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While BTG2 plays an important role in cellular differentiation and cancer, its precise molecular function remains unclear. BTG2 interacts with CAF1 deadenylase through its APRO domain, a defining feature of BTG/Tob factors. Our previous experiments revealed that expression of BTG2 promoted mRNA poly(A) tail shortening through an undefined mechanism. Here we report that the APRO domain of BTG2 interacts directly with the first RRM domain of the poly(A)-binding protein PABPC1. Moreover, PABPC1 RRM and BTG2 APRO domains are sufficient to stimulate CAF1 deadenylase activity in vitro in the absence of other CCR4–NOT complex subunits. Our results unravel thus the mechanism by which BTG2 stimulates mRNA deadenylation, demonstrating its direct role in poly(A) tail length control. Importantly, we also show that the interaction of BTG2 with the first RRM domain of PABPC1 is required for BTG2 to control cell proliferation. BTG2 promotes mRNA poly(A) tail shortening and regulates cellular differentiation. Here, Stupfler et al . show that the BTG2 APRO domain interacts with PABPC1 RRM1, allowing the former to recruit and stimulate the poly(A) tail shortening activity of CAF1 deadenylase and to control cell proliferation.

The adipokine Leptin activates its receptor LEP-R in the hypothalamus to regulate body weight and exerts additional pleiotropic functions in immunity, fertility and cancer. However, the structure and mechanism of Leptin-mediated LEP-R assemblies has remained unclear. Intriguingly, the signaling-competent isoform of LEP-R is only lowly abundant amid several inactive short LEP-R isoforms contributing to a mechanistic conundrum. Here we show by X-ray crystallography and cryo-EM that, in contrast to long-standing paradigms, Leptin induces type I cytokine receptor assemblies featuring 3:3 stoichiometry and demonstrate such Leptin-induced trimerization of LEP-R on living cells via single-molecule microscopy. In mediating these assemblies, Leptin undergoes drastic restructuring that activates its site III for binding to the Ig domain of an adjacent LEP-R. These interactions are abolished by mutations linked to obesity. Collectively, our study provides the structural and mechanistic framework for how evolutionarily conserved Leptin:LEP-R assemblies with 3:3 stoichiometry can engage distinct LEP-R isoforms to achieve signaling. Tsirigotaki et al. unveil how adipokine Leptin induces trimerization of the Leptin receptor to form a cytokine-receptor assembly critical to body weight regulation, immunity, fertility and cancer.

Background Aging is the primary risk factor for sporadic Alzheimer’s disease (AD). While amyloid-beta oligomers (AβOs) accumulation is a key neuropathological process in AD, their specific effects in aged brains and how aging modulates brain response to AβOs remains poorly understood. We investigated how aging contributes to AβO-induced neurotoxicity and cognitive deficits in mice. Methods After biochemical and in vitro characterizations on primary cultures of cortical neurons, AβOs or their vehicle were intracerebrally injected into both 3- and 18-month-old wild-type mice. A broad spectrum of assays including synaptic markers, neuroinflammation, apoptosis and cognitive functions was used to establish a preliminary characterization of the interplay between age and AβOs. In vivo data were analyzed using a multifactorial design (Treatment × Age), with two-way ANOVA or other appropriate statistical models. Results Old mice had significantly reduced synaptic proteins SNAP-25 and PSD-95, elevated neuroinflammatory markers, and increased neuronal apoptosis in hippocampus and cortex, despite showing cognitive performances similar to young mice. All brain biomarkers were worsened after AβO injection in both young and old mice. Age and AβO effects either accumulated or interacted to promote neuroinflammation and apoptosis, depending on brain areas, whereas their effects on synaptic proteins were strictly additive. Moreover, AβO injection induced only mild spatial memory deficits in young mice, in contrast with those observed in old mice in both episodic and spatial memory tests. Discussion Whereas the young brain showed resilience to maintain memory performances after AβO injection, the coping capacities of the aging brain were exceeded by AβO effects. At the neurobiological level, age and AβO effects were mainly additive, but also acted synergistically in a brain region-dependent vulnerability pattern. This study highlights the value of incorporating aging into preclinical models to improve their translational validity and enhance their relevance for drug testing targeting early stages of sporadic AD.

Retinoid X receptors (RXRs) act as homodimers or heterodimerisation partners of class II nuclear receptors. RXR homo- and heterodimers bind direct repeats of the half-site (A/G)G(G/T)TCA separated by 1 nucleotide (DR1). We present a structural characterization of RXR-DNA binding domain (DBD) homodimers on several natural DR1s and an idealized symmetric DR1. Homodimers displayed asymmetric binding, with critical high-affinity interactions accounting for the 3′ positioning of RXR in heterodimers on DR1s. Differing half-site and spacer DNA sequence induce changes in RXR-DBD homodimer conformation notably in the dimerization interface such that natural DR1s are bound with higher affinity than an idealized symmetric DR1. Subtle changes in the consensus DR1 DNA sequence therefore specify binding affinity through altered RXR-DBD-DNA contacts and changes in DBD conformation suggesting a general model whereby preferential half-site recognition determines polarity of heterodimer binding to response elements.

