Explore the vast range of titles available.

The transcriptional control of lineage commitment to various ILC subsets is incompletely understood. Yokoyama and colleagues show that Runx3 is essential for the normal development of ILC1 and ILC3 cells but not ILC2 cells. Subsets of innate lymphoid cells (ILCs) reside in the mucosa and regulate immune responses to external pathogens. While ILCs can be phenotypically classified into ILC1, ILC2 and ILC3 subsets, the transcriptional control of commitment to each ILC lineage is incompletely understood. Here we report that the transcription factor Runx3 was essential for the normal development of ILC1 and ILC3 cells but not of ILC2 cells. Runx3 controlled the survival of ILC1 cells but not of ILC3 cells. Runx3 was required for expression of the transcription factor RORγt and its downstream target, the transcription factor AHR, in ILC3 cells. The absence of Runx3 in ILCs exacerbated infection with Citrobacter rodentium . Therefore, our data establish Runx3 as a key transcription factor in the lineage-specific differentiation of ILC1 and ILC3 cells.

The transcription factor IRF8 is essential for the development of monocytes and dendritic cells (DCs), whereas it inhibits neutrophilic differentiation. It is unclear how Irf8 expression is regulated and how this single transcription factor supports the generation of both monocytes and DCs. Here, we identified a RUNX–CBFβ-driven enhancer 56 kb downstream of the Irf8 transcription start site. Deletion of this enhancer in vivo significantly decreased Irf8 expression throughout the myeloid lineage from the progenitor stages, thus resulting in loss of common DC progenitors and overproduction of Ly6C + monocytes. We demonstrated that high, low or null expression of IRF8 in hematopoietic progenitor cells promotes differentiation toward type 1 conventional DCs, Ly6C + monocytes or neutrophils, respectively, via epigenetic regulation of distinct sets of enhancers in cooperation with other transcription factors. Our results illustrate the mechanism through which IRF8 controls the lineage choice in a dose-dependent manner within the myeloid cell system. The transcription factor IRF8 is required for both DC and monocyte differentiation from common myeloid progenitors. Tamura and colleagues identify an enhancer (+56 kb) in the Irf8 locus that regulates early myeloid lineage choice.

The mechanism underlying how transcription factors regulate mesenchymal stem cell lineage commitment remains unclear. To determine the role of core-binding factor subunit beta (Cbfβ) in osteoblast lineage commitment, we generated three mouse models by deleting Cbfβ at different osteoblast lineage stages. We demonstrated that the Cbfβf/fPrx1-Cre, Cbfβf/fCol2α1-Cre, and Cbfβf/fOsx-Cre mice exhibited severe osteoporosis with substantial accumulation of marrow adipocytes resembling aged bone from enhanced adipogenesis, indicating that mesenchymal stem cells and osteoblasts can be programed and reprogramed, respectively, into adipocytes. Consistently, Cbfβ-deficient calvarial cells and bone marrow mesenchymal stem cells displayed strong adipogenic potential, with 5- to ∼70-fold increased adipocyte gene expression, which can be rescued by Cbfβ overexpression. Canonical Wnt signaling was impeded in the Cbfβ-deficient cells, with ∼80% decrease of Wnt10b expression. Accordingly, ChIP and luciferase assays demonstrated that Cbfβ/RUNX2 binds to Wnt10b promoter driving Wnt10b expression. Furthermore, Wnt3a suppressed adipogenesis but did not rescue osteoblastogenesis in Cbfβ-deficient cells. Notably, mixing culture of Cbfβ-deficient with normal cells demonstrates that Cbfβ functions not only through WNT paracrine pathway but also through endogenous signaling. Further analysis shows that Cbfβ/RUNX2 inhibits c/ebpα expression at transcriptional level. Our results show that, besides its osteogenic role, Cbfβ governs osteoblast–adipocyte lineage commitment both cell nonautonomously through enhancing β-catenin signaling and cell autonomously through suppressing adipogenesis gene expression to maintain osteoblast lineage commitment, indicating Cbfβ may be a therapeutic target for osteoporosis.

