Membrane Lipid Composition Plays a Central Role in the Maintenance of Epithelial Cell Adhesion to the Extracellular Matrix

Abstract

Focal contacts (FC) are membrane-associated multi-protein complexes that mediate cell-extracellular matrix (ECM) adhesion. FC complexes are inserted in detergent-resistant membrane microdomains enriched in phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2); however, the influence of membrane lipid composition in the preservation of FC structures has not been extensively addressed. In the present work, we studied the contribution of membrane lipids to the preservation of renal epithelial cell adhesion structures. We biochemically characterized the lipid composition of membrane-containing FC complexes. By using cholesterol and PtdIns(4,5)P2)affecting agents, we demonstrated that such agents did not affect any particular type of lipid but induced the formation of new FC-containing domains of completely different lipid composition. By using both biochemical approaches and fluorescence microscopy we demonstrated that phospholipid composition plays an essential role in the in vivo maintenance of FC structures involved in cell-ECM adhesion.

Is DRM lipid composition relevant in cell-extracellular matrix adhesion structures?

“…By using a two-step centrifugation procedure and changing sucrose concentration, Triton X-100 resistant membrane microdomains from the microsomal fraction of primary cultured collecting duct cells were isolated, where FA complexes are located. 17 In such DRM, it has been found that vinculin and talin are bound to PI(4,5)P 2 and that both proteins interact, as assessed by immunoprecipitation analysis. The presence of vinculin bound to PI(4,5)P 2 , together with talinvinculin association in DRM, constitutes the biochemical expression of the existence of FA complexes in DRM isolated from rat renal papillae.…”

“…The presence of vinculin bound to PI(4,5)P 2 , together with talinvinculin association in DRM, constitutes the biochemical expression of the existence of FA complexes in DRM isolated from rat renal papillae. 17 Once established that FA complexes were located in DRM, the DRM lipid composition was characterized in comparison with the Triton X-100 soluble fractions. 17 Cholesterol concentration was ten times higher in DRM than in the Triton X-100 soluble fraction.…”

“…17 Once established that FA complexes were located in DRM, the DRM lipid composition was characterized in comparison with the Triton X-100 soluble fractions. 17 Cholesterol concentration was ten times higher in DRM than in the Triton X-100 soluble fraction. As regards the phospholipid profile, DRM showed a 70% increase in sphingomyelin, accompanied by a 30% increase in phosphatidylethanolamine and a 40% decrease in phosphatidylserine, as well as no differences in phosphatidylcholine and phosphatidylinositol concentrations.…”

“…18 It has been proposed that the lipid composition of such DRM corresponds to the physiological environment where FAs are inserted. 17 Previous in vitro studies have demonstrated that the insertion of either vinculin or talin into the lipid bilayer depends on the bilayer phospholipid composition. 19 In order to study the influence of membrane lipid composition on FA preservation in vivo, membrane-affecting agents, such as methyl-β-cyclodextrin (CDex), neomycin and LiCl were used.…”

“…14 It has been observed that apart from its well known action as a PI(4,5)P 2 sequestering-agent, neomycin simultaneously evokes a dramatic decrease in the DRM cholesterol content. 17 Cholesterol is an important determinant of membrane fluidity because it restricts the random movement of the polar heads of the fatty acyl chain, but separates and disperses their tails, causing the inner regions of the bilayer to become slightly more fluid. DRM are rich in cholesterol and sphingolipids.…”