Novel Roles of the E2F-2 Transcription Factor and Regulation of Cyclin E in Promoting Terminal Erythroid Maturation

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E2F-2 is a Retinoblastoma (Rb)-regulated transcription factor induced during terminal erythroid maturation. Cyclin E-mediated Rb hyper-phosphorylation induces E2F transcriptional activator functions. E2F-2-loss causes reduced peripheral red blood cell (RBC) counts, without altering relative abundances of erythroblast subpopulations. To determine how E2F-2 regulates RBC production, we comprehensively studied erythropoiesis using knockout mice and hematopoietic progenitors. We found that efficient stress erythropoiesis in vivo requires E2F-2 and also identified an unappreciated role for E2F-2 in erythroblast enucleation. In particular, E2F-2 deletion impairs nuclear condensation, a morphologic feature of enucleating erythroblasts. Transcriptome profiling of E2F-2 null, mature erythroblasts demonstrated widespread changes in gene expression. Notably, we identified Citron Rho-interacting kinase (CRIK), which has known functions in mitosis and cytokinesis, as induced in erythroblasts in an E2F-2-dependent manner, and we found CRIK activity promotes efficient erythroblast enucleation and nuclear condensation. Together, our data reveal novel, lineage-specific functions for E2F-2 and suggest that some mitotic kinases have additional, specialized roles supporting enucleation of maturing erythroblasts. We previously reported that deregulated cyclin E activity causes defective terminal maturation of nucleated erythroblasts in a knock-in mouse model in which Fbw7-mediated ubiquitination and degradation is ablated. Here, we detailed the consequences of deregulating cyclin E in bone marrow erythroid cells during terminal maturation in vivo. We found that disruption of Fbw7-mediated degradation of cyclin E impairs terminal erythroid differentiation at a discrete stage before enucleation. We also found that normal regulation of cyclin E restrains accumulation of reactive oxygen species (ROS) and expression of genes that promote mitochondrial biogenesis in differentiating cells. Notably, we find maturation defects and elevated ROS associated with deregulated cyclin E is normalized by E2F-2 deletion. Finally, stabilized cyclin E and ROS accumulation induces hyper-methylation at histone 3 lysine 9, disrupting normal transcriptional components of terminal maturation. Thus, regulation of cyclin E is linked to metabolism and gene expression during terminal maturation.

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  • 02/19/2018
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