Ribonucleotide reductase: regulation, regulation, regulation

Serum 25 hydroxyvitamin D in non-scarring alopecia: A systematic review and meta-analysis

INTRODUCTION

Non-scarring alopecia mainly includes androgenetic alopecia (AGA), female pattern hair loss (FPHL), alopecia areata (AA), telogen effluvium (TE), anagen effluvium (AE) and so on. Many studies had investigated the serum 25-hydroxyvitamin D level and vitamin D deficiency of patients with these diseases, but opinions varied, and no conclusion was reached.

METHODS

Relevant articles were retrieved through PubMed, Web of Science, EMBASE, Cochrane Library, China National Knowledge Infrastructure (CNKI) and other databases. Serum 25-hydroxyvitamin D [25(OH) D] levels and vitamin D deficiency were used as our primary outcome. The odds ratio (OR) and the standardized mean difference (SMD) with 95% confidence interval were both examined for vitamin D deficiency and levels.

RESULTS

Our meta-analysis had included a total of 3374 non-scarring alopecia patients and 7296 healthy controls from 23 studies through the inclusion criteria and exclusion criteria. We found non-scarring alopecia had decreased serum 25(OH)D level (WMD -7.29; 95% CI -9.21, -5.38) and increased vitamin D deficiency incidence (OR 3.11 95% CI 2.29, 4.22), compared with healthy controls. This meta-analysis chose to conduct random-effect model and subgroup analysis, because of the high heterogeneity (serum 25(OH)D level: I2 = 95%, vitamin D deficiency: I2 = 0%).

CONCLUSION

Patients with non-scarring alopecia (including AA, FPHL, AGA and TE) have insufficient serum level of 25(OH)D and increased incidence of vitamin D deficiency. Vitamin D supplementation and monitoring for vitamin D deficiency may be helpful in treating non-scarring alopecia.

A Drug Repurposing Approach Reveals Targetable Epigenetic Pathways in Plasmodium vivax Hypnozoites

Radical cure of Plasmodium vivax malaria must include elimination of quiescent 'hypnozoite' forms in the liver; however, the only FDA-approved treatments are contraindicated in many vulnerable populations. To identify new drugs and drug targets for hypnozoites, we screened the Repurposing, Focused Rescue, and Accelerated Medchem (ReFRAME) library and a collection of epigenetic inhibitors against P. vivax liver stages. From both libraries, we identified inhibitors targeting epigenetics pathways as selectively active against P. vivax and P. cynomolgi hypnozoites. These include DNA methyltransferase (DNMT) inhibitors as well as several inhibitors targeting histone post-translational modifications. Immunofluorescence staining of Plasmodium liver forms showed strong nuclear 5-methylcystosine signal, indicating liver stage parasite DNA is methylated. Using bisulfite sequencing, we mapped genomic DNA methylation in sporozoites, revealing DNA methylation signals in most coding genes. We also demonstrated that methylation level in proximal promoter regions as well as in the first exon of the genes may affect, at least partially, gene expression in P. vivax. The importance of selective inhibitors targeting epigenetic features on hypnozoites was validated using MMV019721, an acetyl-CoA synthetase inhibitor that affects histone acetylation and was previously reported as active against P. falciparum blood stages. In summary, our data indicate that several epigenetic mechanisms are likely modulating hypnozoite formation or persistence and provide an avenue for the discovery and development of improved radical cure antimalarials.

Iron Supplementation May Improve the Patient's Level of Satisfaction in Not-Low-Ferritin Telogen Effluvium: A Real-Life Observational Study

Background

Telogen effluvium (TE) is the most common cause of alopecia in women. Treatment should address the etiological factors and may include adjuvant therapies. In practice, physicians may employ modified approaches and utilize various combinations of topical and oral molecules.

Aims

In this real-life observational study, the aim was to evaluate the response of TE to iron supplementation.

Materials and Methods

The population consisted of all patients who sought consultation for TE at our dermatology department between March 2021 and February 2022. Eligible participants were women, aged between 18 and 65, having a clinical diagnosis of TE, and intended for treatment with iron supplementation. Exclusion criteria comprised current pregnancy, chronic or active inflammatory disease, newly discovered dysthyroidism, concurrent use of hair supplements, topical minoxidil, or any other medications. The response was assessed based on the patient's level of satisfaction, a significant indicator, given the substantial psychological impact of TE on women's daily lives.

Results

The analysis included 200 women. The average age was 32.9 ± 11.4 years. A recent history of COVID-19 or treated dysthyroidism was present in 18.5% and 8% of patients, respectively, but did not impact their response. Significantly, patients with baseline ferritin ≥50 ng/ml were mostly "very satisfied", those with baseline ferritin <50 ng/ml were mostly "not satisfied", and those with unknown levels were mostly "partially satisfied" with iron supplementation. A high dose of elemental iron and a prolonged duration of treatment significantly improved the patients' level of satisfaction.

Conclusion

Iron supplementation can improve the patient's level of satisfaction in TE even if serum ferritin is not low.

A missense mutation in the suc22 gene encoding the small subunit of ribonucleotide reductase significantly sensitizes fission yeast to chronic treatment with hydroxyurea

Ribonucleotide reductase (RNR) is essential for the biosynthesis of dNTPs and a therapeutic target. We have identified a missense mutation in suc22 , which encodes the small subunit of RNR in fission yeast. The suc22-S239F mutation significantly sensitizes the cells to chronic but not acute treatment with the RNR inhibitor hydroxyurea. Preliminary data indicate that the drug sensitivity is likely due to decreased RNR activity. Since S239F is the first missense mutation reported for suc22 and the mutated residue is highly conserved, the results will be useful for future yeast genetic studies and potentially, the development of new therapeutics targeting RNR.

Allosteric substrate activation of SAMHD1 shapes deoxynucleotide triphosphate imbalances by interconnecting the depletion and biosynthesis of different dNTPs

SAMHD1 is a dNTPase that impedes replication of HIV-1 in myeloid cells and resting T lymphocytes. Here we elucidate the substrate activation mechanism of SAMHD1 that depends on dNTP binding at allosteric sites and the concomitant tetramerization of the enzyme. The study reveals that SAMHD1 activation involves an inactive tetrameric intermediate with partial occupancy of the allosteric sites. The equilibrium between the inactive and active tetrameric states, which is coupled to cooperative binding/dissociation of at least two allosteric dNTP ligands, controls the dNTPase activity of the enzyme, which, in addition, depends on the identity of the dNTPs occupying the four allosteric sites of the active tetramer. We show how such allosteric regulation determines deoxynucleotide triphosphate levels established in the dynamic equilibria between dNTP production and SAMHD1-catalyzed depletion. Notably, the mechanism enables a distinctive functionality of SAMHD1, which we call facilitated dNTP depletion, whereby elevated biosynthesis of some dNTPs results in more efficient depletion of others. The regulatory relationship between the biosynthesis and depletion of different dNTPs sheds light on the emerging role of SAMHD1 in the biology of dNTP homeostasis with implications for HIV/AIDS, innate antiviral immunity, T cell disorders, telomere maintenance and therapeutic efficacy of nucleoside analogs.

Therapeutic effect of trace elements on multiple myeloma and mechanisms of cancer process

In the human body, trace elements and other micronutrients play a vital role in growth, health and immune system function. The trace elements are Iron, Manganese, Copper, Iodine, Zinc, Cobalt, Fluoride, and Selenium. Estimating the serum levels of trace elements in hematologic malignancy patients can determine the severity of the tumor. Multiple myeloma (MM) is a hematopoietic malignancy and is characterized by plasma cell clonal expansion in bone marrow. Despite the advances in treatment methods, myeloma remains largely incurable. In addition to conventional medicine, treatment is moving toward less expensive noninvasive alternatives. One of the alternative treatments is the use of dietary supplements. In this review, we focused on the effect of three trace elements including iron, zinc and selenium on important mechanisms such as the immune system, oxidative and antioxidant factors and cell cycle. Using some trace minerals in combination with approved drugs can increase patients' recovery speed. Trace elements can be used as not only a preventive but also a therapeutic tool, especially in reducing inflammation in hematological cancers such as multiple myeloma. We hope that the prospect of the correct use of trace element supplements in the future could be promising for the treatment of diseases.

