Near-infrared Activatable Copper Nanoplatforms Synergize with the 5-Azacytidine Prodrug to Potentiate Cuproptosis.

Cuproptosis, a newly discovered cell death modality, is gaining recognition for its crucial role in antitumor therapy. Here, we demonstrated that Ferredoxin 1 (FDX1), a key gene involved in cuproptosis, is negatively correlated with malignancy and T-cell exhaustion in head and neck squamous cell carcinoma (HNSCC). Based on these findings, we developed near-infrared (NIR) light-controlled nanoparticles (NPs), CuD@PM, which can selectively deliver copper to HNSCC cells and induce cuproptosis in the presence of microneedles loaded with triacetylated azacitidine (TAc-AzaC) and 808 nm laser irradiation. Intravenous administration of these NPs significantly suppressed tumor growth in HNSCC animal models and enhanced the antitumor immune response. The NIR-controlled activation of cuproptosis offers great potential as a safe, targeted, and image-guided antitumor therapy for HNSCC.

AB017. NFκB1 regulates FDX1 to facilitate elesclomol-induced cuproptosis against glioblastoma.

BACKGROUND: Ferredoxin 1 (FDX1) plays key roles in promoting elesclomol-induced cuproptosis against cancer, whether it has the potential to be a new therapeutic strategy against glioblastoma has not yet been clarified. METHODS: Glioblastoma cells were treated with elesclomol (20 nM/L) and copper chloride (2 µM/L), and then cell proliferation, migration, and invasion were evaluated by CCK-8, clonogenic and transwell assay. Western blot was performed to detect the expression of cuproptosis-relating proteins FDX1, lipoylated dihydrolipoamide S-acetyltransferase (DLAT), copper transport ATPase (ATP7A), heat shock protein 70 (HSP70), apoptotic markers B cell lymphoma-2 (BCL-2) associated X protein (Bax), and BCL-2, as well as the pan-apoptotic/death markers gasdermin D (GSDMD), solute carrier family 7 member 11 (SLC7A11). The effects of knockdown and overexpression of FDX1 on cell proliferation, migration, and invasion were observed. Bioinformatic analysis was performed to predict the corresponding transcription factors regulating FDX1 expression, and verified by dual luciferase assay. The regulatory relationship between FDX1 and its transcription factors was verified by rescue experiment and further evaluated in vivo. RESULTS: Elesclomol had obvious inhibitory effects on the proliferation, migration, and invasion capacities of tumor cells in a dose-dependent manner. When combined with copper chloride, the inhibitory effects on tumor cells were significantly higher both in vitro and in vivo. FDX1 expression was negatively correlated with overall survival of patients. Nuclear factor κ-light-chain enhancer of activated B cell 1 (NFκB1) was the transcription factor of FDX1 verified by dual luciferase assay. Both FDX1 and NFκB1 were highly expressed in glioblastoma. Knockdown of FDX1 or NFκB1 down-regulated proliferation, migration, and invasion abilities of tumor cells, and increased after FDX1 overexpression. FDX1 expression decreased correspondingly after NFκB1 knockdown. Up-regulation of FDX1 promoted elesclomol-induced cuproptosis against glioblastoma both in vitro and in vivo. FDX1 knockdown can reverse the inhibitory effect of elesclomol on tumor cells. CONCLUSIONS: Elesclomol inhibits glioblastoma development via inducing cuproptosis, regulated by NFκB1/FDX1 axis.

FDX1 downregulation activates mitophagy and the PI3K/AKT signaling pathway to promote hepatocellular carcinoma progression by inducing ROS production.

