Natural killer (NK) cells are central to antitumor immunity but rapidly lose function in the tumor microenvironment (TME). Here, we identify CD55, previously recognized as a complement regulatory protein, as an inducible membrane organizer that coordinates activating receptor signaling to potentiate NK cell-mediated antitumor responses. Upon initial tumor encounter, NK cells upregulate CD55 via an NKG2D-p65 transcriptional axis. Unlike in T-cells, where it has a known co-stimulatory role, CD55 on NK cells directly engages tumor-expressed CD97 in trans to trigger lipid raft aggregation and LCK activation, acting as a self-sufficient primary signal initiator that drives cytotoxicity. However, upon prolonged tumor exposure, CD55 expression on NK cells progressively declines, coinciding with the well‑recognized downregulation of NKG2D upon chronic exposure. Within the TME, this loss of CD55 causally impairs NK-cell function. In cancer patients, low CD55 expression in tumor-infiltrating NK cells correlates with poor clinical outcomes. Restoring CD55 expression in both conventional and chimeric antigen receptor-engineered NK cells augments LCK signaling, enhances effector function and persistence, and improves antitumor efficacy in vivo. Thus, NK cells deploy a CD55-dependent autonomous activation mechanism upon tumor encounter, whereas chronic exposure drives CD55 loss and functional dysfunction, a state that can be therapeutically reversed by CD55 restoration.
Innate immunity provides a critical first line of defense against pathogens and homeostatic perturbations. Pattern recognition receptors detect these disruptions and initiate immune responses through multi-protein complex formation to drive inflammatory signaling and cell death pathways. Key cytosolic complexes formed by these sensors include inflammasomes and PANoptosomes. Inflammasomes induce caspase-1 activation and the subsequent maturation of interleukin (IL)-1β and IL-18, and they can act as integral components of larger PANoptosomes, whose formation and functions have been defined by genetic, biochemical, and single-cell imaging evidence. PANoptosomes induce lytic, inflammatory cell death (PANoptosis) and promote the release of damage-associated molecular patterns (DAMPs) and cytokines beyond IL-1β and IL-18, including TNF, IFNs, IL-6, and others. Given their critical functions in driving cell death and the release of cytokines and DAMPs, dysregulation of innate immune sensors is associated with a wide range of diseases, including infections, autoinflammatory syndromes, cardiovascular disorders, neurodegeneration, metabolic conditions, and cancer. Therefore, understanding innate immune sensors and how they assemble inflammasomes and PANoptosomes to drive cell death is critical for identifying therapeutic strategies. In this review, we discuss innate immune sensors that form inflammasomes and PANoptosomes, such as NLRP1, NLRP3, NLRC4, AIM2, Pyrin, and others. We highlight recent structural and mechanistic insights into these sensors, along with emerging structural studies of inflammasome assemblies and the biochemical and functional evidence supporting the formation of PANoptosomes. Given the physiological relevance of innate immune sensors and the complexes they form across the disease spectrum, an improved understanding of their structure-function relationships will be critical for informing therapeutic strategies that target these molecules, their associated complexes, and their physiological functions.
The derivation of authentic embryonic stem cells (ESCs) across mammalian species remains a major challenge. Here, we report the development of a defined, serum-free culture system, termed 6iL/E4, that enables the derivation and long-term self-renewal of ESCs across diverse mammalian species. Through systematic dissection of signaling pathways, we identified conserved regulatory modules involving GSK3α, WNT, STAT3, PDGFR, and MEK/ERK signaling. The optimized 6iL/E4 conditions support stable derivation and expansion of ESCs from mouse, rat, rabbit, and bovine embryos. For rabbit, ESC derivation required supplementation with the LATS inhibitor TDI-011536 (TDI), and 6iL/TDI-cultured rabbit ESCs exhibited chimera-forming capability. In bovine ESCs, inducible expression of Klf2 and Nanog reinforced pluripotency and promoted in vivo chimeric contribution. Importantly, we demonstrated that 6iL robustly establishes and maintains human pluripotent stem cells in a naïve-like state. These findings reveal conserved principles underlying ESC self-renewal across divergent mammalian species and provide a universal platform for cross-species stem cell research, disease modeling, and biotechnological applications.
