Regulation of the rat CYP4A2 gene promoter by c-Jun and octamer binding protein-1

AP-1 and SP1 trans-activate the expression of hepatic CYP1A1 and CYP2A6 in the bioactivation of AFB1 in chicken

Dietary exposure to aflatoxin B1 (AFB1) is harmful to the health and performance of domestic animals. The hepatic cytochrome P450s (CYPs), CYP1A1 and CYP2A6, are the primary enzymes responsible for the bioactivation of AFB1 to the highly toxic exo-AFB1-8,9-epoxide (AFBO) in chicks. However, the transcriptional regulation mechanism of these CYP genes in the liver of chicks in AFB1 metabolism remains unknown. Dual-luciferase reporter assay, bioinformatics and site-directed mutation results indicated that specificity protein 1 (SP1) and activator protein-1 (AP-1) motifs were located in the core region -1,063/-948, -606/-541 of the CYP1A1 promoter as well as -636/-595, -503/-462, -147/-1 of the CYP2A6 promoter. Furthermore, overexpression and decoy oligodeoxynucleotide technologies demonstrated that SP1 and AP-1 were pivotal transcriptional activators regulating the promoter activity of CYP1A1 and CYP2A6. Moreover, bioactivation of AFB1 to AFBO could be increased by upregulation of CYP1A1 and CYP2A6 expression, which was trans-activated owing to the upregulalion of AP-1, rather than SP1, stimulated by AFB1-induced reactive oxygen species. Additionally, nano-selenium could reduce ROS, downregulate AP-1 expression and then decrease the expression of CYP1A1 and CYP2A6, thus alleviating the toxicity of AFB1. In conclusion, AP-1 and SP1 played important roles in the transactivation of CYP1A1 and CYP2A6 expression and further bioactivated AFB1 to AFBO in chicken liver, which could provide novel targets for the remediation of aflatoxicosis in chicks.

AP-1 binding transcriptionally regulates human neutral ceramidase

Many forms of cellular stress cause an elevation of endogenous ceramide levels leading to growth arrest or apoptosis. Ceramidases (CDase) play a critical role in regulating apoptosis by hydrolyzing ceramide into sphingosine, a precursor for promitogenic sphingosine-1-phosphate. Growth factor induction of neutral CDase (nCDase) has been shown to have a cytoprotective effect against cytokine-induced increases in ceramide levels. To further define the physiological regulation of nCDase, we identified a 200 bp promoter region and demonstrated that serum activated this proximal promoter, which correlated with a serum-induced increase in human nCDase mRNA expression. Computational analysis revealed a putative cis-element for AP-1, a transcription factor activated by serum. Electrophoretic mobility shift assays demonstrated that the identified transcriptional response element binds to AP-1 transcription factors. RNA interference-mediated knockdown of the AP-1 subunit, c-Jun, inhibited the activity of the human nCDase proximal promoter, whereas, c-Jun overexpression increased promoter activity, which directly correlated with human nCDase mRNA transcription, decreased ceramide mass, and protection against caspase 3/7-dependent apoptosis. Taken together, our findings suggest that c-Jun/AP-1 signaling may, in part, regulate serum-induced human nCDase gene transcription.

Characterization of the genetic profile of CYP2C19 in two South African populations

AIMS

This study was aimed at elucidating the common sequence variation present in the CYP2C19 gene within the South African Xhosa population and comparing it with the Cape Mixed Ancestry (CMA) population for possible future pharmacogenetic applications.

MATERIALS & METHODS

Common sequence variation was identified through the resequencing of 15 Xhosa individuals. The detected variants were prioritized for genotyping in an additional 85 Xhosa and 75 CMA individuals, while 5 -upstream variants were analyzed using dual luciferase reporter assays.

RESULTS

Resequencing of the Xhosa population revealed 30 variants, including the novel CYP2C19*27 and CYP2C19*28 alleles. CYP2C19*27, characterized by -1041G>A, caused a twofold decrease in luciferase activity, while CYP2C19*28 is characterized by the nonsynonymous V374I variant. In addition, the previously characterized variants, CYP2C19*2, CYP2C19*9 and CYP2C19*17, were present in both populations, while CYP2C19*3 was only observed in the CMA population.

CONCLUSION

Our data demonstrate that both the Xhosa and CMA populations exhibit unique genetic profiles that could influence the outcome of drug therapy in these populations.

Up-regulation of human CYP2J2 in HepG2 cells by butylated hydroxyanisole is mediated by c-Jun and Nrf2

Cytochrome P450 2J2 oxidizes arachidonic acid to a series of epoxyeicosatrienoic acid (EET) isomers in human tissues. EETs regulate numerous homeostatic processes, including cytoprotective and proliferative responses against injurious stresses. There is little information currently available on the factors that regulate CYP2J2, but strategies to activate expression could use the beneficial effects of EETs in cells. The basic leucine zipper (bZIP) transcription factor c-Jun has been shown previously to maintain CYP2J2 expression in human HepG2 cells; c-Jun forms transcriptionally active dimers with the antioxidant-inducible bZIP factor Nrf2. In the present study, we tested the hypothesis that CYP2J2 expression may be activated in cells by c-Jun/Nrf2 heterodimers. Treatment of HepG2 cells with butylated hydroxyanisole elicited concentration- and time-dependent activation of CYP2J2 expression, as well as the bZIP factors Nrf2 and c-Jun; chromatin immunoprecipitation assays revealed a pronounced increase in binding of these bZIP factors to the CYP2J2 5'-flank. Transient transfection analysis using deletion constructs and gel-shift assays were consistent with a role for the -105/-88 region of CYP2J2 in c-Jun/Nrf2 responsiveness. Using a series of mutant expression plasmids, we identified c-Jun as the critical partner in CYP2J2 transactivation. Coimmunoprecipitation experiments confirmed the importance of the leucine zipper region of Nrf2 in the enhancement of c-Jun-dependent transactivation of CYP2J2. Agents that activate CYP2J2 expression may offer a new approach to using the beneficial effects of EETs in cells.

Soluble epoxide hydrolase is a susceptibility factor for heart failure in a rat model of human disease

We aimed to identify genetic variants associated with heart failure by using a rat model of the human disease. We performed invasive cardiac hemodynamic measurements in F2 crosses between spontaneously hypertensive heart failure (SHHF) rats and reference strains. We combined linkage analyses with genome-wide expression profiling and identified Ephx2 as a heart failure susceptibility gene in SHHF rats. Specifically, we found that cis variation at Ephx2 segregated with heart failure and with increased transcript expression, protein expression and enzyme activity, leading to a more rapid hydrolysis of cardioprotective epoxyeicosatrienoic acids. To confirm our results, we tested the role of Ephx2 in heart failure using knockout mice. Ephx2 gene ablation protected from pressure overload-induced heart failure and cardiac arrhythmias. We further demonstrated differential regulation of EPHX2 in human heart failure, suggesting a cross-species role for Ephx2 in this complex disease.