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Blood, 1 November 2007, Vol. 110, No. 9, pp. 3301-3309.
Prepublished online as a Blood First Edition Paper on August 10, 2007; DOI 10.1182/blood-2007-01-071035.
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NEOPLASIA
Target proteins of C/EBP p30 in AML: C/EBP p30 enhances sumoylation of C/EBP p42 via up-regulation of Ubc9
Mulu Geletu1,
Mumtaz Y. Balkhi1,
Abdul A. Peer Zada1,
Maximilian Christopeit1,
John A. Pulikkan1,
Arun K. Trivedi1,
Daniel G. Tenen2, and
Gerhard Behre1
1 Bone Marrow Transplantation Section, State Center for Cell and Gene Therapy, Department of Internal Medicine IV–Hematology/Oncology, University Hospital of Martin-Luther-University Halle-Wittenberg, Halle, Germany;
2 Harvard Institutes of Medicine, Division of Hematology/Oncology, Boston, MA
CCAAT/enhancer-binding protein (C/EBP ) is a critical regulator for early myeloid differentiation. Mutations in C/EBP occur in 10% of patients with acute myeloid leukemia (AML), leading to the expression of a 30-kDa dominant-negative isoform (C/EBP p30). In the present study, using a global proteomics approach to identify the target proteins of C/EBP p30, we show that Ubc9, an E2-conjugating enzyme essential for sumoylation, is increased in its expression when C/EBP p30 is induced. We confirmed the increased expression of Ubc9 in patients with AML with C/EBP p30 mutations compared with other subtypes. We further confirmed that the increase of Ubc9 expression was mediated through increased transcription. Furthermore, we show that Ubc9-mediated enhanced sumoylation of C/EBP p42 decreases the transactivation capacity on a minimal C/EBP promoter. Importantly, overexpression of C/EBP p30 in granulocyte colony-stimulating factor (G-CSF)–stimulated human CD34+ cells leads to a differentiation block, which was overcome by the siRNA-mediated silencing of Ubc9. In summary, our data indicate that Ubc9 is an important C/EBP p30 target through which C/EBP p30 enhances the sumoylation of C/EBP p42 to inhibit granulocytic differentiation.

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