BACKGROUND: Mitochondrial dysfunction and metabolic reprogramming can lead to the development and progression of hepatocellular carcinoma (HCC). Ferredoxin 1 (FDX1) is a small mitochondrial protein and recent studies have shown that FDX1 plays an important role in tumor cuproptosis, but its role in HCC is still elusive. In this study, we aim to investigate the expression and novel functions of FDX1 in HCC. METHODS: FDX1 expression was first analyzed in publicly available datasets and verified by immunohistochemistry, qRT-PCR and Western blot. In vitro and in vivo experiments were applied to explore the functions of FDX1. Non-targeted metabolomics and RNA-sequencing were used to determine molecular mechanism. mRFP-GFP-LC3 lentivirus transfection, Mito-Tracker Red and Lyso-Tracker Green staining, transmission electron microscopy, flow cytometry, JC-1 staining, etc. were used to analyze mitophagy or ROS levels. Hydrodynamic tail vein injection (HTVi) and patient-derived organoid (PDO) models were used to analyze effect of FDX1 overexpression. RESULTS: FDX1 expression is significantly downregulated in HCC tissues. FDX1 downregulation promotes HCC cell proliferation, invasion in vitro and growth, metastasis in vivo. In addition, FDX1 affects metabolism of HCC cells and is associated with autophagy. We then confirmed that FDX1 deficiency increases ROS levels, activates mitophagy and the PI3K/AKT signaling pathway in HCC cells. Interestingly, scavenging ROS attenuates the tumor-promoting role and mitophagy of FDX1 downregulation. The results of HTVi and PDO models both find that FDX1 elevation significantly inhibits HCC progression. Moreover, low FDX1 expression is associated with shorter survival and is an independent risk factor for prognosis in HCC patients. CONCLUSIONS: Our research had investigated novel functions of FDX1 in HCC. Downregulation of FDX1 contributes to metabolic reprogramming and leads to ROS-mediated activation of mitophagy and the PI3K/AKT signaling pathway. FDX1 is a potential prognostic biomarker and increasing FDX1 expression may be a potential therapeutic approach to inhibit HCC progression.

Cuproptosis, the novel type of oxidation-induced cell death in thoracic cancers: can it enhance the success of immunotherapy?

Copper is an important metal micronutrient, required for the balanced growth and normal physiological functions of human organism. Copper-related toxicity and dysbalanced metabolism were associated with the disruption of intracellular respiration and the development of various diseases, including cancer. Notably, copper-induced cell death was defined as cuproptosis which was also observed in malignant cells, representing an attractive anti-cancer instrument. Excess of intracellular copper leads to the aggregation of lipoylation proteins and toxic stress, ultimately resulting in the activation of cell death. Differential expression of cuproptosis-related genes was detected in normal and malignant tissues. Cuproptosis-related genes were also linked to the regulation of oxidative stress, immune cell responses, and composition of tumor microenvironment. Activation of cuproptosis was associated with increased expression of redox-metabolism-regulating genes, such as ferredoxin 1 (FDX1), lipoic acid synthetase (LIAS), lipoyltransferase 1 (LIPT1), dihydrolipoamide dehydrogenase (DLD), drolipoamide S-acetyltransferase (DLAT), pyruvate dehydrogenase E1 subunit alpha 1 (PDHA1), and pyruvate dehydrogenase E1 subunit beta (PDHB)). Accordingly, copper-activated network was suggested as an attractive target in cancer therapy. Mechanisms of cuproptosis and regulation of cuproptosis-related genes in different cancers and tumor microenvironment are discussed in this study. The analysis of current findings indicates that therapeutic regulation of copper signaling, and activation of cuproptosis-related targets may provide an effective tool for the improvement of immunotherapy regimens.

Curcuminoid PBPD induces cuproptosis and endoplasmic reticulum stress in cervical cancer via the Notch1/RBP-J/NRF2/FDX1 pathway.