Maize LOST SUBSIDIARY CELL encoding a large subunit of ribonucleotide reductase is required for subsidiary cell development and plant growth

The four-celled stomatal complex consists of a pair of guard cells (GCs) and two subsidiary cells (SCs) in grasses, which supports a fast adjustment of stomatal aperture. The formation and development of SCs are thus important for stomatal functionality. Here, we report a maize lost subsidiary cells (lsc) mutant, with many stomata lacking one or two SCs. The loss of SCs is supposed to have resulted from impeded subsidiary mother cell (SMC) polarization and asymmetrical division. Besides the defect in SCs, the lsc mutant also displays a dwarf morphology and pale and striped newly-grown leaves. LSC encodes a large subunit of ribonucleotide reductase (RNR), an enzyme involved in deoxyribonucleotides (dNTPs) synthesis. Consistently, the concentration of dNTPs and expression of genes involved in DNA replication, cell cycle progression, and SC development were significantly reduced in the lsc mutant compared with the wild-type B73 inbred line. Conversely, overexpression of maize LSC increased dNTP synthesis and promoted plant growth in both maize and Arabidopsis. Our data indicate that LSC regulates dNTP production and is required for SMC polarization, SC differentiation, and growth of maize.

Dynamic chromatin accessibility during nutritional iron overload reveals a BMP6-independent induction of cell cycle genes

Iron is essential to organism physiology as it participates in numerous biological processes including oxygen transport, respiration and erythropoiesis. Although iron is critical to physiology, excess iron is toxic to cells and tissues due to generation of reactive oxygen species. Therefore, well-kept iron homeostasis is a mainstay of proper cell and organ function. Iron overload disorders, caused by nutritional or genetic factors, contribute to many pathologies such as diabetes, non-alcoholic steatohepatitis and hepatocellular carcinoma. The liver is not only vulnerable to the effects of iron overload, it is also the major organ controlling iron homeostasis. During iron overload, Bone Morphogenic Protein (BMP) levels increase and initiate a hepatic response aimed at lowering iron levels. The transcriptional effects of iron overload are not well-characterized and the underlining enhancer regulation is uncharted. Here, we profiled the liver's transcriptome and chromatin accessibility following nutritional iron overload. We found marked changes in gene expression and enhancer accessibility following iron overload. Surprisingly, 16% of genes induced following iron overload participate in propagating the cell cycle. Induction of cell cycle genes was independent of BMP. Genome-wide enhancer landscape profiling revealed hundreds of enhancers with altered activity following iron overload. Characterization of transcription factor motifs and footprints in iron-regulated enhancers showed a role for the Activator Protein 1 (AP-1) transcription factor in promoting cell cycle-related transcription. In summary, we found that the transcriptional program at play during iron overload is bifurcated in which BMP signaling controls iron homeostasis genes while an AP-1-driven program controls cell cycle genes.

From a drug repositioning to a structure-based drug design approach to tackle acute lymphoblastic leukemia

Cancer cells utilize the main de novo pathway and the alternative salvage pathway for deoxyribonucleotide biosynthesis to achieve adequate nucleotide pools. Deoxycytidine kinase is the rate-limiting enzyme of the salvage pathway and it has recently emerged as a target for anti-proliferative therapies for cancers where it is essential. Here, we present the development of a potent inhibitor applying an iterative multidisciplinary approach, which relies on computational design coupled with experimental evaluations. This strategy allows an acceleration of the hit-to-lead process by gradually implementing key chemical modifications to increase affinity and activity. Our lead compound, OR0642, is more than 1000 times more potent than its initial parent compound, masitinib, previously identified from a drug repositioning approach. OR0642 in combination with a physiological inhibitor of the de novo pathway doubled the survival rate in a human T-cell acute lymphoblastic leukemia patient-derived xenograft mouse model, demonstrating the proof-of-concept of this drug design strategy.

In vitro anti-proliferative, and in silico ribonucleotide reductase and pharmacokinetics studies of heteroleptic silver(I), nickel(II) and copper(II) complexes of 4-methyl-3-thiosemicarbazones and ibuprofen

OBJECTIVES

The present research focuses on the in vitro anti-proliferative, and in silico ribonucleotide reductase and pharmacokinetics studies of twelve heteroleptic metal complexes of the general formulae [Ag(L^1-4)(ibu)] (1-4) and [M(L^1-4)(ibu)₂] (5-12), where L^1-4 = 2-(1-(4-substitutedphenyl)ethylidene)-N-methylhydrazinecarbothioamide, ibu = non-steroidal anti-inflammatory drug (ibuprofen), and M = Cu(II) and Ni(II).

METHODS

Various spectroscopic techniques were used to authenticate the structure of the synthesized complexes. UV-Vis and cyclic voltammetry techniques were used to analyse the stability and the reducing ability of the complexes. In vitro anti-proliferative studies by MTT assay, apoptotic behaviour and cellular uptake studies were investigated followed by the in silico interaction with ribonucleotide reductase (RNR) enzyme.

RESULTS

The spectral studies predicted distorted tetrahedral geometry around silver(I) ion and distorted octahedral geometry around nickel(II) and copper(II) ions. The reducing ability of the copper(II) complexes was analysed using ascorbic acid by UV-Vis and cyclic voltammetry techniques, which authenticate the reducing ability of the complexes and the possible interactions within the cells. The in vitro anti-proliferative activity of the synthesized complexes against three cancerous (estrogen positive (MCF-7), estrogen negative (MDA-MB-231) and pancreatic (PANC-1)) and one normal (MCF-10a) cell lines by MTT assay showed enhanced activity for copper(II) complexes 11 and 12 containing the hydrophobic substituents. The apoptotic and cellular uptake studies showed that the complex 12 is readily taken up by PANC-1 cell lines and induces ROS-mediated mitochondrial and caspase-dependent apoptosis. The in silico studies indicated hydrogen bonding, hydrophobic and π-pair (π-π, π-σ and π-cation) interactions between the complexes and the ribonucleotide reductase (RNR) enzyme. The in silico pharmacokinetics studies of the complexes predicted the drug-likeness characteristics of the complexes.

CONCLUSION

The synthesized complexes are found to be less toxic to normal cells and inhibit the growth of cancerous cells by inducing mitochondrial-mediated and caspase dependent apoptotic pathway in PANC-1 cells.

Nucleotide metabolism: a pan-cancer metabolic dependency

Metabolic alterations are a key hallmark of cancer cells, and the augmented synthesis and use of nucleotide triphosphates is a critical and universal metabolic dependency of cancer cells across different cancer types and genetic backgrounds. Many of the aggressive behaviours of cancer cells, including uncontrolled proliferation, chemotherapy resistance, immune evasion and metastasis, rely heavily on augmented nucleotide metabolism. Furthermore, most of the known oncogenic drivers upregulate nucleotide biosynthetic capacity, suggesting that this phenotype is a prerequisite for cancer initiation and progression. Despite the wealth of data demonstrating the efficacy of nucleotide synthesis inhibitors in preclinical cancer models and the well-established clinical use of these drugs in certain cancer settings, the full potential of these agents remains unrealized. In this Review, we discuss recent studies that have generated mechanistic insights into the diverse biological roles of hyperactive cancer cell nucleotide metabolism. We explore opportunities for combination therapies that are highlighted by these recent advances and detail key questions that remain to be answered, with the goal of informing urgently warranted future studies.

Ribonucleotide reductase subunit switching in hepatoblastoma drug response and relapse

Prognosis of children with high-risk hepatoblastoma (HB), the most common pediatric liver cancer, remains poor. In this study, we found ribonucleotide reductase (RNR) subunit M2 (RRM2) was one of the key genes supporting cell proliferation in high-risk HB. While standard chemotherapies could effectively suppress RRM2 in HB cells, they induced a significant upregulation of the other RNR M2 subunit, RRM2B. Computational analysis revealed distinct signaling networks RRM2 and RRM2B were involved in HB patient tumors, with RRM2 supporting cell proliferation and RRM2B participating heavily in stress response pathways. Indeed, RRM2B upregulation in chemotherapy-treated HB cells promoted cell survival and subsequent relapse, during which RRM2B was gradually replaced back by RRM2. Combining an RRM2 inhibitor with chemotherapy showed an effective delaying of HB tumor relapse in vivo. Overall, our study revealed the distinct roles of the two RNR M2 subunits and their dynamic switching during HB cell proliferation and stress response.

microRNAs Associated with Gemcitabine Resistance via EMT, TME, and Drug Metabolism in Pancreatic Cancer

Despite extensive research, pancreatic cancer remains a lethal disease with an extremely poor prognosis. The difficulty in early detection and chemoresistance to therapeutic agents are major clinical concerns. To improve prognosis, novel biomarkers, and therapeutic strategies for chemoresistance are urgently needed. microRNAs (miRNAs) play important roles in the development, progression, and metastasis of several cancers. During the last few decades, the association between pancreatic cancer and miRNAs has been extensively elucidated, with several miRNAs found to be correlated with patient prognosis. Moreover, recent evidence has revealed that miRNAs are intimately involved in gemcitabine sensitivity and resistance through epithelial-to-mesenchymal transition, the tumor microenvironment, and drug metabolism. Gemcitabine is the gold standard drug for pancreatic cancer treatment, but gemcitabine resistance develops easily after chemotherapy initiation. Therefore, in this review, we summarize the gemcitabine resistance mechanisms associated with aberrantly expressed miRNAs in pancreatic cancer, especially focusing on the mechanisms associated with epithelial-to-mesenchymal transition, the tumor microenvironment, and metabolism. This novel evidence of gemcitabine resistance will drive further research to elucidate the mechanisms of chemoresistance and improve patient outcomes.

