Cloning and characterization of a functional peroxisome proliferator activator receptor-gamma-responsive element in the promoter of the CAP gene

c-Cbl-associating protein (CAP) is a multifunctional signaling protein that interacts with c-Cbl, facilitating the tyrosine phosphorylation of c-Cbl i n response to insulin, In 3T3-L1 adipocytes and diabetic rodents, CAP gene expression is stimulated by activators of peroxisome proliferator activator receptor gamma (PPAR gamma), such as thiazolidinediones (TZDs), resulting in increased insulin-stimulated c-Cbl phosphorylation, Sequence analysis of 2.5 kilobases of the 5'-flanking region of the CAP gene reveals a predicte d peroxisome proliferator response element (PPRE) from -1085 to -1097, The isolated promoter was functional in 3T3 fibroblasts and adipocytes. Co-tran sfection of the CAP promoter with PPAR gamma and retinoic acid X receptor a lpha caused fold stimulation of promoter activity. The TZD rosiglitazone pr oduced an additional 2-3-fold stimulation of the promoter. Deletion of the predicted PPRE from the CAP promoter abolished its ability to respond to ro siglitazone. Gel shift analysis of the putative PPAR gamma site demonstrate s direct binding of PPAR/retinoid X receptor heterodimers to the PPRE in th e CAP gene. These data demonstrate that TZDs directly stimulate transcripti on of the CAP gene through activation of PPAR gamma.