Curcumin has been shown to have antitumor properties, but its low potency and bioavailability has limited its clinical application. We designed a novel curcuminoid, [1-propyl-3,5-bis(2-bromobenzylidene)-4-piperidinone] (PBPD), which has higher antitumor strength and improves bioavailability. Cell counting kit-8 was used to detect cell activity. Transwell assay was used to detect cell invasion and migration ability. Western blot and quantitative polymerase chain reaction were used to detect protein levels and their messenger RNA expression. Immunofluorescence was used to detect the protein location. PBPD significantly inhibited the proliferation of cervical cancer cells, with an IC50 value of 4.16 µM for Hela cells and 3.78 µM for SiHa cells, leading to the induction of cuproptosis. Transcriptome sequencing analysis revealed that PBPD significantly inhibited the Notch1/Recombination Signal Binding Protein for Immunoglobulin kappa J Region (RBP-J) and nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathways while upregulating ferredoxin 1 (FDX1) expression. Knockdown of Notch1 or RBP-J significantly inhibited NRF2 expression and upregulated FDX1 expression, leading to the inhibition of nicotinamide adenine dinucleotide phosphate activity and the induction of oxidative stress, which in turn activated endoplasmic reticulum stress and induced cell death. The overexpression of Notch1 or RBP-J resulted in the enrichment of RBP-J within the NRF2 promoter region, thereby stimulating NRF2 transcription. NRF2 knockdown resulted in increase in FDX1 expression, leading to cuproptosis. In addition, PBPD inhibited the acidification of tumor niche and reduced cell metabolism to inhibit cervical cancer cell invasion and migration. In conclusion, PBPD significantly inhibits the proliferation, invasion, and migration of cervical cancer cells and may be a novel potential drug candidate for treatment of cervical cancer.

Ferredoxin 1 is essential for embryonic development and lipid homeostasis.

Mammalian ferredoxin 1 and 2 (FDX1/2) belong to an evolutionary conserved family of iron-sulfur cluster containing proteins and act as electron shutters between ferredoxin reductase (FDXR) and numerous proteins involved in critical biological pathways. FDX1 is involved in biogenesis of steroids and bile acids, Vitamin A/D metabolism, and lipoylation of tricarboxylic acid (TCA) cycle enzymes. FDX1 has been extensively characterized biochemically but its role in physiology and lipid metabolism has not been explored. In this study, we generated Fdx1-deficient mice and showed that knockout of both alleles of the Fdx1 gene led to embryonic lethality. We also showed that like Fdxr+/-+/-, Fdx1+/-+/- had a shorter life span and were prone to steatohepatitis. However, unlike Fdxr+/-+/-, Fdx1+/-+/- were not prone to spontaneous tumors. Additionally, we showed that FDX1 deficiency led to lipid droplet accumulation possibly via the ABCA1-SREBP1/2 pathway. Specifically, untargeted lipidomic analysis showed that FDX1 deficiency led to alterations in several classes of lipids, including cholesterol, triacylglycerides, acylcarnitines, ceramides, phospholipids and lysophospholipids. Taken together, our data indicate that FDX1 is essential for mammalian embryonic development and lipid homeostasis at both cellular and organismal levels.

Ferroptosis inducers enhanced cuproptosis induced by copper ionophores in primary liver cancer.

INTRODUCTION: Cuproptosis and ferroptosis are the two newly defined metal-related regulated cell death. However, the crosstalk between cuproptosis and ferroptosis is obscure. MATERIALS AND METHODS: We analyzed the effect of ferroptosis inducers on copper ionophores-induced cell death through CCK-8 assay. Cuproptosis was studied using immunofluorescence and protein soluble-insoluble fraction isolation. GSH assay, qRT-PCR and western blot were adopted to explore the machinery of ferroptosis inducers enhanced cuproptosis. And mouse xenograft model was built to detect the synergy effect of elesclomol-Cu and sorafenib in vivo. RESULTS: Herein we found that ferroptosis inducers sorafenib and erastin could enhance cuproptosis in primary liver cancer cells by increasing copper dependent lipoylated protein aggregation. Mechanically, sorafenib and erastin upregulated protein lipoylation via suppressing mitochondrial matrix-related proteases mediated ferredoxin 1 (FDX1) protein degradation, and reduced intracellular copper chelator glutathione (GSH) synthesis through inhibiting cystine importing. DISCUSSION/CONCLUSION: Our findings proposed that combination of ferroptosis inducers and copper ionophores to co-targeting ferroptosis and cuproptosis could be a novel therapeutic strategy for primary liver cancer.

Tumor cuproptosis and immune infiltration improve survival of patients with hepatocellular carcinoma with a high expression of ferredoxin 1.

