Mechanosensitivity of Membrane-Actin Cortex Adhesion

Duke University, Durham NC

Investigators

Abstract

Physical forces generated by, or applied to, human or animal cells are involved in almost every fundamental cellular function, including division, shape control, volume and internal pressure control, differentiation, and migration, as well as cell death. These forces must pass through the surface of the cell, which consists of a thin lipid membrane on the outside and a mechanically tough biopolymer network, the actin cortex, on the inside. Cells meticulously sense and regulate these forces. In the same way that the straps that tie the fabric of a tent to its supporting frame would be the best place to monitor what the wind is doing to the tent, the prime location for force-sensing machinery in the cell is at the interface between the actin cortex and the lipid membrane. How single cells react to forces and produce their own is important for large-scale dynamics in living organisms, such as tissue and organ development, cancer progression and metastasis, wound healing, and tissue regeneration. However, it remains largely unknown how cells sense and respond to forces. In this project, the team will develop and use a suite of innovative biosensors to study a prominent membrane actin linker protein, ezrin, which is known to regulate stem cell differentiation and cell migration and is implicated in cancer progression. The investigators will use the sensors to probe where the protein accumulates, what conformations it can be in, and what forces it experiences as cells are physically manipulated. The investigators will combine the results from these molecular probes with what we know about the larger-scale mechanics of the cell surface and use manipulation with laser beams, magnetic particles, and elastic micro-cantilevers for micromechanical probing. Computational modeling will be used to simulate ezrin kinetics and interpret the results of these experiments. This work develops an innovative concept, considering the proteins at the interface between the cell membrane and the underlying mechanical skeleton as a sensory machinery supplying crucial signals to control cell behavior. The research aims to discover the important molecular players and determine how they tie into the larger-scale mechanics of the whole cell. The project also drives technical innovation in that it will provide a new suite of biosensors that probe the localization, conformation, and molecular force experienced by a protein that can be observed and directly compared with standard fluorescence microscopy. Cellular mechanosensing is a central part of the physics of living systems, and new insights will have a broad impact on fundamental cell and developmental biology as well as biotechnology and medicine. Mechanosensing and mechanoregulation are particularly relevant for regenerative medicine and for various prominent human pathologies, including cancer and fibrosis. By combining molecular engineering with cell biophysics and theoretical modeling, the project will provide new ways of training future scientists and engineers working in this interdisciplinary area at all levels. Through educational and public outreach, the research will engage new generations of young scientists from diverse communities and stimulate them to participate in research in the broad area of the physics of living systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.