Conservation and specialization of the Ycf2-FtsHi chloroplast protein import motor in green algae.

The protein import motor in chloroplasts plays a pivotal role in their biogenesis and homeostasis by driving the translocation of preproteins into chloroplasts. While the Ycf2-FtsHi complex serves as the import motor in land plants, its evolutionary conservation, specialization, and mechanisms across photosynthetic organisms are largely unexplored. Here, we isolated and determined the cryogenic electron microscopy (cryo-EM) structures of the native Ycf2-FtsHi complex from Chlamydomonas reinhardtii, uncovering a complex composed of up to 19 subunits, including multiple green-algae-specific components. The heterohexameric AAA+ ATPase motor module is tilted, potentially facilitating preprotein handover from the translocon at the inner chloroplast membrane (TIC) complex. Preprotein interacts with Ycf2-FtsHi and enhances its ATPase activity in vitro. Integrating Ycf2-FtsHi and translocon at the outer chloroplast membrane (TOC)-TIC supercomplex structures reveals insights into their physical and functional interplay during preprotein translocation. By comparing these findings with those from land plants, our study establishes a structural foundation for understanding the assembly, function, evolutionary conservation, and diversity of chloroplast protein import motors.

Complement Component 3 Adapts the Cerebrospinal Fluid for Leptomeningeal Metastasis.

We molecularly dissected leptomeningeal metastasis, or spread of cancer to the cerebrospinal fluid (CSF), which is a frequent and fatal condition mediated by unknown mechanisms. We selected lung and breast cancer cell lines for the ability to infiltrate and grow in CSF, a remarkably acellular, mitogen-poor metastasis microenvironment. Complement component 3 (C3) was upregulated in four leptomeningeal metastatic models and proved necessary for cancer growth within the leptomeningeal space. In human disease, cancer cells within the CSF produced C3 in correlation with clinical course. C3 expression in primary tumors was predictive of leptomeningeal relapse. Mechanistically, we found that cancer-cell-derived C3 activates the C3a receptor in the choroid plexus epithelium to disrupt the blood-CSF barrier. This effect allows plasma components, including amphiregulin, and other mitogens to enter the CSF and promote cancer cell growth. Pharmacologic interference with C3 signaling proved therapeutically beneficial in suppressing leptomeningeal metastasis in these preclinical models.

Metastatic Latency and Immune Evasion through Autocrine Inhibition of WNT.

Metastasis frequently develops years after the removal of a primary tumor, from a minority of disseminated cancer cells that survived as latent entities through unknown mechanisms. We isolated latency competent cancer (LCC) cells from early stage human lung and breast carcinoma cell lines and defined the mechanisms that suppress outgrowth, support long-term survival, and maintain tumor-initiating potential in these cells during the latent metastasis stage. LCC cells show stem-cell-like characteristics and express SOX2 and SOX9 transcription factors, which are essential for their survival in host organs under immune surveillance and for metastatic outgrowth under permissive conditions. Through expression of the WNT inhibitor DKK1, LCC cells self-impose a slow-cycling state with broad downregulation of ULBP ligands for NK cells and evasion of NK-cell-mediated clearance. By expressing a Sox-dependent stem-like state and actively silencing WNT signaling, LCC cells can enter quiescence and evade innate immunity to remain latent for extended periods.

TGF-ß Tumor Suppression through a Lethal EMT.

TGF-ß signaling can be pro-tumorigenic or tumor suppressive. We investigated this duality in pancreatic ductal adenocarcinoma (PDA), which, with other gastrointestinal cancers, exhibits frequent inactivation of the TGF-ß mediator Smad4. We show that TGF-ß induces an epithelial-mesenchymal transition (EMT), generally considered a pro-tumorigenic event. However, in TGF-ß-sensitive PDA cells, EMT becomes lethal by converting TGF-ß-induced Sox4 from an enforcer of tumorigenesis into a promoter of apoptosis. This is the result of an EMT-linked remodeling of the cellular transcription factor landscape, including the repression of the gastrointestinal lineage-master regulator Klf5. Klf5 cooperates with Sox4 in oncogenesis and prevents Sox4-induced apoptosis. Smad4 is required for EMT but dispensable for Sox4 induction by TGF-ß. TGF-ß-induced Sox4 is thus geared to bolster progenitor identity, whereas simultaneous Smad4-dependent EMT strips Sox4 of an essential partner in oncogenesis. Our work demonstrates that TGF-ß tumor suppression functions through an EMT-mediated disruption of a lineage-specific transcriptional network.

Selection of bone metastasis seeds by mesenchymal signals in the primary tumor stroma.

How organ-specific metastatic traits arise in primary tumors remains unknown. Here, we show a role of the breast tumor stroma in selecting cancer cells that are primed for metastasis in bone. Cancer-associated fibroblasts (CAFs) in triple-negative (TN) breast tumors skew heterogeneous cancer cell populations toward a predominance of clones that thrive on the CAF-derived factors CXCL12 and IGF1. Limiting concentrations of these factors select for cancer cells with high Src activity, a known clinical predictor of bone relapse and an enhancer of PI3K-Akt pathway activation by CXCL12 and IGF1. Carcinoma clones selected in this manner are primed for metastasis in the CXCL12-rich microenvironment of the bone marrow. The evidence suggests that stromal signals resembling those of a distant organ select for cancer cells that are primed for metastasis in that organ, thus illuminating the evolution of metastatic traits in a primary tumor and its distant metastases.

Structural basis for distinct roles of SMAD2 and SMAD3 in FOXH1 pioneer-directed TGF-ß signaling.

TGF-ß receptors phosphorylate SMAD2 and SMAD3 transcription factors, which then form heterotrimeric complexes with SMAD4 and cooperate with context-specific transcription factors to activate target genes. Here we provide biochemical and structural evidence showing that binding of SMAD2 to DNA depends on the conformation of the E3 insert, a structural element unique to SMAD2 and previously thought to render SMAD2 unable to bind DNA. Based on this finding, we further delineate TGF-ß signal transduction by defining distinct roles for SMAD2 and SMAD3 with the forkhead pioneer factor FOXH1 as a partner in the regulation of differentiation genes in mouse mesendoderm precursors. FOXH1 is prebound to target sites in these loci and recruits SMAD3 independently of TGF-ß signals, whereas SMAD2 remains predominantly cytoplasmic in the basal state and set to bind SMAD4 and join SMAD3:FOXH1 at target promoters in response to Nodal TGF-ß signals. The results support a model in which signal-independent binding of SMAD3 and FOXH1 prime mesendoderm differentiation gene promoters for activation, and signal-driven SMAD2:SMAD4 binds to promoters that are preloaded with SMAD3:FOXH1 to activate transcription.

Publisher Correction: TGF-ß orchestrates fibrogenic and developmental EMTs via the RAS effector RREB1.

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

TGF-ß orchestrates fibrogenic and developmental EMTs via the RAS effector RREB1.

Epithelial-to-mesenchymal transitions (EMTs) are phenotypic plasticity processes that confer migratory and invasive properties to epithelial cells during development, wound-healing, fibrosis and cancer1-4. EMTs are driven by SNAIL, ZEB and TWIST transcription factors5,6 together with microRNAs that balance this regulatory network7,8. Transforming growth factor ß (TGF-ß) is a potent inducer of developmental and fibrogenic EMTs4,9,10. Aberrant TGF-ß signalling and EMT are implicated in the pathogenesis of renal fibrosis, alcoholic liver disease, non-alcoholic steatohepatitis, pulmonary fibrosis and cancer4,11. TGF-ß depends on RAS and mitogen-activated protein kinase (MAPK) pathway inputs for the induction of EMTs12-19. Here we show how these signals coordinately trigger EMTs and integrate them with broader pathophysiological processes. We identify RAS-responsive element binding protein 1 (RREB1), a RAS transcriptional effector20,21, as a key partner of TGF-ß-activated SMAD transcription factors in EMT. MAPK-activated RREB1 recruits TGF-ß-activated SMAD factors to SNAIL. Context-dependent chromatin accessibility dictates the ability of RREB1 and SMAD to activate additional genes that determine the nature of the resulting EMT. In carcinoma cells, TGF-ß-SMAD and RREB1 directly drive expression of SNAIL and fibrogenic factors stimulating myofibroblasts, promoting intratumoral fibrosis and supporting tumour growth. In mouse epiblast progenitors, Nodal-SMAD and RREB1 combine to induce expression of SNAIL and mesendoderm-differentiation genes that drive gastrulation. Thus, RREB1 provides a molecular link between RAS and TGF-ß pathways for coordinated induction of developmental and fibrogenic EMTs. These insights increase our understanding of the regulation of epithelial plasticity and its pathophysiological consequences in development, fibrosis and cancer.

Plasticity of ether lipids promotes ferroptosis susceptibility and evasion.

Ferroptosis-an iron-dependent, non-apoptotic cell death process-is involved in various degenerative diseases and represents a targetable susceptibility in certain cancers1. The ferroptosis-susceptible cell state can either pre-exist in cells that arise from certain lineages or be acquired during cell-state transitions2-5. However, precisely how susceptibility to ferroptosis is dynamically regulated remains poorly understood. Here we use genome-wide CRISPR-Cas9 suppressor screens to identify the oxidative organelles peroxisomes as critical contributors to ferroptosis sensitivity in human renal and ovarian carcinoma cells. Using lipidomic profiling we show that peroxisomes contribute to ferroptosis by synthesizing polyunsaturated ether phospholipids (PUFA-ePLs), which act as substrates for lipid peroxidation that, in turn, results in the induction of ferroptosis. Carcinoma cells that are initially sensitive to ferroptosis can switch to a ferroptosis-resistant state in vivo in mice, which is associated with extensive downregulation of PUFA-ePLs. We further find that the pro-ferroptotic role of PUFA-ePLs can be extended beyond neoplastic cells to other cell types, including neurons and cardiomyocytes. Together, our work reveals roles for the peroxisome-ether-phospholipid axis in driving susceptibility to and evasion from ferroptosis, highlights PUFA-ePL as a distinct functional lipid class that is dynamically regulated during cell-state transitions, and suggests multiple regulatory nodes for therapeutic interventions in diseases that involve ferroptosis.

Influence of nitrogen speciation on Cd-induced toxicity in Landoltia punctata.

Nitrogen (N) plays an important role in plant growth and developmental metabolic processes, research on nitrogen speciation regulating Cd accumulation in duckweed is still limited. In this study, the effects of three nitrogen sources (NH4Cl, Ca(NO3)2 and NH4NO3) on the growth, Cd accumulation, and photosynthetic parameters of Landoltia punctata (L. punctata) were analyzed. The results showed that Cd enrichment in L. punctata was significantly reduced (p < 0.05) with different nitrogen treatments compared to the control (CK). Ammonium nitrogen (NH4-N) is more conducive to the accumulation of Cd in L. punctata than nitrate nitrogen (NO3-N). The sum of the cell wall components and soluble components of Cd in the NH4-N treatment group was greater than that in the NO3-N treatment group. The proportion of FNaCl extracts in the NH4-N treatment group was greater than in the NO3-N treatment group. NO3-N led to a greater reduction in photosynthetic pigment content than NH4-N. Overall, applying different forms of nitrogen can alleviate Cd toxicity in L. punctata, and the detoxification effect of the NH4-N treatment is stronger than that of NO3-N treatment. This study will provide theoretical and practical support for the application of duckweed in Cd phytoremediation even in eutrophic aquatic environments.

Cd pollution has become a major global public environmental issue. Duckweed is an ideal species to restore Cd-polluted waters due to its fast growth, easy harvesting and hyperaccumulation Cd. Currently, no definite conclusion has been given on the detoxification effect of nitrogen morphology regulating the accumulation of Cd in plant. In this study, the influence of different nitrogen forms on Cd-induced toxicity in Landoltia punctata were revealed through the changes in biomass, Cd subcellular distribution, Cd chemical morphology and photosynthetic pigment. These findings can provide a new way of analyzing the mechanism of Cd enrichment in plants, and also provide theoretical and technical support for the remediation of Cd pollution by using duckweed resources. The Cd-accumulation duckweed can be pyrolyzed to produce biochar, which can not only control the second pollution by decomposed plant bodies but also realizes the efficient use of waste.

Cytochrome P450 oxidoreductase contributes to phospholipid peroxidation in ferroptosis.

Ferroptosis is widely involved in degenerative diseases in various tissues including kidney, liver and brain, and is a targetable vulnerability in multiple primary and therapy-resistant cancers. Accumulation of phospholipid hydroperoxides in cellular membranes is the hallmark and rate-limiting step of ferroptosis; however, the enzymes contributing to lipid peroxidation remain poorly characterized. Using genome-wide, CRISPR-Cas9-mediated suppressor screens, we identify cytochrome P450 oxidoreductase (POR) as necessary for ferroptotic cell death in cancer cells exhibiting inherent and induced susceptibility to ferroptosis. By genetic depletion of POR in cancer cells, we reveal that POR contributes to ferroptosis across a wide range of lineages and cell states, and in response to distinct mechanisms of ferroptosis induction. Using systematic lipidomic profiling, we further map POR's activity to the lipid peroxidation step in ferroptosis. Hence, our work suggests that POR is a key mediator of ferroptosis and potential druggable target for developing antiferroptosis therapeutics.

Therapy-induced tumour secretomes promote resistance and tumour progression.

