CdgB Regulates Morphological Differentiation and Toyocamycin Production in Streptomyces diastatochromogenes 1628

Bis (3',5')-cyclic diguanylic acid (c-di-GMP) is a ubiquitous second messenger that controls several metabolic pathways in bacteria. In Streptomyces, c-di-GMP is associated with morphological differentiation, which is related to secondary metabolite production. In this study, we identified and characterized a diguanylate cyclase (DGC), CdgB, from Streptomyces diastatochromogenes 1628, which may be involved in c-di-GMP synthesis, through genetic and biochemical analyses. To further investigate the role of CdgB, the cdgB-deleted mutant strain Δ-cdgB and the cdgB-overexpressing mutant strain O-cdgB were constructed by genetic engineering. A phenotypic analysis revealed that the O-cdgB colonies exhibited reduced mycelium formation, whereas the Δ-cdgB colonies displayed wrinkled surfaces and shriveled mycelia. Notably, O-cdgB demonstrated a significant increase in the toyocamycin (TM) yield by 47.3%, from 253 to 374 mg/L, within 10 days. This increase was accompanied by a 6.7% elevation in the intracellular concentration of c-di-GMP and a higher transcriptional level of the toy cluster within four days. Conversely, Δ-cdgB showed a lower c-di-GMP concentration (reduced by 6.2%) in vivo and a reduced toyocamycin production (decreased by 28.9%, from 253 to 180 mg/L) after 10 days. In addition, S. diastatochromogenes 1628 exhibited a slightly higher inhibitory effect against Fusarium oxysporum f. sp. cucumerinum and Rhizoctonia solani compared to Δ-cdgB, but a lower inhibition rate than that of O-cdgB. The results imply that CdgB provides a foundational function for metabolism and the activation of secondary metabolism in S. diastatochromogenes 1628.

Biosynthesis and function of 7-deazaguanine derivatives in bacteria and phages

SUMMARYDeazaguanine modifications play multifaceted roles in the molecular biology of DNA and tRNA, shaping diverse yet essential biological processes, including the nuanced fine-tuning of translation efficiency and the intricate modulation of codon-anticodon interactions. Beyond their roles in translation, deazaguanine modifications contribute to cellular stress resistance, self-nonself discrimination mechanisms, and host evasion defenses, directly modulating the adaptability of living organisms. Deazaguanine moieties extend beyond nucleic acid modifications, manifesting in the structural diversity of biologically active natural products. Their roles in fundamental cellular processes and their presence in biologically active natural products underscore their versatility and pivotal contributions to the intricate web of molecular interactions within living organisms. Here, we discuss the current understanding of the biosynthesis and multifaceted functions of deazaguanines, shedding light on their diverse and dynamic roles in the molecular landscape of life.

Chemotherapy Mediated by Biomimetic Polymeric Nanoparticles Potentiates Enhanced Tumor Immunotherapy via Amplification of Endoplasmic Reticulum Stress and Mitochondrial Dysfunction

Construction of multifunctional nanoplatforms to elevate chemotherapeutic efficacy and induce long-term antitumor immunity still remains to be an extreme challenge. Herein, the design of an advanced redox-responsive nanomedicine formulation based on phosphorus dendrimer-copper(II) complexes (1G₃ -Cu)- and toyocamycin (Toy)-loaded polymeric nanoparticles (GCT NPs) coated with cancer cell membranes (CM) are reported. The designed GCT@CM NPs with a size of 210 nm are stable under physiological conditions but are rapidly dissociated in the reductive tumor microenvironment to deplete glutathione and release drugs. The co-loading of 1G₃ -Cu and Toy within the NPs causes significant tumor cell apoptosis and immunogenic cell death through 1G₃ -Cu-induced mitochondrial dysfunction and Toy-mediated amplification of endoplasmic reticulum stress, respectively, thus effectively suppressing tumor growth, promoting dendritic cell maturation, and increasing tumor-infiltrating cytotoxic T lymphocytes. Likewise, the coated CM and the loaded 1G₃ -Cu render the GCT@CM NPs with homotypic targeting and T₁ -weighted magnetic resonance imaging of tumors, respectively. With the assistance of programmed cell death ligand 1 antibody, the GCT@CM NP-mediated chemotherapy can significantly potentiate tumor immunotherapy for effective inhibition of tumor recurrence and metastasis. The developed GCT@CM NPs hold a great potential for chemotherapy-potentiated immunotherapy of different tumor types through different mechanisms or synergies.

