Reconstitution of insulin-sensitive glucose transport in fibroblasts requires expression of both PPAR gamma and C/EBP alpha

Adipocyte differentiation is regulated by at least two major transcription factors, CCAAT/enhancer-binding protein alpha (C/EBP alpha) and peroxisome proliferator-activated receptor gamma (PPAR gamma), Expression of PPAR gamm a in fibroblasts converts them to fat-laden cells with an adipocyte-like mo rphology. Here, we investigate the ability of PPAR gamma to confer insulin- sensitive glucose transport to a variety of murine fibroblast cell lines. W hen cultured in the presence of a PPAR gamma ligand, Swiss-3T3 and BALB/c-3 T3 cells ectopically expressing PPAR gamma accumulate lipid droplets, expre ss C/EBP alpha, aP2, insulin-responsive aminopeptidase, and glucose transpo rter isoform 4 (GLUT4), and exhibit highly insulin-responsive 2-deoxyglucos e uptake. In contrast, PPAR gamma-expressing NIH-3T3 cells, despite similar lipid accumulation, adipocyte morphology, and aP2 expression, do not expre ss C/EBP alpha or GLUT4 and fail to acquire insulin sensitivity. In cells e ctopically expressing PPAR gamma, the development of insulin-responsive glu cose uptake correlates with C/EBP alpha expression. Furthermore, ectopic ex pression of C/EBP alpha in NIH-3T3 cells converts them to the adipocyte phe notype and restores insulin-sensitive glucose uptake. We propose that the p athway(s) leading to fat accumulation and morphological changes are distinc t from that leading to insulin-dependent glucose transport. Our results sug gest that although PPAR gamma is sufficient to trigger the adipogenic progr am, C/EBP alpha is required for establishment of insulin-sensitive glucose transport.