Oxidative regulation of chloroplast enzymes by thioredoxin and thioredoxin-like proteins in Arabidopsis thaliana

Plants modulate photosynthesis activity in response to the surrounding environment. It is well known that the redox-responsive protein thioredoxin (Trx) activates photosynthesis-related enzymes in the light. However, the factors involved in deactivating them are not well understood. Recent in vitro experiments suggest that several Trx and Trx-like proteins serve as oxidation factors for Trx-targeted proteins; thus, we examined their functions in vivo. Consequently, we found that f-type Trx and two types of Trx-like proteins, Trx-like 2 and atypical Cys His-rich Trx, were involved in oxidative deactivation of photosynthesis-related enzymes (e.g., fructose-1,6-bisphosphatase, Rubisco activase, and the ATP synthase γ-subunit). Thus, this study reveals the functions of oxidation factors in vivo and elucidates the regulation system for photosynthesis in the dark.

Thioredoxin (Trx) is a protein that mediates the reducing power transfer from the photosynthetic electron transport system to target enzymes in chloroplasts and regulates their activities. Redox regulation governed by Trx is a system that is central to the adaptation of various chloroplast functions to the ever-changing light environment. However, the factors involved in the opposite reaction (i.e., the oxidation of various enzymes) have yet to be revealed. Recently, it has been suggested that Trx and Trx-like proteins could oxidize Trx-targeted proteins in vitro. To elucidate the in vivo function of these proteins as oxidation factors, we generated mutant plant lines deficient in Trx or Trx-like proteins and studied how the proteins are involved in oxidative regulation in chloroplasts. We found that f-type Trx and two types of Trx-like proteins, Trx-like 2 and atypical Cys His-rich Trx (ACHT), seemed to serve as oxidation factors for Trx-targeted proteins, such as fructose-1,6-bisphosphatase, Rubisco activase, and the γ-subunit of ATP synthase. In addition, ACHT was found to be involved in regulating nonphotochemical quenching, which is the mechanism underlying the thermal dissipation of excess light energy. Overall, these results indicate that Trx and Trx-like proteins regulate chloroplast functions in concert by controlling the redox state of various photosynthesis-related proteins in vivo.

Oridonin induces oxidative stress-mediated cancer cells apoptosis via targeting thioredoxin reductase

BACKGROUND

Thioredoxin reductase (TrxR) plays vital role in regulating cellular redox balance as well as redox-mediated signal transduction. Accumulating evidence supports that overactivation of TrxR is closely related to tumorigenesis and that targeting TrxR ablation reverses the growth of numerous malignant tumors, making TrxR a promising target for cancer chemotherapy. Thus, the discovery and development of molecules as promising anticancer agents that target TrxR is of great significance. Oridonin was shown to inhibit TrxR activity, but the detailed cellular mechanism is largely unknown.

OBJECTIVE

The study investigated the mechanism of action and underlying inhibitory properties of oridonin on TrxR in HeLa cells.

METHODS

A covalent docking was performed to reveal the possible interaction between oridonin and TrxR by Schrödinger Software Suite. TrxR activity was determined by 5,5'-dithiobis-2-nitrobenzoic acid reduction assay and endpoint insulin reduction assay. Sulforhodamine B and colony formation assay were employed to assess the viability and growth of cells. Reactive oxygen species level was measured by probe 2', 7'-dichlorfluorescein diacetate, and dihydroethidium. Hoechst 33342 staining, caspase 3 activation, and fluorescein-5-isothiocyanate-conjugated Annexin V and propidium iodide double staining were used to evaluate apoptosis.

RESULTS

Here, we reported the oridonin as a potent inhibitor of TrxR. Inhibition of TrxR results in a decrease of thiols content and total glutathione elevates reactive oxygen species levels, and finally promotes oxidative stress-mediated apoptosis of cancer cells.

CONCLUSION

Targeting TrxR by oridonin discloses a novel molecular mechanism underlying the biological action of oridonin and sheds light on developing oridonin as a potential tumor therapeutic agent.

