Characterization of a c-Jun-responsive module in the 5'-flank of the human CYP2J2 gene that regulates transactivation.

The human cytochrome P450 2J2 (CYP2J2) generates cytoprotective epoxyeicosatrienoic acids from arachidonic acid. Expression of CYP2J2 is decreased in hypoxia, and the resultant decrease in CYP2J2-derived epoxyeicosanoids may contribute to the pathogenesis of cardiac ischaemia. Recent studies have indicated that AP-1 (activator protein-1) regulates CYP2J2 expression in normoxia and hypoxia. Down-regulation of CYP2J2 in hypoxic HepG2 cells was closely associated with the up-regulation of c-fos and transient transfection analysis demonstrated that c-Fos abolishes the activation of CYP2J2 by the AP-1 protein c-Jun. Deletion of the region between nt -122 and -50 upstream of the start codon in CYP2J2 prevented c-Jun transactivation. In this study we demonstrate that the sequence at -105/-95 is a major regulatory element that binds c-Jun and has a prominent role in CYP2J2 gene transactivation. Mutagenesis of both the -105/-95 region and the previously identified element at -56/-63 was required for complete loss of transactivation by c-Jun; separate mutagenesis of the -105/-95 element or, to a lesser extent, the -56/-63 element resulted in a partial loss of gene activation. In contrast to the behaviour of the -56/-63 element, c-Jun homodimers and c-Fos/c-Jun heterodimers bound to the -105/-95 element. These findings demonstrate that the c-Jun-responsive module between -122 and -50 in the CYP2J2 proximal promoter contains an atypical AP-1 element at -105/-95 that has a major role in c-Jun transactivation and acts in conjunction with the -56/-63 element to regulate expression.