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Cell and tissue stiffness have been known to contribute to both developmental and pathological signalling for some time, but the underlying mechanisms remain elusive. Integrins and their associated adhesion signalling complexes (IACs), which form a nexus between the cell cytoskeleton and the extracellular matrix, act as a key force sensing and transducing unit in cells. Accordingly, there has been much interest in obtaining a systems-level understanding of IAC composition. Proteomic approaches have revealed the complexity of IACs and identified a large number of components that are regulated by cytoskeletal force. Here we review the function of the consensus adhesome, an assembly of core IAC proteins that emerged from a meta-analysis of multiple proteomic datasets, in the context of mechanosensing. As IAC components have been linked to a variety of diseases involved with rigidity sensing, the field is now in a position to define the mechanosensing function of individual IAC proteins and elucidate their mechanisms of action., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Integrins are transmembrane adhesion proteins that convey critical topobiological information and exert crucial signalling functions. In skin and hair follicle biology, beta1 integrins and their ligands are of particular interest. It is not yet known whether beta1 integrins play any role in the regulation of human hair growth and the expression pattern of beta1 integrin in the human pilosebaceous unit remains ill-defined. Here, we show that pilosebaceous immunoreactivity for beta1 integrin is most prominent in the outermost layer of the outer root sheath and the surrounding connective tissue sheath of human scalp hair follicles in situ and in vitro. Sites of beta1 integrin immunoreactivity co-express fibronectin and tenascin-C. Contrary to previous reports, beta1 integrin immunoreactivity in situ was not significantly upregulated in the human bulge region. Functionally, two beta1 integrin-activating antibodies (12G10, TS2/16) and ligand-mimicking RGD peptides promoted the growth of microdissected, organ-cultured human scalp hair follicles in vitro and inhibited spontaneous hair follicle regression. This supports the concept that beta1 integrin-mediated signalling is also important in human hair growth control. The physiologically relevant organ culture assay employed here is a potential research tool for exploring whether targeted stimulation of beta1 integrin-mediated signalling is a suitable candidate for human hair loss management.

A preconditioning sciatic nerve crush promotes the capacity of adult sensory neurons to regenerate following a subsequent injury to their axons. The increase in regeneration is detected in cultures of dissociated neurons, as an earlier and enhanced rate of neurite elongation. We compare neurotrophin-stimulated neurite outgrowth from sensory neurons on laminin and fibronectin. There is a poor response of sensory neurons to fibronectin in comparison to laminin, but this is enhanced by a preconditioning lesion to the sciatic nerve 7 days prior to culture. By using specific integrin-binding fibronectin fragments and function-blocking antibodies, we demonstrate that the enhanced preconditioned neurite outgrowth on fibronectin is largely mediated by alpha5beta1 integrin. Preconditioning injury alter the subcellular localisation of alpha5 integrin in preconditioned neurites. We show that alpha5 integrin localises to adhesion complexes in the growth cone and neurites of preconditioned neurons, but not control neurons.

Integrins mediate cell adhesion to the extracellular matrix and initiate intracellular signaling. They play key roles in the central nervous system (CNS), participating in synaptogenesis, synaptic transmission and memory formation, but their precise mechanism of action remains unknown. Here we show that the integrin ligand-mimetic peptide GRGDSP induced NMDA receptor-dependent increases in intracellular calcium levels within seconds of presentation to primary cortical neurons. These were followed by transient activation and nuclear translocation of the ERK1/2 mitogen-activated protein kinase. RGD-induced effects were reduced by the NMDA receptor antagonist MK801, and ERK1/2 signaling was specifically inhibited by ifenprodil and PP2, indicating a functional connection between integrins, Src and NR2B-containing NMDA receptors. GRGDSP peptides were not significantly neuroprotective against excitotoxic insults. These results demonstrate a previously undescribed, extremely rapid effect of RGD peptide binding to integrins on cortical neurons that implies a close, functionally relevant connection between adhesion receptors and synaptic transmission.

Integrins are dynamic membrane proteins that mediate adhesion of cells to the extracellular matrix. Integrins initiate signal transduction, alone and cooperatively with growth factor receptors, and regulate many aspects of cell behavior. We report here that alpha5beta1-mediated adhesion of Ntera2 neuronal cells to fibronectin decreased apoptosis in response to serum withdrawal. Adhesion induced phosphorylation of FAK, and strongly increased the AKT phosphorylation induced by growth factors, demonstrating for the first time in neuronal cells that integrin-mediated adhesion and growth factors cooperate to regulate AKT activity. Integrins exist on cells in different activation states, and cell survival on fibronectin was enhanced by the antibody 12G10, that modulates the conformation of beta1 in favor of its active form. The antibody 12G10 specifically delayed loss of phosphorylation of AKT on serine 473, and GSK-3beta on serine 9, induced by serum withdrawal, suggesting that these kinases are critical sensors of integrin activation on neuronal cells.

We have analyzed the interaction of neural crest cells with fragments of fibronectin corresponding to the different spliced variants of the COOH-terminal cell-binding domain (COOH-ter CBD). We have shown that this domain can support cell adhesion and migration and that both the IIICS and HepII regions are involved in these events. The rate of locomotion is high, although undirectional, compared to that of whole fibronectin. Interactions with the COOH-ter CBD are controlled by alpha4beta1 and maybe other beta1 integrins and cell-surface proteoglycans. These receptors act cooperatively to mediate attachment, spreading, and migration on fibronectin.

Alterations in the rate and pattern of cell movement are prominent features of many human diseases, including inflammation, cardiovascular disease and cancer. The ability to regulate the interactions of cells with each other and with adhesion factors in extracellular matrices therefore offers a novel approach to the treatment of these diseases. The intention of this article is to provide an overview of the role of the adhesive glycoprotein fibronectin and its receptors in the adhesive behavior of tumors, to review ongoing work that is aimed at developing agents with the ability to regulate adhesion to fibronectin, and to highlight aspects of the malignant phenotype that are potential targets for intervention with such agents.