11q23 translocations split the "AT-hook" cruciform DNA-binding region and the transcriptional repression domain from the activation domain of the mixed-lineage leukemia (MLL) gene.
Translocations involving chromosome band 11q23, found in acute lymphoid and myeloid leukemias, disrupt the MLL gene. This gene encodes a putative transcription factor with homology to the zinc fingers and other domains of the Drosophila trithorax gene product and to the "AT-hook" motif of high mobility group proteins. To map potential transcriptional activation or repression domains of the MLL protein, yeast GAL4 DNA-binding domain and MLL hybrid protein-expressing plasmids were cotransfected with chloramphenicol acetyltransferase reporter plasmids in a transient transfection system. We found that MLL contains a strong activation domain and a repression domain. The former, located telomeric (3') to the breakpoint region, activated transcription 18-fold to > 200-fold, depending on the promoter and cell line used for transfection. A repression domain that repressed transcription 4-fold was located centromeric (5') to the breakpoint region of MLL. The MLL AT-hook domain protein was expressed in bacteria and was utilized in a gel mobility shift assay to assess DNA-binding activity. The MLL AT-hook domain could bind cruciform DNA, recognizing structure rather than sequence of the target DNA. In translocations involving MLL, loss of an activation domain with retention of a repression domain and a DNA-binding domain on the der(11) chromosome could alter the expression of downstream target genes, suggesting a potential mechanism of action for MLL in leukemia.
Zeleznik-Le
N J
NJ
Department of Medicine, University of Chicago, IL 60637.
Harden
A M
AM
Rowley
J D
JD
D000818:Animals; D001665:Binding Sites; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis; D002874:Chromosome Mapping; D002880:Chromosomes, Human, Pair 11; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D004330:Drosophila / Q000235:genetics; D017353:Gene Deletion; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic; D017344:Genes, Insect; D006367:HeLa Cells; D011495:Histone-Lysine N-Methyltransferase; D006801:Humans; D015456:Leukemia, Biphenotypic, Acute / Q000235:genetics*; D016296:Mutagenesis; D051788:Myeloid-Lymphoid Leukemia Protein; D011519:Proto-Oncogenes; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D014157:Transcription Factors; D014158:Transcription, Genetic; D014162:Transfection; D014178:Translocation, Genetic; D016335:Zinc Fingers
D004268:DNA-Binding Proteins; C497422:KMT2A protein, human; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D051788:Myeloid-Lymphoid Leukemia Protein; D004247:DNA; D011495:Histone-Lysine N-Methyltransferase; D015500:Chloramphenicol O-Acetyltransferase