The Mechanobiological Mechanisms Of Caveolae/Caveolin-1 In Low Shear Stress-Induced Breast Carcinoma Cell Migration And Invasion

Breast cancer recurrence and metastasis are the leading cause of cancer death among females. Recent reports have shown that the circulating tumour cells could overcome or even adopt the mechanical microenvironment of low shear stress. Caveolin-1(Cav-1), a resident protein of lipid rafts and caveolae, associates with many functions including endocytosis, transcytosis, cholesterol homeostasis, mechanotransduction, cellular signaling and cell proliferation. Phosphorylation of Cav-1 on Tyr-14 facilitates focal adhesion stability and dynamics, directional cell migration, ECM remodelling, caveolar endocytosis in response to specific stimuli. The caveolin scaffolding domain (CSD) can bind to many signaling proteins, such as the Ras/MEK/ERK, tyrosine kinase Src, G-proteins, PI3K and JAK/STAT. Recent researches have shown caveolae/Cav-1 as mechanosensors that respond immediately to mechanical stresses, but the mechanisms are still not well understood. In present study, we used a parallel-plate flow chamber system to mimic the fluid mechanical environment of the microcirculation, and investigated the underlying mechanisms of low shear stress-induced MDA-MB-231 cell metastasis to explore the potential roles of caveolae/Cav-1.By western blot and quantitative PCR assays, it was found that low shear stresses (1.8 or 4 dyn/cm2) upregulated Cav-1 expression in both mRNA and protein levels in breast carcinoma MDA-MB-231 cells. Cav-1 phosphorylation on Tyr-14 was also obviously detected MDA-MB-231 cells after 5min low shear stress exposure. Results from wound healing and invadopodia formation assays showed that low shear stresses could promote the migration and invadopodia formation. Cells incubated with PI3K/Akt/mTOR signal pathway inhibitors resulted in a decrease in the migration capacity. However, the destruction of lipid rafts induced by MβCD inhibited Cav-1 phosphorylation and suppressed the downstream PI3K/Akt/mTOR signal pathway activition. Of interests, more Cav-1 was clustered on cell membrane dramatically, especially in lipid rafts after low shear stress exposure. It was also found that low shear stress stimulated PI3K/Akt activity and accelerated p85 subunit co-location with Cav-1 in cells. Our data further demonstrated that the MT1-MMP expresion increased both in mRNA and protein levels after low shear stress exposure.Furthermore, Cav-1 knockdown dramatically reduced the expression of MT1-MMP, and inhibited the migration of cancer cells and suppressed phosphorylation of p85 and Akt. Cells transfected by Cav-1 shRNA and Cav-1Y14D, were injected through tail vein to assay lung metastasis. It was found that silence of Cav-1 inhibited the distant metastasis to lung significantly in vivo, while Cav-1 Y14D cells elevated the capacity of metastasis. In summary, these findings showed that low shear stress accelerated the breast carcinoma cells MDA-MB-231 metastasis mediated by caveolae/Cav-1 and its downstream signal pathways.