Proteomic analysis of adipocyte differentiation: Evidence that α2 macroglobulin is involved in the adipose conversion of 3T3 L1 preadipocytes

Adipogenesis is an important aspect of energy homeostasis. Here we have used a differential proteome mapping strategy to identify intracellular proteins that are differentially expressed during adipose conversion of 3T3 L1 preadipocytes. Two-dimensional gel electrophoresis analysis identified 8 proteins that are induced following hormone-evoked differentiation. In addition, we found that a α2 macroglobulin fragment was abundantly present in 3T3 L1 preadipocytes, but was virtually undetectable in fully differentiated adipocytes. Metabolic radio-labeling with (35S)methionine and Northern blot analysis indicated that the intracellular α2 macroglobulin fragment in preadipocytes was derived from the extracellular culture medium, not de novo synthesis. Incubation of preadipocytes with an antiα2 macroglobulin polyclonal antibody caused depletion of the intracellular α2 macroglobulin fragments, and also enhanced spontaneous adipose conversion. These results suggest that intracellular α2 macroglobulin fragment inhibits adipocyte differentiation, and that hormone treatment induces differentiation at least in part by suppression of intracellular α2 macroglobulin activity in 3T3 L1 preadipocytes.