Redistribution of cholesterol in oligodendrocyte membrane sheets after activation of distinct signal transduction pathways

cultured oligodendrocytes produce extensive membrane sheets that contain an internal lacy network of vein-like structures composed of microtubules, ac tin filaments, and 2'3'-cyclic nucleotide 3'-phosphohydrolase (CNPase), The se cytoplasmic vein-like structures surround domains of myelin basic protei n (MBP). Using the antibiotic filipin, that binds to cholesterol, the relat ionship between plasma membrane cholesterol and cytoskeleton in membrane sh eets was examined. Our results show that cholesterol was relatively uniform ly distributed within the plasma membranes of prefixed control oligodendroc yte membrane sheets. When live cultures were extracted with Triton X-100, h owever, a subpopulation of cholesterol molecules remained colocalized with cytoskeleton in the membrane sheets. Activation of two well-characterized s ignaling pathways that differentially affect microtubule and actin filament stability in membrane sheets resulted in an apparent massive lateral movem ent of cholesterol molecules away from membrane regions overlying internal MBP domains to membrane tracts directly overlying cytoplasmic cytoskeletal veins. Depolymerization of microtubules by colchicine resulted in redistrib ution of cholesterol directly over actin filaments, whereas depolymerizatio n of actin filaments by cytochalasin B resulted in redistribution of choles terol directly over CNPase/microtubular veins. These data suggest that chol esterol forms an association with cytoskeletal components or proteins assoc iated with cytoskeleton, These data also suggest that cholesterol, via inte ractions with cytoskeleton, plays a role in signaling pathways in oligodend rocyte membrane sheets. (C) 2000 Wiley-Liss, Inc,