MOLECULAR CHARACTERIZATION OF THE ETS-RELATED HUMAN TRANSCRIPTION FACTOR ER81

The PEA3 group is a homogeneous group of the ets transcription factor family and is composed df three known members, PEA3, ERM and ER81, whi ch, on the amino acid (AA) level, are more than 95% identical within t he DNA-binding domain (the Ets domain), more than 85% within a 32 AA d omain (the acidic domain) localized in the amino-terminus and almost 5 0% identical overall. By screening a human kidney cDNA library with a specific probe obtained from mouse ER81 we isolated two clones of 1.6 and 1.5 kb in length encoding a 458 AA open reading frame. When compar ed to mouse ER81, the present human ER81 lacks the last 13 AA of the a cidic domain and the 5 AA contiguous to the carboxy-terminal part of t he acidic domain. Of the 458 AA of the human ER81 protein, 97% are ide ntical to mouse ER81. Gel shift analysis indicates that the full-lengt h human ER81 protein is able to bind specifically to an oligonucleotid e containing the binding sites recognized by most of the Ets proteins. By transient expression in RK13 mammalian cells, human ER81 protein t ransactivated a reporter plasmid containing Ets binding sites, indicat ing that this molecule is a bonafide transcriptional activator, while by expression in Cos-1 transfected cells, we detected the presence of human ER81 protein in the nucleus using immunocytochemistry. In human tissues, ER81 mRNA is very highly expressed in brain, highly expressed in testis, lung and heart, moderately in spleen, small intestine, pan creas and colon, weakly in liver, prostate and thymus, very weakly in skeletal muscle, kidney and ovary and not in placenta and peripheral b lood leukocytes. Analysis of human solid or haematopoietic tumour cell lines showed that most of them did not express ER81 detectably. Datab ase searches revealed that ETV1 mRNA is highly similar to human ER81 d escribed here, although it contains the full-length acidic domain pres ent in mouse ER81. By screening a genomic DNA library, we characterize d the intron-exon junction within the acidic domain of human ER81 and we showed that this junction corresponds to the site where the remaini ng AA of the acidic domain of ETV1 or mouse ER81 are inserted.