The MYND Motif Is Required for Repression of Basal Transcription from the Multidrug Resistance 1 Promoter by the t(8;21) Fusion Protein

ABSTRACT

Chromosomal translocations in acute leukemia that affect the AML-1/CBFβ transcription factor complex create dominant inhibitory proteins. However, the mechanisms by which these proteins act remain obscure. Here we demonstrate that the multidrug resistance 1 (MDR-1) promoter is a target for AML/ETO transcriptional repression. This repression is of basal, not activated, expression from the MDR-1 promoter and thus represents a new mechanism for AML/ETO function. We have defined two domains in AML/ETO that are required for repression of basal transcription from the MDR-1 promoter: a hydrophobic heptad repeat (HHR) motif and a conserved zinc finger (ZnF) domain termed the MYND domain. The HHR mediates formation of AML/ETO homodimers and AML/ETO-ETO heterodimers. Single serine substitutions at conserved cysteine residues within the predicted ZnFs also abrogate transcriptional repression. Finally, we observe that AML/ETO can also inhibit Ets-1 activation of the MDR-1 promoter, indicating that AML/ETO can disrupt both basal and Ets-1-dependent transcription. The fortuitous inhibition of MDR-1 expression in t(8;21)-containing leukemias may contribute to the favorable response of these patients to chemotherapeutic drugs.

ACKNOWLEDGMENTS

We thank Dana King and Yue Hou for technical assistance and Jennifer Westendorf, Randy Fenrick, Shari Meyers, and Noel Lenny for plasmids, insightful discussions, and critical evaluation of data.

This work was supported by NIH/NCI grants RO1-CA64140 and RO1-CA77274, by American Cancer Society grant JFRA-591 (to S.W.H.), by the American Lebanese and Syrian Associated Charities, by the Vanderbilt Cancer Center, and by a center grant from NCI (CA68485).