The leukemic fusion gene AML1-MDS1-EVI1 suppresses CEBPA in acute myeloid leukemia by activation of Calreticulin.
The leukemic fusion gene AML1-MDS1-EVI1 (AME) encodes a chimeric transcription factor that results from the t(3,21)(q26;q22) translocation seen in patients with acute myeloid leukemia, with therapy-related myelodysplastic syndrome, or with chronic myeloid leukemia in blast crisis. The myeloid transcription factor CEBPA is crucial for normal granulopoiesis. Here, we found that conditional expression of AME suppresses CEBPA protein by 90.8% and DNA-binding activity by 93.9%. In contrast, CEBPA mRNA levels remained unchanged. In addition, we detected no differences in CEBPA mRNA levels in leukemic blasts of patients carrying the AME translocation (n = 8) compared to acute myeloid leukemia patients with a normal karyotype (n = 9). CEBPA protein and binding activity, however, were reduced significantly (100% and 92.1%, respectively) in AME patient samples. Furthermore, we observed that calreticulin (CRT), a putative inhibitor of CEBPA translation, was strongly activated after induction of AME in the cell-line system (14.8-fold) and in AME patient samples (12.2-fold). Moreover, inhibition of CRT by small interfering RNA powerfully restored CEBPA levels. These results identify CEBPA as a key target of the leukemic fusion protein AME and suggest that modulation of CEBPA by CRT may represent a mechanism involved in the differentiation block in AME leukemias.
Institute of Medical Oncology, University Hospital, CH-3010 Bern, Switzerland.
Daniel
D
Helbling
Beatrice U
BU
Mueller
Nikolai A
NA
Timchenko
Anne
A
Hagemeijer
Martine
M
Jotterand
Sandrine
S
Meyer-Monard
Andrew
A
Lister
Janet D
JD
Rowley
Barbara
B
Huegli
Martin F
MF
Fey
Thomas
T
Pabst
D000328:Adult; D000368:Aged; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics / Q000502:physiology*; D037282:Calreticulin / Q000502:physiology*; D050676:Core Binding Factor Alpha 2 Subunit; D005260:Female; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000235:genetics* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D015514:Oncogene Proteins, Fusion / Q000235:genetics*; D034741:RNA, Small Interfering / Q000494:pharmacology; D012097:Repressor Proteins / Q000235:genetics*; D014178:Translocation, Genetic; D020298:U937 Cells
C460199:AML1-MDS1-EVI1 fusion protein, human; D022763:CCAAT-Enhancer-Binding Protein-alpha; D037282:Calreticulin; D050676:Core Binding Factor Alpha 2 Subunit; D015514:Oncogene Proteins, Fusion; D034741:RNA, Small Interfering; D012097:Repressor Proteins