Mechanotransduction of Cancer Cells and T Cells in the Fluid Flow Environment of the Circulation

Abstract

Mechanosensitive ion channels respond to a wide range of physical stimuli, such as fluid shear stress, osmotic pressure, matrix stiffness, or cytoskeletal tension. By opening in response to these physical forces, the mechanosensitive ion channels allow for the flux of ions that promote diverse cell signaling pathways. For example, when the mechanosensitive ion channel Piezo1 opens in response to fluid shear stress, it causes calcium influx into the cell. Calcium as a second messenger can then promote diverse signals from proliferation to apoptosis. This thesis investigates how prostate cancer cells and immune cells respond to fluid shear stress. Piezo1 activation by fluid shear stress was found to enhance the sensitivity of cancer cells to the apoptotic ligand known as TRAIL. Yoda1 was then used as a tool to probe the mechanism of how Piezo1 activation sensitizes cancer cells to TRAIL-mediated apoptosis. Piezo1 activation increased cancer cell sensitivity to TRAIL by promoting mitochondrial outer membrane permeability, which resulted in the release of proapoptotic proteins from the mitochondria. The next part of this thesis investigated why certain prostate cancer cells are more or less resistant to elevated fluid shear stress. The resistance of cancer cells to fluid shear stress-induced cell death did not rely on mechanosensitive ion channels. Instead, cancer cells that were more sensitive to fluid shear stress suffered from greater magnitudes of cell membrane damage, had less efficient membrane repair, and were less stiff. By reducing the stiffness of the fluid shear stress resistant DU145 and PC3 prostate cancer cells, both cells were sensitized to cell death induced by fluid shear stress. Last, immortalized Jurkat and primary human T cells were exposed to fluid shear stress while being treated with antibodies against CD3/CD28 to enhance the activation of the T cells. Fluid shear stress treatment significantly increased the activation of proteins essential for T cell activation through a Piezo1 dependent mechanism. The fluid shear stress also enhanced the expression of cytokines important in sustaining T cell activation and for targeting prostate cancer cells.