Interchangeable utilization of metals: New perspectives on the impacts of metal ions employed in ancient and extant biomolecules

Metal ions provide considerable functionality across biological systems, and their utilization within biomolecules has adapted through changes in the chemical environment to maintain the activity they facilitate. While ancient earth's atmosphere was rich in iron and manganese and low in oxygen, periods of atmospheric oxygenation significantly altered the availability of certain metal ions, resulting in ion replacement within biomolecules. This adaptation mechanism has given rise to the phenomenon of metal cofactor interchangeability, whereby contemporary proteins and nucleic acids interact with multiple metal ions interchangeably, with different coordinated metals influencing biological activity, stability, and toxic potential. The ability of extant organisms to adapt to fluctuating metal availability remains relevant in a number of crucial biomolecules, including the superoxide dismutases of the antioxidant defense systems and ribonucleotide reductases. These well-studied and ancient enzymes illustrate the potential for metal interchangeability and adaptive utilization. More recently, the ribosome has also been demonstrated to exhibit interchangeable interactions with metal ions with impacts on function, stability, and stress adaptation. Using these and other examples, here we review the biological significance of interchangeable metal ions from a new angle that combines both biochemical and evolutionary viewpoints. The geochemical pressures and chemical properties that underlie biological metal utilization are discussed in the context of their impact on modern disease states and treatments.

Autophagy Is Involved in the Viability of Overexpressing Thioredoxin o1 Tobacco BY-2 Cells under Oxidative Conditions

Autophagy is an essential process for the degradation of non-useful components, although the mechanism involved in its regulation is less known in plants than in animal systems. Redox regulation of autophagy components is emerging as a possible key mechanism with thioredoxins (TRXs) proposed as involved candidates. In this work, using overexpressing PsTRXo1 tobacco cells (OEX), which present higher viability than non-overexpressing cells after H₂O₂ treatment, we examine the functional interaction of autophagy and PsTRXo1 in a collaborative response. OEX cells present higher gene expression of the ATG (Autophagy related) marker ATG4 and higher protein content of ATG4, ATG8, and lipidated ATG8 as well as higher ATG4 activity than control cells, supporting the involvement of autophagy in their response to H₂O₂. In this oxidative situation, autophagy occurs in OEX cells as is evident from an accumulation of autolysosomes and ATG8 immunolocalization when the E-64d autophagy inhibitor is used. Interestingly, cell viability decreases in the presence of the inhibitor, pointing to autophagy as being involved in cell survival. The in vitro interaction of ATG4 and PsTRXo1 proteins is confirmed by dot-blot and co-immunoprecipitation assays as well as the redox regulation of ATG4 activity by PsTRXo1. These findings extend the role of TRXs in mediating the redox regulation of the autophagy process in plant cells.

COVID-19: A Redox Disease-What a Stress Pandemic Can Teach Us About Resilience and What We May Learn from the Reactive Species Interactome About Its Treatment

Significance: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus causing coronavirus disease 2019 (COVID-19), affects every aspect of human life by challenging bodily, socioeconomic, and political systems at unprecedented levels. As vaccines become available, their distribution, safety, and efficacy against emerging variants remain uncertain, and specific treatments are lacking. Recent Advances: Initially affecting the lungs, COVID-19 is a complex multisystems disease that disturbs the whole-body redox balance and can be long-lasting (Long-COVID). Numerous risk factors have been identified, but the reasons for variations in susceptibility to infection, disease severity, and outcome are poorly understood. The reactive species interactome (RSI) was recently introduced as a framework to conceptualize how cells and whole organisms sense, integrate, and accommodate stress. Critical Issues: We here consider COVID-19 as a redox disease, offering a holistic perspective of its effects on the human body, considering the vulnerability of complex interconnected systems with multiorgan/multilevel interdependencies. Host/viral glycan interactions underpin SARS-CoV-2's extraordinary efficiency in gaining cellular access, crossing the epithelial/endothelial barrier to spread along the vascular/lymphatic endothelium, and evading antiviral/antioxidant defences. An inflammation-driven "oxidative storm" alters the redox landscape, eliciting epithelial, endothelial, mitochondrial, metabolic, and immune dysfunction, and coagulopathy. Concomitantly reduced nitric oxide availability renders the sulfur-based redox circuitry vulnerable to oxidation, with eventual catastrophic failure in redox communication/regulation. Host nutrient limitations are crucial determinants of resilience at the individual and population level. Future Directions: While inflicting considerable damage to health and well-being, COVID-19 may provide the ultimate testing ground to improve the diagnosis and treatment of redox-related stress diseases. "Redox phenotyping" of patients to characterize whole-body RSI status as the disease progresses may inform new therapeutic approaches to regain redox balance, reduce mortality in COVID-19 and other redox diseases, and provide opportunities to tackle Long-COVID. Antioxid. Redox Signal. 35, 1226-1268.

