1. ¹Section of Molecular Hematology and Therapy, Department of Blood and Marrow Transplantation, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
2. ²Department of Clinical Pathology, Juntendo University School of Medicine, Tokyo, Japan
3. ³Section of Bioinformatics, Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
4. ⁴Division of Cell Signaling, Institute of Molecular Medicine, The University of Texas Health Science Center, Houston, TX, USA
5. ⁵Department of Medicine, Division of Hematology/Oncology, Mount Sinai School of Medicine, New York, NY, USA
6. ⁶Department of Biochemistry, Juntendo University School of Medicine, Tokyo, Japan
7. ⁷Department of Transfusion Medicine and Stem Cell Regulation, Juntendo University School of Medicine, Tokyo, Japan

Correspondence: M Konopleva, Department of Blood and Marrow Transplantation, Unit 448, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. Tel: +713 794 1628; Fax: +713 794 4747; E-mail: mkonople@mdanderson.org

Received 18 July 2006; Revised 13 February 2007; Accepted 15 February 2007; Published online 27 April 2007.

Abstract

The chimeric fusion protein AML1-ETO, created by the t(8;21) translocation, recruits histone deacetylase (HDAC) to AML1-dependent promoters, resulting in transcriptional repression of the target genes. We analyzed the transcriptional changes in t(8;21) Kasumi-1 AML cells in response to the HDAC inhibitors, depsipeptide (FK228) and suberoylanilide hydroxamic acid (SAHA), which induced marked growth inhibition and apoptosis. Using cDNA array, annexin A1 (ANXA1) was identified as one of the FK228-induced genes. Induction of ANXA1 mRNA was associated with histone acetylation in ANXA1 promoter and reversal of the HDAC-dependent suppression of C/EBP by AML1-ETO with direct recruitment of C/EBP to ANXA1 promoter. This led to increase in the N-terminal cleaved isoform of ANXA1 protein and accumulation of ANXA1 on cell membrane. Neutralization with anti-ANXA1 antibody or gene silencing with ANXA1 siRNA inhibited FK228-induced apoptosis, suggesting that the upregulation of endogenous ANXA1 promotes cell death. FK228-induced ANXA1 expression was associated with massive increase in cell attachment and engulfment of Kasumi-1 cells by human THP-1-derived macrophages, which was completely abrogated with ANXA1 knockdown via siRNA transfection or ANXA1 neutralization. These findings identify a novel mechanism of action of HDAC inhibitors, which induce the expression and externalization of ANXA1 in leukemic cells, which in turn mediates the phagocytic clearance of apoptotic cells by macrophages.