Toward understanding the emergence of life: A dual function of the system of nucleotides in the metabolically closed autopoietic organization

General structure of metabolism includes the reproduction of catalysts that govern metabolism. In this structure, the system becomes autopoietic in the sense of Maturana and Varela, and it is closed to efficient causation as defined by Robert Rosen. The autopoietic maintenance and operation of the catalysts takes place via the set of free nucleotides while the synthesis of catalysts occurs via the information encoded by the set of nucleotides arranged in polymers of RNA and DNA. Both energy charge and genetic information use the components of the same pool of nucleoside triphosphates, which is equilibrated by thermodynamic buffering enzymes such as nucleoside diphosphate kinase and adenylate kinase. This occurs in a way that the system becomes internally stable and metabolically closed, which initially could be realized at the level of ribozymes catalyzing basic metabolic reactions as well as own reproduction. The function of ATP, GTP, UTP, and CTP is dual, as these species participate both in the general metabolism as free nucleotides and in the transfer of genetic information via covalent polymerization to nucleic acids. The changes in their pools directly impact both bioenergetic pathways and nucleic acid turnover. Here we outline the concept of metabolic closure of biosystems grounded in the dual function of nucleotide coenzymes that serve both as energetic and informational molecules and through this duality generate the autopoietic performance and the ability for codepoietic evolutionary transformations of living systems starting from the emergence of prebiotic systems.

Ribonucleotide Reductase Subunit Switching in Hepatoblastoma Drug Response and Relapse

Prognosis of children with high-risk hepatoblastoma (HB), the most common pediatric liver cancer, remains poor. In this study, we found ribonucleotide reductase (RNR) subunit M2 ( RRM2 ) was one of the key genes supporting cell proliferation in high-risk HB. While standard chemotherapies could effectively suppress RRM2 in HB cells, they induced a significant upregulation of the other RNR M2 subunit, RRM2B . Computational analysis revealed distinct signaling networks RRM2 and RRM2B were involved in HB patient tumors, with RRM2 supporting cell proliferation and RRM2B participating heavily in stress response pathways. Indeed, RRM2B upregulation in chemotherapy-treated HB cells promoted cell survival and subsequent relapse, during which RRM2B was gradually replaced back by RRM2. Combining an RRM2 inhibitor with chemotherapy showed an effective delaying of HB tumor relapse in vivo. Overall, our study revealed the distinct roles of the two RNR M2 subunits and their dynamic switching during HB cell proliferation and stress response.

Requirement and functional redundancy of two large ribonucleotide reductase subunit genes for cell cycle, chloroplast biogenesis and photosynthesis in tomato

BACKGROUND AND AIMS

Ribonucleotide reductase (RNR), functioning in the de novo synthesis of deoxyribonucleoside triphosphates (dNTPs), is crucial for DNA replication and cell cycle progression. In most plants, the large subunits of RNR have more than one homologous gene. However, the different functions of these homologous genes in plant development remain unknown. In this study, we obtained the mutants of two large subunits of RNR in tomato and studied their functions.

METHODS

The mutant ylc1 was obtained by ethyl methyl sulfonate (EMS) treatment. Through map-based cloning, complementation and knock-out experiments, it was confirmed that YLC1 encodes a large subunit of RNR (SlRNRL1). The expression level of the genes related to cell cycle progression, chloroplast biogenesis and photosynthesis was assessed by RNA-sequencing. In addition, we knocked out SlRNRL2 (a SlRNRL1 homologue) using CRISPR-Cas9 technology in the tomato genome, and we down-regulated SlRNRL2 expression in the genetic background of slrnrl1-1 using a tobacco rattle virus-induced gene silencing (VIGS) system.

KEY RESULTS

The mutant slrnrl1 exhibited dwarf stature, chlorotic young leaves and smaller fruits. Physiological and transcriptomic analyses indicated that SlRNRL1 plays a crucial role in the regulation of cell cycle progression, chloroplast biogenesis and photosynthesis in tomato. The slrnrl2 mutant did not exhibit any visible phenotype. SlRNRL2 has a redundant function with SlRNRL1, and the double mutant slrnrl1slrnrl2 is lethal.

CONCLUSIONS

SlRNRL1 is essential for cell cycle progression, chloroplast biogenesis and photosynthesis. In addition, SlRNRL1 and SlRNRL2 possess redundant functions and at least one of these RNRLs is required for tomato survival, growth and development.

NCOA4 links iron bioavailability to DNA metabolism

Iron is essential for deoxyribonucleotides production and for enzymes containing an Fe-S cluster involved in DNA replication and repair. How iron bioavailability and DNA metabolism are coordinated remains poorly understood. NCOA4 protein mediates autophagic degradation of ferritin to maintain iron homeostasis and inhibits DNA replication origin activation via hindrance of the MCM2-7 DNA helicase. Here, we show that iron deficiency inhibits DNA replication, parallel to nuclear NCOA4 stabilization. In iron-depleted cells, NCOA4 knockdown leads to unscheduled DNA synthesis, with replication stress, genome instability, and cell death. In mice, NCOA4 genetic inactivation causes defective intestinal regeneration upon dextran sulfate sodium-mediated injury, with DNA damage, defective cell proliferation, and cell death; in intestinal organoids, this is fostered by iron depletion. In summary, we describe a NCOA4-dependent mechanism that coordinates iron bioavailability and DNA replication. This function prevents replication stress, maintains genome integrity, and sustains high rates of cell proliferation during tissue regeneration.

Transcript-Targeted Therapy Based on RNA Interference and Antisense Oligonucleotides: Current Applications and Novel Molecular Targets

The development of novel target therapies based on the use of RNA interference (RNAi) and antisense oligonucleotides (ASOs) is growing in an exponential way, challenging the chance for the treatment of the genetic diseases and cancer by hitting selectively targeted RNA in a sequence-dependent manner. Multiple opportunities are taking shape, able to remove defective protein by silencing RNA (e.g., Inclisiran targets mRNA of protein PCSK9, permitting a longer half-life of LDL receptors in heterozygous familial hypercholesteremia), by arresting mRNA translation (i.e., Fomivirsen that binds to UL123-RNA and blocks the translation into IE2 protein in CMV-retinitis), or by reactivating modified functional protein (e.g., Eteplirsen able to restore a functional shorter dystrophin by skipping the exon 51 in Duchenne muscular dystrophy) or a not very functional protein. In this last case, the use of ASOs permits modifying the expression of specific proteins by modulating splicing of specific pre-RNAs (e.g., Nusinersen acts on the splicing of exon 7 in SMN2 mRNA normally not expressed; it is used for spinal muscular atrophy) or by downregulation of transcript levels (e.g., Inotersen acts on the transthryretin mRNA to reduce its expression; it is prescribed for the treatment of hereditary transthyretin amyloidosis) in order to restore the biochemical/physiological condition and ameliorate quality of life. In the era of precision medicine, recently, an experimental splice-modulating antisense oligonucleotide, Milasen, was designed and used to treat an 8-year-old girl affected by a rare, fatal, progressive form of neurodegenerative disease leading to death during adolescence. In this review, we summarize the main transcriptional therapeutic drugs approved to date for the treatment of genetic diseases by principal regulatory government agencies and recent clinical trials aimed at the treatment of cancer. Their mechanism of action, chemical structure, administration, and biomedical performance are predominantly discussed.

