| Human cells experience a variety of physical forces, such as tension, compression, and shear stress, during key biological processes including embryonic and adult development, wound healing, and cancer progression. These forces stimulate intracellular mechano-transduction signaling pathways. Mechano-receptors at cell surface points of adhesion sense mechanical force and trigger biochemical events throughout the cell's cytoplasm that result in genetic responses in the nucleus. β-catenin protein is a key signaling molecule involved in human development processes and human cancers. Identifying and understanding regulators of β-catenin signaling under these conditions is key to determining and targeting its morpho-mechanical, developmental, and oncogenic properties. This research investigated the effects of mechanical force on β-catenin signaling in epithelial cell systems. The laminar flow assay technique was used to apply fluid flow-induced shear stress to human cells. This form of physiological mechanical force triggered a mechano-transduction pathway that was analyzed in terms of its nuclear response and output phenotype. The mechano-transduction signaling pathway was mapped from the cell sensory mechanism at the membrane surface through the cytoplasm and into the nucleus. This research determined that β-catenin nuclear signaling activity is regulated by mechanical force applied to cells. Mechanical force is transmitted through the cell by a β-catenin signaling pathway that results in the down-regulation of cyclin D1 gene expression and blocks the cell cycle in the G1 phase. These pauses in the cell cycle provide opportunities for damaged or defective DNA to be repaired. The mechano-sensor/transducer for the shear flow-regulated β-catenin signaling pathway is identified as the integrin α6β4 cell surface receptor. Key cytoplasmic components of the shear flow-regulated β-catenin signaling pathway are identified as phosphoinositide 3 (PI3) kinase and Rac1 proteins. This is the first demonstration of the involvement of integrins, PI3 kinase, and Rac1 in the regulation of β-catenin signaling. The results of this research identify regulators of a biological control system that can potentially be targeted for therapeutic purposes in a plethora of related biological process such as developmental defects, cancer, and wound healing. This research demonstrates the benefit of implementing mechanical engineering principles and techniques to help solve biological problems. |
