During the differentiation of 3T3-L1 pre-adipocytes, vimentin intermediate filaments are reorganized to form cage-like structures around the nascent lipid droplets. Initial studies with 3T3-L1 cells indicated that aggregation of vimentin filaments by nocodazole treatment during or shortly after induction of adipose conversion dramatically reduced the lipid droplet content of 3T3-L1 cells 96–120 hours after induction. Specific but transient disruption of vimentin following anti-IFA antibody injection also resulted in a decrease in lipid droplet formation in differentiating cells. To specifically and stably affect filament organization, 3T3-L1 cells lines were established by transfection with a glucocorticoid-regulatable, dominant negative mutant vimentin cDNA expression plasmid. Treatment of these cells (83 delta C) with dexamethasone resulted in expression of vimentin with a carboxyl-terminal deletion, which led to the disruption of the endogenous filament network. Induction of adipose conversion in 83 delta C cells lead to the formation of lipid droplets comparable to those seen in untransfected 3T3-L1 cells. Addition of dexamethasone during the adipose conversion of 83 delta C cells did not affect the induction of the marker enzyme glycerol-3-phosphate dehydrogenase or the incorporation of [14C]palmitate into triglycerides during a 10 minute pulse label. There was, however, a failure to form prominent lipid droplets and to accumulate [14C]palmitate-labeled triglycerides. Pulse-chase experiments indicated that the failure of these cells to accumulate triglyceride was associated with an increased rate of turnover. These studies indicate that vimentin filaments provide a function that influences lipid stability during adipose conversion of 3T3-L1 cells.

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