AML1–ETO downregulates the granulocytic differentiation factor C/EBPα in t(8;21) myeloid leukemia

Abstract

The transcription factor CCAAT/enhancer binding protein alpha, or C/EBPalpha, encoded by the CEBPA gene, is crucial for the differentiation of granulocytes. Conditional expression of C/EBPalpha triggers neutrophilic differentiation, and Cebpa knockout mice exhibit an early block in maturation. Dominant-negative mutations of CEBPA have been found in some patients with acute myeloid leukemia (AML), but not in AML with the t(8;21) translocation which gives rise to the fusion gene RUNX1-CBF2T1 (also known as AML1-ETO) encoding the AML1-ETO fusion protein. RUNX1-CBF2T1 positive-AML blasts had eight-fold lower CEBPA RNA levels and undetectable C/EBPalpha protein levels compared with other subgroups of AML patients. Conditional expression of RUNX1-CBF2T1 in U937 cells downregulated CEBPA mRNA, protein and DNA binding activity. AML1-ETO appears to suppress C/EBPalpha expression indirectly by inhibiting positive autoregulation of the CEBPA promoter. Conditional expression of C/EBPalpha in AML1-ETO-positive Kasumi-1 cells results in neutrophilic differentiation. We suggest that restoring C/EBPalpha expression will have therapeutic implications in RUNX1-CBF2T1-positive leukemias.

ELA2 is regulated by hematopoietic transcription factors, but not repressed by AML1-ETO

“…The same observation is made when AML1-ETO is inducibly expressed in U937 cells. Although it need not be true that AML1-ETO suppresses gene expression of every gene at which it may find a promoter-binding site, our observations are not in line with the expectation that AML1-ETO acts predominantly as a transcriptional repressor, particularly at a gene that is also regulated by C/EBPa Pabst et al, 2001).…”

“…For one of these factors, C/EBPa, coassociation with AML1-ETO suppresses its own expression and that of C/EBPa target genes Pabst et al, 2001). We observed that AML1-ETO does repress expression of C/EBPa in both Kasumi-1 and U937 cells, …”

“…AML1-ETO interacts with C/EBPa and PU.1 (Zhang et al, 1996;Petrovick et al, 1998;Westendorf et al, 1998;Pabst et al, 2001), two transcription factors implicated in the regulation of hELA2 expression. For one of these factors, C/EBPa, coassociation with AML1-ETO suppresses its own expression and that of C/EBPa target genes Pabst et al, 2001).…”

“…Figure 5b illustrates that effective reduction of AML1-ETO expression in Kasumi-1 cells can be achieved within 48 h. This results in only a modest increase in hELA2 levels (Figure 5c). AML1-ETO has also been implicated in suppressing expression of C/EBPa (Zhang et al, 1996;Petrovick et al, 1998;Westendorf et al, 1998;Pabst et al, 2001), which in turn could suppress expression of hELA2 in Kasumi-1 cells. Real-time PCR and Western blot readily detect C/EBPa transcripts and protein in Kasumi-1 nuclear protein extracts (Figures 3a and 5d), in contrast to an earlier report .…”

Immunohistochemical analysis of C/EBPα in non-small cell lung cancer reveals frequent down-regulation in stage II and IIIA tumors: A correlative study of E3590

“…The association of C/ EBPα and cancer has been elucidated in acute myeloid leukemia (AML) (19), where C/ EBPα expression is reduced in leukemias carrying the t(8;21) translocation (20) and C/ EBPα mutations confer improved prognosis in a small subgroup of AML patients with normal cytogenetics (21,22). In epithelial tissues, C/EBPα is expressed in the breast, colon, prostate, and the respiratory epithelium (23).…”