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Researchers observe the dynamics of protein interactions in living cells

The Deborah Leckband and Ying Xiao Wang (University of California, San Diego) groups have collaborated to design a new fluorescent protein that directly reports the transduction of force at cell-to-cell adhesions into intracellular biochemical signals in living cells—a process referred to as "mechanotransduction". At sites of cell-to-cell adhesion, a cytosolic protein alpha catenin was proposed to carry out this process, but its direct activation by force had not been demonstrated. Leckband and Wang are the first to design a "protein biosensor that directly reports biochemical force transduction by this essential protein, alpha catenin, at mechanical connections between living cells". They then used this sensor to follow force transduction in the cells and observe the dynamics of subsequently triggered biochemical events

FRET/ECFP (top) and differential interference contrast (DIC; bottom) images of DLD1-R2/7 cells transfected with the sensor, before (left) and after (right) treatment with 50 μg/ml DECMA-1 antibody.
Fluorescence images (top) and differential interference contrast (DIC; bottom) images of cells transfected that contain the alpha catenin sensor. In cells on the left, tension across both the cell-to-cell contact and alpha catenin is high, but the fluorescence signal increases (top, right) after treating the cell s with an antibody that lowers the cell-to-cell tension.

Catenins are proteins involved in cell-to-cell adhesion, and they mechanically connect adhesion proteins (cadherins) to actin filaments in the cytoplasm. Cadherins are the molecular Velcro that holds cells together in tissues, and actin fibers are mechanical cables that control cell shape and stiffness. Cadherins, actin, and alpha catenin are all required for tissue formation, for cell shape control, cell movement in tissues, and for many tissue functions. Leckband and Wang's work now provide an important tool for 'seeing' when and where force is transduced at cell-to-cell junctions during biological processes such as during tissue formation in embryos. Professor Leckband states, "This is a tool that will be used to study a number of biological processes like morphogenesis.  Alpha catenin is a critical protein for maintaining cell cohesion, and there are many examples where cadherins and alpha catenin together regulate how tightly cells stick together in different mechanical contexts.  For example, hypertension degrades the tight cadherin adhesions between cells in the kidney that regulate the flow of fluid, proteins, and ions from the bloodstream. In hardened, aged arteries, the more contractile cells exert greater force on cadherin adhesions between cells lining the blood vessels, and this increased stress makes blood vessels leakier.  Even the migration of leukocytes from the bloodstream requires disrupting cadherin adhesions between endothelial cells.  Alpha catenin is involved in all of these processes, so I hope to see this applied broadly to understand how mechanical cues regulate tissue functions." She also says, "For me, the most exciting part of this work is now being able to see what is going on in a living cell as it converts mechanical information into biochemical signals that control cell functions. Now we have a unique tool that we can use to visualize when and where this conformation change occurs in tissues, and to understand how mutations linked to disease affect its ability to transduce mechanical force. As an example of the possibilities, we are collaborating with a team in Canada that is studying the role of alpha catenin in embryonic development in Drosophila. They are planning to use our reporter in live embryos to follow alpha catenin conformations in different tissues at different stages of development. We are also collaborating with a group at UI Chicago that studies ventilator induced lung injury. This reporter may enable us to identify critical processes caused by lung inflation that lead to cardiovascular disease."

The highlights of the research were:

  • α-catenin FRET sensor exhibits cadherin- and force-dependent conformation switching
  • α-catenin acts as a reversible, elastic spring in series with cadherin and actin
  • The fast force-activation of α-catenin is followed by slower biochemical changes in the cell

Their research was published in the January 19, 2015 issue of Current Biology.

Dynamic visualization of α-catenin reveals rapid, reversible conformation switching between tension states. Kim, T.-J. | Zheng, S. | Sun, J. | Muhamed, I. | Wu, J. | Lei, L. | Kong, X. | Leckband, D.E. | Wang, Y.

The National Institutes of Health supported this research.

School of Chemical Sciences
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Professor Jonathan Sweedler

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