Our goal is to discover the molecular mechanisms by which integrins sense and transduce mechanical cues. Integrins are heterodimeric transmembrane proteins that link the cell's cytoskeleton to the extracellular matrix (ECM). Cells use integrins to migrate, exert force on their surroundings, and to sense the physical properties of the ECM. This latter property, termed mechanotransduction, is particularly important in human health and disease. Physical tension transmitted through integrins activates intracellular signaling that in turn exerts profound effects on processes as diverse as immune function, stem cell differentiation, and cancer cell metastasis. Despite this great physiological and medical importance, the physical mechanisms by which integrins sense mechanical force are not known.
We aim to close this fundamental gap in our understanding of cell biology. In published work, we have developed F?rster resonance energy transfer (FRET) based molecular tension sensors (MTSs) that report on the mechanical tensions experienced by individual integrins in living cells. We have since combined MTSs and superresolution light microscopy to, for the first time, map force transmission within integrin adhesions with nanometer spatial resolution. The qualitatively new capabilities of MTS-based imaging allow us to tackle two fundamental questions in integrin biology that until now could not be directly addressed.
In Aim 1, we will determine the physical mechanisms by which integrins sense mechanical tension. In particular, we will examine the overarching hypothesis that different integrin classes sense tension via fundamentally different mechanisms, and that these differences allow the cell to sense mechanical stimuli over a wide range of forces and timescales.
In Aim 2, we will characterize the force transducing and sensing machinery in micron-sized integrin assemblies, termed focal adhesions (FAs), for the first time. Specifically, we will test the hypothesis that FAs contain highly coordinated, force-sensing microdomains, a prediction that cannot be tested using conventional techniques. This work will transform our understanding of cellular mechanotransduction by uncovering the molecular assemblies and biophysical mechanisms by which cells sense and transduce mechanical signals. More broadly, the mechano-responsiveness and compositional complexity that characterize FAs are also present in many other cellular structures. The conceptual and technical approaches developed in this project have the capacity to transform multiple fields of research by introducing powerful new single-molecule biophysical measurements in the context of intact, living cells.

Public Health Relevance

The purpose of this project is to discover how living cells sense mechanical force. All living cells are sensitive to mechanical stimuli. Cellular responses to muscle stretch and blood flow are what underlie the health benefits of exercise. However, faulty cellular mechanical sensing is also a key and poorly understood contributor to cancer growth and metastasis. Discovering how cells sense mechanical inputs has great potential to contribute to human health and welfare.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Intercellular Interactions (ICI)
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Nie, Zhongzhen
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Stanford University
Engineering (All Types)
Schools of Engineering
United States
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Dunn, Alexander R (2018) Mechanobiology: ubiquitous and useful. Mol Biol Cell 29:1917-1918
Owen, Leanna M; Adhikari, Arjun S; Patel, Mohak et al. (2017) A cytoskeletal clutch mediates cellular force transmission in a soft, three-dimensional extracellular matrix. Mol Biol Cell 28:1959-1974
Mekhdjian, Armen H; Kai, FuiBoon; Rubashkin, Matthew G et al. (2017) Integrin-mediated traction force enhances paxillin molecular associations and adhesion dynamics that increase the invasiveness of tumor cells into a three-dimensional extracellular matrix. Mol Biol Cell 28:1467-1488
Sun, Zhiqi; Tseng, Hui-Yuan; Tan, Steven et al. (2016) Kank2 activates talin, reduces force transduction across integrins and induces central adhesion formation. Nat Cell Biol 18:941-53
Chang, Alice C; Mekhdjian, Armen H; Morimatsu, Masatoshi et al. (2016) Single Molecule Force Measurements in Living Cells Reveal a Minimally Tensioned Integrin State. ACS Nano 10:10745-10752
Morimatsu, Masatoshi; Mekhdjian, Armen H; Chang, Alice C et al. (2015) Visualizing the interior architecture of focal adhesions with high-resolution traction maps. Nano Lett 15:2220-8
Xu, Alexander M; Aalipour, Amin; Leal-Ortiz, Sergio et al. (2014) Quantification of nanowire penetration into living cells. Nat Commun 5:3613