PPAR-GAMMA INDUCES CELL-CYCLE WITHDRAWAL - INHIBITION OF E2F DP DNA-BINDING ACTIVITY VIA DOWN-REGULATION OF PP2A/

PPAR gamma is an adipose-selective nuclear hormone receptor that plays a key role in the control of adipocyte differentiation. Previous stud ies indicated that activation of ectopically expressed PPAR gamma indu ces differentiation when cells have ceased growth because of confluenc e. We show here that ligand activation of PPAR gamma is sufficient to induce growth arrest in fibroblasts and SV40 large T-antigen transform ed, adipogenic HIB1B cells. Cell cycle withdrawal is accompanied by a decrease in the DNA-binding and transcriptional activity of the E2F/DP complex, which is attributable to an increase in the phosphorylation of these proteins, especially DP-1. This effect is a consequence of de creased expression of the catalytic subunit of the serine-threonine ph osphatase PP2A. These data suggest an important role for PP2A in the c ontrol of E2F/DP activity and a new mode of cell cycle control in diff erentiation.