Concentrative Nucleoside Transporter, CNT, Results in Selective Toxicity of Toyocamycin against Candida albicans

Toyocamycin (TM) is an adenosine-analog antibiotic isolated from Streptomyces toyocaensis. It inhibits Candida albicans, several plant fungal pathogens, and human cells, but many fungi, including Saccharomyces cerevisiae, are much less susceptible to TM. Aiming to clarify why TM and its analogs tubercidin and 5-iodotubercidin are active against C. albicans but not S. cerevisiae, this study focused on the absence of purine nucleoside transport activity from S. cerevisiae. When the concentrative nucleoside transporter (CNT) of C. albicans was expressed in S. cerevisiae, the recombinant strain became sensitive to TM and its analogs. The expression of C. albicans purine nucleoside permease in S. cerevisiae did not result in sensitivity to TM. Clustered regularly interspaced short palindromic repeat-mediated disruption of CNT was performed in C. albicans. The CNTΔ strain of C. albicans became insensitive to TM and its analogs. These data suggest that the toxicity of TM and its analogs toward C. albicans results from their transport via CNT. Interestingly, S. cerevisiae also became sensitive to TM and its analogs if human CNT3 was introduced into cells. These findings enhance our understanding of the mechanisms of action of adenosine analogs toward Candida pathogens and human cells. IMPORTANCE We investigated the mechanism of toxicity of TM and its analogs to C. albicans. Inspired by the effect of the copresence of TM and purine nucleosides on cell growth of C. albicans, we investigated the involvement of CNT in the toxicity mechanism by expressing CNT of C. albicans (CaCNT) in S. cerevisiae and deleting CaCNT in C. albicans. Our examinations clearly demonstrated that CaCNT is responsible for the toxicity of TM to C. albicans. S. cerevisiae expressing the human ortholog of CaCNT also became sensitive to TM and its analogs, and the order of effects of the TM analogs was a little different between CaCNT- and hCNT3-expressing S. cerevisiae. These findings are beneficial for an understanding of the mechanisms of action of adenosine analogs toward Candida pathogens and human cells and also the development of new antifungal drugs.

Protein X0P338, a GntR-type pleiotropic regulator for morphological differentiation and secondary metabolites production in Streptomyces diastatochromogenes 1628

The nucleoside antibiotic, toyocamycin (TM) exhibits excellent potent activity against several phytopathogenic fungi. Despite of its importance, little is known about key factors regulating TM biosynthesis and morphological differentiation in S. diastatochromogenes 1628. Based on proteomics data obtained from the analysis between wild-type (WT) S. diastatochromogenes 1628 strain and mutant strain 1628-T62 having a low-yield of TM, we observed that the differentially expressed protein, X0P338, which was proposed to be a regulator of the GntR-family, exhibited a higher expression level in S. diastatochromogenes 1628. Therefore, in this study, to explore whether protein X0P338 was involved in morphological differentiation and biosynthesis of secondary metabolites, especially TM, the gene called the gntR _sd -encoding protein X0P338 was cloned and over-expressed in WT strain 1628 and mutant strain 1628-T62, respectively. The results indicated that the over-expression of gntR _sd enhanced TM production in both strain 1628 (120.6 mg/L vs. 306.6 mg/L) and strain 1628-T62 (15.6 mg/L vs. 258.9 mg/L). Besides, the over-expression of gntR _sd had positive and negative effects on morphological differentiation in strain 1628 and strain 1628-T62, respectively. The results also showed opposite effects on tetraene macrolide production during the over-expression of gntR _sd in strain 1628 and strain 1628-T62. Moreover, transcription levels of genes involved in morphological differentiation and secondary metabolites production were affected by the over-expression of gntR _sd gene, both in strain 1628 and strain 1628-T62. These results confirm that X0P338 as a GntR-type pleiotropic regulator that regulates the morphological differentiation and biosynthesis of secondary metabolites, and especially has a positive effect on TM biosynthesis. This article is protected by copyright. All rights reserved.

