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Updated: Aug 18, 2026
Proliferation and Differentiation of Murine Myeloid Precursor 32D/G-CSF-R Cells
Published on: February 21, 2018
CBFB-SMMHC is correlated with increased calreticulin expression and suppresses the granulocytic differentiation
Daniel Helbling1, Beatrice U Mueller, Nikolai A Timchenko
1Department of Clinical Research, University Hospital, Berne, Switzerland.
Abstract:
The pericentric inversion of chromosome 16, inv(16)(p13q22), is associated with acute myeloid leukemia (AML) subtype M4Eo that is characterized by the presence of myelomonocytic blasts and atypical eosinophils. This rearrangement fuses the CBFB and MYH11 genes, with the latter encoding the smooth muscle myosin heavy chain (SMMHC). The myeloid transcription factor CCAAT/enhancer-binding protein alpha (CEBPA) is crucial for normal granulopoiesis. Alterations of structure and expression of CEBPA have been implicated in particular subtypes of AML. Here, we found that conditional expression of core-binding factor beta (CBFB)-SMMHC in U937 cells suppresses CEBPA protein expression and binding activity. However, CEBPA mRNA levels remained unchanged. No differences were detected in CEBPA mRNA levels in patients with inv(16) AML-M4Eo (n = 12) compared to patients with AML with a normal karyotype and M4 subtype (n = 6), whereas CEBPA protein and binding activity were significantly reduced in patients with CBFB-SMMHC. Furthermore, calreticulin, an inhibitor of CEBPA translation, was induced on mRNA and protein level in CBFB-SMMHC patients with AML and after expression of CBFB-SMMHC in the U937-cell system. Inhibition of calreticulin by siRNA restored CEBPA levels. Our results suggest that modulation of CEBPA by calreticulin represents a novel mechanism involved in the differentiation block in CBFB-SMMHC AML.
Insights
The CBFB-MYH11 fusion protein in acute myeloid leukemia (AML) reduces CCAAT/enhancer-binding protein alpha (CEBPA) activity by increasing calreticulin. This mechanism explains the differentiation block in inv(16) AML.
Area of Science:
- Hematology
- Molecular Biology
- Cancer Genetics
Background:
- Acute myeloid leukemia (AML) with inv(16)(p13q22) involves the CBFB-MYH11 fusion gene.
- CCAAT/enhancer-binding protein alpha (CEBPA) is vital for granulopoiesis, and its dysfunction is implicated in AML subtypes.
- The CBFB-MYH11 fusion protein's effect on CEBPA in AML remains unclear.
Purpose of the Study:
- To investigate the impact of the CBFB-MYH11 fusion protein on CEBPA expression and activity.
- To elucidate the role of calreticulin in the CBFB-MYH11-mediated AML pathogenesis.
Main Methods:
- Conditional expression of CBFB-SMMHC in U937 cells.
- Analysis of CEBPA mRNA and protein levels and DNA binding activity.
- Measurement of calreticulin expression in patient samples and cell lines.
- siRNA-mediated inhibition of calreticulin.
Main Results:
- CBFB-SMMHC suppressed CEBPA protein expression and binding activity without altering mRNA levels.
- CEBPA protein and binding activity were significantly reduced in inv(16) AML patients.
- Calreticulin was upregulated at both mRNA and protein levels in CBFB-SMMHC-expressing cells and patients.
- Calreticulin inhibition restored CEBPA levels.
Conclusions:
- CBFB-SMMHC fusion protein downregulates CEBPA activity via calreticulin-mediated translational inhibition.
- Calreticulin plays a key role in the differentiation block observed in CBFB-SMMHC-driven AML.
- Targeting calreticulin may offer a therapeutic strategy for inv(16) AML.
