Publications (3)2.48 Total impact
Article: Functional mapping of tissue-specific elements of the human alpha-fetoprotein gene enhancer.[show abstract] [hide abstract]
ABSTRACT: Serum alpha-fetoprotein (AFP) levels in hepatocellular carcinoma (HCC) patients and expression of the protein in cultured HCC cell lines are highly variable. These observations may arise from features correlated with tissue-specific expression of the gene. Extremely strong and potent liver-specific enhancer activity is confined from -4.1 to -3.3 kb upstream to the human AFP gene in contrast with that of the rodent which exists in three widely separated regions. To understand the tissue-specific expression of AFP, we examined cis-acting elements in the enhancer. Results revealed binding sites for selected liver-enriched transcription factors (LETFs) in both domains A (-4120 to -3756 bp) and B (-3492 to -3300 bp) of the gene. These sites included: one hepatocyte nuclear factor (HNF)-1 and HNF-4, two HNF-3, and two C/EBP binding sites in domain A. An adjacent domain B contained one HNF-3 site and three C/EBP sites plus a previously identified HNF-1 site. Each of these elements alone has the ability to stimulate heterogeneous promoter activity in a dose-dependent manner when transfected into AFP producing cells. A comparative study showed that the presence of two HNF-1 and one HNF-4 site is a characteristic feature of human but not rodent AFP enhancer. The mRNA levels of the liver-enriched transcription factors (LETFs) were variable in individual HCC cell lines and together with silencer activities may underlie differential expression of the AFP gene.Biochemical and Biophysical Research Communications 07/2004; 318(3):773-85. · 2.48 Impact Factor
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ABSTRACT: Glucocorticoids inhibit rodent α-fetoprotein (AFP) gene activity but stimulate expression of the human homologue. Like human, activity of the AFP promoter from other primates was stimulated by the synthetic glucocorticoid dexamethasone (Dex) in various cell lines. A glucocorticoid responsive element (GRE) is located within 180 bp upstream of the transcription initiation site of all AFP genes examined. Comparative analysis of the GRE in the two different groups of promoters revealed a common 3′ hexamer, 5′-TGTCCT-3′, but the 5′ hexamers were different. This difference converts the rodent GRE to a DR-1 motif. DR-1 is a binding site for members of the nuclear receptor superfamily including the orphan receptor hepatocyte nuclear factor-4 (HNF-4). The presence of DR-1 in the rodent but not human may underlie the opposite actions of Dex on the AFP promoter. We tested this hypothesis using a transient transfection assay. In hepatoma cells that expressed GR and HNF-4, reporter-activity was inhibited by Dex. The same construct in nonhepatoma cells was strongly induced by over expression of HNF-4 and the induced activity was inhibited by Dex. The findings show that Dex induction of human AFP is mediated by a GRE. But Dex repression of the rodent promoter requires a DR-1 motif that interacts with GR and HNF-4.Biochemical and Biophysical Research Communications.
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ABSTRACT: Apollpoprotein A1 (Apo A1) is the major protein component of high density Ilpoprotein (HDL) particles. HDL particles mediate the removal of cholesterol from extra-hepatic tissues via a process known as reverse cholesterol transport. Augmented production of Apo A1 will likely be beneficial to those who suffer from the consequences of hypercholesterolemla. One approach to increase expression of the protein is to identify nuclear factor(s) that enhance Apo A1 promoter activity. Therefore, we have used transient transfectlon to study a limited portion (∼474 to − 7) of the gene and showed that a cls-regulatory element, site C had a permissive effect on the ability of an adjacent site B to increase promoter activity by 30-fold. The Importance of element C prompted us to identify the factors) that interact with this site. Results showed that HNF-4, a new member of the thyroid/steroid hormone receptor superfamlly interacts with site C to enhance activity of the promoter. Based on this observation and that of the known Inhibitory effects of ARP-1 on site C, we postulate a model which may account for the tissue-specific expression of the rat Apo A1 gene.