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Blood, 1 August 2007, Vol. 110, No. 3, pp. 994-1003.
Prepublished online as a Blood First Edition Paper on May 2, 2007; DOI 10.1182/blood-2007-03-078303.
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Submitted March 5, 2007
Accepted April 24, 2007
High levels of the BCR/ABL oncoprotein are required for the MAPK-hnRNP E2-dependent suppression of C/EBP -driven Myeloid Differentiation
Ji Suk Chang, Ramasamy Santhanam, Rossana Trotta, Paolo Neviani, Anna M Eiring, Edward Briercheck, Mattia Ronchetti, Denis C. Roy, Bruno Calabretta, Michael A. Caligiuri, and Danilo Perrotti*
Department of Microbiology Virology and Medical Genetics, Human Cancer Genetics Program and The Comprehensive Cancer Center, The Ohio State University, Columbus, OH, United States
Department of Microbiology and Immunology, Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, PA, United States
Division of Hematology-Immunology, Maisonneuve-Rosemont Hospital Research Center, Montreal, Canada
* Corresponding author; email: danilo.perrotti{at}osumc.edu.
The inability of myeloid chronic myelogenous leukemia blast crisis (CML-BC) progenitors to undergo neutrophil differentiation depends on suppression of C/EBP expression through the translation inhibitory activity of the RNA binding protein hnRNP E2. Here we show that "oncogene dosage" is a determinant factor for suppression of differentiation in CML-BC. In fact, high levels of p210-BCR/ABL are required for enhanced hnRNP E2 expression, which depends on phosphorylation of hnRNP E2 serines 173, 189, 272 and threonine 213 by the BCR/ABL-activated MAPKERK1/2. Serine/threonine to alanine substitution abolishes hnRNP E2 phosphorylation and markedly decreases its stability in BCR/ABL-expressing myeloid precursors. Similarly, pharmacologic inhibition of MAPKERK1/2 activity decreases hnRNP E2 binding to the 5'UTR of C/EBP mRNA by impairing hnRNP E2 phosphorylation and stability. This, in turn, restores in vitro and/or in vivo C/EBP expression and G-CSF-driven neutrophilic maturation of differentiation-arrested BCR/ABL+ cell lines, primary CML-BCCD34+ patient-cells and lineage-negative mouse bone marrow cells expressing high levels of p210-BCR/ABL. Thus, increased BCR/ABL oncogenic tyrosine kinase activity is essential for suppression of myeloid differentiation of CML-BC progenitors as it is required for sustained activation of the MAPKERK1/2-hnRNP E2-C/EBP differentiation-inhibitory pathway. Furthermore, these findings suggest the inclusion of clinically-relevant MAPK inhibitors in the therapy of CML-BC.

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