Transcriptional activation of cytochrome P450 CYP2C45 by drugs is mediated by the chicken xenobiotic receptor (CXR) interacting with a phenobarbital response enhancer unit

Cytochromes P450 (CYP)-2C enzymes fulfill an important role in xenobiotic metabolism and therefore have extensively been studied in rodents and humans. However, no CYP2C genes have been described in avian species to date. In this paper, we report the cloning, functional analysis, and regulation of chicken CYP2C45. The sequence shares up to 58% amino acid identity with CYP2Cs in other species. The overexpression of CYP2C45 in chicken hepatoma cells leghorn male hepatoma (LMH) led to increased scoparone metabolism. CYP2C45 regulation was studied in LMH cells at the mRNA level and in reporter gene assays using a construct containing 2.6 kb of its 5'-flanking region. Exposure of LMH cells to phenobarbital or metyrapone led to a 95- or 210-fold increase in CYP2C45 mRNA and a 140- or 290-fold increase in reporter gene expression, respectively. A phenobarbital response enhancer unit (PBRU) of 239 bp containing a DR-4 nuclear receptor binding site was identified within the 2.6-kb fragment. Site-specific mutation of the DR-4 revealed the requirement of this motif for CYP2C45 induction by drugs. The chicken xenobiotic receptor CXR interacted with the PBRU in electromobility shift and transactivation assays. Furthermore, the related nuclear receptors, mouse PXR and mouse CAR, transactivated this enhancer element, suggesting evolutionary conservation of nuclear receptor-DNA interactions in CYP2C induction.     

Effects of phenylarsine oxide on expression of heme oxygenase-1 reporter constructs in transiently transfected cultures of chick embryo liver cells

Heme oxygenase catalyzes the first and rate-controlling step of heme catabolism. Induction of heme oxygenase-1 can be caused by numerous factors, including heme, other metalloporphyrins, transition metal ions, heat shock, ultraviolet light, phorbol esters, sodium arsenite, and phenylarsine oxide (PAO). Induction of this enzyme may protect cells from oxidative damage. Using heme oxygenase-1 promoter/reporter gene constructs, we have previously reported that the sodium arsenite-mediated induction of heme oxygenase-1 in chick embryo liver cells and chicken hepatoma (LMH) cells involves an AP-1 element. We have now investigated whether the PAO-mediated induction of heme oxygenase-1 also involves an AP-1 element. Primary cultures of chick embryo liver cells were transiently transfected with heme oxygenase-1 promoter/reporter gene constructs, treated with PAO, and reporter gene activities were measured. We found that the PAO-mediated increase in reporter gene activity was dose- and time-dependent. This activity was decreased by prior treatment with N-acetylcysteine. Studies with mutated constructs showed that both an AP-1 element and a metal responsive element are involved in the PAO-mediated induction of the heme oxygenase-1 reporter construct. Electrophoretic mobility shift assays showed that nuclear proteins from PAO-treated cells had increased binding to an AP-1 probe, and that this increase was abrogated by N-acetylcysteine. These findings support the hypothesis that the PAO-mediated induction of heme oxygenase-1 is caused by activation of AP-1 and MRE/cMyc elements and may involve nuclear proteins whose states of phosphorylation determine binding to regulatory elements, and thus the level of expression of heme oxygenase-1.     

Expression of endogenous and transfected apolipoprotein II and vitellogenin II genes in an estrogen responsive chicken liver cell line

