Modulation of α5β1 integrin functions by the phospholipid and cholesterol contents of cell membranes

Abstract

Several modifications of the alpha5beta1 integrin, which alter its intracellular and extracellular interaction with fibronectin and other proteins, have been reported. However, the significance of the lateral mobility of integrin molecules in the plasma membrane, as a regulator of their distribution and function, is poorly understood. We examined this problem by increasing the cholesterol content of plasma membranes, and consequently modifying the fluidity of membrane phospholipids, in rat fibroblasts. Under these conditions, the clustering of alpha5beta1 integrin molecules in focal adhesions, their adhesion to the cell-binding domain of fibronectin, and their association with the cytoskeletal protein talin were significantly enhanced as compared to control cells. However, the activation of MAP-kinase pathways by the association of fibronectin with alpha5beta1 integrin, and its association with integrin-linked kinase (ilk), were suppressed. The treated cells also showed distinct changes in shape, and their actin stress fiber network was more dense and thick as compared to control cells. The changes in fluidity of phospholipids occurred differentially and fluidity of phosphatidyl-ethanolamine increased, while that of phosphatidyl-choline was reduced. Our results suggest that proteins in focal adhesions could be partitioned in specific lipid domains, which regulate specific aspects of alpha5beta1 integrin functions.

Cholesterol-independent Interactions with CD47 Enhance αvβ3 Avidity

“…Thus, IgV-GPI appeared to be superior to wild-type CD47 in its ability to confer protection against cyclodextrin-induced disruption of cell adhesion as a result of its increased enrichment in cyclodextrin-resistant membrane domains. A correlation between raft localization and integrin clustering has been previously reported in fibroblasts, where membrane cholesterol levels affected the clustering of ␣ 5 ␤ 1 (23), and in T-cells, where LFA-1-mediated cell binding was shown to be enhanced by clustering of membrane rafts via the GPI-anchored protein CD24 (24). In raft membranes, integrin-integrin contacts may be promoted by a more extreme hydrophobic environment, or by other physical properties such as membrane thickness (37).…”

“…Membrane cholesterol levels have been reported to affect the clustering of ␣ 5 ␤ 1 in rat fibroblasts (23), and in T-cells, via the GPI-anchored protein CD24 (24). Because we have shown that anti-LIBS binding is not significantly affected by cyclodextrin treatment (Fig.…”

“…2A). While it is not known precisely how cholesterol depletion disrupted cell adhesion, alteration of the membrane environment could in theory influence either the ligand binding conformation of both ␣ v ␤ 3 and ␣ v ␤ 5 , or the clustering of integrin molecules, as has been reported for ␣ 5 ␤ 1 and LFA-1 (23). However, expression of either CD47 or IgV-GPI partially protected against this effect ( Fig.…”

Adipocyte functions are modulated by cell size change: potential involvement of an integrin/ERK signalling pathway

“…b 1 -Integrin subunit is indeed expressed in many cell types including fibroblasts, the precursors of adipocytes. 30 We first looked for the presence of b 1 -integrin in isolated large and small adipocytes. Western blot analysis clearly shows that b 1 -integrin is detected in adipocytes; furthermore, there was a 60% increase in the concentration of b 1 -integrin in large compared to small cells (1.670.07, n ¼ 6 and 1.070.06, n ¼ 6, arbitrary units per cell, respectively, Po0.01).…”

“…This pathway is also regulated by the lipid composition of plasma membrane, and Gopalakrishna et al 30 have demonstrated in rat fibroblasts that an increase in membrane cholesterol diminishes ERKs activation through regulation of b 1 -integrin function. If such a mechanism exists in adipose cell, the decrease in membrane cholesterol content that we observed in large adipocytes 20 could be a signal for the modulation of b 1 -integrin activity and the subsequent activation of ERKs pathway.…”