Mapping of protein-DNA interactions at single-cell resolution remains a central challenge in epigenomics, particularly for transcription factors (TFs), whose sparse binding limits reliable detection. Here, we establish DeChIC-seq (DNA Deaminase-based Chromatin Immuno-Conversion sequencing), a conversion-based strategy that uses a protein A-DddAtox fusion to directly record protein-DNA interactions by inducing localized C-to-U conversions near antibody-bound chromatin. Retaining genome-wide background sequence information without immunoprecipitation, DeChIC-seq enables profiling of histone modifications and sensitive detection of TF binding. Integration with single-cell whole-genome amplification extends DeChIC-seq to single-cell applications (scDeChIC-seq), enabling chromatin profiling of individual cells. Applied to mouse embryogenesis, scDeChIC-seq resolves lineage-specific chromatin states through profiling of H3K4me3, CTCF, and RAD21 and sensitively detects TF binding, including that of NR5A2, TFAP2C, and KLF5, from extremely limited blastomere inputs. This underscores its strong potential for detecting TF-binding sites in scarce biological samples. DeChIC-seq establishes a conversion-based framework for chromatin profiling that enables mechanistic dissection of TF-driven gene regulation across rare cells, developmental systems, and disease contexts.
C5a, the most potent anaphylatoxin in the complement system, exerts its effects through the canonical G protein-coupled receptor C5aR1 and the arrestin-coupled receptor C5aR2. Despite the critical role of C5aR2 in immunomodulation, the molecular mechanisms underlying its biased signaling, ligand recognition, and associated pathophysiology remain poorly understood. Here, we report cryo-electron microscopy structures of β-arrestin 1-bound C5aR2 and C5aR1 stimulated by C5a or its metabolite C5adesArg. By combining structural analysis with functional assays, we identified the key structural determinants that prevent G protein coupling and confer intrinsic bias toward β-arrestins. Comparative analysis elucidated the distinct ligand recognition mechanism of C5aR2 and explained the retained affinity of C5adesArg for C5aR2. These findings guided the rational design of ZQ105, a highly selective C5aR2 agonist. Leveraging ZQ105 as a chemical probe, functional studies revealed that selective C5aR2 activation induces distinct pro-inflammatory responses and receptor internalization in neutrophils. This study provides novel structural insights into transducer engagement and ligand recognition by C5aR2, yielding a valuable pharmacological tool for exploring C5aR2-related pathophysiological processes.
Sex pheromones play a central role in regulating animal behavior and reproduction. In insects, these signals are perceived through specialized odorant receptors (ORs) that mediate species-specific communication and safeguard genetic integrity. However, the structural basis of sex pheromone detection remains largely unresolved. Here, we identified two ORs in the pea aphid Acyrthosiphon pisum, along with the conserved OR co-receptor (Orco), which together mediate recognition of the pheromone components nepetalactone and nepetalactol. Functional assays demonstrated that ApOR21-Orco and ApOR22-Orco specifically respond to nepetalactol and nepetalactone, respectively. Using cryo-electron microscopy, we resolved the structure of the ApOR22-Orco complex in three states - unbound closed, nepetalactone-bound closed, and nepetalactone-bound open - revealing a heterotetrameric ion channel formed by one ApOR22 and three ApOrco subunits. Ligand binding to ApOR22 triggers conformational rearrangements that induce asymmetric pore dilation, thereby enabling ion conduction. Together, these results provide a mechanistic framework for understanding sex pheromone perception in insects and establish a structural foundation for the rational development of environmentally sustainable pest-control strategies.
