Role of Collaborator Proteins in HOXA9/MEIS1-Mediated Leukemogenesis.

[摘要] HOXA9 is a homeodomain-containing transcription factor that plays important roles in hematopoietic stem cell proliferation and is commonly deregulated in human acute leukemias. More than 50% of acute myeloid leukemia (AML) cases have high expression levels of HOXA9, almost always in association with high level expression of its cofactor MEIS1.In a study of gene expression in human AMLs, high expression of HOXA9 was the single most predictive marker for poor prognosis. Understanding HOXA9-mediated leukemogenesis first requires a better understanding of what confers binding specificity of HOX family proteins.In this study I functionally establish C/EBPa as a critical collaborator required for Hoxa9/Meis1-mediated leukemogenesis. I show that C/EBPa is required for the proliferation of Hoxa9/Meis1-transformed cells in culture, and that this decrease of proliferation is not accompanied by an increase in apoptosis or differentiation of cells. Using an in vivo murine leukemogenesis assay, I show that loss of C/EBPa greatly improves survival in both primary and secondary models of Hoxa9/Meis1-induced leukemia. In addition, the in vivo assay uncovered a strong selective pressure for maintaining high C/EBPa levels in Hoxa9/Meis1-transformed cells, which could be recapitulated in cell culture systems. Finally, I found a requirement for C/EBPa in HOXA9-high human acute leukemias, as cases with double mutant alleles of CEBPA do not have high expression of HOXA9. These results provide strong evidence for C/EBPa acting as a critical collaborator of HOXA9 in acute leukemia. To begin to identify the mechanism through which C/EBPa collaborates with Hoxa9 in leukemic transformation, I performed ChIP-seq for Hoxa9 and C/EBPa in our transformed cell lines and RNA-seq after loss of either protein. Over 50% of Hoxa9 genome-wide binding sites are cobound by C/EBPa, which coregulate a number of downstream target genes involved in the regulation of cell proliferation and differentiation. Specifically, I show that Hoxa9 represses expression of Cdkn2a/b in concert with C/EBPa to overcome a block in G1 cell cycle progression. Together these results suggest a novel function for C/EBPa in maintaining the proliferation required for Hoxa9/Meis1-mediated leukemogenesis.

[发布机构] University of Michigan

[效力级别] transcriptional regulation

[关键词] leukemia;transcriptional regulation;HOXA9;CEBPA;Molecular;Cellular and Developmental Biology;Oncology and Hematology;Pathology;Health Sciences;Science;Molecular and Cellular Pathology