Adipocyte-type fatty acid-binding protein as inter-compartmental shuttle for peroxisome proliferator activated receptor γ agonists in cultured cell

We and others showed earlier that liver-type, epidermal-type and adipocyte-type (A-) fatty acid-binding proteins (FABPs) mediate peroxisome proliferator activated receptor (PPAR) dependent gene expression by channelling their ligand (fatty acid or drug) to the nuclear receptors via direct protein/protein interaction. To clarify mechanistic details of this signaling path, we address here A-FABP import into the nucleus and its interaction with PPARγ. Making use of COS cells transfected with wild-type or mutant A-FABPs, we exclude posttranslational modification of A-FABP as import signal and provide evidence for both, ligand-dependent and ligand-independent nuclear translocation. With the aid of in vitro pull down assay we demonstrate that specific interaction of A-FABP with PPARγ isoforms does not require ligand. Moreover, A-FABP binds not only to the ligand-binding domain including hinge domain (domains DEF), but also to the DNA-binding domain including AB domains (domains ABC) of PPARγ.