AtpΘ is an inhibitor of F0F1 ATP synthase to arrest ATP hydrolysis during low-energy conditions in cyanobacteria

Biological processes in all living cells are powered by ATP, a nearly universal molecule of energy transfer. ATP synthases produce ATP utilizing proton gradients that are usually generated by either respiration or photosynthesis. However, cyanobacteria are unique in combining photosynthetic and respiratory electron transport chains in the same membrane system, the thylakoids. How cyanobacteria prevent the futile reverse operation of ATP synthase under unfavorable conditions pumping protons while hydrolyzing ATP is mostly unclear. Here, we provide evidence that the small protein AtpΘ, which is widely conserved in cyanobacteria, is mainly fulfilling this task. The expression of AtpΘ becomes induced under conditions such as darkness or heat shock, which can lead to a weakening of the proton gradient. Translational fusions of AtpΘ to the green fluorescent protein revealed targeting to the thylakoid membrane. Immunoprecipitation assays followed by mass spectrometry and far western blots identified subunits of ATP synthase as interacting partners of AtpΘ. ATP hydrolysis assays with isolated membrane fractions, as well as purified ATP synthase complexes, demonstrated that AtpΘ inhibits ATPase activity in a dose-dependent manner similar to the F₀F₁-ATP synthase inhibitor N,N-dicyclohexylcarbodimide. The results show that, even in a well-investigated process, crucial new players can be discovered if small proteins are taken into consideration and indicate that ATP synthase activity can be controlled in surprisingly different ways.

Oxidative Cysteine Modification of Thiol Isomerases in Thrombotic Disease: A Hypothesis

Significance: Oxidative stress is a characteristic of many systemic diseases associated with thrombosis. Thiol isomerases are a family of oxidoreductases important in protein folding and are exquisitely sensitive to the redox environment. They are essential for thrombus formation and represent a previously unrecognized layer of control of the thrombotic process. Yet, the mechanisms by which thiol isomerases function in thrombus formation are unknown. Recent Advances: The oxidoreductase activity of thiol isomerases in thrombus formation is controlled by the redox environment via oxidative changes to active site cysteines. Specific alterations can now be detected owing to advances in the chemical biology of oxidative cysteine modifications. Critical Issues: Understanding of the role of thiol isomerases in thrombus formation has focused largely on identifying single disulfide bond modifications in isolated proteins (e.g., α_IIbβ₃, tissue factor, vitronectin, or glycoprotein Ibα [GPIbα]). An alternative approach is to conceptualize thiol isomerases as effectors in redox signaling pathways that control thrombotic potential by modifying substrate networks. Future Directions: Cysteine-based chemical biology will be employed to study thiol-dependent dynamics mediated by the redox state of thiol isomerases at the systems level. This approach could identify thiol isomerase-dependent modifications of the disulfide landscape that are prothrombotic.

Corynebacterium glutamicum Mycoredoxin 3 protects against multiple oxidative stresses and displays thioredoxin-like activity

Glutaredoxins (Grxs) and thioredoxins (Trxs) play a critical role in resistance to oxidative conditions. However, physiological and biochemical roles of Mycoredoxin 3 (Mrx3) that shared a high amino acid sequence similarity to Grxs remain unknown in Corynebacterium glutamicum. Here we showed that mrx3 deletion strains of C. glutamicum was involved in the protection against oxidative stress. Recombinant Mrx3 not only catalytically reduced the disulfide bonds in ribonucleotide reductase (RNR), insulin and 5,5'-dithiobis-(2-nitro-benzoicacid) (DTNB), but also reduced the mixed disulphides between mycothiol (MSH) and substrate, which was exclusively linked to the thioredoxin reductase (TrxR) electron transfer pathway by a dithiol mechanism. Site-directed mutagenesis confirmed that the conserved Cys17 and Cys20 in Mrx3 were necessary to maintain its activity. The mrx3 deletion mutant showed decreased resistance to various stress, and these sensitive phenotypes were almost fully restored in the complementary strain. The physiological roles of Mrx3 in resistance to various stress were further supported by the induced expression of mrx3 under various stress conditions, directly under the control of the stress-responsive extracytoplasmic function-sigma (ECF-σ) factor SigH. Thus, we presented the first evidence that Mrx3 protected against various oxidative stresses by acting as a disulfide oxidoreductase behaving like Trx.