CBF-β is shown to regulate the ability of HIV-1 to evade host restriction mediated by the deaminase APOBEC3. Vif–CBF-β interaction an anti-HIV-1 target The transcription cofactor CBF-β (core binding factor β) regulates the DNA binding activity of RUNX family proteins. Two independent studies now show that CBF-β also regulates the ability of HIV-1 to evade host restriction mediated by the cDNA deaminase APOBEC3G, a host factor that blocks viral replication. They show that it associates with the HIV protein Vif, and is essential for the assembly of the Vif-Cul5 E3 ubiquitin ligase complex, which mediates the ubiquitination and destruction of APOBEC3. Both groups suggest that disrupting the Vif–CBF-β interaction could provide a new therapeutic target against HIV-1 infection. The human APOBEC3 cytidine deaminases are potent inhibitors of diverse retroviruses, including human immunodeficiency virus-1 (HIV-1) 1 , 2 , 3 , 4 , 5 , 6 . HIV-1 Vif forms an E3 ubiquitin ligase complex with cullin 5 (CUL5), elongin B and elongin C 7 , 8 , 9 , which promotes the polyubiquitination and degradation of APOBEC3 substrates 7 , 10 , 11 , 12 , 13 , 14 . Here we demonstrate in human T cells that core binding factor β (CBF-β) is a key regulator of the evasion of HIV-1 from the host defence mediated by APOBEC3. CBF-β, the non-DNA-binding subunit of a heterodimeric transcription factor, regulates the folding and DNA-binding activity of partner RUNX family proteins, which have important roles in the development and differentiation of diverse cell types, including T lymphocytes 15 , 16 . In our study, knockdown of endogenous CBF-β blocked Vif-induced APOBEC3G polyubiquitination and degradation. CBF-β was not required for the interaction between Vif and APOBEC3G, yet was essential for the assembly of the Vif–CUL5 E3-ubiquitin-ligase complex. CBF-β proved to be a unique regulator of primate lentiviral Vif and not a general component of the CUL5 E3 ubiquitin ligase. We show that Vif and CBF-β physically interact, and that the amino-terminal region of Vif is required for this interaction. Furthermore, interactions with Vif required regions in CBF-β that are not involved in RUNX protein binding 17 , 18 , 19 . Considering the importance of the interaction between Vif and CBF-β, disrupting this interaction represents an attractive pharmacological intervention against HIV-1.

This study provides a crystal structure of the Vif–CBF-β–CUL5–ELOB–ELOC complex, which shows that Vif mimics the action of SOCS2 to interact with CUL5 and ELOC. Mechanism of action of HIV-1 Vif protein During infection with human immunodeficiency virus 1 (HIV-1), the viral protein Vif subverts the activity of antiviral host factors by hijacking the core-binding factor subunit beta (CBF-β) and the E3 ligase complex CUL5–ELOB–ELOC simultaneously. How it does this has been unclear. Zhiwei Huang and colleagues have now determined the crystal structure of the Vif–CBF-β–CUL5–ELOB–ELOC complex. They find that Vif mimics the action of SOCS2 to interact with CUL5 and ELOC. Vif protein is absolutely required for HIV-1 replication, making it an important target for antiviral drug development, and the mechanistic details reported here should contribute to the design of novel drugs that can target both Vif and the pentameric complex. The human immunodeficiency virus (HIV)-1 protein Vif has a central role in the neutralization of host innate defences by hijacking cellular proteasomal degradation pathways to subvert the antiviral activity of host restriction factors 1 , 2 , 3 , 4 , 5 , 6 ; however, the underlying mechanism by which Vif achieves this remains unclear. Here we report a crystal structure of the Vif–CBF-β–CUL5–ELOB–ELOC complex. The structure reveals that Vif, by means of two domains, organizes formation of the pentameric complex by interacting with CBF-β, CUL5 and ELOC. The larger domain (α/β domain) of Vif binds to the same side of CBF-β as RUNX1, indicating that Vif and RUNX1 are exclusive for CBF-β binding. Interactions of the smaller domain (α-domain) of Vif with ELOC and CUL5 are cooperative and mimic those of SOCS2 with the latter two proteins. A unique zinc-finger motif of Vif, which is located between the two Vif domains, makes no contacts with the other proteins but stabilizes the conformation of the α-domain, which may be important for Vif–CUL5 interaction. Together, our data reveal the structural basis for Vif hijacking of the CBF-β and CUL5 E3 ligase complex, laying a foundation for rational design of novel anti-HIV drugs.

The leukemia fusion gene CBFB-MYH11 requires RUNX1 for leukemogenesis, but the underlying mechanism is unclear. By in vitro studies, we found that CBFβ-SMMHC, the chimeric protein encoded by CBFB-MYH11, could enhance the binding affinity between RUNX1 and its target DNA. Increased RUNX1-DNA binding was also observed in myeloid progenitor cells from mice expressing CBFβ-SMMHC. Moreover, only CBFβ-SMMHC variants able to enhance the DNA binding affinity by RUNX1 could induce leukemia in mouse models. Marked transcriptomic changes, affecting genes associated with inflammatory response and target genes of CBFA2T3, were observed in mice expressing leukemogenic CBFβ-SMMHC variants. Finally, we show that CBFβ-SMMHC could not induce leukemia in mice with a Runx1-R188Q mutation, which reduces RUNX1 DNA binding but does not affect its interaction with CBFβ-SMMHC or its sequestration to cytoplasm by CBFβ-SMMHC. Our data suggest that, in addition to binding RUNX1 to regulate gene expression, enhancing RUNX1 binding affinity to its target DNA is an important mechanism by which CBFβ-SMMHC contributes to leukemogenesis, highlighting RUNX1-DNA interaction as a potential therapeutic target in inv(16) acute myeloid leukemia.

