Two liver-enriched trans-acting factors support the tissue-specific basal transcription from the rat tyrosine aminotransferase promoter.
The rat tyrosine aminotransferase gene (TAT) is a glucocorticoid-inducible gene, specifically expressed in liver. Using gel retardation assays, we have shown that its promoter (nt + 1 to -350; TAT.35) binds a combination of both ubiquitous and liver-specific trans-acting factors. Cis-acting sequences spanning: (i) nt -65 to -85 bound NF-Y, an ubiquitous "AACCAAT" box binding factor; (ii) nt -157 to -171 bound a liver-enriched member of the NF1 gene family [NF1Liver (NF1L hereafter)]; (iii) nt -266 to -281 bound the liver specific factor HNF1; and (iv) nt -283 to -288 bound ubiquitous "CCAAT" box binding factor(s). Moreover, the TAT gene promoter was able to drive liver-specific basal transcription, even in an in vitro assay using TAT-expressing (liver) vs non-expressing (spleen) crude nuclear extracts (NEs). Competition studies in transcription with both unmutated and mutated ds-oligonucleotides (ds-oligos) demonstrated that NF1L and HNF1 supported approx. 60 and 25% of the basal transcriptional activity sustained by TAT.35 in the liver, respectively. Neither of these oligos affected the very low level of transcription sustained by spleen NEs. This suggests a minor role for HNF1 in liver-specific basal TAT gene expression, consistent with previous observations with dedifferentiated C2 hepatoma cells (which does not express HNF1) [Deschatrette and Weiss. Biochimie 56 (1974) 1603-1611 and Cereghini et al. EMBO Jl9 (1990) 2257-2263]. Competition studies in liver-specific in vitro transcription with ds-oligo -265/-290 yielded a 90% inhibition, suggesting either that sequences spanning nt -283 to -288 sequester "CCAAT-box" binding factor(s) that may be relevant elsewhere for TAT promoter function (e.g. NF-Y which interacts with nt -65 to -85), or that such a factor interacts functionally with HNF1.
Schweizer-Groyer
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G
INSERM U. 33, Le Kremlin-Bicêtre, France.
Groyer
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A
Cadepond
F
F
Grange
T
T
Baulieu
E E
EE
Pictet
R
R
D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D022762:CCAAT-Enhancer-Binding Proteins; D002467:Cell Nucleus / Q000502:physiology; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051537:Hepatocyte Nuclear Factor 1; D051538:Hepatocyte Nuclear Factor 1-alpha; D051539:Hepatocyte Nuclear Factor 1-beta; D007527:Isoenzymes / Q000235:genetics*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D005810:Multigene Family; D009687:Nuclear Proteins; D010957:Plasmids; D011401:Promoter Regions, Genetic; D051381:Rats; D011919:Rats, Inbred Strains; D013154:Spleen / Q000201:enzymology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014444:Tyrosine Transaminase / Q000235:genetics*
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D051538:Hepatocyte Nuclear Factor 1-alpha; C496489:Hnf1a protein, rat; D007527:Isoenzymes; D009687:Nuclear Proteins; D014157:Transcription Factors; D051537:Hepatocyte Nuclear Factor 1; D051539:Hepatocyte Nuclear Factor 1-beta; D004247:DNA; D014444:Tyrosine Transaminase