Fatty Acid-binding Proteins Interact with Comparative Gene Identification-58 Linking Lipolysis with Lipid Ligand Shuttling*

Peter Hofer, Andras Boeszoermenyi, Doris Jaeger, Ursula Feiler, Haribabu Arthanari, Nicole Mayer, Fabian Zehender, Gerald Rechberger, Monika Oberer, Robert Zimmermann, Achim Lass, Guenter Haemmerle, Rolf Breinbauer, Rudolf Zechner, Karina Preiss-Landl

The coordinated breakdown of intracellular triglyceride (TG) stores requires the exquisitely regulated interaction of lipolytic enzymes with regulatory, accessory and scaffolding proteins. Together they form a dynamic multi-protein network designated as the "lipolysome". Adipose triglyceride lipase (ATGL) catalyzes the initiating step of TG hydrolysis and requires comparative gene identification-58 (CGI-58) as potent activator of enzyme activity. Here, we identify adipocyte-type fatty acid-binding protein (A-FABP) and other members of the fatty acid-binding protein (FABP) family as interaction partners of CGI-58. Co-immuno-precipitation, microscale thermophoresis, and solid phase assays proved direct protein-protein interaction between A-FABP and CGI-58. Using nuclear magnetic resonance titration experiments and site-directed mutagenesis, we located a potential contact region on A-FABP. In functional terms, A-FABP stimulates ATGL-catalyzed TG hydrolysis in a CGI-58-dependent manner. Additionally, transcriptional transactivation assays with a luciferase reporter system revealed that FABPs enhance the ability of ATGL/CGI-58-mediated lipolysis to induce the activity of peroxisome proliferator-activated receptors. Our studies identify FABPs as crucial structural and functional components of the lipolysome.