CCAAT-enhancer binding protein delta functions as a tumor suppressor gene in acute myeloid leukemia

There is a continued need for identification of novel disease drivers of acute myeloid leukemia (AML) as many patients experience relapse and have poor clinical outcomes. Using genomic analyses of a study dataset of paired diagnosis and relapse specimens (n = 59), we identified recurrent downregulation of CCAAT-enhancer binding protein delta (CEBPD) expression at relapse and inferred CEBPD as one of the key regulators of gene transcription in a subset of relapse patients. Three independent public datasets validated downregulation of CEBPD expression at relapse and predicted it as a candidate tumor suppressor gene in AML. To evaluate CEBPD's tumor suppressor function, we performed complementary loss- and gain-of-function experiments in human AML cell lines OCI-AML2 and OCI-AML5. Consistent with the prediction, knockdown of CEBPD expression led to activation of MAPK signaling and upregulation of downstream effectors cyclin D1 and TNFα expression with concomitant increase in leukemic growth, while CEBPD overexpression resulted in induction of myeloid differentiation marker CD14 expression in the cell lines. Consistent with prior reports, our integrative genomic analyses and azacytidine treatment experiments further suggest a role for DNA methylation in downregulation of CEBPD expression during AML progression. Collectively, our results provide direct functional evidence for a tumor suppressor function of CEBPD in human cell lines and support prior studies implicating its epigenetic silencing in human AML.