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Blood, 15 December 2007, Vol. 110, No. 13, pp. 4445-4454. Prepublished online as a Blood First Edition Paper on September 12, 2007; DOI 10.1182/blood-2007-05-090514.
NEOPLASIA A role for the MLL fusion partner ENL in transcriptional elongation and chromatin modification1 Department of Genetics, University Erlangen, Erlangen, Germany; 2 Department of Pathology, University of Michigan Medical School, Ann Arbor; and 3 Department of Hematology and Oncology, Dr. von Haunersches Kinderspital, Munich, Germany Chimeric proteins joining the histone methyltransferase MLL with various fusion partners trigger distinctive lymphoid and myeloid leukemias. Here, we immunopurified proteins associated with ENL, a protein commonly fused to MLL. Identification of these ENL-associated proteins (EAPs) by mass spectrometry revealed enzymes with a known role in transcriptional elongation (RNA polymerase II C-terminal domain kinase [RNAPolII CTD] positive transcription elongation factor b [pTEFb]), and in chromatin modification (histone-H3 methyltransferase DOT1L) as well as other frequent MLL partners (AF4, AF5q31, and LAF4), and polycomb group members (RING1, CBX8, and BCoR). The composition of EAP was further verified by coimmunoprecipitation, 2-hybrid analysis, pull-down, and colocalization experiments. Purified EAP showed a histone H3 lysine 79–specific methylase activity, displayed a robust RNAPolII CTD kinase function, and counteracted the effect of the pTEFb inhibitor 5,6-dichloro-benzimidazole-riboside. In vivo, an ENL knock-down diminished genome-wide as well as gene-specific H3K79 dimethylation, reduced global run-on elongation, and inhibited transient transcriptional reporter activity. According to structure-function data, DOT1L recruitment was important for transformation by the MLL-ENL fusion derivative. These results suggest a function of ENL in histone modification and transcriptional elongation.
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