Background: Cuproptosis is a novel cell death pathway dependent on cellular copper ions and ferredoxin 1 (FDX1). Hepatocellular carcinoma (HCC) is derived from healthy liver as a central organ for copper metabolism. It remains no conclusive evidence whether cuproptosis is involved in survival improvement of patients with HCC. Method: A 365-liver hepatocellular carcinoma (LIHC) cohort with RNA sequencing data and paired clinical and survival information was obtained from the The Cancer Genome Atlas (TCGA) dataset. A retrospective cohort of 57 patients with HCC with stages I/II/III was collected by Zhuhai People's Hospital from August 2016 to January 2022. Low- or high-FDX1 groups were divided according to the median value of FDX1 expression. Cibersort, single-sample gene set enrichment analysis, and multiplex immunohistochemistry analyzed immune infiltration in LIHC and HCC cohorts. Cell proliferation and migration of HCC tissues and hepatic cancer cell lines were evaluated using the Cell Counting Kit-8. Quantitative real-time PCR and RNA interference measured and downregulated FDX1 expression. Statistical analysis was conducted by R and GraphPad Prism software. Results: High FDX1 expression significantly enhanced survival of patients with LIHC from the TCGA dataset, which was also demonstrated through a retrospective cohort with 57 HCC cases. Immune infiltration was different between the low- and high-FDX1 expression groups. Natural killer cells, macrophages, and B cells were significantly enhanced, and PD-1 expression was low in the high-FDX1 tumor tissues. Meanwhile, we found that a high expression of FDX1 decreased cell viability in HCC samples. HepG2 cells with FDX1 expression are sensitive to Cu2+, and interference of FDX1 promoted proliferation and migration of tumor cells. The consistent results were also demonstrated in Hep3B cells. Conclusion: This study reveals that cuproptosis and tumor immune microenvironment were together involved in improvement of survival in patients with HCC with a high expression of FDX1.

Expression of Ferredoxin1 in cisplatin­resistant ovarian cancer cells confers their resistance against ferroptosis induced by cisplatin.

Ovarian cancer (OC) is a refractory cancer that shows recurrence due to the acquisition of resistance to anticancer drugs, including cisplatin. However, the molecular mechanism underlying the acquisition of cisplatin resistance by cancer cells remains largely unknown. In the present study, two sets of ovarian endometrioid carcinoma cell lines were used: The parental A2780 cell line, the OVK18 cell line, and their derived cisplatin­resistant cells. It was found that cisplatin could induce ferroptosis in these parental cells by enhancing mitochondrial membrane potential and lipid peroxidation as assessed by flow cytometric analysis, and that expression of Ferredoxin1 (Fdx1), an iron­sulfur protein localized to the mitochondria, could be upregulated in cisplatin­resistant cells in the absence of cisplatin. Intriguingly, it was shown that the siRNA­mediated depletion of Fdx1 in cisplatin­resistant cells resulted in enhanced ferroptosis by increasing the mitochondrial membrane potential and lipid peroxidation induced by cisplatin. By examining Fdx1 expression with immunohistochemical analysis in clinical specimens from patients with OC, higher expression of Fdx1 was detected in cisplatin­resistant specimens than in cisplatin­sensitive specimens. Collectively, these results indicated that Fdx1 may be a novel and suitable diagnostic/prognostic marker and therapeutic molecular target for the treatment of cisplatin­resistant OC.

Pan-cancer integrated bioinformatics analysis reveals cuproptosis related gene FDX1 is a potential prognostic and immunotherapeutic biomarker for lower-grade gliomas.

