Caco-2 cells labeled for tight junction molecule cingulin (green), actin (red), vinculin (pink) and DNA (blue).
Epithelial cells growing on a patterned adhesive surface with the shape of the Weizmann Institute tree.
Desmosomes in mouse tongue epithelium (by transmission electron microscope).
Porcine aortic endothelial cell, double-labeled for actin (green) and phospho-tyrosine (red).
“Molecular composition map” of focal adhesions and stress fibers.
Myeloma cancer cell responding to shear flow (by scanning electron microscope).
Fibroblast polarization is a matrix-rigidity-dependent process controlled by focal adhesion mechanosensing
Background
Cells adhering to the extracellular matrix can sense and respond to a wide variety of chemical and physical features of the adhesive surface, including the molecular nature of the adhesive ligands and their local densities, as well as surface topography
and rigidity. Rigidity sensing (the capacity to differentially respond to substrates with varying degrees of stiffness) is a general phenomenon affecting multiple cellular properties, including morphology, migratory capacity, gene expression profile and, eventually, cell differentiation and fate.
Rationale
Addressing the molecular mechanisms that underly two basic properties of cultured fibroblasts: their ability to distinguish between extracellular matrices with varying degrees of stiffness, and their ability to acquire a polarized morphology following interaction with an appropriate substrate.
Methods
To gain insights into the role of extracellular matrix rigidity in the polarization of adherent fibroblasts, we used a short interfering RNA (siRNA)-mediated knockdown approach to perturb a central signalling system; namely, PTKs in cultured human foreskin fibroblasts (HFF), plated on matrices of varying rigidities.
Results
By selecting the knockdown cells that significantly differed from controls in their ability to polarize on substrates of varying degrees of stiffness, we identified 20 genes that are potentially involved in rigidity-dependent cell polarization. Examination of the ability of these knockdown cells to form focal adhesions on substrates with varying rigidities, together with estimations of the traction forces generated by these cells, provided insights into the molecular mechanisms underlying focal-adhesion/stressfibre mechanosensitivity, as well as rigidity-dependent cell polarization.
Conclusions
This study, based on monitoring the concerted progression of cell polarization, focal adhesion development and traction force generation in control cells, as well as in cells in which specific PTKs were knocked down, highlights the central role of mechanosensing in cell polarization. It also points to specific stages in cell polarization that are regulated by focal adhesion reorganization, and identifies genes that are involved in controlling these processes.
Contact person: Prof. Alexander D. Bershadsky
Further Reading
(2011).
Fibroblast polarization is a matrix-rigidity-dependent process controlled by focal adhesion mechanosensing.
Nature Cell Biology.
13
(12):1457-1465.