A recently described chicken liver cell line, LMH, was characterized to evaluate responsiveness to estrogen. Expression of the endogenous apolipoprotein (apo) II gene was induced by 17 beta-estradiol when LMH cells were cultured with chicken serum. The response was low and yielded apoll mRNA at only 0.3% of the level seen in estrogenized rooster liver. Higher levels of apoll mRNA were achieved when LMH cells were transiently transfected with an expression plasmid for estrogen receptor. A transfected apoll gene was strongly expressed only when cotransfected with receptor. Expression of the endogenous vitellogenin (VTG) II gene was not detected. However, when cotransfected with a receptor expression plasmid, VTG II reporter plasmids were expressed in LMH cells in response to 17 beta-estradiol. These results suggest that estrogen responsiveness of LMH cells is limited by the availability of functional receptor. Low levels of estrogen receptor mRNA were detected in LMH cells, and receptor binding sites and mRNA were greatly increased following transient transfection with a receptor expression plasmid. Using this transient transfection protocol, several VTG II reporter plasmids were compared in LMH cells and chick embryo fibroblasts. A plasmid containing VTG II estrogen response elements linked to a heterologous promoter was regulated by estrogen in both cell types. In contrast, reporter plasmids containing the VTG II promoter were regulated by estrogen in LMH cells but were not expressed at all in chick embryo fibroblasts. These results suggest that regulation of the VTG II gene involves cell type-specific elements in addition to estrogen response elements.(ABSTRACT TRUNCATED AT 250 WORDS)     

Involvement of Intronic Sequences in Cell-Specific Expression of the Peripherin Gene

Peripherin is an intermediate filament protein expressed in restricted populations of neurons. Our previous study of the chromatin structure of the mouse peripherin gene in cells that do or do not express peripherin suggested that the region located between -1,500 and +800 bp of the gene could be involved in its cell specificity. In the present work, we performed an in vitro functional analysis of the 5' flanking region of the mouse peripherin gene and observed that this region up to 9 kb contained both enhancer and inhibiting activities; however, it was insufficient to achieve a complete extinction of reporter gene expression in peripherin-negative cells. Furthermore, analysis of the first three introns with the 5' flanking sequences of the gene showed that intron I greatly increased specificity of the gene expression. Intron I also conferred the same properties to thymidine kinase heterologous promoter. DNase I footprinting experiments performed with intron I revealed at least two protected regions (Inl A and Inl B). Inl A encompasses an AP-2-like binding site that interacted with both neuroblast and fibroblast nuclear factors, as well as with the recombinant AP-2alpha protein. However, gel shift experiments suggested that the interacting nuclear factors are distinct from AP-2alpha itself and probably belong to the AP-2 family. Inl B perfectly matched the consensus binding site for Sp1 and specifically interacted with nuclear protein factors that showed the same binding properties as the Sp1 family members. Fine deletion analysis of intron I indicated that the Inl A element alone is responsible for its enhancing properties, whereas a region located between +789 and +832 gives to intron I its silencer activity.     

Characterization of DNA sequences localized 11 to 17.5 kb upstream of the chicken embryonic pi-globin gene

We have analyzed the DNA fragment localized about 11 to 17.5 kb upstream of the chicken alpha-globin gene domain (the fragment was designed as alpha-0). The nucleotide sequence of its 3.3 kb-long 5' part was established and interactions with nuclear matrix proteins were studied. The DNA region localized about 16 kb upstream of the embryonic pi-globin gene showed high affinity to nuclear matrices in vitro. Two palindromes and a cluster of inverted repeats were co-localized in the same region. The whole 6.6 kb alpha-0 fragment decreased the activity of linked CAT reporter gene when transfected into chicken erythroblastoid cells.     

鸡卵清蛋白基因启动子调控GFP基因在鸡原代输卵管上皮细胞和中国仓鼠卵巢细胞的表达

特异性扩增家鸡卵清蛋白基因上游调控序列 1340bp～ +16 5 5bp片段和第一内含子 +49bp～ +16 5 5bp片段 ,去除pG FP N2载体自身的CMV启动子 ,分别构建了P_2.9koval GFP和P_1.5koval GFP两种表达载体 ,经测序和酶切鉴定表达载体构建正确。采用脂质体转染法分别将这两种载体、pGFP N2 (阳性对照 )质粒及阴性对照转染鸡原代输卵管上皮细胞和中国仓鼠卵巢细胞。用荧光倒置显微镜观测绿色荧光蛋白的表达。结果表明 :两种表达质粒在鸡原代输卵管上皮细胞和中国仓鼠卵巢细胞中都可以表达荧光蛋白。结果既显示卵清蛋白第一内含子对基因的表达起到一定的调控作用 ,也显示卵清蛋白启动子对输卵管上皮细胞和卵巢细胞不存在特异性 ,并且不存在种属差异性。