Expression of CEBPA is reduced in RUNX1-mutated acute myeloid leukemia
Authors: V Grossmann, U Bacher, A Kohlmann, K Butschalowski, A Roller, S Jeromin, F Dicker, W Kern, S Schnittger, T Haferlach, C Haferlach
Journal: Blood Cancer Journal (2012)

CEBPA (CCAAT/enhancer-binding protein alpha) is a member of the C/EBP family of bZIP transcription factors encoding two different translational protein isoforms.The CEBPA transcription factor is involved in cell cycle arrest, repression of self-renewal and myeloid differentiation during normal hematopoiesis.In acute myeloid leukemia (AML), mutations in CEBPA result in a cellular differentiation block. 1 They occur in around 8% of normal karyotype AML (CN-AML).Approximately half of the patients harbor two CEPBA mutations associated to a favorable prognosis.CEBPA function can also be affected by promoter methylation 2 or alterations in other oncogenes, for example through the t(8;21)(q22;q22)/RUNX1-RUNX1T1, which suppresses CEBPA mRNA expression.The t(8;21)(q22;q22) translocation replaces the C terminus, including the transactivation domain (TAD) of RUNX1, with RUNX1T1. 3 RUNX1-RUNX1T1 in t(8;21) blocks CEBPAdependent activation of its own (CEBPA) promoter and thereby inhibits autoregulation. 4Other leukemic fusion proteins involving core-binding factor (CBF) family members, for example t(3;21)(q26;q22)/RUNX1-EVI1 or inv(16)(p13q22)/CBFB-MYH11, did not suppress CEBPA mRNA, indicating a RUNX1-RUNX1T1-specific effect on CEBPA transcriptional control. 1 Intragenic RUNX1 mutations confer an adverse prognosis in AML.Previously, we identified RUNX1 mutations in 32.7% of CN-AML or with non-complex chromosomal imbalances. 5RUNX1 mutations are absent in CBF-AML and acute promyelocytic leukemia. 6They are inversely correlated with CEBPA mutations. 5,6o clarify whether intragenic RUNX1 mutations such as RUNX1-RUNXT1 fusions also result in CEBPA mRNA downregulation, we investigated 359 AML patients consisting of two independent cohorts: cohort 1 with 209 AML cases (109 males/100 females; median age 65.4 years; 19.7-88.1 years) from different cytogenetic subgroups (normal karyotype (n ¼ 93), t(8;21)(q22;q22)/RUNX1-RUNX1T1 (n ¼ 16), t(15;17)(q22;q12)/PML-RARA (n ¼ 15), sole þ 8 (n ¼ 12), sole þ 13 (n ¼ 10), complex karyotypes (n ¼ 10) and other rare noncomplex genetic abnormalities (n ¼ 53)).Cohort 2 comprised 150 normal karyotype patients selected according to RUNX1 mutation status (92 males/58 females; median age, 69.7 years; 18.3-88.1 years; 81/150 (54.0%)RUNX1 mutated) with survival data in 124 cases.Bone marrow and/or peripheral blood samples were sent to the MLL Munich Leukemia Laboratory in 2005-2011.All patients gave their written informed consent to genetic analysis and scientific studies.Chromosome-banding analysis was performed in all cases, when needed, combined with fluorescent in situ hybridization.RUNX1 mutations were analyzed by Sanger sequencing or an amplicon-based high-throughput deep-sequencing assay (454 Life Sciences, Branford, CT, USA).CEBPA (mRNA) expression was quantified in cohort 1 by gene expression microarray profiling (Affymetrix HG-U133 Plus 2.0 microarrays; Santa Clara, CA, USA).The gene expression raw data were processed according to the manufacturer's recommendations.Detection calls, that is present, marginal, or absent expression, were determined by default