Thioredoxins m are major players in the multifaceted light-adaptive response in Arabidopsis thaliana

Thioredoxins (TRXs) are well-known redox signalling players, which carry out post-translational modifications in target proteins. Chloroplast TRXs are divided into different types and have central roles in light energy uptake and the regulation of primary metabolism. The isoforms TRX m1, m2, and m4 from Arabidopsis thaliana are considered functionally related. Knowing their key position in the hub of plant metabolism, we hypothesized that the impairment of the TRX m signalling would not only have harmful consequences on chloroplast metabolism but also at different levels of plant development. To uncover the physiological and developmental processes that depend on TRX m signalling, we carried out a comprehensive study of Arabidopsis single, double, and triple mutants defective in the TRX m1, m2, and m4 proteins. As light and redox signalling are closely linked, we investigated the response to high light (HL) of the plants that are gradually compromised in TRX m signalling. We provide experimental evidence relating the lack of TRX m and the appearance of novel phenotypic features concerning mesophyll structure, stomata biogenesis, and stomatal conductance. We also report new data indicating that the isoforms of TRX m fine-tune the response to HL, including the accumulation of the protective pigment anthocyanin. These results reveal novel signalling functions for the TRX m and underline their importance for plant growth and fulfilment of the acclimation/response to HL conditions.

Understanding Metabolic Remodeling in Mycobacterium smegmatis to Overcome Energy Exigency and Reductive Stress Under Energy-Compromised State

Mycobacteria such as Mycobacterium tuberculosis, the causative agent of tuberculosis that annually kills several million people worldwide, and Mycobacterium smegmatis, the non-pathogenic fast-growing mycobacteria, require oxidative phosphorylation to meet their energy requirements. We have previously shown that deletion of one of the two copies of atpD gene that codes for the ATP synthase β-subunit establishes an energy-compromised state in M. smegmatis. Here we report that upon such deletion, a major routing of electron flux occurs through the less energy-efficient complexes of its respiratory chain. ΔatpD bacterium also shows an increased reduced state which is further confirmed by the overexpression of WhiB3, a major redox sensor. We show a substantial modulation of the biosynthesis of cell wall associated lipids and triacylglycerol (TAG). An accumulation of TAG-containing lipid bodies is further confirmed by using ¹⁴C oleate incorporation. Interestingly, the mutant also shows an overexpression of TAG-degrading lipase genes, and the intracellular lipolytic enzymes mediate TAG hydrolysis for their utilization as energy source. We believe that our in vitro energy-depleted model will allow us to explore the critical link between energy metabolism, redox homeostasis, and lipid biosynthesis during ATP-depleted state, which will enhance our understanding of the bacterial adaptation, and will allow us to identify novel drug targets to counter mycobacterial infections.

Uncovering the Metabolic and Stress Responses of Human Embryonic Stem Cells to FTH1 Gene Silencing

Embryonic stem cells (ESCs) are pluripotent cells with indefinite self-renewal ability and differentiation properties. To function properly and maintain genomic stability, ESCs need to be endowed with an efficient repair system as well as effective redox homeostasis. In this study, we investigated different aspects involved in ESCs' response to iron accumulation following stable knockdown of the ferritin heavy chain (FTH1) gene, which encodes for a major iron storage protein with ferroxidase activity. Experimental findings highlight unexpected and, to a certain extent, paradoxical results. If on one hand FTH1 silencing does not correlate with increased ROS production nor with changes in the redox status, strengthening the concept that hESCs are extremely resistant and, to a certain extent, even refractory to intracellular iron imbalance, on the other, the differentiation potential of hESCs seems to be affected and apoptosis is observed. Interestingly, we found that FTH1 silencing is accompanied by a significant activation of the nuclear factor (erythroid-derived-2)-like 2 (Nrf2) signaling pathway and pentose phosphate pathway (PPP), which crosstalk in driving hESCs antioxidant cascade events. These findings shed new light on how hESCs perform under oxidative stress, dissecting the molecular mechanisms through which Nrf2, in combination with PPP, counteracts oxidative injury triggered by FTH1 knockdown.

