Human annexin A5 is a ubiquitous protein implicated in diverse signal transduction processes associated with cell growth and differentiation, and its gene regulation is an important component of this function. Promoter transcriptional activity was determined for a wide 5′ portion of the human annexin A5 gene, from bp −1275 to +79 relative to the most 5′ of several discrete transcription start points. Transfection experiments carried out in HeLa cells identified the segment from bp −202 to +79 as the minimal promoter conferring optimal transcriptional activity. Two canonical Sp1 sites in the immediate 5′ flanking region of a CpG island were required for significant transcription. Strong repressive activity in the distal promoter region between bp −717 to −1153 was attributed to the presence of an endogenous retroviral long terminal repeat, homologous with long terminal repeat 47B. The downstream sequence from bp position +31 to +79 in untranslated exon 1 was also essential for transcription, as its deletion from any of the plasmid constructs abolished activity in transfection assays. Electrophoretic mobility-shift assays, Southwestern-blot analysis and affinity chromatography were used to identify a protein doublet of relative molecular mass 35kDa that bound an octanucleotide palindromic sequence in exon 1. The DNA cis-element resembled an E-box, but did not bind higher molecular mass transcription factors, such as upstream stimulatory factor or activator protein 4. The discovery of a downstream element crucial for annexin A5 gene transcription, and its interaction with a potentially novel transcription factor or complex, may provide a clue to understanding the initiation of transcription by TATA-less, multiple start site promoters.
Abbreviations used: CAT, chloramphenicol acetyltransferase; EMSA, electrophoretic mobility-shift assay; tsp, transcription start point; DMEM, Dulbecco's modified Eagle's medium; DTT, dithiothreitol; EST, expressed sequence tag; LTR, long terminal repeat; AP, activator protein; USF, upstream stimulatory factor; MED-1, multiple start site element downstream; NCBI, National Center for Biotechnology Information.