Ferroptosis is an iron-dependent form of cell death driven by oxidation of polyunsaturated fatty acid (PUFA) phospholipids. Large-scale genetic screens have uncovered a specialized role for PUFA ...ether phospholipids (ePLs) in promoting ferroptosis. Understanding of the enzymes involved in PUFA-ePL production, however, remains incomplete. Here we show, using a combination of pathway mining of genetic dependency maps, AlphaFold-guided structure predictions and targeted lipidomics, that the uncharacterized transmembrane protein TMEM164-the genetic ablation of which has been shown to protect cells from ferroptosis-is a cysteine active center enzyme that selectively transfers C20:4 acyl chains from phosphatidylcholine to lyso-ePLs to produce PUFA ePLs. Genetic deletion of TMEM164 across a set of ferroptosis-sensitive cancer cell lines caused selective reductions in C20:4 ePLs with minimal effects on C20:4 diacyl PLs, and this lipid profile produced a variable range of protection from ferroptosis, supportive of an important but contextualized role for C20:4 ePLs in this form of cell death.
TLRs are a family of pattern recognition receptors that recognize conserved molecular structures/products from a wide variety of microbes. Following recognition of ligands, TLRs recruit signaling ...adapters to initiate a pro-inflammatory signaling cascade culminating in the activation of several transcription factor families. Additionally, TLR signals lead to activation of PI3K, affecting many aspects of the cellular response, including cell survival, proliferation and regulation of the pro-inflammatory response. The recent discovery of BCAP as a TLR signaling adaptor, crucial for linking TLRs to PI3K activation, allows new questions of the importance of PI3K activation downstream of TLRs. Here, we summarize the current understanding of signaling pathways activated by TLRs and provide our perspective on TLR mediated activation of PI3K and its impact on regulating cellular processes.
Hedgehog (Hh) signaling during development and in postembryonic tissues requires activation of the 7TM oncoprotein Smoothened (Smo) by mechanisms that may involve endogenous lipidic modulators. ...Exogenous Smo ligands previously identified include the plant sterol cyclopamine (and its therapeutically useful synthetic mimics) and hydroxylated cholesterol derivatives (oxysterols); Smo is also highly sensitive to cellular sterol levels. The relationships between these effects are unclear because the relevant Smo structural determinants are unknown. We identify the conserved extracellular cysteine-rich domain (CRD) as the site of action for oxysterols on Smo, involving residues structurally analogous to those contacting the Wnt lipid adduct in the homologous Frizzled CRD; this modulatory effect is distinct from that of cyclopamine mimics, from Hh-mediated regulation, and from the permissive action of cellular sterol pools. These results imply that Hh pathway activity is sensitive to lipid binding at several Smo sites, suggesting mechanisms for tuning by multiple physiological inputs.
•Select oxysterols that activate Smo bind its extracellular cysteine-rich domain (CRD)•CRD binding determinants are analogous to those in Frizzled that bind the Wnt lipid•Candidate endogenous modulators that act via the Smo CRD include 7-keto oxysterols•Diverse sterol modulatory effects act via distinct Smo structural determinants
Hydroxylated cholesterol derivatives (oxysterols) activate the heptahelical Smoothened transducer protein in the Hedgehog pathway, but the underlying mechanism is incompletely understood. Myers et al. show that oxysterols bind to the extracellular Smoothened cysteine-rich domain, revealing multiple sterol-modulatory effects that impinge on Hedgehog signal response at the level of Smoothened.
Lacking any discernible sequence similarity, interleukin-34 (IL-34) and colony stimulating factor 1 (CSF-1) signal through a common receptor CSF-1R on cells of mononuclear phagocyte lineage. Here, ...the crystal structure of dimeric IL-34 reveals a helical cytokine fold homologous to CSF-1, and we further show that the complex architecture of IL-34 bound to the N-terminal immunoglobulin domains of CSF-1R is similar to the CSF-1/CSF-1R assembly. However, unique conformational adaptations in the receptor domain geometry and intermolecular interface explain the cross-reactivity of CSF-1R for two such distantly related ligands. The docking adaptations of the IL-34 and CSF-1 quaternary complexes, when compared to the stem cell factor assembly, draw a common evolutionary theme for transmembrane signaling. In addition, the structure of IL-34 engaged by a Fab fragment reveals the mechanism of a neutralizing antibody that can help deconvolute IL-34 from CSF-1 biology, with implications for therapeutic intervention in diseases with myeloid pathogenic mechanisms.