Monitoring cellular redox dynamics using newly developed BRET-based redox sensor proteins

Reactive oxygen species are key factors that strongly affect the cellular redox state and regulate various physiological and cellular phenomena. To monitor changes in the redox state, we previously developed fluorescent redox sensors named Re-Q, the emissions of which are quenched under reduced conditions. However, such fluorescent probes are unsuitable for use in the cells of photosynthetic organisms because they require photoexcitation that may change intracellular conditions and induce autofluorescence, primarily in chlorophylls. In addition, the presence of various chromophore pigments may interfere with fluorescence-based measurements because of their strong absorbance. To overcome these problems, we adopted the bioluminescence resonance energy transfer (BRET) mechanism for the sensor and developed two BRET-based redox sensors by fusing cyan fluorescent protein–based or yellow fluorescent protein–based Re-Q with the luminescent protein Nluc. We named the resulting redox-sensitive BRET-based indicator probes “ROBINc” and “ROBINy.” ROBINc is pH insensitive, which is especially vital for observation in photosynthetic organisms. By using these sensors, we successfully observed dynamic redox changes caused by an anticancer agent in HeLa cells and light/dark-dependent redox changes in the cells of photosynthetic cyanobacterium Synechocystis sp. PCC 6803. Since the newly developed sensors do not require excitation light, they should be especially useful for visualizing intracellular phenomena caused by redox changes in cells containing colored pigments.

The temperature-regulated DEAD-box RNA helicase CrhR interactome: Autoregulation and photosynthesis-related transcripts

RNA helicases play crucial functions in RNA biology. In plants, RNA helicases are encoded by large gene families, performing roles in abiotic stress responses, development, the post-transcriptional regulation of gene expression as well as house-keeping functions. Several of these RNA helicases are targeted to the organelles, mitochondria and chloroplasts. Cyanobacteria are the direct evolutionary ancestors of plant chloroplasts. The cyanobacterium Synechocystis 6803 encodes a single DEAD-box RNA helicase, CrhR, that is induced by a range of abiotic stresses, including low temperature. Though the ΔcrhR mutant exhibits a severe cold-sensitive phenotype, the physiological function(s) performed by CrhR have not been described. To identify transcripts interacting with CrhR, we performed RNA co-immunoprecipitation with extracts from a Synechocystis crhR deletion mutant expressing the FLAG-tagged native CrhR or a K57A mutated version with an anticipated enhanced RNA binding. The composition of the interactome was strikingly biased towards photosynthesis-associated and redox-controlled transcripts. A transcript highly enriched in all experiments was the crhR mRNA, suggesting an auto-regulatory molecular mechanism. The identified interactome explains the described physiological role of CrhR in response to the redox poise of the photosynthetic electron transport chain and characterizes CrhR as an enzyme with a diverse range of transcripts as molecular targets.

Calvin-Benson cycle regulation is getting complex

Oxygenic phototrophs use the Calvin-Benson cycle to fix CO₂ during photosynthesis. In the dark, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and phosphoribulokinase (PRK), two enzymes of the Calvin-Benson cycle, form an inactive complex with the regulatory protein CP12, mainly under the control of thioredoxins and pyridine nucleotides. In the light, complex dissociation allows GAPDH and PRK reactivation. The GAPDH/CP12/PRK complex is conserved from cyanobacteria to angiosperms and coexists in land plants with an autoassembling GAPDH that is analogously regulated. With the recently described 3D structures of PRK and GAPDH/CP12/PRK, the structural proteome of this ubiquitous regulatory system has been completed. This outcome opens a new avenue for understanding the regulatory potential of photosynthetic carbon fixation by laying the foundation for its knowledge-based manipulation.

Aim32 is a dual-localized 2Fe-2S mitochondrial protein that functions in redox quality control

Yeast is a facultative anaerobe and uses diverse electron acceptors to maintain redox-regulated import of cysteine-rich precursors via the mitochondrial intermembrane space assembly (MIA) pathway. With the growing diversity of substrates utilizing the MIA pathway, understanding the capacity of the intermembrane space (IMS) to handle different types of stress is crucial. We used MS to identify additional proteins that interacted with the sulfhydryl oxidase Erv1 of the MIA pathway. Altered inheritance of mitochondria 32 (Aim32), a thioredoxin-like [2Fe-2S] ferredoxin protein, was identified as an Erv1-binding protein. Detailed localization studies showed that Aim32 resided in both the mitochondrial matrix and IMS. Aim32 interacted with additional proteins including redox protein Osm1 and protein import components Tim17, Tim23, and Tim22. Deletion of Aim32 or mutation of conserved cysteine residues that coordinate the Fe-S center in Aim32 resulted in an increased accumulation of proteins with aberrant disulfide linkages. In addition, the steady-state level of assembled TIM22, TIM23, and Oxa1 protein import complexes was decreased. Aim32 also bound to several mitochondrial proteins under nonreducing conditions, suggesting a function in maintaining the redox status of proteins by potentially targeting cysteine residues that may be sensitive to oxidation. Finally, Aim32 was essential for growth in conditions of stress such as elevated temperature and hydroxyurea, and under anaerobic conditions. These studies suggest that the Fe-S protein Aim32 has a potential role in general redox homeostasis in the matrix and IMS. Thus, Aim32 may be poised as a sensor or regulator in quality control for a broad range of mitochondrial proteins.