Smc5/6 Complex Promotes Rad3ATR Checkpoint Signaling at the Perturbed Replication Fork through Sumoylation of the RecQ Helicase Rqh1

Smc5/6, like cohesin and condensin, is a structural maintenance of chromosomes complex crucial for genome stability. Unlike cohesin and condensin, Smc5/6 carries an essential Nse2 subunit with SUMO E3 ligase activity. While screening for new DNA replication checkpoint mutants in fission yeast, we have identified two previously uncharacterized mutants in Smc5/6. Characterization of the mutants and a series of previously reported Smc5/6 mutants uncovered that sumoylation of the RecQ helicase Rqh1 by Nse2 facilitates the checkpoint signaling at the replication fork. We found that mutations that eliminate the sumoylation sites or the helicase activity of Rqh1 compromised the checkpoint signaling similar to a nse2 mutant lacking the ligase activity. Surprisingly, introducing a sumoylation site mutation to a helicase-inactive rqh1 mutant promoted cell survival under stress. These findings, together with other genetic data, support a mechanism that sumoylation of Rqh1 by Smc5/6-Nse2 recruits Rqh1 or modulates its helicase activity at the fork to facilitate the checkpoint signaling. Since the Smc5/6 complex, Rqh1, and the replication checkpoint are conserved in eukaryotes, a similar checkpoint mechanism may be operating in human cells.

De Novo Transcriptome of the Flagellate Isochrysis galbana Identifies Genes Involved in the Metabolism of Antiproliferative Metabolites

Haptophytes are important primary producers in the oceans, and among the phylum Haptophyta, the flagellate Isochrysis galbana has been found to be rich in high-value compounds, such as lipids, carotenoids and highly branched polysaccharides. In the present work, I. galbana was cultured and collected at both stationary and exponential growth phases. A transcriptomic approach was used to analyze the possible activation of metabolic pathways responsible for bioactive compound synthesis at the gene level. Differential expression analysis of samples collected at the exponential versus stationary growth phase allowed the identification of genes involved in the glycerophospholipid metabolic process, the sterol biosynthetic process, ADP-ribose diphosphatase activity and others. I. galbana raw extracts and fractions were tested on specific human cancer cells for possible antiproliferative activity. The most active fractions, without affecting normal cells, were fractions enriched in nucleosides (fraction B) and triglycerides (fraction E) for algae collected in the exponential growth phase and fraction E for stationary phase samples. Overall, transcriptomic and bioactivity data confirmed the activation of metabolic pathways involved in the synthesis of bioactive compounds giving new insights on possible Isochrysis applications in the anticancer sector.

Metabolic response to radiation therapy in cancer

Tumor metabolism has emerged as a hallmark of cancer and is involved in carcinogenesis and tumor growth. Reprogramming of tumor metabolism is necessary for cancer cells to sustain high proliferation rates and enhanced demands for nutrients. Recent studies suggest that metabolic plasticity in cancer cells can decrease the efficacy of anticancer therapies by enhancing antioxidant defenses and DNA repair mechanisms. Studying radiation-induced metabolic changes will lead to a better understanding of radiation response mechanisms as well as the identification of new therapeutic targets, but there are few robust studies characterizing the metabolic changes induced by radiation therapy in cancer. In this review, we will highlight studies that provide information on the metabolic changes induced by radiation and oxidative stress in cancer cells and the associated underlying mechanisms.

Platycodon D-induced A549 cell apoptosis through RRM1-regulated p53/VEGF/MMP2 pathway

BACKGROUND

Lung cancer is one of the leading causes of cancer-related deaths worldwide. Platycodin D (PD), a major pharmacological constituent from the Chinese medicinal herb named Platycodonis Radix, has shown potent anti-tumor activity. Also, it is also reported that PD could inhibit cellular growth in the non-small-cell lung carcinoma (NSCLC) A549 cell line. However, the underlying mechanism is not fully clarified.

METHODS

Cell proliferation was measured by MTT assay. Annexin V and propidium iodide (PI) assay were employed to study the apoptosis effects of PD on A549 cells. Western blot analysis was used to evaluate protein expression. Also, we used a siRNA against p53, as well as a plasmid-based RRM1 over-expression to investigate their functions.

RESULTS

It demonstrated PD inhibited A549 cell proliferation in a dose- and time-dependent manner. Further investigations showed that PD induced cell apoptosis, which was supported by dose-dependent and time-dependent caspase-3 activation and p53/VEGF/MMP2 pathway regulation. Also, PD demonstrated the inhibition effect of ribonucleotide reductase M1 (RRM1), whose role in various tumors is contradictory. Remarkably, in this work, RRM1 overexpression in A549 cells could have a negative impact on the regulation of the p53/VEGF/MMP2 pathway induced by PD treatment. Note as well that RRM1 overexpression also attenuated cell apoptosis and inhibition of cell proliferation of A549 treated with PD.

CONCLUSION

The results suggested that PD could inhibit A549 cell proliferation and induce cell apoptosis by regulating p53/VEGF/MMP2 pathway, in which RRM1 plays an important role directly.

Nucleotide biosynthesis links glutathione metabolism to ferroptosis sensitivity

The tumor suppressor protein p53 inhibits ferroptosis by reducing the consumption of glutathione in nucleotide biosynthesis.

Nucleotide synthesis is a metabolically demanding process essential for DNA replication and other processes in the cell. Several anticancer drugs that inhibit nucleotide metabolism induce apoptosis. How inhibition of nucleotide metabolism impacts non-apoptotic cell death is less clear. Here, we report that inhibition of nucleotide metabolism by the p53 pathway is sufficient to suppress the non-apoptotic cell death process of ferroptosis. Mechanistically, stabilization of wild-type p53 and induction of the p53 target gene CDKN1A (p21) leads to decreased expression of the ribonucleotide reductase (RNR) subunits RRM1 and RRM2. RNR is the rate-limiting enzyme of de novo nucleotide synthesis that reduces ribonucleotides to deoxyribonucleotides in a glutathione-dependent manner. Direct inhibition of RNR results in conservation of intracellular glutathione, limiting the accumulation of toxic lipid peroxides and preventing the onset of ferroptosis in response to cystine deprivation. These results support a mechanism linking p53-dependent regulation of nucleotide metabolism to non-apoptotic cell death.

RNR-R2 Upregulation by a Short Non-Coding Viral Transcript

DNA viruses require dNTPs for replication and have developed different strategies to increase intracellular dNTP pools. Hepatitis B virus (HBV) infects non-dividing cells in which dNTPs are scarce and the question is how viral replication takes place. Previously we reported that the virus induces the DNA damage response (DDR) pathway culminating in RNR-R2 expression and the generation of an active RNR holoenzyme, the key regulator of dNTP levels, leading to an increase in dNTPs. How the virus induces DDR and RNR-R2 upregulation is not completely known. The viral HBx open reading frame (ORF) was believed to trigger this pathway. Unexpectedly, however, we report here that the production of HBx protein is dispensable. We found that a small conserved region of 125 bases within the HBx ORF is sufficient to upregulate RNR-R2 expression in growth-arrested HepG2 cells and primary human hepatocytes. The observed HBV mRNA embedded regulatory element is named ERE. ERE in isolation is sufficient to activate the ATR-Chk1-E2F1-RNR-R2 DDR pathway. These findings demonstrate a non-coding function of HBV transcripts to support its propagation in non-cycling cells.

Pre-Clinical and Clinical Applications of Small Interfering RNAs (siRNA) and Co-Delivery Systems for Pancreatic Cancer Therapy

Pancreatic cancer (PC) is one of the leading causes of death and is the fourth most malignant tumor in men. The epigenetic and genetic alterations appear to be responsible for development of PC. Small interfering RNA (siRNA) is a powerful genetic tool that can bind to its target and reduce expression level of a specific gene. The various critical genes involved in PC progression can be effectively targeted using diverse siRNAs. Moreover, siRNAs can enhance efficacy of chemotherapy and radiotherapy in inhibiting PC progression. However, siRNAs suffer from different off target effects and their degradation by enzymes in serum can diminish their potential in gene silencing. Loading siRNAs on nanoparticles can effectively protect them against degradation and can inhibit off target actions by facilitating targeted delivery. This can lead to enhanced efficacy of siRNAs in PC therapy. Moreover, different kinds of nanoparticles such as polymeric nanoparticles, lipid nanoparticles and metal nanostructures have been applied for optimal delivery of siRNAs that are discussed in this article. This review also reveals that how naked siRNAs and their delivery systems can be exploited in treatment of PC and as siRNAs are currently being applied in clinical trials, significant progress can be made by translating the current findings into the clinical settings.