Metal-Phenolic-Network-Coated Dendrimer-Drug Conjugates for Tumor MR Imaging and Chemo/Chemodynamic Therapy via Amplification of Endoplasmic Reticulum Stress

Amplification of endoplasmic reticulum stress (ERS) to realize enhanced cancer therapy has been considered to be unique in current cancer nanomedicine design. Herein, the design of metal-phenolic-network-coated dendrimer-drug conjugates as a novel theranostic nanoplatform based on ERS amplification is reported. In the design, acetylated generation-5 poly(amidoamine) dendrimers are conjugated with an ERS drug, toyocamycin (Toy), through the attached phenylboronic acid moiety, and coated with an iron (Fe)-tannic acid (TF) network. The generated nanocomplexes with a size of 50.2 nm are stable under the physiological environment, and can rapidly release Toy under the tumor microenvironment due to the pH- and reactive-oxygen-species-responsive boronic ester bonds to effectively inhibit the ERS-mediated cancer cell adaptation. Meanwhile, the coated TF network enables the nanocomplexes to generate cytotoxic hydroxyl radicals through a Fenton reaction, amplifying the ERS for improved chemo/chemodynamic therapy of cancer cells in vitro and a xenografted breast tumor model in vivo. Moreover, the coating of TF also renders the complexes with an eminent r₁ relaxivity for in vivo T₁ -weighted tumor magnetic resonance imaging. The created intelligent nanocomplexes may represent an advanced nanomedicine formulation uniquely integrated with a metal-phenolic network and dendrimer nanotechnology for imaging-guided cancer therapy through ERS amplification.

Enhancement of toyocamycin production through increasing supply of precursor GTP in Streptomyces diastatochromogenes 1628

The nucleoside antibiotic toyocamycin (TM), which is produced by Streptomyces diastatochromogenes 1628, exhibits potent activity against a broad range of phytopathogenic fungi. TM was synthesized through a multi-step reaction, using guanosine triphosphate (GTP) as precursor. Based on a comparison of proteomics data from S. diastatochromogenes 1628 and rifamycin-resistant mutant 1628-T15 with high yield of TM, we determined that the differentially expressed protein X0NBV6 called ribose-phosphate pyrophosphokinase (RHP), which is a rate-limiting enzyme involved in the de novo biosynthesis of GTP, exhibits a higher expression level in mutant 1628-T15. In this study, to elucidate the relationships between RHP, GTP, and TM production, the gene rhp _sd encoding RHP was cloned and overexpressed in S. diastatochromogenes strain 1628. The recombinant strain S. diastatochromogenes 1628-RHP exhibited better performance at the transcriptional level of the rhp _sd gene, as well as RHP enzymatic activity, intracellular GTP concentration, and TM production, compared to S. diastatochromogenes 1628. Finally, the yield of TM produced by S. diastatochromogenes 1628-RHP (340.2 mg/L) was 133.3% higher than that produced by S. diastatochromogenes1628. Moreover, the transcriptional level of toy genes involved in TM biosynthesis was enhanced due to the overexpression of the rhp _sd gene.