Cell cycle-coupled changes in the level of reactive oxygen species support the proliferation of human pluripotent stem cells

The study of proliferation regulation in human pluripotent stem cells is crucial to gain insights into understanding the physiology of these cells. However, redox regulation of the pluripotent cell cycle remains largely unexplored. Here, using human embryonic stem cells (hESCs) as well as human induced pluripotent stem cells (hiPSCs), we demonstrate that the level of reactive oxygen species (ROS) in pluripotent cells oscillates in accordance with the cell cycle progression with the peak occurring at transition from S to G₂ /M phase of the cycle. A decrease of this level by antioxidants leads to hindered S-phase initiation and progression but does not affect the early-G₁ -phase or mitosis. Cells exposed to antioxidants in the early-G₁ -phase accumulate the phosphorylated retinoblastoma protein and overcome the restriction point but are unable to accumulate the main regulators of the S phase-CYCLIN A and GEMININ. Based on the previous findings that CYCLIN A stability is affected by redox homeostasis disturbances in somatic cells, we compared the responses to antioxidant treatments in hESCs and in their differentiated fibroblast-like progeny cells (difESCs). In difESCs, similar to hESCs, a decrease in ROS level results in the disruption of S-phase initiation accompanied by a deficiency of the CYCLIN A level. Moreover, in antioxidant-treated cells, we revealed the accumulation of DNA breaks, which was accompanied by activation of the apoptosis program in pluripotent cells. Thus, we conclude that maintaining the physiological ROS level is essential for promotion of proliferation and accurate DNA synthesis in pluripotent cells and their differentiated descendants.

NNT mediates redox-dependent pigmentation via a UVB- and MITF-independent mechanism

Ultraviolet (UV) light and incompletely understood genetic and epigenetic variations determine skin color. Here we describe an UV- and microphthalmia-associated transcription factor (MITF)-independent mechanism of skin pigmentation. Targeting the mitochondrial redox-regulating enzyme nicotinamide nucleotide transhydrogenase (NNT) resulted in cellular redox changes that affect tyrosinase degradation. These changes regulate melanosome maturation and, consequently, eumelanin levels and pigmentation. Topical application of small-molecule inhibitors yielded skin darkening in human skin, and mice with decreased NNT function displayed increased pigmentation. Additionally, genetic modification of NNT in zebrafish alters melanocytic pigmentation. Analysis of four diverse human cohorts revealed significant associations of skin color, tanning, and sun protection use with various single-nucleotide polymorphisms within NNT. NNT levels were independent of UVB irradiation and redox modulation. Individuals with postinflammatory hyperpigmentation or lentigines displayed decreased skin NNT levels, suggesting an NNT-driven, redox-dependent pigmentation mechanism that can be targeted with NNT-modifying topical drugs for medical and cosmetic purposes.

Chloroplast Lipids Metabolism and Function. A Redox Perspective

Plant productivity is determined by the conversion of solar energy into biomass through oxygenic photosynthesis, a process performed by protein-cofactor complexes including photosystems (PS) II and I, and ATP synthase. These complexes are embedded in chloroplast thylakoid membrane lipids, which thus function as structural support of the photosynthetic machinery and provide the lipid matrix to avoid free ion diffusion. The lipid and fatty acid composition of thylakoid membranes are unique in chloroplasts and cyanobacteria, which implies that these molecules are specifically required in oxygenic photosynthesis. Indeed, there is extensive evidence supporting a relevant function of glycerolipids in chloroplast biogenesis and photosynthetic efficiency in response to environmental stimuli, such as light and temperature. The rapid acclimation of higher plants to environmental changes is largely based on thiol-based redox regulation and the disulphide reductase activity thioredoxins (Trxs), which are reduced by ferredoxin (Fdx) via an Fdx-dependent Trx reductase. In addition, chloroplasts harbour an NADPH-dependent Trx reductase C, which allows the use of NADPH to maintain the redox homeostasis of the organelle. Here, we summarise the current knowledge of chloroplast lipid metabolism and the function of these molecules as structural basis of the complex membrane network of the organelle. Furthermore, we discuss evidence supporting the relevant role of lipids in chloroplast biogenesis and photosynthetic performance in response to environmental cues in which the redox state of the organelle plays a relevant role.

