A cis-acting element located between the cAMP response elements and CCAAT box augments cell-specific expression of the glycoprotein hormone alpha subunit gene

Abstract

Several cis-acting elements interact through their cognate trans-acting factors to confer placenta-specific expression to the alpha subunit gene of glycoprotein hormones. These elements include two tandemly arranged cAMP response elements (CREs, located between base pairs (bp) -146 and -111 relative to the transcription start site), an upstream regulatory element (URE, located between -180 and -150), and a CCAAT box (located between bp -100 and -80). Here, we identify a new regulatory region, junctional regulatory element (JRE), with critical nucleotides located between the CREs and CCAAT box (bp -120 to -100). Although the binding site of the JRE abuts the 3' CRE, methylation interference assays indicate that no overlap occurs between the contact points of the proteins that bind to the JRE and CRE. This new regulatory element is highly conserved across species and contains a palindromic binding site for a 50-kDa nuclear factor(s) which is distinct from the factors that bind the URE, CRE, and CCAAT box of the alpha subunit gene. Finally, gene transfer studies suggest that, although JRE binding activity is found in several cell types, this element acts relatively cell-specifically. We conclude that this element and its cognate trans-acting factor act in conjunction with the complexes formed over the URE, CREs, and CCAAT box to enhance the placenta-specific activity of the alpha subunit promoter.