FDX1 participates in cuproptosis, a copper-dependent cell death mode, which might influence tumor progressions like ferroptosis and pyroptosis. However, the role of FDX1 in tumors remains to be explored. This study investigated FDX1 expression features, and correlations to prognosis, tumor stages, immune microenvironment, and cuproptosis from a pan-cancer perspective based on integrated bioinformatics. FDX1 mRNA and clinical data were obtained from The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), and Broad Institute Cancer Cell Line Encyclopedia (CCLE) databases. Differential expression of FDX1 in tumor stages was performed on GEPIA2.0. Cox proportional hazard regression and survival curve were used to analyze the prognostic value of FDX1. The relationships between FDX1 expression and immune infiltration, immune cells, immune checkpoints, tumor mutation burden (TMB), microsatellite instability (MSI), mismatch repair (MMR), and DNA methyltransferase (DNMT) were explored. GSEA was utilized to find the biological function of FDX1 in LGG. Results showed that FDX1 was abnormally expressed in multiple tumor types and demonstrated variability in various tumor stages. Survival analysis revealed FDX1 predicted poor prognosis in glioma (GBMLGG), brain lower-grade glioma (LGG), and good prognosis in the pan-kidney cohort (KIPAN), and kidney renal clear cell carcinoma (KIRC). Immune correlation analysis suggested FDX1 showed positive correlations to StromalScore, ImmuneScore, ESTIMATEScore in LGG and negative correlation in KIRC. Additionally, positive correlations were observed between FDX1 and immune cells infiltration, immune checkpoints, tumor stemness, homologous recombination deficiency (HRD), and TMB in LGG in the pan-cancer analysis. Validation with CGGA suggested prognostic value and immune correlation of FDX1 in LGG. Specifically, high expression of FDX1 was accompanied by high expression of immune checkpoints such as CD276 (B7-H3), CD274 (PD-L1), PDCD1LG2 (PD-L2), CTLA4, and HAVCR2. These findings illustrated that FDX1 might be considered a potential poor prognosis biomarker and immunotherapy predictor in LGG.

FDX1 expression predicts favourable prognosis in clear cell renal cell carcinoma identified by bioinformatics and tissue microarray analysis.

Ferredoxin 1 (FDX1), an iron-sulphur protein, is responsible for electron transfer in a range of metabolic redox reactions. Clear cell renal cell carcinoma (ccRCC) is an aggressive cancer characterised by metabolic reprogramming, and FDX1 is a critical regulator of cuproptosis. However, the expression profile and prognostic value of FDX1 associated with clinicopathological features in ccRCC remain largely unelucidated. In this study, we integrated a series of public bioinformatic analysis to explore the mRNA and protein profiles of FDX1 across human cancers and cell lines and validated its expression and prognostic value, especially in ccRCC. In this study, FDX1 mRNA and protein expression were aberrantly downregulated and associated with ccRCC grade, stage, and nodal metastasis, whereas in adjacent non-tumour kidney tissue, it was abundantly expressed and cytoplasmically localised in renal tubular epithelial cells. Multivariate analysis indicated that low FDX1 expression contributed to unfavourable overall and disease-free survival. The functional enrichment of FDX1 co-expressed genes in ccRCC involved mainly mitochondrial dysfunction in various metabolic processes and biological oxidation, besides iron-sulphur cluster biogenesis. Furthermore, FDX1 modulates immunological infiltration to affect prognosis. Thus, FDX1 downregulation is mechanistically because of ccRCC tumourigenesis and is a promising prognostic biomarker to stratify patients with ccRCC.

Characterization of the functional effects of ferredoxin 1 as a cuproptosis biomarker in cancer.

Background: Cuproptosis is a recently discovered form of programmed cell death. Ferredoxin 1 (FDX1) is a key gene that mediates this process. However, the role of FDX1 in human tumors is not clear. Methods: We comprehensively analyzed the differential expression and genetic alterations of FDX1 using multiomics data from The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression (GTEx) database. Subsequently, we explored the association between FDX1 and tumor parameters such as genomic instability, RNA methylation modifications, immune infiltration and pathway activity. In addition, we performed functional enrichment analysis and assessed the sensitivity potential of FDX1-related drugs. Finally, we experimentally verified the functional effects of FDX1. Results: The analysis revealed differential expression of FDX1 in a variety of tumors. By analyzing the association of FDX1 expression with genomic instability, immune cell infiltration, signaling pathway etc. We explored the role of FDX1 in regulating cell activity. Also, we evaluated the function of FDX1 in biologic process and drug sensitivity. Our experimental results demonstrated that FDX1 exerts its antitumor effects through cuproptosis in liver hepatocellular carcinoma and non-small cell lung cancer cell lines. Conclusion: Our study reveals the functional effects of FDX1 in tumors and deepens the understanding of the effects of FDX1. We validated the inhibitory effect of FDX1 in copper induced cell-death, confirming the role of FDX1 as a cuproptosis biomarker.

Cuproptosis-related gene FDX1 expression correlates with the prognosis and tumor immune microenvironment in clear cell renal cell carcinoma.

