Modulation of TEL transcription activity by interaction with the ubiquitin-conjugating enzyme UBC9

The E-26 transforming specific (ETS)related gene TEL, also known as ETV6, i s involved in a large number of chromosomal rearrangements associated with leukemia and congenital fibrosarcoma. The encoded protein contains two func tional domains: a helix-loop-helix (HLH) domain (also known as pointed doma in) located at the N terminus and a DNA-binding domain located at the C ter minus. The HLH domain is involved in protein-protein interaction with itsel f and other members of the ETS family of transcription factors such as FL11 . TEL is a transcription factor, and we and others have shown that it is a repressor of gene expression. To understand further the role of TEL in the cell, we have used an in vivo interaction system to identify proteins that interact with TEL. We show that a protein, UBC9, interacts specifically wit h TEL in vitro and in vivo. UBC9 is a member of the family of ubiquitin-con jugating enzymes. These enzymes usually are involved in proteosome-mediated degradation; however, our data suggest that interaction of TEL with UBC9 d oes not lead to TEL degradation. Our studies show that UBC9 binds to TEL; e xclusively through the HLH domain of TEL, We also show that TEL expressed a s fusion to the DNA-binding domain of Gal4 completely represses a Gal4-resp onsive promoter, but that the coexpression of UBC9 in the same system resto res the activity of the promoter. Targeted paint mutation of conserved amin o acids in UBC9 essential for enzymatic ubiquitination of proteins does not affect interaction nor transcriptional activity. Based on our data, we con clude that UBC9 physically interacts with TEL through the HLH domain and th at the interaction leads to modulation of the transcription activity of TEL .