Both TEL and AML-1 Contribute Repression Domains to the t(12;21) Fusion Protein

Abstract

t(12;21) is the most frequent translocation found in pediatric B-cell acute lymphoblastic leukemias. This translocation fuses a putative repressor domain from the TEL DNA-binding protein to nearly all of the AML-1B transcription factor. Here, we demonstrate that fusion of the TEL pointed domain to the GAL4 DNA-binding domain resulted in sequence-specific transcriptional repression, indicating that the pointed domain is a portable repression motif. The TEL pointed domain functioned equally well when the GAL4 DNA-binding sites were moved 600 bp from the promoter, suggesting an active mechanism of repression. This lead us to demonstrate that wild-type TEL and the t(12;21) fusion protein bind the mSin3A corepressor. In the fusion protein, both TEL and AML-1B contribute mSin3 interaction domains. Deletion mutagenesis indicated that both the TEL and AML-1B mSin3-binding domains contribute to repression by the fusion protein. While both TEL and AML-1B associate with mSin3A, TEL/AML-1B appears to bind this corepressor much more stably than either wild-type protein, suggesting a mode of action for the t(12;21) fusion protein.

ACKNOWLEDGMENTS

We thank Yue Hou for technical assistance, and we thank David Strom, John Nip, and Noel Lenny for plasmids, insightful discussions, and computer assistance.

This work was supported by NIH/NCI grants RO1-CA64140 (S.W.H.), RO1-CA77274 (S.W.H.), and PO1 CA71907-03 (J.R.D.), by American Cancer Society grant JFRA-591 (S.W.H.), by the American Lebanese and Syrian Associated Charities (J.R.D.), by a Center grant from the National Cancer Institute (CA68485), and by the Vanderbilt Cancer Center. R.F. and J.J.W. (F32-CA77167) are recipients of National Research Service Awards from NIH. B.L. is a fellow of the Leukemia Society of America.