First Evidence of Function for Schistosoma japonicumriok-1 and RIOK-1

Protein kinases are known as key molecules that regulate many biological processes in animals. The right open reading frame protein kinase (riok) genes are known to be essential regulators in model organisms such as the free-living nematode Caenorhabditis elegans. However, very little is known about their function in parasitic trematodes (flukes). In the present study, we characterized the riok-1 gene (Sj-riok-1) and the inferred protein (Sj-RIOK-1) in the parasitic blood fluke, Schistosoma japonicum. We gained a first insight into function of this gene/protein through double-stranded RNA interference (RNAi) and chemical inhibition. RNAi significantly reduced Sj-riok-1 transcription in both female and male worms compared with untreated control worms, and subtle morphological alterations were detected in the ovaries of female worms. Chemical knockdown of Sj-RIOK-1 with toyocamycin (a specific RIOK-1 inhibitor/probe) caused a substantial reduction in worm viability and a major accumulation of mature oocytes in the seminal receptacle (female worms), and of spermatozoa in the sperm vesicle (male worms). These phenotypic alterations indicate that the function of Sj-riok-1 is linked to developmental and/or reproductive processes in S. japonicum.

Cloning and Overexpression of the Toy Cluster for Titer Improvement of Toyocamycin in Streptomyces diastatochromogenes

The nucleoside antibiotic toyocamycin (TM) is a potential fungicide that can control plant diseases, and it has become an attractive target for research. Streptomyces diastatochromogenes 1628, a TM-producing strain, was isolated by our laboratory and was considered to be a potent industrial producer of TM. Recently, the putative TM biosynthetic gene cluster (toy cluster) in S. diastatochromogenes 1628 was found by genome sequencing. In this study, the role of toy cluster for TM biosynthesis in S. diastatochromogenes 1628 was investigated by heterologous expression, deletion, and complementation. The extract of the recombinant strain S. albusJ1074-TC harboring a copy of toy cluster produced TM as shown by HPLC analysis. The Δcluster mutant completely lost its ability to produce TM. TM production in the complemented strain was restored to a level comparable to that of the wild-type strain. These results confirmed that the toy cluster is responsible for TM biosynthesis. Moreover, the introduction of an extra copy of the toy cluster into S. diastatochromogenes 1628 led to onefold increase in TM production (312.9 mg/l vs. 152.1 mg/l) as well as the transcription of all toy genes. The toy gene cluster was engineered in which the native promoter of toyA gene, toyM gene, toyBD operon, and toyEI operon was, respectively, replaced by permE^∗ or SPL57. To further improve TM production, the engineered toy gene cluster was, respectively, introduced and overexpressed in S. diastatochromogenes 1628 to generate recombinant strains S. diastatochromogenes 1628-EC and 1628-SC. After 84 h, S. diastatochromogenes 1628-EC and 1628-SC produced 456.5 mg/l and 638.9 mg/l TM, respectively, which is an increase of 2- and 3.2-fold compared with the wild-type strain.

Targeting the Unfolded Protein Response as a Potential Therapeutic Strategy in Renal Carcinoma Cells Exposed to Cyclosporine A

BACKGROUND/AIM

Organ transplant patients treated with the immunosuppressive drug cyclosporine A often present malignant kidney tumors. Cyclosporine A can promote oncogenesis in a cell-intrinsic manner by increasing the production of vascular endothelial growth factor (VEGF).

MATERIALS AND METHODS

We explored the impact of cyclosporine A and the role of the unfolded protein response (UPR) on three human renal cell carcinoma (RCC) cell lines under normoxic and hypoxic (1% O₂) conditions.

RESULTS

Cyclosporine A regulated the expression of VEGF at the post-transcriptional level. Cyclosporine A induced the inositol requiring enzyme-1α (IRE1α) arm of the UPR and stabilized neosynthesized proteins in RCC cells. Toyocamycin, an inhibitor of IRE1α, abolished the clonogenic growth of RCC cells and reduced induction of VEGF by cyclosporine A under hypoxia.