Osteoarthritis (OA) is a degenerative joint disease that involves the destruction of articular cartilage and eventually leads to disability. Molecules that promote the selective differentiation of multipotent mesenchymal stem cells (MSCs) into chondrocytes may stimulate the repair of damaged cartilage. Using an image-based high-throughput screen, we identified the small molecule kartogenin, which promotes chondrocyte differentiation (median effective concentration = 100 nM), shows chondroprotective effects in vitro, and is efficacious in two OA animal models. Kartogenin binds filamin A, disrupts its interaction with the transcription factor core-binding factor β subunit (CBFβ), and induces chondrogenesis by regulating the CBFβ-RUNX1 transcriptional program. This work provides new insights into the control of chondrogenesis that may ultimately lead to a stem cell— based therapy for osteoarthritis.

RUNX1 is generally considered a tumor suppressor in myeloid neoplasms. Inactivating RUNX1 mutations have frequently been found in patients with myelodysplastic syndrome (MDS) and cytogenetically normal acute myeloid leukemia (AML). However, no somatic RUNX1 alteration was found in AMLs with leukemogenic fusion proteins, such as core-binding factor (CBF) leukemia and MLL fusion leukemia, raising the possibility that RUNX1 could actually promote the growth of these leukemia cells. Using normal human cord blood cells and those expressing leukemogenic fusion proteins, we discovered a dual role of RUNX1 in myeloid leukemogenesis. RUNX1 overexpression inhibited the growth of normal cord blood cells by inducing myeloid differentiation, whereas a certain level of RUNX1 activity was required for the growth of AML1-ETO and MLL-AF9 cells. Using a mouse genetic model, we also showed that the combined loss of Runx1/Cbfb inhibited leukemia development induced by MLL-AF9. RUNX2 could compensate for the loss of RUNX1. The survival effect of RUNX1 was mediated by BCL2 in MLL fusion leukemia. Our study unveiled an unexpected prosurvival role for RUNX1 in myeloid leukemogenesis. Inhibiting RUNX1 activity rather than enhancing it could be a promising therapeutic strategy for AMLs with leukemogenic fusion proteins.

Translation and transcription are frequently dysregulated in cancer. These two processes are generally regulated by distinct sets of factors. The CBFB gene, which encodes a transcription factor, has recently emerged as a highly mutated driver in a variety of human cancers including breast cancer. Here we report a noncanonical role of CBFB in translation regulation. RNA immunoprecipitation followed by deep sequencing (RIP-seq) reveals that cytoplasmic CBFB binds to hundreds of transcripts and regulates their translation. CBFB binds to mRNAs via hnRNPK and enhances translation through eIF4B, a general translation initiation factor. Interestingly, the RUNX1 mRNA, which encodes the transcriptional partner of CBFB, is bound and translationally regulated by CBFB. Furthermore, nuclear CBFB/RUNX1 complex transcriptionally represses the oncogenic NOTCH signaling pathway in breast cancer. Thus, our data reveal an unexpected function of CBFB in translation regulation and propose that breast cancer cells evade translation and transcription surveillance simultaneously through downregulating CBFB. CBFB is highly mutated in breast cancers and is known to interact with RUNX proteins to regulate transcription. Here, the authors describe a non-canonical role of CBFB in translation regulation in which it binds to mRNAs through hnRNPK, facilitating translation by eIF4B.

HIV-1 Vif recruits host cullin-RING-E3 ubiquitin ligase and CBFβ to degrade the cellular APOBEC3 antiviral proteins through diverse interactions. Recent evidence has shown that Vif also degrades the regulatory subunits PPP2R5(A–E) of cellular protein phosphatase 2A to induce G2/M cell cycle arrest. As PPP2R5 proteins bear no functional or structural resemblance to A3s, it is unclear how Vif can recognize different sets of proteins. Here we report the cryogenic-electron microscopy structure of PPP2R5A in complex with HIV-1 Vif–CBFβ–elongin B–elongin C at 3.58 Å resolution. The structure shows PPP2R5A binds across the Vif molecule, with biochemical and cellular studies confirming a distinct Vif–PPP2R5A interface that partially overlaps with those for A3s. Vif also blocks a canonical PPP2R5A substrate-binding site, indicating that it suppresses the phosphatase activities through both degradation-dependent and degradation-independent mechanisms. Our work identifies critical Vif motifs regulating the recognition of diverse A3 and PPP2R5A substrates, whereby disruption of these host–virus protein interactions could serve as potential targets for HIV-1 therapeutics. The authors solve a cryo-EM structure of the regulatory subunit of human protein phosphatase 2A in complex with HIV-1 Vif-containing E3 ligase, leading to improvement of our understanding of host–virus protein interactions.