Counterintuitive effect of extracellular fluid viscosity on enhancing motility and metastasis

Cells respond to physical stimuli, such as stiffness, fluid shear stress and hydraulic pressure. Extracellular fluid viscosity is a key physical cue that varies under physiological and pathological conditions, such as cancer. However, its impact on cancer biology and the mechanism by which cells sense and respond to changes in viscosity is unknown. We demonstrate that elevated viscosity counterintuitively increases the motility of various cell types on two-dimensional (2D) surfaces, in confinement, and cell dissemination from 3D tumor spheroids. Increased mechanical loading imposed by elevated viscosity induces an Actin Related Protein 2/3 (Arp2/3) complex-dependent dense actin network, which enhances Na+/H+ exchanger 1 (NHE1) polarization via its actin-binding partner ezrin. NHE1 promotes cell swelling and increased membrane tension which, in turn, activates transient receptor potential cation vanilloid 4 (TRPV4) and mediates calcium influx, leading to increased RhoA-dependent cell contractility. The coordinated action of actin remodeling/dynamics, NHE1-mediated swelling and RhoA-based contractility facilitates enhanced motility at elevated viscosities. Breast cancer cells pre-exposed to elevated viscosity acquire TRPV4-dependent mechanical memory via transcriptional control of the Hippo pathway, leading to increased migration in zebrafish, extravasation in chick embryos and lung metastasis in mice. Cumulatively, extracellular viscosity is a physical cue that regulates both short- and long-term cellular processes with pathophysiological relevance to cancer biology. Comparative gene expression profiling analysis of RNA-seq data for scramble or shTRPV4 MDA-MB-231 cells subjected to media at 0.77 cP or 8 cP.