Regulation of lipoprotein lipase synthesis by recombinant tumor necrosis factor--the primary regulatory role of the hormone in 3T3-L1 adipocytes.

Tumor necrosis factor (TNF), a protein homologous to cachectin, has been implicated in mediating cachexia. This effect at least in part has been suggested to occur through the influence of the hormone on adipose tissue metabolism. Using fully differentiated 3T3-L1 adipocytes as a model system, we have been investigating the effects of recombinant TNF (rTNF) on key features of adipocyte metabolism. Exposure of fully differentiated 3T3-L1 adipocytes to recombinant tumor necrosis factor resulted in a dose and time-dependent suppression of the activity of lipoprotein lipase. The loss in activity results from an effect on the synthesis of the enzyme, as determined by a decreased incorporation of [35S]methionine into immunoprecipitable lipoprotein lipase. No effect of rTNF on the half-life of the enzyme was observed. General protein synthesis, as judged by [35S]methionine incorporation into acid-insoluble protein, was minimally affected by exposure of the cells to rTNF; this was further confirmed by sodium dodecyl sulfate-polyacrylamide gel analysis of total cellular protein. As opposed to our previously reported results with crude preparations of TNF, no effect on either the ability of the adipocytes to synthesize and store or mobilize triacylglycerol was observed. Our results are consistent with the hypothesis that other hormones present in crude preparations of TNF acting either alone or synergistically with TNF play a major role in the further metabolic derangements associated with adipose tissue during cachexia.