The Binding in Vitro of Modified LDL to the Intermediate Filament Protein Vimentin

Abstract

Membrane-associated proteins with specific binding properties to modified LDL were investigated in J774 macrophages and Mono Mac 6 sr cells. Ligand blotting of membrane proteins revealed a 54-kDa protein which bound oxidized and acetylated but not native LDL. The 54-kDa protein, isolated by 2D-PAGE, was identified as vimentin. 125I-AcLDL bound to purified vimentin and desmin in a saturable manner, with an approximate Kd of 1.7 × 10−7 M (89 μg/ml) and 8.0 × 10−8 M (41 μg/ml), respectively. Blots of vimentin mutant proteins with deletions in the positively charged N-terminal head domain showed that amino acids 26–39 are essential for the binding of AcLDL by vimentin. Taken together, our data indicate that vimentin binds modified LDL, but not native LDL, in a specific and saturable manner. Vimentin filaments extend throughout the cytoplasm as far as the inner surfaces of plasma and vesicular membranes. Vimentin may thus play a role in membrane-associated steps involved in the intracellular processing of oxidized LDL, contributing to its unregulated uptake and intracellular retention by cells of the atherogenic plaque.