Drug resistance invariably limits the clinical efficacy of targeted therapy with kinase inhibitors against cancer. Here we show that targeted therapy with BRAF, ALK or EGFR kinase inhibitors induces a complex network of secreted signals in drug-stressed human and mouse melanoma and human lung adenocarcinoma cells. This therapy-induced secretome stimulates the outgrowth, dissemination and metastasis of drug-resistant cancer cell clones and supports the survival of drug-sensitive cancer cells, contributing to incomplete tumour regression. The tumour-promoting secretome of melanoma cells treated with the kinase inhibitor vemurafenib is driven by downregulation of the transcription factor FRA1. In situ transcriptome analysis of drug-resistant melanoma cells responding to the regressing tumour microenvironment revealed hyperactivation of several signalling pathways, most prominently the AKT pathway. Dual inhibition of RAF and the PI(3)K/AKT/mTOR intracellular signalling pathways blunted the outgrowth of the drug-resistant cell population in BRAF mutant human melanoma, suggesting this combination therapy as a strategy against tumour relapse. Thus, therapeutic inhibition of oncogenic drivers induces vast secretome changes in drug-sensitive cancer cells, paradoxically establishing a tumour microenvironment that supports the expansion of drug-resistant clones, but is susceptible to combination therapy.

Regulation of RAS palmitoyltransferases by accessory proteins and palmitoylation.

Palmitoylation of cysteine residues at the C-terminal hypervariable regions in human HRAS and NRAS, which is necessary for RAS signaling, is catalyzed by the acyltransferase DHHC9 in complex with its accessory protein GCP16. The molecular basis for the acyltransferase activity and the regulation of DHHC9 by GCP16 is not clear. Here we report the cryo-electron microscopy structures of the human DHHC9-GCP16 complex and its yeast counterpart-the Erf2-Erf4 complex, demonstrating that GCP16 and Erf4 are not directly involved in the catalytic process but stabilize the architecture of DHHC9 and Erf2, respectively. We found that a phospholipid binding to an arginine-rich region of DHHC9 and palmitoylation on three residues (C24, C25 and C288) were essential for the catalytic activity of the DHHC9-GCP16 complex. Moreover, we showed that GCP16 also formed complexes with DHHC14 and DHHC18 to catalyze RAS palmitoylation. These findings provide insights into the regulatory mechanism of RAS palmitoyltransferases.

Stratifying Ferroptosis Sensitivity in Cells and Tissues with PALP.

Ferroptosis is emerging as a promising strategy for suppressing multiple types of human cancers. Rapid and accurate assessment of the relative sensitivity to ferroptosis in biological samples will accelerate the development of ferroptosis-targeted therapies. We previously demonstrated that photochemical activation of membrane lipid peroxidation (PALP) that uses high-power lasers to induce localized polyunsaturated fatty acyl (PUFA)-lipid peroxidation can efficiently report ferroptosis sensitivity in live cells and tissues in situ. Here, we describe the experimental details for PALP analysis, including preparation of tissue sections, preparation of fluorescent lipid peroxidation reporter, sample staining, lipid peroxidation induced by laser source, and data processing. We envision predicting the relative sensitivity to ferroptosis of cellular and tissue samples is potentially useful for basic research and clinical investigations.

Dynamic Regulation of Ferroptosis by Lipid Metabolism.

Significance: Ferroptosis is featured by the accumulation of polyunsaturated-lipid peroxidation on cellular membranes in an iron-dependent manner. Ferroptosis has been implicated in various pathophysiological processes, including cancer, neurodegeneration, and ischemia-reperfusion tissue injury. However, our understanding about the dynamic and context-specific regulation of ferroptosis remains incomplete. Recent Advances: As the major substrate for peroxidation, the cellular lipidome regulates ferroptosis sensitivity and execution by controlling the abundance and availability of polyunsaturated-lipids for peroxidative modifications. In turn, the cellular lipidome is regulated by a complex network of enzymes and transporters, as well as upstream layers of receptors, kinases, and transcription factors. A number of research has shed light on the link between lipid metabolism and ferroptosis. Here, we summarize our current knowledge on the role of the lipidome and associated protein regulators in various stages of ferroptosis, ranging from initiation, execution to cell death evasion by cells experiencing ferroptotic stress. Critical Issues: This review provides an overview of the mechanisms underlying lipid peroxidation and ferroptosis by discussing the lipid species that directly contribute to lipid peroxidation and ferroptosis, how cells regulate the abundances of these pro-ferroptosis lipids, how lipid peroxidation causes cell death, and how cells prevent and repair membrane lipid damage under ferroptotic conditions. Future Directions: Cell fate regulation in vivo could be different from in vitro culture settings. We envision that a comprehensive and detailed understanding about these important questions in the dynamic regulation of ferroptosis in vivo will accelerate our development of ferroptosis-targeted therapies to improve human health.

