The Polymerase Associated Factor Complex-Protein Arginine Methyltransferase Axis: A Mechanism of Acute Leukemia

[摘要] Transcriptional and epigenetic mechanisms are pivotal to the maintenance of gene programs responsible for cellular homeostasis. Like many cancers, acute myeloid leukemia (AML) is a disease associated with transcriptional and epigenetic dysregulation. Chromosomal translocations involving the 11q23 locus harboring the H3K4 methyltransferase Mixed Lineage Leukemia 1 (MLL1), are found in AML and generate oncogenic fusion proteins with deregulated transcriptional potential. The Polymerase Associated Factor complex (PAFc) is an epigenetic co-activator complex that makes direct contact with MLL fusion proteins and wild type MLL. Disruption of this interaction impedes leukemic progression and diminishes MLL-fusion driven target gene expression. However, the role of the PAFc in AML remains incompletely understood. Conditional excision of the PAFc subunit Cdc73, relieved the differentiation block of AML cells, induced global epigenetic changes, and halted leukemic growth and cell cycling. To mechanistically assess these phenotypes, we explored the transcriptional targets regulated by the PAFc that facilitate leukemia by performing RNA-sequencing after conditional loss of Cdc73. We found Cdc73 promotes expression of an early hematopoietic progenitor gene program that prevents differentiation. Among the target genes, we confirmed the protein arginine methyltransferase (Prmt) family is broadly downregulated upon excision of Cdc73. Phenotypic analysis revealed that Prmt1, Prmt4, and Prmt5 knockdown could hinder leukemic progression in vitro. We determined that Prmt5 is a direct target that is positively regulated by a transcriptional unit that includes the PAFc, MLL1, Hoxa9, and Stat5 in leukemic cells. We observed reduced Prmt5-mediated H4R3me2s following excision of Cdc73 placing this histone modification downstream of the PAFc and revealing an epigenetic axis between the PAFc and Prmt5. Knockdown or pharmacologic inhibition of Prmt5 causes a G1 arrest and reduced proliferation resulting in extended leukemic disease latency in vivo. Notably, we observed a strong selective pressure to maintain Prmt5 in vitro and in vivo supporting its role in leukemic progression. Additionally, chemical inhibition of PRMT5 disrupted the proliferation of a range of human derived leukemic cell lines suggesting a broader relevance for a PAFc-Prmt5 axis beyond MLL-fusion AML. Overall, we demonstrate the PAFc-Prmt5 axis facilitates leukemic development and is a potential therapeutic target for AMLs.

[发布机构] University of Michigan

[效力级别] Polymerase Associated Factor Complex

[关键词] Transcriptional and Epigenetic Regulation in Leukemia;Polymerase Associated Factor Complex;Protein Arginine Methyltransferases;Molecular;Cellular and Developmental Biology;Oncology and Hematology;Pathology;Health Sciences;Science;Molecular & Cellular Pathology