Glucocorticoid stimulates primate but inhibits rodent alpha-fetoprotein gene promoter.
Glucocorticoids inhibit rodent alpha-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.
Nakabayashi
H
H
Department of Biochemistry, Hokkaido University Graduate School of Medicine, N15 W7, Kita-ku, Sapporo 060-8638, Japan. hnakabay@med.hokudai.ac.jp
Koyama
Y
Y
Sakai
M
M
Li
H M
HM
Wong
N C
NC
Nishi
S
S
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001665:Binding Sites; D019556:COS Cells; D004268:DNA-Binding Proteins; D003907:Dexamethasone / Q000494:pharmacology*; D019281:Dimerization; D005786:Gene Expression Regulation / Q000187:drug effects*; D020868:Gene Silencing / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology*; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism; D006071:Gorilla gorilla; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D002679:Pan troglodytes; D010750:Phosphoproteins / Q000378:metabolism / Q000494:pharmacology; D011148:Pongo pygmaeus; D011401:Promoter Regions, Genetic / Q000187:drug effects*; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000037:antagonists & inhibitors; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D047488:Retinoid X Receptors; D016415:Sequence Alignment; D013045:Species Specificity; D014157:Transcription Factors / Q000378:metabolism / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D000509:alpha-Fetoproteins / Q000096:biosynthesis / Q000235:genetics*
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D005938:Glucocorticoids; D051557:Hepatocyte Nuclear Factor 4; C403128:MLX protein, human; D010750:Phosphoproteins; D018160:Receptors, Cytoplasmic and Nuclear; D011965:Receptors, Glucocorticoid; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; C501970:Tcfl4 protein, mouse; D014157:Transcription Factors; D000509:alpha-Fetoproteins; C075995:down-regulator of transcription 1; D003907:Dexamethasone; D005982:Glutathione Transferase