ADIPOCYTE-SPECIFIC TRANSCRIPTION FACTOR-ARF6 IS A HETERODIMERIC COMPLEX OF 2 NUCLEAR HORMONE RECEPTORS, PPAR-GAMMA AND RXR-ALPHA

Previously, we identified a novel transcription factor, ARF6, as a key regulator of the tissue-specific adipocyte P2 (aP2) enhancer, In orde r to identify the proteins which comprise the adipocyte ARF6 complex, we have purified this DNA binding activity from a cultured adipocyte c ell line. We have developed a system for growth and differentiation of HIB-1B brown adipocytes in suspension culture that facilitates the pr oduction of large quantities of adipocyte nuclear extract, ARF6 was pu rified from HIB-1B nuclear extract by a combination of conventional an d sequence-specific DNA affinity chromotography. Chemical sequencing a nd mass spectral analysis of tryptic peptides derived from the purifie d polypeptides identifies the ARF6 complex as a heterodimer of the ret inoid X receptor alpha (RXR alpha) and the murine peroxisome prolifera tor activated receptor gamma (PPAR gamma). Of the known PPAR gamma iso forms, PPAR gamma is the predominant form expressed in adipose tissue, These results suggest that PPAR gamma 2 serves a unique function amon g PPAR family members as an important regulator of adipocyte-specific gene expression.