Unsymmetrical Trifluoromethyl Methoxyphenyl β-Diketones: Effect of the Position of Methoxy Group and Coordination at Cu(II) on Biological Activity

Copper(II) complexes with 1,1,1-trifluoro-4-(4-methoxyphenyl)butan-2,4-dione (HL1) were synthesized and characterized by elemental analysis, FT-IR spectroscopy, and single crystal X-ray diffraction. The biological properties of HL1 and cis-[Cu(L1)₂(DMSO)] (3) were examined against Gram-positive and Gram-negative bacteria and opportunistic unicellular fungi. The cytotoxicity was estimated towards the HeLa and Vero cell lines. Complex 3 demonstrated antibacterial activity towards S. aureus comparable to that of streptomycin, lower antifungal activity than the ligand HL1 and moderate cytotoxicity. The bioactivity was compared with the activity of compounds of similar structures. The effect of changing the position of the methoxy group at the aromatic ring in the ligand moiety of the complexes on their antimicrobial and cytotoxic activity was explored. We propose that complex 3 has lower bioavailability and reduced bioactivity than expected due to strong intermolecular contacts. In addition, molecular docking studies provided theoretical information on the interactions of tested compounds with ribonucleotide reductase subunit R2, as well as the chaperones Hsp70 and Hsp90, which are important biomolecular targets for antitumor and antimicrobial drug search and design. The obtained results revealed that the complexes displayed enhanced affinity over organic ligands. Taken together, the copper(II) complexes with the trifluoromethyl methoxyphenyl-substituted β-diketones could be considered as promising anticancer agents with antibacterial properties.

Hydroxyurea-The Good, the Bad and the Ugly

Hydroxyurea (HU) is mostly referred to as an inhibitor of ribonucleotide reductase (RNR) and as the agent that is commonly used to arrest cells in the S-phase of the cycle by inducing replication stress. It is a well-known and widely used drug, one which has proved to be effective in treating chronic myeloproliferative disorders and which is considered a staple agent in sickle anemia therapy and—recently—a promising factor in preventing cognitive decline in Alzheimer’s disease. The reversibility of HU-induced replication inhibition also makes it a common laboratory ingredient used to synchronize cell cycles. On the other hand, prolonged treatment or higher dosage of hydroxyurea causes cell death due to accumulation of DNA damage and oxidative stress. Hydroxyurea treatments are also still far from perfect and it has been suggested that it facilitates skin cancer progression. Also, recent studies have shown that hydroxyurea may affect a larger number of enzymes due to its less specific interaction mechanism, which may contribute to further as-yet unspecified factors affecting cell response. In this review, we examine the actual state of knowledge about hydroxyurea and the mechanisms behind its cytotoxic effects. The practical applications of the recent findings may prove to enhance the already existing use of the drug in new and promising ways.

Triapine Analogues and Their Copper(II) Complexes: Synthesis, Characterization, Solution Speciation, Redox Activity, Cytotoxicity, and mR2 RNR Inhibition

Three new thiosemicarbazones (TSCs) HL¹–HL³ as triapine analogues bearing a redox-active phenolic moiety at the terminal nitrogen atom were prepared. Reactions of HL¹–HL³ with CuCl₂·2H₂O in anoxic methanol afforded three copper(II) complexes, namely, Cu(HL¹)Cl₂ (1), [Cu(L²)Cl] (2′), and Cu(HL³)Cl₂ (3), in good yields. Solution speciation studies revealed that the metal-free ligands are stable as HL¹–HL³ at pH 7.4, while being air-sensitive in the basic pH range. In dimethyl sulfoxide they exist as a mixture of E and Z isomers. A mechanism of the E/Z isomerization with an inversion at the nitrogen atom of the Schiff base imine bond is proposed. The monocationic complexes [Cu(L^1–3)]⁺ are the most abundant species in aqueous solutions at pH 7.4. Electrochemical and spectroelectrochemical studies of 1, 2′, and 3 confirmed their redox activity in both the cathodic and the anodic region of potentials. The one-electron reduction was identified as metal-centered by electron paramagnetic resonance spectroelectrochemistry. An electrochemical oxidation pointed out the ligand-centered oxidation, while chemical oxidations of HL¹ and HL² as well as 1 and 2′ afforded several two-electron and four-electron oxidation products, which were isolated and comprehensively characterized. Complexes 1 and 2′ showed an antiproliferative activity in Colo205 and Colo320 cancer cell lines with half-maximal inhibitory concentration values in the low micromolar concentration range, while 3 with the most closely related ligand to triapine displayed the best selectivity for cancer cells versus normal fibroblast cells (MRC-5). HL¹ and 1 in the presence of 1,4-dithiothreitol are as potent inhibitors of mR2 ribonucleotide reductase as triapine.

Three triapine analogues HL¹−HL³ bearing a phenolic redox-active moiety showed moderate antiproliferative activity, while one of the oxidation products HL^2c′·CH3COOH revealed high cytotoxicity in Colo205 and Colo320 cancer cell lines. Coordination of HL¹−HL³ to copper(II) increased strongly the cytotoxicity, with complex 2′ showing IC₅₀ values of 0.181 and 0.159, respectively. The highest cytotoxicity of 2′ is likely due to the highest thermodynamic stability, more negative reduction potential, and the lowest rate of reduction by GSH.

Knockdown of RRM1 with Adenoviral shRNA Vectors to Inhibit Tumor Cell Viability and Increase Chemotherapeutic Sensitivity to Gemcitabine in Bladder Cancer Cells

RRM1-an important DNA replication/repair enzyme-is the primary molecular gemcitabine (GEM) target. High RRM1-expression associates with gemcitabine-resistance in various cancers and RRM1 inhibition may provide novel cancer treatment approaches. Our study elucidates how RRM1 inhibition affects cancer cell proliferation and influences gemcitabine-resistant bladder cancer cells. Of nine bladder cancer cell lines investigated, two RRM1 highly expressed cells, 253J and RT112, were selected for further experimentation. An RRM1-targeting shRNA was cloned into adenoviral vector, Ad-shRRM1. Gene and protein expression were investigated using real-time PCR and western blotting. Cell proliferation rate and chemotherapeutic sensitivity to GEM were assessed by MTT assay. A human tumor xenograft model was prepared by implanting RRM1 highly expressed tumors, derived from RT112 cells, in nude mice. Infection with Ad-shRRM1 effectively downregulated RRM1 expression, significantly inhibiting cell growth in both RRM1 highly expressed tumor cells. In vivo, Ad-shRRM1 treatment had pronounced antitumor effects against RRM1 highly expressed tumor xenografts (p < 0.05). Moreover, combination of Ad-shRRM1 and GEM inhibited cell proliferation in both cell lines significantly more than either treatment individually. Cancer gene therapy using anti-RRM1 shRNA has pronounced antitumor effects against RRM1 highly expressed tumors, and RRM1 inhibition specifically increases bladder cancer cell GEM-sensitivity. Ad-shRRM1/GEM combination therapy may offer new treatment options for patients with GEM-resistant bladder tumors.

Red and processed meat consumption and cancer outcomes: Umbrella review

The purpose of this umbrella review was to evaluate the quality of evidence, validity and biases of the associations between red and processed meat consumption and multiple cancer outcomes according to existing systematic reviews and meta-analyses. The umbrella review identified 72 meta-analyses with 20 unique outcomes for red meat and 19 unique outcomes for processed meat. Red meat consumption was associated with increased risk of overall cancer mortality, non-Hodgkin lymphoma (NHL), bladder, breast, colorectal, endometrial, esophageal, gastric, lung and nasopharyngeal cancer. Processed meat consumption might increase the risk of overall cancer mortality, NHL, bladder, breast, colorectal, esophageal, gastric, nasopharyngeal, oral cavity and oropharynx and prostate cancer. Dose-response analyses revealed that 100 g/d increment of red meat and 50 g/d increment of processed meat consumption were associated with 11%-51% and 8%-72% higher risk of multiple cancer outcomes, respectively, and seemed to be not correlated with any benefit.