Background: Cuproptosis, a newly discovered form of cell death, is regulated by protein lipoylation and is related to mitochondrial metabolism. However, further research is needed to determine how the cuproptosis-related gene ferredoxin 1 (FDX1) affects the tumor immune response and its prognostic significance in clear cell renal cell carcinoma (ccRCC). Methods: The Cancer Genome Atlas was used to screen for FDX1 gene expression in ccRCC and healthy tissue samples. The results were validated using the Gene Expression Omnibus and the Human Protein Atlas. Multivariable analysis and Kaplan-Meier survival curves were used to examine the relationship between FDX1 gene expression, clinicopathological parameters, and overall survival (OS). The protein network containing FDX1 gene interaction was constructed using the online Search Tool for the Retrieval of Interacting Genes/Proteins. The relationship between FDX1 gene expression and immune cell infiltration in ccRCC was examined using Gene Ontology, gene set enrichment analysis (GSEA), and a single-sample GSEA. Using the Gene Expression Profiling Interactive Analysis and Tumor Immune Estimation Resource databases, we investigated the relationship between FDX1 gene expression, the degree of immune cell infiltration, and the corresponding gene marker sets. Results: ccRCC samples had significantly (p < 0.05) lower FDX1 gene expression levels than normal tissue samples. Lower FDX1 gene expression levels were strongly associated with higher cancer grades and more advanced tumor-node-metastasis stages. The findings of multivariate and univariate analyses illustrated that the OS in ccRCC patients with low FDX1 expression is shorter than in patients with high FDX1 expression (p < 0.05). Ferredoxin reductase and CYP11A1 are key proteins interacting with the FDX1 gene, and ccRCC with an FDX1 enzyme defect was associated with a low number of invading immune cells and their corresponding marker. Conclusion: In ccRCC, decreased FDX1 expression was linked to disease progression, an unfavorable prognosis, and dysregulated immune cell infiltration.

Cuproptosis-Related Gene - SLC31A1, FDX1 and ATP7B - Polymorphisms are Associated with Risk of Lung Cancer.

Background: Cuproptosis is a novel copper-dependent cell death, and the copper level was increased in lung cancer patients. However, few studies evaluated the association between single-nucleotide polymorphisms (SNPs) in cuproptosis-related genes and lung cancer risk. Methods: Six SNPs of the SLC31A1, FDX1 and ATP7B genes were genotyped in a case-control cohort including 650 lung cancer cases and 650 controls using the MassARRAY platform. Results: The minor alleles of SLC31A1-rs10981694 and FDX1-rs10488764 were associated with an increased risk of lung cancer (rs10981694: OR=1.455, 95% CI: 1.201-1.763, p<0.001; rs10488764: OR=1.483, 95% CI: 1.244-1.768, p<0.001). In contrast, the minor alleles of rs9535826 and rs9535828 in ATP7B were related to a decreased risk of the disease (rs9535826: OR=0.714, 95% CI: 0.608-0.838 p<0.001; rs9535828: OR=0.679, 95% CI: 0.579-0.796, p<0.001). The frequencies of rs10981694-TG/GG and rs10488764-GA/AA genotypes were significantly higher in lung cancer cases than that in controls, making them risk genotypes for the disease (p < 0.001); while the rs9535826-TG/GG and rs9535828-GA/AA genotypes were protective genotypes and associated with a reduced risk of the disease (p<0.001). Genetic model evaluation revealed that SLC31A1-rs10981694 and FDX1-rs10488764 were associated with a growing risk of lung cancer in dominant, recessive and log-additive models (p<0.001). Moreover, rs9535826 and rs9535828 in ATP7B were related to a declining risk of the disease in three genetic models (p<0.001). In addition, stratification analysis showed that FDX1-rs10488764 was risk variant for lung cancer in both smokers and nonsmokers, and was associated with risk of each pathological type of lung cancer (p<0.008). Conclusion: The results shed new light on the correlation between cuproptosis-related genes and risk of lung cancer.

Ferredoxin 1 is downregulated by the accumulation of abscisic acid in an ABI5-dependent manner to facilitate rice stripe virus infection in Nicotiana benthamiana and rice.