Myelodysplastic syndromes (MDS) are hematological disorders associated with bone marrow failure and abnormal hematopoietic cell growth, often progressing to acute myeloid leukemia (AML). Current treatments for AML and high-risk MDS are limited in efficacy, highlighting the need for new therapies. Recent studies show ferroptosis induction, alone or with standard chemotherapy, as a promising strategy for treating MDS/AML cells. Here, we report two novel compounds, HA344 and #231, that target both ferroptosis and apoptosis pathways to effectively eradicate MDS/AML cell lines and patient-derived bone-marrow blasts. RNASeq analysis reveals oxidative stress and apoptosis as key pathways activated by these compounds in different AML cell lines. In cellulo click-chemistry experiments coupled to mass spectrometry analysis identified glutathione peroxidase 4 (GPX4) and thioredoxin reductase 1 (TXNRD1) as primary targets of both compounds, inhibiting GPX4 and TXNRD1 in the micromolar range. Mass spectrometry analysis confirms that HA344 and #231 covalently bind GPX4; with however a higher affinity for selenium-containing GPX4 (GPX4-Se) than for sulfur-containing GPX4 (GPX4-S). These findings design HA344 and #231 as potential therapeutic options for MDS/AML treatment.

hTTLL12 is a member of the tubulin tyrosine ligase (TTL) family that is highly conserved in phylogeny. It has both SET-like and TTL-like domains, suggesting that it could have histone methylation and tubulin tyrosine ligase activities. Altered expression of hTTLL12 in human cells leads to specific changes in H4K20 trimethylation, and tubulin detyrosination, hTTLL12 does not catalyse histone methylation or tubulin tyrosination in vitro, as might be expected from the lack of critical amino acids in its SET-like and TTLL-like domains. hTTLL12 misexpression increases mitotic duration and chromosome numbers. These results suggest that hTTLL12 has non-catalytic functions related to tubulin and histone modification, which could be linked to its effects on mitosis and chromosome number stability.

The human UHRF1 protein (ubiquitin-like containing PHD and RING finger domains 1) has emerged as a potential cancer target due to its implication in cell cycle regulation, maintenance of DNA methylation after replication and heterochromatin formation. UHRF1 functions as an adaptor protein that binds to histones and recruits histone modifying enzymes, like HDAC1 or G9a, which exert their action on chromatin. In this work, we show the binding specificity of the PHD finger of human UHRF1 (huUHRF1-PHD) towards unmodified histone H3 N-terminal tail using native gel electrophoresis and isothermal titration calorimetry. We report the molecular basis of this interaction by determining the crystal structure of huUHRF1-PHD in complex with the histone H3 N-terminal tail. The structure reveals a new mode of histone recognition involving an extra conserved zinc finger preceding the conventional PHD finger region. This additional zinc finger forms part of a large surface cavity that accommodates the side chain of the histone H3 lysine K4 (H3K4) regardless of its methylation state. Mutation of Q330, which specifically interacts with H3K4, to alanine has no effect on the binding, suggesting a loose interaction between huUHRF1-PHD and H3K4. On the other hand, the recognition appears to rely on histone H3R2, which fits snugly into a groove on the protein and makes tight interactions with the conserved aspartates D334 and D337. Indeed, a mutation of the former aspartate disrupts the formation of the complex, while mutating the latter decreases the binding affinity nine-fold.

Self-compartmentalizing proteases orchestrate protein turnover through an original architecture characterized by a central catalytic chamber. Here we report the first structure of an archaeal member of a new self-compartmentalizing protease family forming a cubic-shaped octamer with D(4) symmetry and referred to as CubicO. We solved the structure of the Pyrococcus abyssi Pab87 protein at 2.2 A resolution using the anomalous signal of the high-phasing-power lanthanide derivative Lu-HPDO3A. A 20 A wide channel runs through this supramolecular assembly of 0.4 MDa, giving access to a 60 A wide central chamber holding the eight active sites. Surprisingly, activity assays revealed that Pab87 degrades specifically d-amino acid containing peptides, which have never been observed in archaea. Genomic context of the Pab87 gene showed that it is surrounded by genes involved in the amino acid/peptide transport or metabolism. We propose that CubicO proteases are involved in the processing of d-peptides from environmental origins.

Translationally Controlled Tumor Protein (TCTP) is anti-apoptotic, key in development and cancer, however without the typical Bcl2 family members’ structure. Here we report that TCTP contains a BH3-like domain and forms heterocomplexes with Bcl-xL. The crystal structure of a Bcl-xL deletion variant-TCTP 11–31 complex reveals that TCTP refolds in a helical conformation upon binding the BH3-groove of Bcl-xL, although lacking the h1 -subregion interaction. Experiments using in vitro-vivo reconstituted systems and TCTP +/− mice indicate that TCTP activates the anti-apoptotic function of Bcl-xL, in contrast to all other BH3-proteins. Replacing the non-conserved h1 of TCTP by that of Bax drastically increases the affinity of this hybrid for Bcl-xL, modifying its biological properties. This work reveals a novel class of BH3-proteins potentiating the anti-apoptotic function of Bcl-xL.