Increasing attention has been paid recently to the desmoplastic/stromal reaction in pancreatic cancer and its putative role in cancer progression. Studies in vitro and in vivo have provided strong evidence of the existence of an interaction between pancreatic stellate cells (PSCs, the cells known to produce the stromal reaction in pancreatic cancer) and tumor cells.
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.
1 The alkylamine drug orphenadrine (ORPH) is an inducer and inhibitor of the microsomal cytochrome P450 (CYP) system in mammals. This study evaluated the selectivity of CYP induction by ORPH in rat liver. 2 Immunoblot analysis indicated that ORPH was a selective inducer of the phenobarbitone (PB)-inducible CYP2B in rat liver. CYP2B protein was increased to B14-fold of levels in untreated rat liver. By comparison PB increased CYP2B expression 40-fold. Corresponding increases in the activity of CYP2B-dependent androstenedione 16b-hydroxylation were measured in microsomes from ORPH and PB-induced rats. 3 Northern analysis indicated that CYP2B1/2 mRNA was increased in ORPH-induced rat liver. Consistent with this finding, ORPH was found to activate a PB-responsive enhancer module in constitutive androstane receptor (CAR)-transfected Hep G2 cells. 4 Other alkylamines like troleandomycin impair CYP turnover. We tested whether ORPH induction of CYP2B may include a post-translational component. In PB-pretreated animals ORPH administration delayed the loss of CYP2B after PB withdrawal, but no evidence for altered turnover was found. 5 These studies establish ORPH as a selective inducer of CYP2B in rat liver. Induction appears to be mediated pretranslationally by CAR activation of CYP2B gene transcription. Post-translational stabilisation by an ORPH metabolite does not elicit induction. Induction of CYP2B may influence pharmacokinetic interactions involving ORPH.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.