Three Putative Negative Regulatory Proteins Are Involved in PSG5 Gene Repression in Non-Placental Cells

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

Bariloche

Congreso; XXXIX Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2003

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB)

The human pregnancy-specific glycoprotein 5 gene (PSG5) expression is maximal in placenta. Its minimal promoter lacks TATA-box, but contains a GC-like box acting as a core promoter element, recognized by the ubiquitous Sp1 transcription factor in both PSG-producing and non-producing cell lines. The proximal 5´ regulatory sequence bears at least four footprint motives (FP1-FP4). To get further insight into the regulatory factors involved in PSG5 gene expression, we have now investigated the nature of the transcription factors that recognize the FP3 and FP4 cis elements in placenta as well as in different cell lines which do not express endogenous PSG genes. The incubation of protein extracts from these cell lines with FP3 and FP4 probes yielded, in both cases, specific DNA-protein complexes that were abolished by an excess of unlabelled competitor DNA but not by mutated FP3 or FP4, respectively, nor by unrelated oligonucleotides. However, these complexes were absent when extracts of human term placenta were employed. UV-crosslinking assays revealed that two proteins of 71 ± 2 KDa and 142 ± 6 KDa are involved in complex formation with FP3 cis-acting element, and a 115 ± 3 KDa protein is involved in FP4 complex formation. Disruption of these sequences in PSG5-CAT constructs showed increased transcriptional activity in transient-expression assays in COS7 cells. We propose that placenta specific expression of PSG5 gene is mainly achieved through an impairment of these repressing functions.