The Challenge of Combining Chemo- and Radiotherapy with Checkpoint Kinase Inhibitors

Preclinical models of cancer have demonstrated enhanced efficacy of cell-cycle checkpoint kinase inhibitors when used in combination with genotoxic agents. This combination therapy is predicted to be exquisitely toxic to cells with a deficient G1-S checkpoint or cells with a genetic predisposition leading to intrinsic DNA replication stress, as these cancer cells become fully dependent on the intra-S and G2-M checkpoints for DNA repair and cellular survival. Therefore, abolishing remaining cell-cycle checkpoints after damage leads to increased cell death in a tumor cell-specific fashion. However, the preclinical success of these drug combinations is not consistently replicated in clinical trials. Here, we provide a perspective on the translation of preclinical studies into rationally designed clinical studies. We will discuss successes and failures of current treatment combinations and drug regimens and provide a detailed overview of all clinical trials using ATR, CHK1, or WEE1 inhibitors in combination with genotoxic agents. This highlights the need for revised patient stratification and the use of appropriate pharmacodynamic biomarkers to improve the success rate of clinical trials.

Reversing oncogenic transformation with iron chelation

Cancer cells accumulate iron to supplement their aberrant growth and metabolism. Depleting cells of iron by iron chelators has been shown to be selectively cytotoxic to cancer cells in vitro and in vivo. Iron chelators are effective at combating a range of cancers including those which are difficult to treat such as androgen insensitive prostate cancer and cancer stem cells. This review will evaluate the impact of iron chelation on cancer cell survival and the underlying mechanisms of action. A plethora of studies have shown iron chelators can reverse some of the major hallmarks and enabling characteristics of cancer. Iron chelators inhibit signalling pathways that drive proliferation, migration and metastasis as well as return tumour suppressive signalling. In addition to this, iron chelators stimulate apoptotic and ER stress signalling pathways inducing cell death even in cells lacking a functional p53 gene. Iron chelators can sensitise cancer cells to PARP inhibitors through mimicking BRCAness; a feature of cancers trademark genomic instability. Iron chelators target cancer cell metabolism, attenuating oxidative phosphorylation and glycolysis. Moreover, iron chelators may reverse the major characteristics of oncogenic transformation. Iron chelation therefore represent a promising selective mode of cancer therapy.

Cobalt: An Essential Micronutrient for Plant Growth?

Cobalt is a transition metal located in the fourth row of the periodic table and is a neighbor of iron and nickel. It has been considered an essential element for prokaryotes, human beings, and other mammals, but its essentiality for plants remains obscure. In this article, we proposed that cobalt (Co) is a potentially essential micronutrient of plants. Co is essential for the growth of many lower plants, such as marine algal species including diatoms, chrysophytes, and dinoflagellates, as well as for higher plants in the family Fabaceae or Leguminosae. The essentiality to leguminous plants is attributed to its role in nitrogen (N) fixation by symbiotic microbes, primarily rhizobia. Co is an integral component of cobalamin or vitamin B₁₂, which is required by several enzymes involved in N₂ fixation. In addition to symbiosis, a group of N₂ fixing bacteria known as diazotrophs is able to situate in plant tissue as endophytes or closely associated with roots of plants including economically important crops, such as barley, corn, rice, sugarcane, and wheat. Their action in N₂ fixation provides crops with the macronutrient of N. Co is a component of several enzymes and proteins, participating in plant metabolism. Plants may exhibit Co deficiency if there is a severe limitation in Co supply. Conversely, Co is toxic to plants at higher concentrations. High levels of Co result in pale-colored leaves, discolored veins, and the loss of leaves and can also cause iron deficiency in plants. It is anticipated that with the advance of omics, Co as a constitute of enzymes and proteins and its specific role in plant metabolism will be exclusively revealed. The confirmation of Co as an essential micronutrient will enrich our understanding of plant mineral nutrition and improve our practice in crop production.

Myosin dynamics during relaxation in mouse soleus muscle and modulation by 2'-deoxy-ATP

KEY POINTS

Skeletal muscle relaxation has been primarily studied by assessing the kinetics of force decay. Little is known about the resultant dynamics of structural changes in myosin heads during relaxation. The naturally occurring nucleotide 2-deoxy-ATP (dATP) is a myosin activator that enhances cross-bridge binding and kinetics. X-ray diffraction data indicate that with elevated dATP, myosin heads were extended closer to actin in relaxed muscle and myosin heads return to an ordered, resting state after contraction more quickly. Molecular dynamics simulations of post-powerstroke myosin suggest that dATP induces structural changes in myosin heads that increase the surface area of the actin-binding regions promoting myosin interaction with actin, which could explain the observed delays in the onset of relaxation. This study of the dATP-induced changes in myosin may be instructive for determining the structural changes desired for other potential myosin-targeted molecular compounds to treat muscle diseases.

ABSTRACT

Here we used time-resolved small-angle X-ray diffraction coupled with force measurements to study the structural changes in FVB mouse skeletal muscle sarcomeres during relaxation after tetanus contraction. To estimate the rate of myosin deactivation, we followed the rate of the intensity recovery of the first-order myosin layer line (MLL1) and restoration of the resting spacing of the third and sixth order of meridional reflection (SM3 and SM6 ) following tetanic contraction. A transgenic mouse model with elevated skeletal muscle 2-deoxy-ATP (dATP) was used to study how myosin activators may affect soleus muscle relaxation. X-ray diffraction evidence indicates that with elevated dATP, myosin heads were extended closer to actin in resting muscle. Following contraction, there is a slight but significant delay in the decay of force relative to WT muscle while the return of myosin heads to an ordered resting state was initially slower, then became more rapid than in WT muscle. Molecular dynamics simulations of post-powerstroke myosin suggest that dATP induces structural changes in myosin that increase the surface area of the actin-binding regions, promoting myosin interaction with actin. With dATP, myosin heads may remain in an activated state near the thin filaments following relaxation, accounting for the delay in force decay and the initial delay in recovery of resting head configuration, and this could facilitate subsequent contractions.

RecQ DNA Helicase Rqh1 Promotes Rad3ATR Kinase Signaling in the DNA Replication Checkpoint Pathway of Fission Yeast

Rad3 is the orthologue of ATR and the sensor kinase of the DNA replication checkpoint in Schizosaccharomyces pombe Under replication stress, it initiates checkpoint signaling at the forks necessary for maintaining genome stability and cell survival. To better understand the checkpoint initiation process, we have carried out a genetic screen in fission yeast by random mutation of the genome, looking for mutants defective in response to the replication stress induced by hydroxyurea. In addition to the previously reported mutant with a C-to-Y change at position 307 encoded by tel2 (tel2-C307Y mutant) (Y.-J. Xu, S. Khan, A. C. Didier, M. Wozniak, et al., Mol Cell Biol 39:e00175-19, 2019, https://doi.org/10.1128/MCB.00175-19), this screen has identified six mutations in rqh1 encoding a RecQ DNA helicase. Surprisingly, these rqh1 mutations, except for a start codon mutation, are all in the helicase domain, indicating that the helicase activity of Rqh1 plays an important role in the replication checkpoint. In support of this notion, integration of two helicase-inactive mutations or deletion of rqh1 generated a similar Rad3 signaling defect, and heterologous expression of human RECQ1, BLM, and RECQ4 restored the Rad3 signaling and partially rescued a rqh1 helicase mutant. Therefore, the replication checkpoint function of Rqh1 is highly conserved, and mutations in the helicase domain of these human enzymes may cause the checkpoint defect and contribute to the cancer predisposition syndromes.

Genomic Instability in Fungal Plant Pathogens

Fungi and fungal-like organisms (oomycetes) that cause diseases in plants have impacted human communities for centuries and probably from the dawn of agriculture. In modern agriculture, there is a constant race between new strategies to manage fungal plant pathogens and their ability to adapt. An important component in this race is fungal genetic diversity. Mechanisms such as sexual and parasexual recombination that contribute to the creation of novel allele combinations in fungal plant pathogens are briefly discussed in the first part of this review. Advances in genomics have enabled the investigation of chromosomal aberrations of agriculturally important fungal isolates at the nucleotide level. Some of these cases are summarized in the second part of this review; it is claimed that the effect of chromosomal aberrations on pathogenicity should be studied mechanistically. More data on the effect of gene copy number variations on phenotypes that are relevant to agriculture are especially needed. Genome rearrangements through translocations have shaped the genome of fungal plant pathogens by creating lineage-specific chromosome territories encoding for genes participating in plant diseases. Pathogenicity chromosomes are unique cases of such lineage-specific genetic elements, interestingly these chromosomes can be transferred horizontally and thus transforming a non-pathogenic strain to a pathogenic one. The third part of this review describes our attempts to reveal mutators in fungal plant pathogens by identifying fungi that lack important DNA repair genes or respond to DNA damage in an unconventional way. We found that a group of fungal plant pathogens lack conserved genes that are needed for an important Holliday junction resolution pathway. In addition, in Fusarium oxysporum, the rate-limiting step in dNTP production is not induced under DNA replication stress. This is very different from organisms from bacteria to humans. It remains to be seen if these mechanisms promote genetic instability in fungal plant pathogens.

