The t(8;21) fusion protein interferes with AML-1B-dependent transcriptional activation.
The AML-1/CBF beta transcription factor complex is targeted by both the t(8;21) and the inv(16) chromosomal alterations, which are frequently observed in acute myelogenous leukemia. AML-1 is a site-specific DNA-binding protein that recognizes the enhancer core motif TGTGGT. The t(8;21) translocation fuses the first 177 amino acids of AML-1 to MTG8 (also known as ETO), generating a chimeric protein that retains the DNA-binding domain of AML-1. Analysis of endogenous AML-1 DNA-binding complexes suggested the presence of at least two AML-1 isoforms. Accordingly, we screened a human B-cell cDNA library and isolated a larger, potentially alternatively spliced, form of AML1, termed AML1B. AML-1B is a protein of 53 kDa that binds to a consensus AML-1-binding site and complexes with CBF beta. Subcellular fractionation experiments demonstrated that both AML-1 and AML-1/ETO are efficiently extracted from the nucleus under ionic conditions but that AML-1B is localized to a salt-resistant nuclear compartment. Analysis of the transcriptional activities of AML-1, AML-1B, and AML-1/ETO demonstrated that only AML-1B activates transcription from the T-cell receptor beta enhancer. Mixing experiments indicated that AML-1/ETO can efficiently block AML-1B-dependent transcriptional activation, suggesting that the t(8;21) translocation creates a dominant interfering protein.
Meyers
S
S
Department of Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105.
Lenny
N
N
Hiebert
S W
SW
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D002451:Cell Compartmentation; D002467:Cell Nucleus / Q000737:chemistry; D003001:Cloning, Molecular; D016384:Consensus Sequence; D050676:Core Binding Factor Alpha 2 Subunit; D050660:Core Binding Factors; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000235:genetics; D005786:Gene Expression Regulation; D015470:Leukemia, Myeloid, Acute / Q000235:genetics; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D011485:Protein Binding; D011518:Proto-Oncogene Proteins; D000075142:RUNX1 Translocation Partner 1 Protein; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation
D050676:Core Binding Factor Alpha 2 Subunit; D050660:Core Binding Factors; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D000075142:RUNX1 Translocation Partner 1 Protein; C082222:RUNX1T1 protein, human; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors