title: A retinoic acid response element that overlaps an estrogen response element mediates multihormonal sensitivity in transcriptional activation of the lactoferrin gene.
abstract: The lactoferrin gene is highly expressed in many different tissues, and its expression is controlled by different regulators. In this report, we have defined a retinoic acid response element (RARE) in the 5'-flanking region of the lactoferrin gene promoter. The lactoferrin-RARE is composed of two AGGTCA-like motifs arranged as a direct repeat with 1-bp spacing (DR-1). A gel retardation assay demonstrated that it bound strongly with retinoid X receptor (RXR) homodimers and RXR-retinoic acid receptor (RAR) heterodimers as well as chicken ovalbumin upstream promoter transcription factor (COUP-TF) orphan receptor. In CV-1 cells, the lactoferrin-RARE linked with a heterologous thymidine kinase promoter was strongly activated by RXR homodimers in response to 9-cis-retinoic acid (9-cis-RA) but not to all-trans-RA. When the COUP-TF orphan receptor was cotransfected, the 9-cis-RA-induced RXR homodimer activity was strongly repressed. A unique feature of the lactoferrin-RARE is that it has an AGGTCA-like motif in common with an estrogen-responsive element (ERE). The composite RARE/ERE contributes to the functional interaction between retinoid receptors and the estrogen receptor (ER) and their ligands. In CV-1 cells, cotransfection of the retinoid and estrogen receptors led to mutual inhibition of the other's activity, while an RA-dependent inhibition of ER activity was observed in breast cancer cells. Furthermore, the lactoferrin-RARE/ERE showed differential transactivation activity in different cell types. RAs could activate the lactoferrin-RARE/ERE in human leukemia HL-60 cells and U937 cells but not in human breast cancer cells. By gel retardation analyses, we demonstrated that strong binding of the endogenous COUP-TF in breast cancer cells to the composite element contributed to diminished RA response in these cells. Thus, the lactoferrin-RARE/ERE functions as a signaling switch module that mediates multihormonal responsiveness in the regulation of lactoferrin gene expression.
authors.affiliation: La Jolla Cancer Research Foundation, Cancer Research Center, California 92037, USA.
authors.forename: M O
authors.initials: MO
authors.lastname: Lee
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.forename: X K
authors.initials: XK
authors.lastname: Zhang
mesh_terms: D001483:Base Sequence; D051838:COUP Transcription Factor I; D004268:DNA-Binding Proteins / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007781:Lactoferrin / Q000096:biosynthesis / Q000235:genetics*; D007938:Leukemia / Q000378:metabolism; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D047488:Retinoid X Receptors; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014212:Tretinoin / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D051838:COUP Transcription Factor I; D004268:DNA-Binding Proteins; D004967:Estrogens; C497589:NR2F1 protein, human; D018168:Receptors, Retinoic Acid; D011994:Recombinant Proteins; D047488:Retinoid X Receptors; D014157:Transcription Factors; D014212:Tretinoin; D007781:Lactoferrin