Transcriptional activation of the human ucp1 gene in a rodent cell line. Synergism of retinoids, isoproterenol, and thiazolidinedione is mediated by a multipartite response element

Uncoupling protein 1 (UCP1) is uniquely expressed in brown adipocytes and generates heat production by uncoupling respiration from ATP synthesis. The activatory effects of norepinephrine and retinoic acid (RA) on rodent ucp1 gene transcription have been well characterized. These effects are mediated by a 211-base pair (bp) enhancer which is also sufficient to restrict expression to brown adipose tissue. The molecular mechanisms controlling the transcription of the human ucp1 gene are unknown. In order to study the transcriptional regulation of the human gene, we set up chloramphenicol acetyltransferase constructs containing the entire or deleted 5' regions upstream of the transcriptional start site of the gene. These constructs were transiently transfected in a mouse cell line. A 350-bp hormone response region showing a significant homology with the rat ucp1 enhancer and located between the BclI polymorphic site and an AatII site (bp -3820/-3470) was detected. This region was sufficient to mediate the stimulation by RA and by combined treatments (RA + isoproterenol (ISO), RA + thiazolidinedione (TZD), or RA + ISO + TZD). The highest stimulation, a 26-fold increase in basal activity, was obtained by RA + ISO + TZD treatment. In contrast to the rodent gene, under our conditions, the effect of ISO and/or TZD is dependent on RA stimulation. Analysis of 105 bp inside the 350-bp element by site-directed mutagenesis and gel retardation experiments demonstrated that a multipartite response element mediates the drug stimulation. This region binds RARs and RXRs nuclear factors, CREB/ATF factors, and also PPARgamma despite the absence of a consensus peroxisome-proliferator response element. The activation of the human ucp1 gene transcription by certain hormones or drugs, and the identification of the cis-elements involved, will help to identify new compounds activating fat oxidation and energy expenditure in humans.