The rat hepatic CYP2EI gene becomes transcriptionally activated within 1 day after birth. This activation can be mimicked by using the 5' end of the gene in a cell-free nuclear extract prepared from hepatocytes taken from rats at different developmental stages. Deletion analysis revealed that a positive element located between -127 and -89 was responsible for 90% of the in vitro transcription activity of adult liver extracts. Protein binding studies revealed that this region was operationally equivalent to the binding site for the factor HNF-1. Two other protein-binding regions were uncovered, one of which corresponded to the site for a CCAATbinding factor NFY. The other site was a palindrome sequence unique to the CYP2EI gene. These latter two factors did not significantly contribute to transcriptional activity in vitro and were not conserved between the rat and human CYP2EI genes. Extracts prepared from fetal and newborn livers were transcriptionally inactive, whereas extracts from livers of 3-day-old rats were fully active toward the CYP2EI gene. DNase I footprinting patterns indistinguishable between fetal and adult extracts were obtained for all three factors. However, gel mobility shift assays revealed a second, higher-mobility band produced by fetal and newborn liver extracts bound to the HNF-1 oligomer. UV-cross-linking studies showed that adult and fetal extracts had only a single 98-kilodalton protein that bound to this oligomer. In contrast, adult lung samples, also transcriptionally inactive toward the CYP2EI gene, contained two proteins of slightly greater than 110 kilodaltons. These results suggest that the CYP2EI gene is positively regulated in adult rats by HNF-1 or a protein similar in DNA-binding properties to HNF-1. The role of this factor or other protein-protein interactions in the lack of CYP2EI transcription in fetal and newborn animals remains unclear.Control of gene transcription has been extensively studied in rat hepatocytes. A number of transcriptional activator proteins have been found to control liver-specific gene transcription (reviewed in reference 17). Several of these, including HNF-1 (2, 8), C/EBP (21), and DBP (26), have been cloned. Other factors such as HNF-3 and HNF-4 that are rich in hepatocytes and hepatoma cells have also been identified (6). Indeed, control of hepatic gene expression may involve combinational participation of two or more factors acting on multiple individual subdomains upstream of the transcription start site (17).The cytochrome P-450s represent a superfamily of gene products (13, 27). Many P-450s, especially those involved in drug oxidation, are expressed primarily in liver, although some forms are produced to a lesser extent in tissues such as lung, kidney, and intestine. A number of P-450 genes are expressed at low or undetectable levels unless the animal is administered inducing agents such as the dioxins, phenobarbital, synthetic steroids, and hypolipidemic agents. Other P-450 genes are actively transcribed in the absence of inducers. Many of thes...

The insulin-like growth factor II (rIGFII) is a mitogenic polypeptide, the expression of which is high in most rat tissues during embryonic development, yet is barely detectable in adult tissues except for some of neurogenic origin. The gene is present as a single copy in the genome but has three alternative leader exons, E1, E2 and E3, thereby with three independent transcriptional promoters. We analysed the expression of rIGFII and the relative efficiency of each promoter in hepatocarcinogen-treated livers, primary hepatomas and established hepatoma lines. The E3-specific product was first detected after 6 weeks of 3'-methyl-4-dimethylaminoazobenzene treatment and those of E1 and E2 also after 9 weeks. The levels gradually increased according to the sum of the treatment period, but reactivation was nil in the regenerating liver. Consistently high levels of expression were observed in all primary tumors, but the relative promoter activity varied with the tumor. The significance of rIGFII reactivation was discussed in the light of the hepatocarcinogenesis.

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GenBank accession no. M33190 The rat CYP2A subfamily is composed of three members designated CYP2AI, CYP2A2 and CYP2A3. The CYP2AJ gene is expressed in livers of female rats and is transiently expressed in young males then expression is extinguished when male rats reach puberty (1). The CYP2A2 gene is expressed in livers of postpubertal male rats but is not expressed in females at any stage of development (1). Both genes have been cloned and sequenced and found to possess nine exons (2), typical of other CYP2 subfamily members sequenced to date (3). In contrast to the CYP2AJ and CYP2A2 genes, the CYP2A3 gene is not expressed in livers but is expressed in rat lung (4). To begin experiments to understand the mechanism of tissue specific regulation of this gene, it was cloned from a rat XEMBL3 genomic library and completely sequenced by random shotgun cloning into M13 and the Sanger dideoxynucleotide chain termination methodology using Sequenase® (see ref. 2). The transcription start site was determined (Fig. 1, +1) using both SI mapping and primer extension analyses. Upstream and downstream DNA of 3421 and 2816 bp was also sequenced. The gene contained a TATA box and nine exons typical of other CYP2 family genes. No evidence of earlier gene conversions between CYP2A3 and the other two CYP2A genes was uncovered.