CONCLUSION

Our findings highlight the impact of cyclosporine A on the proteostasis of RCC cells, and suggest the potential therapeutic interest of targeting the UPR against tumors arising in the context of organ transplantation.

Identification of Toyocamycin, an agent cytotoxic for multiple myeloma cells, as a potent inhibitor of ER stress-induced XBP1 mRNA splicing

The IRE1α-XBP1 pathway, a key component of the endoplasmic reticulum (ER) stress response, is considered to be a critical regulator for survival of multiple myeloma (MM) cells. Therefore, the availability of small-molecule inhibitors targeting this pathway would offer a new chemotherapeutic strategy for MM. Here, we screened small-molecule inhibitors of ER stress-induced XBP1 activation, and identified toyocamycin from a culture broth of an Actinomycete strain. Toyocamycin was shown to suppress thapsigargin-, tunicamycin- and 2-deoxyglucose-induced XBP1 mRNA splicing in HeLa cells without affecting activating transcription factor 6 (ATF6) and PKR-like ER kinase (PERK) activation. Furthermore, although toyocamycin was unable to inhibit IRE1α phosphorylation, it prevented IRE1α-induced XBP1 mRNA cleavage in vitro. Thus, toyocamycin is an inhibitor of IRE1α-induced XBP1 mRNA cleavage. Toyocamycin inhibited not only ER stress-induced but also constitutive activation of XBP1 expression in MM lines as well as primary samples from patients. It showed synergistic effects with bortezomib, and induced apoptosis of MM cells including bortezomib-resistant cells at nanomolar levels in a dose-dependent manner. It also inhibited growth of xenografts in an in vivo model of human MM. Taken together, our results suggest toyocamycin as a lead compound for developing anti-MM therapy and XBP1 as an appropriate molecular target for anti-MM therapy.

Identification of inhibitors of ribozyme self-cleavage in mammalian cells via high-throughput screening of chemical libraries

We have recently described an RNA-only gene regulation system for mammalian cells in which inhibition of self-cleavage of an mRNA carrying ribozyme sequences provides the basis for control of gene expression. An important proof of principle for that system was provided by demonstrating the ability of one specific small molecule inhibitor of RNA self-cleavage, toyocamycin, to control gene expression in vitro and vivo. Here, we describe the development of the high-throughput screening (HTS) assay that led to the identification of toyocamycin and other molecules capable of inhibiting RNA self-cleavage in mammalian cells. To identify small molecules that can serve as inhibitors of ribozyme self-cleavage, we established a cell-based assay in which expression of a luciferase (luc) reporter is controlled by ribozyme sequences, and screened 58,076 compounds for their ability to induce luciferase expression. Fifteen compounds able to inhibit ribozyme self-cleavage in cells were identified through this screen. The most potent of the inhibitors identified were toyocamycin and 5-fluorouridine (FUR), nucleoside analogs carrying modifications of the 7-position and 5-position of the purine or pyrimidine bases. Individually, these two compounds were able to induce gene expression of the ribozyme-controlled reporter approximately 365-fold and 110-fold, respectively. Studies of the mechanism of action of the ribozyme inhibitors indicate that the compounds must be incorporated into RNA in order to inhibit RNA self-cleavage.

Adenovirus messenger RNA in mammalian cells: failure of polyribosome association in the absence of nuclear cleavage

The nuclear synthesis of adenovirus-specific RNA late in the infectious cycle in the presence of toyocamycin (an adenosine analogue) has been investigated. There is reduced synthesis of viral RNA with an accumulation of virus-specific RNA in the molecular weight range of at least 4 to 8 x 10(6). No new viral RNA associates with cytoplasmic polyribosomes. In addition, hybridization competition experiments indicate a 70% competition between these large nuclear transcripts and polyribosome-associated viral RNA that was synthesized in the absence of inhibitor. These data are consistent with the following interpretations: complete nuclear processing of viral RNA is necessary for polyribosome association, and precursor viral message(s) contain sequences that are lost normally during post-transcriptional processing.