The Sex Differences in Uveal Melanoma: Potential Roles of EIF1AX, Immune Response and Redox Regulation

BACKGROUND

Uveal melanoma (UVM) is a rare cancer that shows sex difference in incidence and survival, with little previous report for the underlying mechanism.

METHODS

This study used the SEER data (1974-2016) for an age-dependent analysis on sex difference in UVM, and further used the TCGA-UVM genomics dataset for analyzing the differential gene expression profiles in tumors from men and women.

RESULTS

Our results demonstrate a sex difference in older age (≥40 years) but not in younger patients, with men exhibiting a higher incidence rate than women. However, younger women have shown a continuous increasing trend since 1974. Examining the 11 major oncogenes and tumor suppressors in UVM revealed that EIF1AX showed a significant sex difference in mRNA accumulation and copy number variation, with female tumors expressing higher levels of EIF1AX and exhibiting more variations in copy numbers. EIF1AX mRNA levels were significantly inversely correlated with EIF1AX copy numbers in female tumors only, but not in male tumors. Differential gene expression analysis at the whole genomic level identified a set of 92 protein-coding and 16 RNA-coding genes which exhibited differential expression in men and women (fold of change cutoff at 1.7, adjusted p value < 0.05, FDR < 0.05). Network analysis showed significant difference in immune response and in disulfide bond formation, with EGR1/EGR2 and PDIA2 genes as regulators for immune response and disulfide bond formation, respectively. The melanocortin pathway which is linked to both melanin synthesis and obesity seems to be altered with unclear significance, as the sex difference in POMC, DCT/TYRP2, and MRAP2 was observed but with no clear direction.

CONCLUSION

This study reveals possible mechanisms for the sex difference in tumorigenesis of UVM which has potentials for better understanding and prevention of UVM.

Hypertrophy of Rat Skeletal Muscle Is Associated with Increased SIRT1/Akt/mTOR/S6 and Suppressed Sestrin2/SIRT3/FOXO1 Levels

Despite the intensive investigation of the molecular mechanism of skeletal muscle hypertrophy, the underlying signaling processes are not completely understood. Therefore, we used an overload model, in which the main synergist muscles (gastrocnemius, soleus) of the plantaris muscle were surgically removed, to cause a significant overload in the remaining plantaris muscle of 8-month-old Wistar male rats. SIRT1-associated pro-anabolic, pro-catabolic molecular signaling pathways, NAD and H₂S levels of this overload-induced hypertrophy were studied. Fourteen days of overload resulted in a significant 43% (p < 0.01) increase in the mass of plantaris muscle compared to sham operated animals. Cystathionine-β-synthase (CBS) activities and bioavailable H₂S levels were not modified by overload. On the other hand, overload-induced hypertrophy of skeletal muscle was associated with increased SIRT1 (p < 0.01), Akt (p < 0.01), mTOR, S6 (p < 0.01) and suppressed sestrin 2 levels (p < 0.01), which are mostly responsible for anabolic signaling. Decreased FOXO1 and SIRT3 signaling (p < 0.01) suggest downregulation of protein breakdown and mitophagy. Decreased levels of NAD⁺, sestrin2, OGG1 (p < 0.01) indicate that the redox milieu of skeletal muscle after 14 days of overloading is reduced. The present investigation revealed novel cellular interactions that regulate anabolic and catabolic processes in the hypertrophy of skeletal muscle.

[Potential Anticancer Activity of Auranofin]

Gold compounds have been employed throughout history to treat various types of disease, from ancient times to the present day. In the year 1985, auranofin, a gold-containing compound, was approved by U.S. Food and Drug Administration (FDA) as a therapeutic agent to target rheumatoid arthritis that would facilitate easy oral drug administration as opposed to conventional intramuscular injection used in treatments. Furthermore, auranofin demonstrates promising results for the treatment of various diseases beyond rheumatoid arthritis, including cancer, neurodegenerative diseases, acquired immune deficiency syndrome, and bacterial and parasitic infections. Various potential novel applications for auranofin have been proposed for treating human diseases. Auranofin has previously been demonstrated to inhibit thioredoxin reductase (TrxR) involved within the thioredoxin (Trx) system that comprises one of the critical cellular redox systems within the body. TrxR comprises the sole known enzyme that catalyzes Trx reduction. With cancers in particular, TrxR inhibition facilitates an increase in cellular oxidative stress and suppresses tumor growth. In this review, we describe the potential of auranofin to serve as an anticancer agent and further drug repurposing to utilize this as a strategy for further appropriate drug developments.

