REORGANIZATION OF A NOVEL VIMENTIN-ASSOCIATED PROTEIN IN 3T3-L1 CELLSDURING ADIPOSE CONVERSION

We have found that the antibody A2, a marker for the capsule of steroi dogenic lipid droplets, reacts with an intermediate filament-associate d protein, P-200, in 3T3-L1 preadipocytes. Supporting evidence came fr om the colocalization pattern of P-200 with vimentin in double label e xperiments. The association of P-200 with vimentin was further confirm ed by its copurification with vimentin after high salt extraction and colocalization of these two proteins in high salt-extracted and vinbla stine-treated cells. In preadipocytes this protein was distributed an the vimentin filament network. At the early stage of adipose conversio n, this protein was found to encircle nascent lipid droplets ranging f rom 0.1 to 0.2 mu m, accompanied with a decreased distribution on the vimentin filament system. This infers a possible translocation of P-20 0 from the vimentin filaments to the droplet surface. Meanwhile, the v imentin filaments remained in a normal distribution in the cytoplasm a nd were apparently not associated with the nascent droplet. The associ ation of vimentin filaments to droplet surfaces became prominent in li pid droplets larger than 0.2 mu m, forming a typical vimentin cage. Im munogold staining also confirmed the translocation oi P-200 immunoreac tivity from the droplet surface to the vimentin cage. The relocation o f P-200 from the cytoplasmic vimentin filaments to the droplet surface prior to the formation of the vimentin cage, as well as the reorganiz ation of this protein in the vimentin cage, suggests a stabilizing rol e in the lipid droplet formation and an inducing function of this prot ein in the formation of the vimentin cage. (C) 1997 Wiley-Liss, Inc.