Adipocyte-specific transcription factor ARF6 is a heterodimeric complex of two nuclear hormone receptors, PPAR7 and RXRa

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Abstract
Previously, we Identified a novel transcription factor, ARF6, as a key regulator of the tissue-specific adipocyte P2 (aP2) enhancer. In order to identify the proteins which comprise the adipocyte ARF6 complex, we have purified this DNA binding activity from a cultured adipocyte cell line. We have developed a system for growth and differentiation of HIB-1B brown adlpocytes in suspension culture that facilitates the production of large quantities of adipocyte nuclear extract. ARF6 was purified from HIB-1B nuclear extract by a combination of conventional and sequence-specific DNA affinity chromotography. Chemical sequencing and mass spectral analysis of tryptlc peptldes derived from the purified polypeptides Identifies the ARF6 complex as a heterodlmer of the retlnold X receptor α (RXRα) and the murine peroxisome proliferator activated receptor γ (PPARγ). Of the known PPARγ isoforms, PPARγ Is the predominant form expressed In adipose tissue. These results suggest that PPARγ serves a unique function among PPAγ family members as an important regulator of adipocyte-specific gene expression.