► Structure of human IL-34 reveals a dimeric four-helix bundle cytokine fold ► Studies in solution confirm bivalent assembly and high affinity of IL-34 with CSF-1R ► The IL-34/CSF-1R complex structure shares a common architecture with CSF-1/CSF-1R ► CSF-1R employs distinct domain adaptations for binding to IL-34 and CSF-1
Toll like receptors (TLRs) use Toll–IL-1 receptor (TIR) domain-containing adapters, such as myeloid differentiation primary response gene 88 (MyD88) and TIR domain-containing adapter inducing IFN-β ...(TRIF), to induce activation of transcription factors, including NF-κB, MAP kinases, and IFN regulatory factors. TLR signaling also leads to activation of PI3K, but the molecular mechanism is not understood. Here we have discovered a unique role for B-cell adapter for PI3K (BCAP) in the TLR-signaling pathway. We find that BCAP has a functional N-terminal TIR homology domain and links TLR signaling to activation of PI3K. In addition, BCAP negatively regulates proinflammatory cytokine secretion upon TLR stimulation. In vivo, the absence of BCAP leads to exaggerated recruitment of inflammatory myeloid cells following infections and enhanced susceptibility to dextran sulfate sodium-induced colitis. Our results demonstrate that BCAP is a unique TIR domain-containing TLR signaling adapter crucial for linking TLRs to PI3K activation and regulating the inflammatory response.
The crystal structure of a Wnt morphogen bound to its Frizzled receptor ectodomain provides insights into the evolutionary provenance of this complex fold and offers an explanation for why Wnts ...utilize both lipid- and protein-mediated contacts to engage Frizzleds.
Interleukin-1 (IL-1)-family cytokines are mediators of innate and adaptive immunity. They exert proinflammatory effects by binding a primary receptor that recruits a receptor accessory protein to ...form a signaling-competent heterotrimeric complex. Here we present the crystal structure of IL-1β bound to its primary receptor IL-1RI and its receptor accessory protein IL-1RAcP, providing insight into how IL-1-type cytokines initiate signaling and revealing an evolutionary relationship with the fibroblast growth factor receptor family.
The recently discovered cytokine IL-27 belongs to the IL-6/IL-12 family of cytokines and induced proliferation of naive CD4(+) T cells and the generation of a Th1-type adaptive immune response. ...Although binding of IL-27 to the cytokine receptor WSX-1 was demonstrated, this interaction proved insufficient to mediate cellular effects. Hence, IL-27 was believed to form a heteromeric signaling receptor complex with WSX-1 and another, yet to be identified, cytokine receptor subunit. In this study, we describe that WSX-1 together with gp130 constitutes a functional signal-transducing receptor for IL-27. We show that neither of the two subunits itself is sufficient to mediate IL-27-induced signal transduction, but that the combination of both is required for this event. Expression analysis of WSX-1 and gp130 by quantitative PCR suggests that IL-27 might have a variety of cellular targets besides naive CD4(+) T cells: we demonstrate gene induction of a subset of inflammatory cytokines in primary human mast cells and monocytes in response to IL-27 stimulation. Thus, IL-27 not only contributes to the development of an adaptive immune response through its action on CD4(+) T cells, it also directly acts on cells of the innate immune system.
Anaplastic lymphoma kinase (ALK)
and the related leukocyte tyrosine kinase (LTK)
are recently deorphanized receptor tyrosine kinases
. Together with their activating cytokines, ALKAL1 and ALKAL2
...(also called FAM150A and FAM150B or AUGβ and AUGα, respectively), they are involved in neural development
, cancer
and autoimmune diseases
. Furthermore, mammalian ALK recently emerged as a key regulator of energy expenditure and weight gain
, consistent with a metabolic role for Drosophila ALK
. Despite such functional pleiotropy and growing therapeutic relevance
, structural insights into ALK and LTK and their complexes with cognate cytokines have remained scarce. Here we show that the cytokine-binding segments of human ALK and LTK comprise a novel architectural chimera of a permuted TNF-like module that braces a glycine-rich subdomain featuring a hexagonal lattice of long polyglycine type II helices. The cognate cytokines ALKAL1 and ALKAL2 are monomeric three-helix bundles, yet their binding to ALK and LTK elicits similar dimeric assemblies with two-fold symmetry, that tent a single cytokine molecule proximal to the cell membrane. We show that the membrane-proximal EGF-like domain dictates the apparent cytokine preference of ALK. Assisted by these diverse structure-function findings, we propose a structural and mechanistic blueprint for complexes of ALK family receptors, and thereby extend the repertoire of ligand-mediated dimerization mechanisms adopted by receptor tyrosine kinases.
Birth defects result from interactions between genetic and environmental factors, but the mechanisms remain poorly understood. We find that mutations and teratogens interact in predictable ways to ...cause birth defects by changing target cell sensitivity to Hedgehog (Hh) ligands. These interactions converge on a membrane protein complex, the MMM complex, that promotes degradation of the Hh transducer Smoothened (SMO). Deficiency of the MMM component MOSMO results in elevated SMO and increased Hh signaling, causing multiple birth defects. In utero exposure to a teratogen that directly inhibits SMO reduces the penetrance and expressivity of birth defects in Mosmo-/- embryos. Additionally, tissues that develop normally in Mosmo-/- embryos are refractory to the teratogen. Thus, changes in the abundance of the protein target of a teratogen can change birth defect outcomes by quantitative shifts in Hh signaling. Consequently, small molecules that re-calibrate signaling strength could be harnessed to rescue structural birth defects.
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