Rigidity Sensing at the Leading Edge through αvβ3 Integrins and RPTPα

Abstract

Cells require optimal substrate stiffness for normal function and differentiation. The mechanisms for sensing matrix rigidity and durotaxis, however, are not clear. Here we showed that control, Shp2-/-, integrin beta1-/-, and talin1-/- cell lines all spread to a threefold greater area on fibronectin (FN)-coated rigid polyacrylamide surfaces than soft. In contrast, RPTPalpha-/- cells spread to the same area irrespective of rigidity on FN surfaces but spread 3x greater on rigid collagen IV-coated surfaces than soft. RPTPalpha and alphavbeta3 integrins were shown previously to be colocalized at leading edges and antibodies to alphavbeta3 blocked FN rigidity sensing. When FN beads were held with a rigid laser trap at the leading edge, stronger bonds to the cytoskeleton formed than when held with a soft trap; whereas back from the leading edge and in RPTPalpha-/- cells, weaker bonds were formed with both rigid and soft laser traps. From the rigidity of the trap, we calculate that a force of 10 pN generated in 1 s is sufficient to activate the rigidity response. We suggest that RPTPalpha and alphavbeta3 at the leading edge are critical elements for sensing FN matrix rigidity possibly through SFK activation at the edge and downstream signaling.

RPTPα is required for rigidity-dependent inhibition of extension and differentiation of hippocampal neurons

“…Substrate rigidity is known to affect the response to growth factors (Opas and Dziak, 1990), cell morphology, cytoskeletal architecture and migration (Choquet et al, 1997;Friedl and Brocker, 2000;Lo et al, 2000;Peyton and Putnam, 2005;Yeung et al, 2005). A different approach, in which cells are cultured on chemically stable polyacrylamide gels of varying rigidities (Pelham, Jr and Wang, 1997), was used by our group and others to determine the effect of matrix rigidity on cellular behavior (Engler et al, 2004;Jiang et al, 2006;Kostic and Sheetz, 2006;Wang et al, 2000).…”

“…Receptor-like protein tyrosine phosphatase ␣ (RPTP␣) has been implicated in the regulation of various signaling pathways including fibronectin (FN)-rigidity response (Jiang et al, 2006;Kostic and Sheetz, 2006). No soluble RPTP␣ ligands have been identified so far, but lateral activation of RPTP␣ by contactin and NCAM has previously been reported and these complexes are believed to regulate neurite extension (Bodrikov et al, 2005;Zeng et al, 1999).…”

Contribution of Bone Tissue Modulus to Breast Cancer Metastasis to Bone

“…It is important to note that tissues, as well as natural and synthetic matrices used to investigate the effects of rigidity on cell fate, exhibit viscoelastic mechanical properties, where the relationship between stress and strain is not linear but dependent on the magnitude of the force and the time scale of the deformation [50]. However, for the typically small deformations (e.g., 100-150 nm [57,58]) relevant to mechanotransduction, the elastic modulus is a reasonable approximation for the rigidity of the matrix. In response to an applied external force, cells generate contractile traction forces against the matrix that are mediated by Rho-associated kinase (ROCK).…”

“…In response to an applied external force, cells generate contractile traction forces against the matrix that are mediated by Rho-associated kinase (ROCK). Recent studies have suggested that in order for cells to respond to matrix rigidity, a threshold force must be obtained that generates a matrix displacement of approximately 100-150 nm [50,57,58]. Thus when cultured on rigid substrates, cells generate larger traction forces than on compliant substrates, which may be due to the fact that rigid substrates require larger contractile forces to maintain matrix strain [50,59].…”

“…Several studies suggest that cells sense rigidity based on whether a threshold force is obtained when the displacement of the substrate is in the range of 100-150 nm [50,57,58]. The magnitude of the elastic modulus of the substrate that would likely result in a displacement of 100 nm has been estimated to be 10 nN/ μm 2 [50].…”