α5β1 integrin mediates strong tissue cohesion

Abstract

Integrins and cadherins are considered to have distinct and opposing functions. Integrins are traditionally cited for their role in cell-substratum interactions, whereas cadherins are thought to mediate strong intercellular cohesion. Together, these adhesion systems play crucial roles in a wide variety of cellular and developmental processes including cell migration, morphology, differentiation and proliferation. In this manuscript we present evidence that integrins possess the ability to mediate strong intercellular cohesion when cells are grown as 3D aggregates. Much of the data elucidating the role of integrins as mediators of cell-extracellular matrix (ECM) interactions have been generated using conventional cell culture techniques in which cells are plated onto ECM-coated 2D surfaces. In vivo, cells are embedded in a 3D meshwork of ECM proteins. We hypothesized that, within this meshwork, integrin-ECM interactions may impart cohesivity to an aggregate of cells by linking adjacent cells together. To test this hypothesis, we transfected Chinese hamster ovary (CHO-B2) cells to express α5β1 integrin and found that these cells formed compact, spherical aggregates. We measured aggregate cohesivity using tissue surface tensiometry, a novel technique that quantifies cell-cell cohesivity of spheroids under physiological conditions. We determined that α5β1 integrin is capable of conferring strong cohesivity (σ=8.22±0.68 dynes/cm) to aggregates of α5-integrin-transfected cells. This cohesion was found to be independent of cadherin expression and was significantly greater than the cohesivity conferred onto CHO-B2 cells transfected with N-cadherin (σ=3.14±0.20 dynes/cm, P≤0.0001), a more traditional cell-cell cohesion system. Fibronectin-null CHO cells that express α5β1 integrin but do not secrete endogenous fibronectin do not form aggregates in fibronectin-depleted medium. Addition of increasing amounts of exogenous dimeric fibronectin to these cells resulted in a dose-dependent compaction. However, compaction failed to occur in the presence of fibronectin monomers. These data indicate that fibronectin is required for α5β1-mediated compaction and that the dimeric structure of fibronectin is essential for this process. Additionally, aggregate formation of the α5 integrin transfectants was inhibited by an RGD peptide thus confirming α5β1 integrin specificity. Collectively, these data confirm our hypothesis that α5β1 integrin acts through fibronectin to link adjacent cells together, thus promoting strong intercellular cohesion in 3D cellular aggregates.

Engineering biological structures of prescribed shape using self-assembling multicellular systems

“…Here we used aggregates of N-cadherin transfected CHO cells, whose liquidity has been established earlier (49). It is quite likely that when structure formation is induced by the methods described here, aggregates of other cell types (in particular stem cells) will behave similarly to embryonic tissues, as far as their liquidity and ability to fuse is concerned.…”

Morphologic Instability and Cancer Invasion

“…Pleiotropic effects include cell proliferation, motility, differentiation, and survival, as shown in the collagen invasion assay (23) where cells are observed to form branched structures and invade a threedimensional collagen gel. Strong cell-cell and cell-matrix adhesion forces generated by cell adhesion molecules such as E-cadherins and integrins can attenuate such potentially invasive morphologies (24).…”

Biophysical measurement of brain tumor cohesion

“…Previous studies have demonstrated that TST can be used to predict and control the spatial relationship between different embryonic tissues 16,17 and also between genetically engineered cells, 18 can strongly influence the ability of tissues to interact with biomaterials, 19 correlates with invasive potential of lung tumors, 20 fibrosarcomas 21 and prostate cancers 22 and can be altered not only through direct manipulation of cadherin-based intercellular cohesion 18 -20 but also by manipulation of key extracellular matrix (ECM) molecules such as fibronectin (FN). 23,24 Any strategy aimed at increasing intercellular cohesive energy between tumor cells may be useful in restraining cells from detaching from the tumor mass. Dexamethasone (Dex) is a synthetic glucocorticoid that has broad uses in oncology.…”