Role of activator protein-1 in the down-regulation of the human CYP2J2 gene in hypoxia

Abstract

The cytochrome P450 (CYP) 2J2 arachidonic acid epoxygenase gene was down-regulated at a pre-translational level in human hepatoma-derived HepG2 cells incubated in a hypoxic environment; under these conditions, the expression of c-Jun and c-Fos mRNA and protein was increased. The 5'-upstream region of the CYP2J2 gene was isolated by amplification of a 2341 bp fragment and putative regulatory elements that resembled activator protein-1 (AP-1)-like sequences were identified. From transient transfection analysis, c-Jun was found to strongly activate a CYP2J2 -luciferase reporter construct, but co-transfection with plasmids encoding c-Fos or c-Fos-related antigens, Fra-1 and -2, abrogated reporter activity. Using a series of deletion-reporter constructs, a c-Jun-responsive module was identified between bp -152 and -50 in CYP2J2 : this region contained an AP-1-like element between bp -56 and -63. The capacity of this element to interact directly with c-Jun, but not c-Fos, was confirmed by electromobility-shift assay analysis. Mutagenesis of the -56/-63 element abolished most, but not all, of the activation of CYP2J2 by c-Jun, thus implicating an additional site within the c-Jun-responsive region. The present results establish an important role for c-Jun in the control of CYP2J2 expression in liver cells. Activation of c-Fos expression by hypoxia promotes the formation of c-Jun/c-Fos heterodimers, which decrease the binding of c-Jun to the CYP2J2 upstream region, leading to gene down-regulation.

Up-Regulation of Human CYP2J2 in HepG2 Cells by Butylated Hydroxyanisole Is Mediated by c-Jun and Nrf2

“…Thus, c-Jun homodimers supported CYP2J2 expression in HepG2 cells cultured in a normoxic environment and activated CYP2J2-luciferase reporter constructs via AP-1-like gene elements in the CYP2J2 upstream region. Under hypoxic conditions (ϳ1% O 2 ), another bZIP factor, c-Fos, was activated, resulting in impaired regulation of CYP2J2; in accord with this finding, c-Jun/c-Fos heterodimers abrogated the activity of CYP2J2-driven luciferase reporters (Marden et al, 2003). Thus, the intracellular composition of bZIP transcription factors has emerged as an important determinant of constitutive CYP2J2 expression in cells.…”

“…The interplay between members of the activator protein-1 (AP-1) complex of leucine zipper (bZIP) transcription factors has been found to regulate basal CYP2J2 expression in human liverderived cells (Marden et al, 2003;Marden and Murray, 2005). Thus, c-Jun homodimers supported CYP2J2 expression in HepG2 cells cultured in a normoxic environment and activated CYP2J2-luciferase reporter constructs via AP-1-like gene elements in the CYP2J2 upstream region.…”

Cytochrome P450 epoxygenases 2C8 and 2C9 are implicated in hypoxia-induced endothelial cell migration and angiogenesis

“…Although the expression of CYP 2C8/9 in cultured cells can be restored by different stimuli, the mechanisms involved in its regulation are not well understood (for a review, see Fleming, 2004). The expression of several CYP enzymes is modulated by changes in oxygen tension, for example, hypoxia downregulates CYP 2J2 (Marden et al, 2003) whereas transient cerebral ischemia elicits the upregulation of CYP 2C11 in rats (Alkayed et al, 2002). Furthermore, the exposure of rats to hypoxia for 48 hours induces the expression of a sulfaphenazole-sensitive CYP epoxygenase, most probably CYP 2C11 (Earley et al, 2003).…”

The Pharmacology of the Cytochrome P450 Epoxygenase/Soluble Epoxide Hydrolase Axis in the Vasculature and Cardiovascular Disease

“…In addition, the hypoxiainduced decrease in the myogenic response was normalized by the CYP2C inhibitor sulfaphenazole (Earley et al, 2003). Clearly not all P450 enzymes are induced by hypoxia because the expression of CYP2J2 decreases at lower O 2 tensions (Marden et al, 2003) Given the size of the P450 family of proteins, it is not surprising that there is considerable interisoform variation in the regulation of gene expression and mRNA stability as well as post-translational modification of the P450 protein. Regulation of the CYP2 family involves nuclear receptors related to the steroid hormone receptor superfamily, such as the constitutive androstane receptor and the retinoic acid receptor.…”