Abstract
OBJECTIVE: Expression of zinc finger protein 423 (ZFP423), a key proadipogenic transcription factor in adipocyte precursor cells, is regulated by interaction of the proadipogenic early B-cell factor 1 (EBF1) and antiadipogenic ZFP521. The ubiquitin ligase seven-in-absentia homolog 2 (SIAH2) targets ZFP521 for degradation. This study asked whether SIAH2 is expressed in adipocyte precursor cells and whether SIAH2 interacts with ZFP521 and EBF1 to regulate ZFP521 protein levels during adipogenesis. METHODS: SIAH2 expression in precursor cells was assessed in primary cells and tissues from wild-type and SIAH2 null mice fed a control or high-fat diet. Primary cells, 3T3-L1 preadipocytes, and HEK293T cells were used to analyze Siah2, Ebf1, and Zfp521 expression and SIAH2-mediated changes in ZFP521 and EBF1 protein levels. RESULTS: Siah2 is expressed in platelet-derived growth factor receptor α (PDGFRα)(+) and stem cell antigen-1 (SCA1)(+) adipocyte precursor cells. SIAH2 depletion reduces Ebf1 gene expression and increases EBF1 protein levels in early but not late adipogenesis. In early adipogenesis, SIAH2 forms a protein complex with EBF1 and ZFP521 to enhance SIAH2-mediated ubiquitylation and degradation of ZFP521 while increasing EBF1 protein levels. CONCLUSIONS: Siah2 is expressed in PDGFRα+ adipocyte precursor cells and is linked to precursor cell commitment to adipogenesis by interacting with EBF1 and ZFP521 proteins to target the antiadipogenic ZFP521 for degradation.