Transcriptional Regulation of the Human Trophoblast Specific PSG5 Gene Associated with Normal Placental Function

NORES, R.; PATRITO, L.; PANZETTA-DUTARI, G.

Iguazú

Simposio; Symposium ?Gene Expression and RNA Processing?. International Centre For Genetic Engineering And Biotechnology (ICGEB) Meeting; 2003

International Centre For Genetic Engineering And Biotechnology (ICGEB)

Pregnancy-specific glycoprotein 5 gene (PSG5) belongs to a human gene family of highly similar and active genes. High levels of PSG biosynthesis are restricted to the placenta syncytiotrophoblast and are essential for the maintenance of normal gestation. In order to reveal the molecular bases involved in placenta specific transcription of PSG5 gene, we have performed sequence analysis, DNA-protein interaction assays and transient transfection experiments in cell lines that do or do not express PSG genes. The TATA-less promoter (-254/-43) was equally active and down regulated by a proximal repressor region (PRR: -605 to -254) and a distal repressor region (-3204 to -706), in all cell lines tested. Mutations in either the core promoter element (CPE-box, -147/-140) or the upstream FP1-motif (-455/-433) markedly reduced the activity of PSG5-CAT constructs. Both elements bear a similar GT-box motif involved in complex formation with term placenta tissue and PSG-non-expressing COS-7 cell extracts. In both extracts, the ubiquitous SP1 protein was identified as the major transcription factor recognizing both cis-elements. In addition, SP1 trans-activated PSG5-CAT constructs and was detected in syncytiotrophoblast cells. The negative activity of the PRR was largely dependent on the FP3 (-512/ -505) motif and on the -605/-524 sequence that included FP4. FP3 and FP4 probes yield specific DNA-protein complexes with extracts from different cell lines. However, these complexes were absent in placental cell extracts. FP3 specific complex include proteins of 71 ± 2 KDa and 142 ± 6 KDa. FP4 involved a 115 ± 3 KDa protein. Disruption of these sequences in PSG5-CAT constructs allowed increased transcriptional activity in COS-7 cells. We propose that Sp1 provides for basal PSG5 gene transcription, meanwhile placenta specific expression requires the impairment of the repressing function of the negative factors active in PSG non-expressing cells.