Molecular and Cellular Mechanisms of Cytotoxic Activity of Vanadium Compounds against Cancer Cells

Discovering that metals are essential for the structure and function of biomolecules has given a completely new perspective on the role of metal ions in living organisms. Nowadays, the design and synthesis of new metal-based compounds, as well as metal ion binding components, for the treatment of human diseases is one of the main aims of bioinorganic chemistry. One of the areas in vanadium-based compound research is their potential anticancer activity. In this review, we summarize recent molecular and cellular mechanisms in the cytotoxic activity of many different synthetic vanadium complexes as well as inorganic salts. Such mechanisms shall include DNA binding, oxidative stress, cell cycle regulation and programed cell death. We focus mainly on cellular studies involving many type of cancer cell lines trying to highlight some new significant advances.

A tel2 Mutation That Destabilizes the Tel2-Tti1-Tti2 Complex Eliminates Rad3ATR Kinase Signaling in the DNA Replication Checkpoint and Leads to Telomere Shortening in Fission Yeast

In response to perturbed DNA replication, ATR (ataxia telangiectasia and Rad3-related) kinase is activated to initiate the checkpoint signaling necessary for maintaining genome integrity and cell survival. To better understand the signaling mechanism, we carried out a large-scale genetic screen in fission yeast looking for mutants with enhanced sensitivity to hydroxyurea. From a collection of ∼370 primary mutants, we found a few mutants in which Rad3 (ATR ortholog)-mediated phospho-signaling was significantly compromised. One such mutant carried an uncharacterized mutation in tel2, a gene encoding an essential and highly conserved eukaryotic protein. Previous studies in various biological models have shown that Tel2 mainly functions in Tel2-Tti1-Tti2 (TTT) complex that regulates the steady-state levels of all phosphatidylinositol 3-kinase-like protein kinases, including ATR. We show here that although the levels of Rad3 and Rad3-mediated phospho-signaling in DNA damage checkpoint were moderately reduced in the tel2 mutant, the phospho-signaling in the DNA replication checkpoint was almost completely eliminated. In addition, the tel2 mutation caused telomere shortening. Since the interactions of Tel2 with Tti1 and Tti2 were significantly weakened by the mutation, destabilization of the TTT complex likely contributes to the observed checkpoint and telomere defects.

Gemcitabine, vinorelbine and cyclooxygenase inhibitors in the treatment of glioblastoma. Ultrastructural analyses in C6 glioma in vitro

OBJECTIVES

To define ultrastructural features accompanying to antitumor effects of gemcitabine, vinorelbine and cyclooxygenase inhibitors in C6 glioma cells in vitro. Vinorelbine is a semisynthetic vinca alkaloid and recent studies showed its antitumor activity in pediatric optic and pontine gliomas. Vinorelbine infusion induces a severe tumor site-pain in systemic cancers, but it is unknown whether algesia and inflammation contribute to its antitumor effects. Gemcitabine is a nucleoside-chemotherapeutic which was recently shown to act as a radiosensitizer in high-grade glioma. Some studies showed synergism of anti-inflammatory cyclooxygenase-inhibitors with microtubule inhibitors and gemcitabine. DMSO is a solvent and blocks both cylooxygenase and ribonucleotide reductase, another target of gemcitabine. Rofecoxib is withdrawn from the market, yet we used it for investigational purposes, since it blocks cylooxygenase-2 1000-times more potently than cylooxygenase -1 and is also a selective inhibitor of crinophagy.

METHODS

Plating efficacy, 3D-spheroid S-phase analysis with BrdU labelling and transmission electron microscopical analyses were performed.

RESULTS

Vinorelbine induced frequent mitotic slippage/apoptosis and autophagy. Despite both DMSO and rofecoxib induced autophagy alone and in synergy, they reduced mitotic catastrophe and autophagy triggered by vinorelbine, which was also reflected by reduced inhibition of spheroid S-phase. Gemcitabine induced karyolysis and margination of coarse chromatin towards the nuclear membrane, abundant autophagy, gutta adipis formation and decrease in mitochondria, which were enhanced by DMSO and rofecoxib.

CONCLUSIONS

Detailed ultrastructural analysis of the effects of chemotherapeutic drugs may provide a broader insight about their actions and pave to develop better strategies in treatment of glioblastoma.

Ribonucleotide reductase from Fusarium oxysporum does not Respond to DNA replication stress

Ribonucleotide reductase (RNR) catalyzes the rate limiting step in dNTP biosynthesis and is tightly regulated at the transcription and activity levels. One of the best characterized responses of yeast to DNA damage is up-regulation of RNR transcription and activity and consequently, elevation of the dNTP pools. Hydroxyurea is a universal inhibitor of RNR that causes S phase arrest. It is used in the clinic to treat certain types of cancers. Here we studied the response of the fungal plant pathogen Fusarium oxysporum to hydroxyurea in order to generate hypotheses that can be used in the future in development of a new class of pesticides. F. oxysporum causes severe damage to more than 100 agricultural crops and specifically threatens banana cultivation world-wide. Although the recovery of F. oxysporum from transient hydroxyurea exposure was similar to the one of Saccharomyces cerevisiae, colony formation was strongly inhibited in F. oxysporum in comparison with S. cerevisiae. As expected, genomic and phosphoproteomic analyses of F. oxysporum conidia (spores) exposed to hydroxyurea showed hallmarks of DNA replication perturbation and activation of recombination. Unexpectedly and strikingly, RNR was not induced by either hydroxyurea or the DNA-damaging agent methyl methanesulfonate as determined at the RNA and protein levels. Consequently, dNTP concentrations were significantly reduced, even in response to a low dose of hydroxyurea. Methyl methanesulfonate treatment did not induce dNTP pools in F. oxysporum, in contrast to the response of RNR and dNTP pools to DNA damage and hydroxyurea in several tested organisms. Our results are important because the lack of a feedback mechanism to increase RNR expression in F. oxysporum is expected to sensitize the pathogen to a fungal-specific ribonucleotide inhibitor. The potential impact of our observations on F. oxysporum genome stability and genome evolution is discussed.

Iron and Cancer

This review explores the multifaceted role that iron has in cancer biology. Epidemiological studies have demonstrated an association between excess iron and increased cancer incidence and risk, while experimental studies have implicated iron in cancer initiation, tumor growth, and metastasis. The roles of iron in proliferation, metabolism, and metastasis underpin the association of iron with tumor growth and progression. Cancer cells exhibit an iron-seeking phenotype achieved through dysregulation of iron metabolic proteins. These changes are mediated, at least in part, by oncogenes and tumor suppressors. The dependence of cancer cells on iron has implications in a number of cell death pathways, including ferroptosis, an iron-dependent form of cell death. Uniquely, both iron excess and iron depletion can be utilized in anticancer therapies. Investigating the efficacy of these therapeutic approaches is an area of active research that promises substantial clinical impact.

Circulating essential metals and lung cancer: Risk assessment and potential molecular effects

OBJECTIVE

Essential metals play important roles in the carcinogenic process. However, seldom longitudinal investigations have evaluated their roles in lung cancer development. We aimed to investigate the associations between multiple essential metals and lung cancer incidence and to explore the potential mechanisms.

METHODS

A nested case-control study of 440 incident lung cancer cases and 1:3 frequency matched 1320 healthy controls from the Dongfeng-Tongji Cohort was conducted. The baseline plasma concentrations of 11 essential metals (cobalt, copper, iron, manganese, molybdenum, rubidium, selenium, strontium, stannum, vanadium, and zinc) were measured, and their associations with lung cancer incidence were estimated. Effect of positive metal (zinc) on 4-year telomere attrition was then evaluated among an occupational cohort of 724 workers. We also assessed the transcriptional regulation effects of plasma zinc on mRNA expression profiles, and the expressions of zinc-related genes were further compared in pair-wised lung tumor and normal tissues.

