DIFFERENTIATION-DEPENDENT EXPRESSION OF THE BROWN ADIPOCYTE UNCOUPLING PROTEIN GENE - REGULATION BY PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR-GAMMA

Uncoupling protein (UCP) is expressed only in brown adipocytes and is responsible for the unique thermogenic properties of this cell type. T he novel brown preadipocyte cell line, HIB-1B, expresses UCP in a stri ctly differentiation-dependent manner. Transgenic mice studies have sh own that a region from kb -2.8 to -1.0 of the murine UCP gene is requi red for brown adipocyte-specific expression, Subsequent analysis ident ified a potent 220-bp enhancer from kb -2.5 to -2.3. We show that this enhancer is active only in differentiated HIB-1B adipocytes, and we i dentify a peroxisome proliferator-activated receptor gamma (PPAR gamma ) response element, referred to as UCP regulatory element 1 (URE1), wi thin the enhancer. URE1 has differentiation-dependent enhancing activi ty in HIB-1B cells and is required for enhancer action, since mutation s of URE1 that block protein binding abolish enhancer activity. We als o show that PPAR gamma antibodies block binding to URE1 of nuclear ext racts from cultured brown adipocytes and from the brown adipose tissue of cold-exposed mice. Protein binding to URE1 increases substantially during differentiation of HIB-1B preadipocytes, and PPAR gamma mRNA l evels increase correspondingly. Although forced expression of PPAR gam ma and retinoid X receptor alpha activates the enhancer in HIB-1B prea dipocytes, these receptors are not capable of activating the enhancer in NIH 3T3 fibroblasts. Our results show that PPAR gamma is a regulato r of the differentiation-dependent expression of UCP and suggest that there are additional factors in HIB-1B cells required for brown adipoc yte-specific UCP expression.