(25c) The Fluid Shear Stress Sensor TRPM7 Regulates Cell Intravasation

Cell migration and intravasation play a crucial role in the metastatic dissemination of cancer cells. Cells in vivo migrate through 3-dimensional extracellular matrices and longitudinal channel-like tracks occurring in diverse anatomical features. For migrating cells to intravasate, they must cross the endothelial cell layer and resist the exposure to shear stress from the circulating fluid, which is believed to be detrimental to the tumor cell. As such, intravasation preferentially occurs in regions of decreased fluid flow which is believed to facilitate tumor cell survival in the circulation. We herein provide a molecular interpretation of this behavior based on cells’ ability to sense and respond to shear stress during their transition from migration to intravasation.

To specifically investigate the process of intravasation by single cells, we designed a microfluidic system using soft lithography to probe cell behavior when they migrate through in vivo like confined channels and reach an orthogonal fluid flow of physiologically relevant shear stress levels. Cell motility and reversal phenotypes were tracked using time-lapse live microscopy. We used shRNA and CRISPR/Cas9 based gene-editing tools, calcium imaging, fluorescently tagged live-cell reporters, and FLIM/FRET microscopy to evaluate the molecular signaling pathways. We also verified our findings with electrophysiological activity measurements and overexpression of mechanosensitive ion channel and spatiotemporal modulation of signaling proteins using optogenetic tools. Finally, we utilized a chick embryo intravasation model and intravital imaging to extend our findings into physiological settings.

We discovered that when non-tumor cells sense fluid flow, they reverse their migration direction and re-enter confined channels to escape from shear stress (Fig 1A). Such shear sensitivity and downstream signaling is triggered by the mechanosensitive ion channel (MIC), TRPM7 (Fig 1B). Interestingly tumor cells have reduced expression of shear-sensitive MICs and much higher tolerance of shear stress, leading to successful intravasation. When we engineered sarcoma cells to overexpress TRPM7, their ability to intravasate reduced both in vitro and in vivo (Fig 1C). This presentation will discuss the use of cutting-edge molecular biology, quantitative microscopy, and optogenetic tools to decipher how TRPM7 induces shear sensitive tumor and normal cell reversal via the RhoA/Myosin II and calmodulin/IQGAP1/Cdc42 pathways. It will also discuss how to sensitize cancer cells to shear flow and thus reduce their in vivo intravasation.

Recent works have revealed how mechano-sensation alters cell behavior, providing plasticity for migration and invasion. This work reports on how normal fibroblasts detect and avoid shear flow, discouraging them from entering the blood stream. More interestingly, we propose that tumor cells can intravasate by suppressing this mechanism through reduced TRPM7 activity and/or downstream signaling.