TISSUE-SPECIFIC AND BETA-ADRENERGIC REGULATION OF THE MITOCHONDRIAL UNCOUPLING PROTEIN GENE - CONTROL BY CIS-ACTING ELEMENTS IN THE 5'-FLANKING REGION

Uncoupling protein (UCP) gene expression is tightly restricted to ther mogenic brown adipocytes and is rapidly activated by norepinephrine re leased after cold exposure. To identify cis-acting regulatory elements controlling this gene, a region encompassing 4.5 kilobases of DNA ups tream of the transcription start site was analyzed using hybrid UCP-ch loramphenicol acetyltransferase reporter gene constructs. Evidence for the presence of both tissue-specific and beta-adrenergic response ele ments in this 4.5-kilobase region was obtained by comparing the expres sion of these reporter genes in transfected brown adipocytes (in vitro differentiated), brown preadipocytes, white adipocytes, and Chinese h amster ovary (CHO) cells and from experiments in transgenic animals. D eletion analyses in transfected cells indicated that the minimal regio n exhibiting promoter activity and tissue specificity is located betwe en -157 and -57 base pairs (bp). A 211-bp activator element located be tween -2494 and -2283 bp was necessary for full expression in brown ad ipocytes. This element also activated expression of the homologous -15 7-bp promoter and expression of a heterologous promoter in both brown adipocytes and CHO cells. A second region, downstream of the activator and possibly located between positions -400 and -157 bp, inhibited th e UCP promoter in CHO cells. In mice transgenic for a chloramphenicol acetyltransferase reporter gene containing these elements, expression was both tissue specific and regulatable by environmental temperature changes. These results indicate that both positive and negative cis-ac ting elements participate in the regulation of UCP gene expression.