NTRC Effects on Non-Photochemical Quenching Depends on PGR5

Non-photochemical quenching (NPQ) protects plants from the detrimental effects of excess light. NPQ is rapidly induced by the trans-thylakoid proton gradient during photosynthesis, which in turn requires PGR5/PGRL1-dependent cyclic electron flow (CEF). Thus, Arabidopsis thaliana plants lacking either protein cannot induce transient NPQ and die under fluctuating light conditions. Conversely, the NADPH-dependent thioredoxin reductase C (NTRC) is required for efficient energy utilization and plant growth, and in its absence, transient and steady-state NPQ is drastically increased. How NTRC influences NPQ and functionally interacts with CEF is unclear. Therefore, we generated the A. thaliana line pgr5 ntrc, and found that the inactivation of PGR5 suppresses the high transient and steady-state NPQ and impaired growth phenotypes observed in the ntrc mutant under short-day conditions. This implies that NTRC negatively influences PGR5 activity and, accordingly, the lack of NTRC is associated with decreased levels of PGR5, possibly pointing to a mechanism to restrict upregulation of PGR5 activity in the absence of NTRC. When exposed to high light intensities, pgr5 ntrc plants display extremely impaired photosynthesis and growth, indicating additive effects of lack of both proteins. Taken together, these findings suggest that the interplay between NTRC and PGR5 is relevant for photoprotection and that NTRC might regulate PGR5 activity.

Redox-active cysteines in TGACG-BINDING FACTOR 1 (TGA1) do not play a role in salicylic acid or pathogen-induced expression of TGA1-regulated target genes in Arabidopsis thaliana

Salicylic acid (SA) is an important signaling molecule of the plant immune system. In Arabidopsis thaliana, SA biosynthesis is indirectly modulated by the closely related transcription factors TGACG-BINDING FACTOR 1 and 4 (TGA1 and TGA4, respectively). They activate expression of SYSTEMIC ACQUIRED RESISTANCE DEFICIENT1, the gene product of which regulates the key SA biosynthesis gene ISOCHORISMATE SYNTHASE 1. Since TGA1 interacts with the SA receptor NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1) in a redox-dependent manner and since the redox state of TGA1 is altered in SA-treated plants, TGA1 was assumed to play a role in the NPR1-dependent signaling cascade. Here, we identified 193 out of 2090 SA-induced genes that require TGA1/TGA4 for maximal expression after SA treatment. One robustly TGA1/TGA4-dependent gene encodes for the SA hydroxylase DOWNY MILDEW RESISTANT 6-LIKE OXYGENASE 1, suggesting an additional regulatory role of TGA1/TGA4 in SA catabolism. Expression of TGA1/TGA4-dependent genes in mock/SA-treated or Pseudomonas-infected plants was rescued in the tga1 tga4 double mutant after introduction of a mutant genomic TGA1 fragment encoding a TGA1 protein without any cysteines. Thus, the functional significance of the observed redox modification of TGA1 in SA-treated tissues remains enigmatic.

Natural Molecules Targeting Thioredoxin System and Their Therapeutic Potential

Significance: Thioredoxin (Trx) and thioredoxin reductase are two core members of the Trx system. The system bridges the gap between the universal reducing equivalent NADPH and various biological molecules and plays an essential role in maintaining cellular redox homeostasis and regulating multiple cellular redox signaling pathways. Recent Advance: In recent years, the Trx system has been well documented as an important regulator of many diseases, especially tumorigenesis. Thus, the development of potential therapeutic molecules targeting the system is of great significance for disease treatment. Critical Issues: We herein first discuss the physiological functions of the Trx system and the role that the Trx system plays in various diseases. Then, we focus on the introduction of natural small molecules with potential therapeutic applications, especially the anticancer activity, and review their mechanisms of pharmacological actions via interfering with the Trx system. Finally, we further discuss several natural molecules that harbor therapeutic potential and have entered different clinical trials. Future Directions: Further studies on the functions of the Trx system in multiple diseases will not only improve our understanding of the pathogenesis of many human disorders but also help develop novel therapeutic strategies against these diseases. Antioxid. Redox Signal. 34, 1083-1107.