ECSASB2 mediates MLL degradation during hematopoietic differentiation.

Department of Pathology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Mixed lineage leukemia (MLL) is a key epigenetic regulator of normal hematopoietic development and chromosomal translocations involving MLL are one of the most common genetic alterations in human leukemia. Here we show that ASB2, a component of the ECS(ASB) E3 ubiquitin ligase complex, mediates MLL degradation through interaction with the PHD/Bromodomain region of MLL. Forced expression of ASB2 degrades MLL and reduces MLL transactivation activity. In contrast, the MLL-AF9 fusion protein does not interact with ASB2 and is resistant to ASB2 mediated degradation. Increased expression of ASB2 during hematopoietic differentiation is associated with decreased levels of MLL protein and down-regulation of MLL target genes. Knockdown of ASB2 leads to increased expression of HOXA9 and delayed cell differentiation. Our data support a model whereby ASB2 contributes to hematopoietic differentiation, in part, through MLL degradation and HOX gene down-regulation. Moreover, deletion of the PHD/Bromo region renders MLL fusion proteins resistant to ASB2-mediated degradation and may contribute to leukemogenesis.
Mesh Terms:
Cell Differentiation, Cells, Cultured, Cullin Proteins, HEK293 Cells, Hematopoiesis, Hematopoietic Stem Cells, Humans, K562 Cells, Leukemia, Multiprotein Complexes, Myeloid-Lymphoid Leukemia Protein, Protein Processing, Post-Translational, Proteolysis, SKP Cullin F-Box Protein Ligases, Suppressor of Cytokine Signaling Proteins, Transcription Factors, Transfection
Blood Feb. 02, 2012; 119(5);1151-61 [PUBMED:22174154]
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