction in migratory and invasive capacity only in MDA-MB-231, which is an aggressive triple-negative breast cancer (TNBC) cell line. CLU loss led also to a significant reduction of Slug and Snail mRNA expression in these cells without a measurable effect on the expression and localization of either E-Cadherin or Vimentin. Moreover, we observed that after CLU knock-down the well-organized F-actin/tubulin network structure that supports cell motility was lost only in MDA-MB-231. In addition, these cells showed a significantly reduced pAkt/Akt and pNF-kB/NF-kB ratio, and a reduction of MMP9 expression, highlighting a role for CLU in ECM remodeling through the activation of these two pathways. In conclusion, our work suggests that CLU may act as a positive modulator of tumorigenesis only in advanced stages of disease, possibly depending on the surface receptors status. Moreover, our results may have translational implications in the development of combinatorial therapeutic strategies for TNBC based on the association between CLU antisense oligonucleotides and traditional chemotherapeutics.