RESULTS

Elevated plasma level of zinc was associated with lower incident risk of lung cancer [OR (95% CI) = 0.89 (0.79, 0.99)] and decreased 4-year telomere attrition [β (95% CI) = -0.73 (-1.27, -0.19)]. These effects were pronounced among males. In particularly, zinc could regulate the expressions of 8 cancer-related genes, including SOD1, APE, TP53BP1, WDR33, LAPTM4B, TRIT1, HUWE1, and ZNF813, which were over-expressed in lung tumor tissues.

CONCLUSIONS

We propose that high plasma zinc could prevent incident lung cancer, probably by slowing down telomere attrition and regulating the expressions of cancer-related genes. These results provided a new insight into lung cancer prevention.

Functional link between mitochondria and Rnr3, the minor catalytic subunit of yeast ribonucleotide reductase

Ribonucleotide reductase (RNR) is an essential holoenzyme required for de novo synthesis of dNTPs. The Saccharomyces cerevisiae genome encodes for two catalytic subunits, Rnr1 and Rnr3. While Rnr1 is required for DNA replication and DNA damage repair, the function(s) of Rnr3 is unknown. Here, we show that carbon source, an essential nutrient, impacts Rnr1 and Rnr3 abundance: Non-fermentable carbon sources or limiting concentrations of glucose down regulate Rnr1 and induce Rnr3 expression. Oppositely, abundant glucose induces Rnr1 expression and down regulates Rnr3. The carbon source dependent regulation of Rnr3 is mediated by Mec1, the budding yeast ATM/ATR checkpoint response kinase. Unexpectedly, this regulation is independent of all currently known components of the Mec1 DNA damage response network, including Rad53, Dun1, and Tel1, implicating a novel Mec1 signalling axis. rnr3Δ leads to growth defects under respiratory conditions and rescues temperature sensitivity conferred by the absence of Tom6, a component of the mitochondrial TOM (translocase of outer membrane) complex responsible for mitochondrial protein import. Together, these results unveil involvement of Rnr3 in mitochondrial functions and Mec1 in mediating the carbon source dependent regulation of Rnr3.

MiR-20a-5p regulates gemcitabine chemosensitivity by targeting RRM2 in pancreatic cancer cells and serves as a predictor for gemcitabine-based chemotherapy

Ribonucleotide reductase subunit M2 (RRM2) acts as an important gemcitabine resistance-related gene in pancreatic cancer (PC). Here, we aimed to investigate the potential microRNA that regulates gemcitabine chemosensitivity by targeting RRM2 and explores the clinical significance of candidate miRNA in PC. MTT assay and Western blot analysis revealed that long-time gemcitabine treatment in PC cells induced drug resistance and RRM2 increase, and silence of RRM2 blocked gemcitabine resistance. Among the predicted eight RRM2-related microRNAs, the expression of miR-20a-5p showed the most significant discrepancy between gemcitabine-resistant cells and parental cells. Furthermore, the Dual-Luciferase reporter gene assay indicated that miR-20a-5p directly targeted RRM2 3'UTR, thus inhibited expression of RRM2 and overcame gemcitabine resistance of PC cells. Retrospective study suggested that plasma miR-20a-5p level was correlated with gemcitabine resistance in PC patient. ROC curve showed that miR-20a-5p abundant level might predict gemcitabine resistance with an AUC of 89% (P<0.0001). Additionally, the PFS of patients with high and low expression levels miR-20a-5p was 2.8 and 4.5 months (P<0.001), respectively. Taken together, our results suggests that miR-20a-5p regulated gemcitabine chemosensitivity by targeting RRM2 in PC cells and could serve as a predictor for predicting the efficacy of gemcitabine-based chemotherapy in first-line treatment of PC patients.

Ironing out the role of the cyclin-dependent kinase inhibitor, p21 in cancer: Novel iron chelating agents to target p21 expression and activity

Iron (Fe) has become an important target for the development of anti-cancer therapeutics with a number of Fe chelators entering human clinical trials for advanced and resistant cancer. An important aspect of the activity of these compounds is their multiple molecular targets, including those that play roles in arresting the cell cycle, such as the cyclin-dependent kinase inhibitor, p21. At present, the exact mechanism by which Fe chelators regulate p21 expression remains unclear. However, recent studies indicate the ability of chelators to up-regulate p21 at the mRNA level was dependent on the chelator and cell-type investigated. Analysis of the p21 promoter identified that the Sp1-3-binding site played a significant role in the activation of p21 transcription by Fe chelators. Furthermore, there was increased Sp1/ER-α and Sp1/c-Jun complex formation in melanoma cells, suggesting these complexes were involved in p21 promoter activation. Elucidating the mechanisms involved in the regulation of p21 expression in response to Fe chelator treatment in neoplastic cells will further clarify how these agents achieve their anti-tumor activity. It will also enhance our understanding of the complex roles p21 may play in neoplastic cells and lead to the development of more effective and specific anti-cancer therapies.

miR-148a regulates expression of the transferrin receptor 1 in hepatocellular carcinoma

Transferrin receptor 1 (TFR1) is a transmembrane glycoprotein that allows for transferrin-bound iron uptake in mammalian cells. It is overexpressed in various cancers to satisfy the high iron demand of fast proliferating cells. Here we show that in hepatocellular carcinoma (HCC) TFR1 expression is regulated by miR-148a. Within the TFR1 3′UTR we identified and experimentally validated two evolutionarily conserved miRNA response elements (MREs) for miR-148/152 family members, including miR-148a. Interestingly, analyses of RNA sequencing data from patients with liver hepatocellular carcinoma (LIHC) revealed a significant inverse correlation of TFR1 mRNA levels and miR-148a. In addition, TFR1 mRNA levels were significantly increased in the tumor compared to matched normal healthy tissue, while miR-148a levels are decreased. Functional analysis demonstrated post-transcriptional regulation of TFR1 by miR-148a in HCC cells as well as decreased HCC cell proliferation upon either miR-148a overexpression or TFR1 knockdown. We hypothesize that decreased expression of miR-148a in HCC may elevate transferrin-bound iron uptake, increasing cellular iron levels and cell proliferation.

New Water-Soluble Copper(II) Complexes with Morpholine-Thiosemicarbazone Hybrids: Insights into the Anticancer and Antibacterial Mode of Action

Six morpholine-(iso)thiosemicarbazone hybrids HL¹–HL⁶ and their Cu(II) complexes with good-to-moderate solubility and stability in water were synthesized and characterized. Cu(II) complexes [Cu(L^1–6)Cl] (1–6) formed weak dimeric associates in the solid state, which did not remain intact in solution as evidenced by ESI-MS. The lead proligands and Cu(II) complexes displayed higher antiproliferative activity in cancer cells than triapine. In addition, complexes 2–5 were found to specifically inhibit the growth of Gram-positive bacteria Staphylococcus aureus with MIC₅₀ values at 2–5 μg/mL. Insights into the processes controlling intracellular accumulation and mechanism of action were investigated for 2 and 5, including the role of ribonucleotide reductase (RNR) inhibition, endoplasmic reticulum stress induction, and regulation of other cancer signaling pathways. Their ability to moderately inhibit R2 RNR protein in the presence of dithiothreitol is likely related to Fe chelating properties of the proligands liberated upon reduction.

Pharmacogenetic variation influences sensory neuropathy occurrence in Southern Africans treated with stavudine-containing antiretroviral therapy

BACKGROUND

The use of the HIV antiretroviral drug stavudine (d4T), a thymidine analogue, is associated with the development of mitochondrial toxicities such as sensory neuropathy (SN). Genetic variation in genes relating to d4T transport and metabolism, as well as genetic variation in the thymidine synthesis pathway, could influence occurrence of d4T-related toxicity.

METHODS

We examined this hypothesis in a cohort of HIV-positive South African adults exposed to d4T, including 143 cases with SN and 120 controls without SN. Ten SNPs in four genes associated with stavudine transport, and 16 SNPs in seven genes of the thymidine synthesis / phosphorylation pathway were genotyped using Agena mass spectrometry methods. Associations between sensory neuropathy and genetic variants were evaluated using PLINK by univariate and multivariable analyses.

RESULTS

Age and height were significantly associated with SN occurrence. Using logistic regression with age and height as covariates, and uncorrected empirical p-values, genetic variation in SLC28A1, SAMHD1, MTHFR and RRM2B was associated with SN in South Africans using d4T.

CONCLUSION

Variation in genes relating to d4T transport and metabolism, as well as genetic variation in the thymidine synthesis pathway may influence occurrence of d4T-related SN. These data contribute to the characterisation of African pharmacogenetic variation and its role in adverse response to antiretroviral therapy.