Ferredoxin 1 (FD1) accepts and distributes electrons in the electron transfer chain of plants. Its expression is universally downregulated by viruses and its roles in plant immunity have been brought into focus over the past decade. However, the mechanism by which viruses regulate FD1 remains to be defined. In a previous report, we found that the expression of Nicotiana benthamiana FD1 (NbFD1) was downregulated following infection with potato virus X (PVX) and that NbFD1 regulates callose deposition at plasmodesmata to play a role in defense against PVX infection. We now report that NbFD1 is downregulated by rice stripe virus (RSV) infection and that silencing of NbFD1 also facilitates RSV infection, while viral infection was inhibited in a transgenic line overexpressing NbFD1, indicating that NbFD1 also functions in defense against RSV infection. Next, a RSV-derived small interfering RNA was identified that contributes to the downregulation of FD1 transcripts. Further analysis showed that the abscisic acid (ABA) which accumulates in RSV-infected plants also represses NbFD1 transcription. It does this by stimulating expression of ABA insensitive 5 (ABI5), which binds the ABA response element motifs in the NbFD1 promoter, resulting in negative regulation. Regulation of FD1 by ABA was also confirmed in RSV-infected plants of the natural host rice. The results therefore suggest a mechanism by which virus regulates chloroplast-related genes to suppress their defense roles.

Involvement of the chloroplast gene ferredoxin 1 in multiple responses of Nicotiana benthamiana to Potato virus X infection.

The chloroplast protein ferredoxin 1 (FD1), with roles in the chloroplast electron transport chain, is known to interact with the coat proteins (CPs) of Tomato mosaic virus and Cucumber mosaic virus. However, our understanding of the roles of FD1 in virus infection remains limited. Here, we report that the Potato virus X (PVX) p25 protein interacts with FD1, whose mRNA and protein levels are reduced by PVX infection or by transient expression of p25. Silencing of FD1 by Tobacco rattle virus-based virus-induced gene silencing (VIGS) promoted the local and systemic infection of plants by PVX. Use of a drop-and-see (DANS) assay and callose staining revealed that the permeability of plasmodesmata (PDs) was increased in FD1-silenced plants together with a consistently reduced level of PD callose deposition. After FD1 silencing, quantitative reverse transcription-real-time PCR (qRT-PCR) analysis and LC-MS revealed these plants to have a low accumulation of the phytohormones abscisic acid (ABA) and salicylic acid (SA), which contributed to the decreased callose deposition at PDs. Overexpression of FD1 in transgenic plants manifested resistance to PVX infection, but the contents of ABA and SA, and the PD callose deposition were not increased in transgenic plants. Overexpression of FD1 interfered with the RNA silencing suppressor function of p25. These results demonstrate that interfering with FD1 function causes abnormal plant hormone-mediated antiviral processes and thus enhances PVX infection.

Classifying chemical mode of action using gene networks and machine learning: a case study with the herbicide linuron.

The herbicide linuron (LIN) is an endocrine disruptor with an anti-androgenic mode of action. The objectives of this study were to (1) improve knowledge of androgen and anti-androgen signaling in the teleostean ovary and to (2) assess the ability of gene networks and machine learning to classify LIN as an anti-androgen using transcriptomic data. Ovarian explants from vitellogenic fathead minnows (FHMs) were exposed to three concentrations of either 5α-dihydrotestosterone (DHT), flutamide (FLUT), or LIN for 12h. Ovaries exposed to DHT showed a significant increase in 17ß-estradiol (E2) production while FLUT and LIN had no effect on E2. To improve understanding of androgen receptor signaling in the ovary, a reciprocal gene expression network was constructed for DHT and FLUT using pathway analysis and these data suggested that steroid metabolism, translation, and DNA replication are processes regulated through AR signaling in the ovary. Sub-network enrichment analysis revealed that FLUT and LIN shared more regulated gene networks in common compared to DHT. Using transcriptomic datasets from different fish species, machine learning algorithms classified LIN successfully with other anti-androgens. This study advances knowledge regarding molecular signaling cascades in the ovary that are responsive to androgens and anti-androgens and provides proof of concept that gene network analysis and machine learning can classify priority chemicals using experimental transcriptomic data collected from different fish species.