Nascent Integrin Adhesions Form on All Matrix Rigidities after Integrin Activation

Abstract

Integrin adhesions assemble and mature in response to ligand binding and mechanical factors, but the molecular-level organization is not known. We report that ∼100-nm clusters of ∼50 β3-activated integrins form very early adhesions under a wide variety of conditions on RGD surfaces. These adhesions form similarly on fluid and rigid substrates, but most adhesions are transient on rigid substrates. Without talin or actin polymerization, few early adhesions form, but expression of either the talin head or rod domain in talin-depleted cells restores early adhesion formation. Mutation of the integrin binding site in the talin rod decreases cluster size. We suggest that the integrin clusters constitute universal early adhesions and that they are the modular units of cell matrix adhesions. They require the association of activated integrins with cytoplasmic proteins, in particular talin and actin, and cytoskeletal contraction on them causes adhesion maturation for cell motility and growth.

Embryonically inspired scaffolds regulate tenogenically differentiating cells

“…At the microscale, alginate concentrations below 3% (w/v) will produce gels with moduli as low as HH 28 tendon. However, we chose to focus on the effects of nanoscale moduli on TPC responses because integrins that mediate cell-matrix interactions are nanoscale in dimension (Changede et al, 2015; Nermut et al, 1988). …”

“…Considering integrins are nanoscale in dimension (Changede et al, 2015; Chen and Singer, 1982; Erb et al, 1997; Franz and Muller, 2005; Kanchanawong et al, 2010), we examined TPC responses to different nanoscale elastic moduli. RGD-alg gels differentially regulated tendon marker expression as a function of embryonic stage-specific nanoscale modulus after 7 days of culture.…”

Talin – the master of integrin adhesions

“…A C-terminal fragment of talin from IBS2 to ABS3 rescues the proliferation defects in epithelial cells lacking talin (Wang et al, 2011), and the IBS2 region is needed for talin to form the initial clusters of ∼50 integrins in nascent adhesions (Changede et al, 2015). For talin interactions alone to be sufficient to generate integrin clusters larger than four integrins, one integrin might need to be able to bind to more than one talin molecule, thus forming a network of integrins that are separated by the distance between the two IBSs in the talin molecule or dimer (Fig.…”

“…Zervas et al, 2011), and thirdly, how integrins adopt a regular spacing within adhesions (Rossier et al, 2012). However, fragments of the head or rod domains can function in place of talin in forming nascent adhesion clusters (Changede et al, 2015), suggesting that single IBSs can function with other IAPs in generating this matrix.…”

Cellular mechanosensing of the biophysical microenvironment: A review of mathematical models of biophysical regulation of cell responses

“…Sheetz et al show that cell adhesions are loose aggregates of integrin clusters. These tight clusters of integrins each have a size of ~100 nm, and is each composed of ~20–50 molecules [131]. Interestingly, it has been concluded that clustered, but not individually distributed, plasma membrane proteins ( e.g.…”