CD7 in acute myeloid leukemia: correlation with loss of wild-type CEBPA, consequence of epigenetic regulation

Background: CD7 is a negative prognostic marker in myeloid malignancies. In acute myeloid leukemia (AML), an inverse correlation exists between expression of wild-type CEBPA and CD7. Aim of this study was to find out whether C/EBP alpha is a negative regulator of CD7 and which other regulatory mechanisms might be involved. Results: As already described for primary AML cells, the majority of AML cell lines tested were either C/EBP alpha(+)/CD7(-) or C/EBP alpha(-)/CD7(+). However, the existence of isolated CD7(+) cell lines expressing wild-type C/EBP alpha challenges the notion that C/EBP alpha acts as a unique repressor of CD7. Furthermore, ectopic expression of CEBPA did not reduce CD7 in CD7(+) cells and knock-down of C/EBP alpha failed to induce CD7 in CD7(-) cells. In contrast, the DNA demethylating agent Aza-2'deoxycytidine triggered CD7 expression in CD7(-)AML and in T-cell lines suggesting epigenetic regulation of CD7. Bisulfite sequencing data confirmed that CpGs in the CD7 exon1 region are methylated in CD7- cell lines, and unmethylated in CD7(+) cell lines. Conclusion: We confirmed an inverse correlation between the expression of wild-type CEBPA and of CD7 in AML cells. Our results contradict the hypothesis that C/EBP alpha acts as repressor for CD7, and instead show that epigenetic mechanisms are responsible for CD7 regulation, in AML cells as well as in T-cells, the typical CD7 expressing cell type.