Mechanism of ubiquitous expression of mouse uncoupling protein 2 mRNA: control by cis-acting DNA element in 5′-flanking region

Uncoupling protein (UCP) 2 is a member of the uncoupling-protein family, and it appears to function as an uncoupler of oxidative phosphorylation. To identify cis-acting regulatory elements controlling this gene's expression, we cloned an approx. 6.2-kb region upstream from the translation-initiation site of the mouse UCP2 gene and analysed its transcription activity using chimaeric mouse UCP2 promoter-placental-alkaline-phosphatase (PLAP) reporter-gene constructs. Sequence analysis showed that the 5'-flanking region of the mouse UCP2 gene was not similar to those of mouse UCP1 or UCP3. For the mouse UCP2, the region near the transcription-initiation site lacked the typical TATA box, but was GC-rich, resulting in presence of several potential specificity protein 1 (Sp-1), activator protein (AP)-1 and AP-2 binding sites. The putative regulatory motifs for muscle-regulatory protein (MyoD), brown-fat regulatory element, CCAAT box, cAMP-response element and Y box were also found in the mouse UCP2 promoter region by computer-assisted analysis. From the results of Northern-blot analysis and transient expression assay, we found that the mouse UCP2 gene responded to the cAMP-dependent protein kinase alpha-catalytic subunit signal activation at the transcription level. Additionally, deletion analysis of the UCP2 promoter-PLAP constructs indicated that the minimal region exhibiting the promoter activity was located between nt -33 and +100, and that a strong enhancer was present within 601 bp of the 5'-promoter region. In particular, the region from nt -233 to -34 significantly induced PLAP activity in the cell lines derived from various tissues and in the primary culture cells of rat brown adipose tissue, suggesting that this region is most important for the ubiquitous expression of mouse UCP2 mRNA. Furthermore, it was shown that two silencer elements were involved in the mouse UCP2 gene; one was located between nt -2746 and -602, and the other was identified in intron 1. These regions deprived the enhancer of the ability to induce PLAP activity. This study shows a fundamental role for positive and negative cis-acting DNA elements in regulating the basal and cAMP-induced transcription activity of the mouse UCP2 gene.