Raft-phosphatidylinositol-4,5-bisphosphate (PI- 4,5-P2) is essential for the maintenance of mature focal adhesion (FA) plaques

MARQUEZ MG; LEOCATA NIETO F; GAGLIANO ML; FERNADEZ-TOME MC; FAVALE N; STERIN-SPEZIALE N

Corsica, France.

Congreso; 46th International Conference on the Bioscience of Lipids; 2005

International Conference on the Bioscience of Lipids

Renal papilla is a highly organized tissue whose functionality depends on tubular organization by cell attachment to the extracellular matrix. Mature focal adhesión plaques (FA) are the most stable cell-matrix points of adhesion which involves the FA-protein vinculin (V). PI-4,5-P2, a minor membrane phospholipid usually implicated in cell signaling, is now recognized to be a principal molecule in tissue organization since is required for activation of vinculin. Since, it has been found that raft-microdomains are enriched in PI-4,5-P2 it has been recently suggested that FA have a lipidraft- like composition, however, no direct evidence is available respect to FA localization in specific raft microdomains in any cellular type. In the present work we describe, in rat renal papilla, a specific FA-raft microdomain enriched in the typical raft lipids: sphingomyelin and cholesterol. Such microdomains are also largely enriched in PI-4P and PI-4,5-P2 (32- and 5-fold increase) and in unsaturated phosphatidylethanolamine. Immunofluorescence analysis of cultured collecting duct cells treated with cyclodextrine evoked disappearance of FA but V and PI-4,5-P2 still remained in the plasma membrana denoting that FA assembly needs raft integrity. LiCl or neomycin treatment decreased the amount of raft associated-V and induced FA dissipation, reflecting that such proteins have to be bound to PI-4,5-P2 to be assembled in a FA structure. These results demonstrate that the existence of PI-4,5- P2 enriched-raft is a requirement for the maintenance of mature FAplaques that ensures the tubular organization of adult renal tissue.