Role of suppressor of cytokine signaling 3 in lipid metabolism: analysis based on a phage-display human liver cDNA library.

Suppressor of cytokine signaling 3 (SOCS3) is a likely mediator of feedback inhibition on the leptin receptor and may cause physiological leptin-resistance, leading to the development of obesity. The aim of this study was to identify potential peptides interacting with purified SOCS3 by using a phage-display human liver cDNA library. We developed a T7 select phage-display system with purified SOCS3 as bait to screen a human liver cDNA library. After 4 rounds of screening and sequencing analysis, we found that phage-presenting peptide RGGVVTSNPLGF show significant binding to SOCS3. The peptide sequence was similar to the sequence of amino acids 644-655 of C-terminal extra-polypeptide of very-long-chain acyl-CoA dehydrogenase (VLCAD), which is 1 of 4 flavoproteins that catalyzing the initial step of the mitochondrial fatty acid β-oxidation, implying a close relationship between SOCS3 and VLCAD. We identified VLCAD as a novel SOCS3 interacting protein both in vitro and vivo, and found that SOCS3 mediates the ubiquitination pathway for proteasomal degradation of VLCAD C-terminal extra-polypeptide via its SOCS-box. Animal experimentation demonstrated that VLCAD is functionally involved in SOCS3 binding and thus, SOCS3 play an important role in the regulation of fatty acid β-oxidation. In conclusion, SOCS3 is an important factor for lipid metabolism and a potential drug-target for treatment of widespread obesity.