A Minimally-Invasive Method for Serial Cerebrospinal Fluid Collection and Injection in Rodents with High Survival Rates.

Cerebrospinal fluid (CSF) is an important sample source for diagnosing diseases in the central nervous system (CNS), but collecting and injecting CSF in small animals is technically challenging and often results in high mortality rates. Here, we present a cost-effective and efficient method for accessing the CSF in live rodents for fluid collection and infusion purposes. The key element of this protocol is a metal needle tool bent at a unique angle and length, allowing the successful access of the CSF through the foramen magnum. With this method, we can collect 5-10 µL of the CSF from mice and 70-100 µL from rats for downstream analyses, including mass spectrometry. Moreover, our minimally-invasive procedure enables iterative CSF collection from the same animal every few days, representing a significant improvement over prior protocols. Additionally, our method can be used to inject solutions into mice cisterna magna with high success rates and high postoperative recovery rates. In summary, we provide an efficient and minimally-invasive protocol for collecting and infusing reagents into the CSF in live rodents. We envision this protocol will facilitate biomarker discovery and drug development for diseases in the central nervous system.

Stratifying ferroptosis sensitivity in cells and mouse tissues by photochemical activation of lipid peroxidation and fluorescent imaging.

Ferroptosis is a non-apoptotic iron-dependent cell death. Here we present a protocol for stratifying ferroptosis sensitivity in cells and mouse tissues. This protocol uses photochemical activation of lipid peroxidation (PALP) coupled with fluorescent imaging to assess the relative sensitivity to ferroptosis. Using commercial reagents and common equipment, PALP is readily accessible to most laboratories. One remaining challenge is the inability to multiplex this technique in analyzing multiple tissues or regions simultaneously. This protocol may have applications in developing ferroptosis-targeted therapies. For complete details on the use and execution of this protocol, please refer to Wang et al. (2021).

PALP: A rapid imaging technique for stratifying ferroptosis sensitivity in normal and tumor tissues in situ.

Ferroptosis is an emerging cancer suppression strategy. However, how to select cancer patients for treating with ferroptosis inducers remains challenging. Here, we develop photochemical activation of membrane lipid peroxidation (PALP), which uses targeted lasers to induce localized polyunsaturated fatty acyl (PUFA)-lipid peroxidation for reporting ferroptosis sensitivity in cells and tissues. PALP captured by BODIPY-C11 can be suppressed by lipophilic antioxidants and iron chelation, and is dependent on PUFA-lipid levels. Moreover, we develop PALPv2, for studying lipid peroxidation on selected membranes along the z axis in live cells using two-photon microscopes. Using PALPv1, we detect PUFA-lipids in multiple tissues, and validate a PUFA-phospholipid reduction during muscle aging as previously reported. Patterns of PALPv1 signals across multiple cancer cell types in vitro and in vivo are concordant with their ferroptosis susceptibility and PUFA-phospholipid levels. We envision that PALP will enable rapid stratification of ferroptosis sensitivity in cancer patients and facilitate PUFA-lipid research.

Comparison of toxicokinetics and toxic effects of PFOS and its novel alternative OBS in zebrafish larvae.

Sodium p-perfluorous nonenoxybenzene sulfonate (OBS), a novel alternative to perfluorooctanesulfonate (PFOS), is widely used in industry as a surfactant, firefighting foam and photographic material. The occurrence of OBS in the aquatic environment has been recently reported, but little information is available on its accumulation and toxic effects in aquatic organisms. In this study, zebrafish larvae (3 d post-fertilization) were subjected to OBS (10, 100 µg/L) and PFOS (10 µg/L) for a period of 48 h, followed by a 24 h of depuration period. The bioconcentration and depuration kinetics, oxidative stress and possible molecular mechanisms of OBS and PFOS were investigated in zebrafish larvae. Our results showed that the uptake and depuration of both OBS and PFOS fitted well with a first-order kinetic model. The uptake rate constant of OBS was similar to that of PFOS, but the depuration rate constant was much higher than PFOS with a half-life of 69.7-85 h for OBS and 222.2 h for PFOS. The calculated BCFs of OBS and PFOS were 238.0-242.5 and 644.2, respectively. In our acute toxicity assay, the enhanced expression of Nrf2 protein accompanied by the upregulation of CAT and SOD protein expressions indicated OBS and PFOS induced oxidative stress in zebrafish larvae, and the Nrf2-ARE signaling pathway was involved in this process. Collectively, OBS has a lower bioconcentration potential than PFOS, but its toxic effect on oxidative stress was comparable to PFOS in zebrafish larvae.