E2F-2 Promotes Nuclear Condensation and Enucleation of Terminally Differentiated Erythroblasts.

E2F-2 is a retinoblastoma (Rb)-regulated transcription factor induced during terminal erythroid maturation. Cyclin E-mediated Rb hyperphosphorylation induces E2F transcriptional activator functions. We previously reported that deregulated cyclin E activity causes defective terminal maturation of nucleated erythroblasts in vivo Here, we found that these defects are normalized by E2F-2 deletion; however, anemia in mice with deregulated cyclin E is not improved by E2F-2-loss, which itself 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 we also identified an unappreciated role for E2F-2 in erythroblast enucleation. In particular, E2F-2 deletion impairs nuclear condensation, a morphological feature of maturing 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 that 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 specialized roles supporting enucleation of maturing erythroblasts.

Chromosome instability underlies hematopoietic stem cell dysfunction and lymphoid neoplasia associated with impaired Fbw7-mediated cyclin E regulation.

The Fbw7 ubiquitin ligase critically regulates hematopoietic stem cell (HSC) function, though the precise contribution of individual substrate ubiquitination pathways to HSC homeostasis is unknown. In the work reported here, we used a mouse model in which we introduced two knock-in mutations (T74A and T393A [changes of T to A at positions 74 and 393]) to disrupt Fbw7-dependent regulation of cyclin E, its prototypic substrate, and to examine the consequences of cyclin E dysregulation for HSC function. Serial transplantation revealed that cyclin E(T74A T393A) HSCs self-renewed normally; however, we identified defects in their multilineage reconstituting capacity. By inducing hematologic stress, we exposed an impaired self-renewal phenotype in cyclin E knock-in HSCs that was associated with defective cell cycle exit and the emergence of chromosome instability (CIN). Importantly, p53 deletion induced both defects in self-renewal and multilineage reconstitution in cyclin E knock-in HSCs with serial transplantation and CIN in hematopoietic stem and progenitor cells. Moreover, CIN was a feature of fatal T-cell malignancies that ultimately developed in recipients of cyclin E(T74A T393A); p53-null HSCs. Together, our findings demonstrate the importance of Fbw7-dependent cyclin E control to the hematopoietic system and highlight CIN as a characteristic feature of HSC dysfunction and malignancy induced by deregulated cyclin E.

Inhibition of allergic inflammation by supplementation with 5-hydroxytryptophan.

Clinical reports indicate that patients with allergy/asthma commonly have associated symptoms of anxiety/depression. Anxiety/depression can be reduced by 5-hydroxytryptophan (5-HTP) supplementation. However, it is not known whether 5-HTP reduces allergic inflammation. Therefore, we determined whether 5-HTP supplementation reduces allergic inflammation. We also determined whether 5-HTP decreases passage of leukocytes through the endothelial barrier by regulating endothelial cell function. For these studies, C57BL/6 mice were supplemented with 5-HTP, treated with ovalbumin fraction V (OVA), house dust mite (HDM) extract, or IL-4, and examined for allergic lung inflammation and OVA-induced airway responsiveness. To determine whether 5-HTP reduces leukocyte or eosinophil transendothelial migration, endothelial cells were pretreated with 5-HTP, washed and then used in an in vitro transendothelial migration assay under laminar flow. Interestingly, 5-HTP reduced allergic lung inflammation by 70-90% and reduced antigen-induced airway responsiveness without affecting body weight, blood eosinophils, cytokines, or chemokines. 5-HTP reduced allergen-induced transglutaminase 2 (TG2) expression and serotonylation (serotonin conjugation to proteins) in lung endothelial cells. Consistent with the regulation of endothelial serotonylation in vivo, in vitro pretreatment of endothelial cells with 5-HTP reduced TNF-α-induced endothelial cell serotonylation and reduced leukocyte transendothelial migration. Furthermore, eosinophil and leukocyte transendothelial migration was reduced by inhibitors of transglutaminase and by inhibition of endothelial cell serotonin synthesis, suggesting that endothelial cell serotonylation is key for leukocyte transendothelial migration. In summary, 5-HTP supplementation inhibits endothelial serotonylation, leukocyte recruitment, and allergic inflammation. These data identify novel potential targets for intervention in allergy/asthma.