Analysis of the promoter region of human placenta-specific DSCR4 gene

The gene DSCR4 locates in the band q22.2 of human chromosome 21 and encodes a protein of 118 amino acids. Expression of DSCR4 is restricted to human placenta and placental choriocarcinoma cell lines BeWo and JEG3. The 5'-RACE method using RNA from human placenta indicated the major transcription start site at 93 nt upstream (nt -93) of the initiation codon. Transfection assay using a series of deletion constructs of the 5'-flanking region fused to the luciferase reporter gene identified three positive regions nt -2200 to -2088, nt -2064 to -1924, nt -810 to -632 and two negative regions nt -1923 to -1740, nt -631 to -425. The computer analysis predicted the presence of several cis-elements in these regions and the promoter assay using various mutants of consensus sequence identified two distinct cis-elements for OLF-1 and E47. The electrophoretic mobility shift assay (EMSA) using the extracts of DSCR4-expressing cells confirmed the binding of certain protein factors to these cis-elements. In fact, OLF-1-like transcription factor, EBF-3 and EBF-4 were detected in the DSCR4-expressing cell lines and human placenta. Based on these data, we postulated that transcription of DSCR4 gene is regulated positively by binding of OLF-1-like transcription factor and negatively by binding of E47-like transcription factor.