The same xenobiotic response element is required for constitutive and inducible expression of the mammalian aldehyde dehydrogenase-3 gene

The mammalian aldehyde dehydrogenase-3 gene (ALDH3) exhibits several aspect s of tissue-specific expression. Certain normal tissues, such as the cornea , constitutively express ALDH3 at very high levels. Other tissues, such as normal liver, do not express ALDH3. In liver, ALDH3 is inducible by polycyc lic aromatic hydrocarbon xenobiotics by an Ah-receptor (AhR)-mediated pathw ay in which a liganded AhR complexes with nuclear ARNT protein, and the com plex binds to a xenobiotic response element (XRE) sequence located near -3. 0 kb in the ALDH3 5' flanking region and initiates transcription. We used o ur recently developed rat corneal epithelium culture model (Boesch ct at, J . Biol. Chem. 271, 5150-5157, 1996) to study the molecular basis of constit utive ALDH3 expression. Transient transfection assays of corneal epithelium using a battery of ALDH3 5' flanking region-CAT reporter gene constructs i ndicate that high constitutive ALDH3 expression involves the same cis-actin g elements as xenobiotic-induced ALDH3 expression in liver. These elements include a strong basal promoter region and the XRE located near -3.0 kb. We stern analysis confirms the presence of AhR and ARNT proteins in 3-methylch olanthrene-treated rat liver, as well as ARNT protein in rat corneal epithe lium. No AhR protein is found in rat cornea. The -3.0-kb ALDH3 XRE region c ontains multiple overlapping transcription factor binding sequences, includ ing consensus sites for AhR, ARNT, HNF1, HNF4, and C/ebp. Electrophoretic m obility shift assays (EMSAs) indicate that constitutive expression of ALDH3 in cornea involves binding of ARNT, HNF1, and HNF4 to the ALDH3-XRE in an Ah-receptor-independent, ARNT-requiring manner. Transient transfection of A LDH3-CAT reporter gene constructs possessing a mutation in either the ARNT- or HNF4-DNA binding sites of the XRE confirms the functional importance of these sequence motifs in constitutive ALDH3 expression. (C) 1999 Academic Press.