α2β1 integrin controls association of Rac with the membrane and triggers quiescence of endothelial cells

Abstract

SummaryIntegrin receptors and their extracellular matrix ligands provide cues to cell proliferation, survival, differentiation and migration. Here, we show that 21 integrin, when ligated to the basement membrane component laminin-1, triggers a proliferation arrest in primary endothelial cells. Indeed, in the presence of strong growth signals supplied by growth factors and fibronectin, 21 engagement alters assembly of mature focal adhesions by 51 and leads to impairment of downstream signaling and cell-cycle arrest in the G1 phase. Although the capacity of 51 to signal for GTP loading of Rac is preserved, the joint engagement of 21 interferes with membrane anchorage of Rac. Adapting the 'split-ubiquitin' sensor to screen for membrane-proximal 2 integrin partners, we identified the CD9 tetraspanin and further establish its requirement for destabilization of focal adhesions, control of Rac subcellular localization and growth arrest induced by 21 integrin. Altogether, our data establish that 21 integrin controls endothelial cell commitment towards quiescence by triggering a CD9-dependent dominant signaling.

Laminin-Binding Integrins Induce Dll4 Expression and Notch Signaling in Endothelial Cells

“…We either overexpressed or knocked down Dll4 and assessed proliferation ability of EC plated on either Fn, which binds ␣5 integrin, or Lm ( Figure 3A and 3B). As previously reported, 23,24 EC proliferated on Fn but remained quiescent on Lm ( Figure 3C and 3D). Interestingly, mimicking the effect of Lm, Dll4 overexpression induced arrest of proliferation in cells plated on Fn ( Figure 3C).…”

“…36 This conforms to a role of laminin in the maintenance of a quiescent vasculature. We previously involved ␣2␤1 integrin in EC growth arrest imposed by Lm in culture, 23 and this study suggests a contribution of Lm through ␣2␤1 and ␣6␤1 integrin signaling to control vascular branching. Interestingly, integrin ␣2-deficient and ␣6-deficient mice display enhanced adult angiogenesis.…”

“…18 -21 Integrin ␣2␤1 serves as an Lm receptor in EC and signals for cell proliferation arrest. 23 We investigated whether Dll4 plays a role downstream of ␣2 integrin to control EC proliferation. We either overexpressed or knocked down Dll4 and assessed proliferation ability of EC plated on either Fn, which binds ␣5 integrin, or Lm ( Figure 3A and 3B).…”

“…23 To identify the integrins involved in Lm-induced Dll4 expression, each ␣ subunit was selectively knocked-down. Because ␣2 is critical for Lm adhesion, ␣2 knocked-down cells were plated on a mixed matrix (FnϩLm), which allows cell adhesion and Dll4 expression ( Figure 1B).…”

Fibronectin Interaction and Enhancement of Growth Factors: Importance for Wound Healing

“…For example, under the same GF conditions, cell binding to FN through a5b1 actives Rac and cell-cycle progression, whereas a2b1-mediated adhesion to laminin results in growth arrest. 65,66 ECM stiffness by generating increased focal adhesion complexes and cytoskeletal organization can also condition cells to generate different responses. 67 For example, ECM of differing stiffness differentially regulate stem cell differentiation.…”