Effect of phosphate and amino acids on echinomycin biosynthesis by Streptomyces echinatus

Microbial chassis engineering drives heterologous production of complex secondary metabolites

The cryptic secondary metabolite biosynthetic gene clusters (BGCs) far outnumber currently known secondary metabolites. Heterologous production of secondary metabolite BGCs in suitable chassis facilitates yield improvement and discovery of new-to-nature compounds. The two juxtaposed conventional model microorganisms, Escherichia coli, Saccharomyces cerevisiae, have been harnessed as microbial chassis to produce a bounty of secondary metabolites with the help of certain host engineering. In last decade, engineering non-model microbes to efficiently biosynthesize secondary metabolites has received increasing attention due to their peculiar advantages in metabolic networks and/or biosynthesis. The state-of-the-art synthetic biology tools lead the way in operating genetic manipulation in non-model microorganisms for phenotypic optimization or yields improvement of desired secondary metabolites. In this review, we firstly discuss the pros and cons of several model and non-model microbial chassis, as well as the importance of developing broader non-model microorganisms as alternative programmable heterologous hosts to satisfy the desperate needs of biosynthesis study and industrial production. Then we highlight the lately advances in the synthetic biology tools and engineering strategies for optimization of non-model microbial chassis, in particular, the successful applications for efficient heterologous production of multifarious complex secondary metabolites, e.g., polyketides, nonribosomal peptides, as well as ribosomally synthesized and post-translationally modified peptides. Lastly, emphasis is on the perspectives of chassis cells development to access the ideal cell factory in the artificial intelligence-driven genome era.

Bacterial natural products in the fight against mosquito-transmitted tropical diseases

Covering: up to 2019 Secondary metabolites of microbial origin have long been acknowledged as medically relevant, but their full potential remains largely unexploited. Of the countless natural compounds discovered thus far, only 5-10% have been isolated from microorganisms. At the same time, while whole-genome sequencing has demonstrated that bacteria and fungi often encode natural products, only a few genera have yet been mined for new compounds. This review explores the contributions of bacterial natural products to combatting infection by malaria parasites, filarial worms, and arboviruses such as dengue, Zika, Chikungunya, and West Nile. It highlights how molecules isolated from microorganisms ranging from marine cyanobacteria to mosquito endosymbionts can be exploited as antimicrobials and antivirals. Pursuit of this mostly untapped source of chemical entities will potentially result in new interventions against these tropical diseases, which are urgently needed to combat the increase in the incidence of resistance.

Total synthesis of sandramycin and its analogues via a multicomponent assemblage

The total synthesis of sandramycin has been accomplished by using a Staudinger/aza-Wittig/diastereoselective Ugi three-component reaction sequence as a key step to obtain a linear pentadepsipeptide. Subsequent [5 + 5] coupling of the penptapeptide, macrolactamization, and introduction of the quinaldin chromophores afforded sandramycin. Dihydroxy and diacetoxy analogues were also prepared, and the cytotoxic activity of these analogues against a range of human cancer cell lines was evaluated.

Hypoxia inducible factor pathway inhibitors as anticancer therapeutics

Hypoxia is a significant feature of solid tumor cancers. Hypoxia leads to a more malignant phenotype that is resistant to chemotherapy and radiation, is more invasive and has greater metastatic potential. Hypoxia activates the hypoxia inducible factor (HIF) pathway, which mediates the biological effects of hypoxia in tissues. The HIF complex acts as a transcription factor for many genes that increase tumor survival and proliferation. To date, many HIF pathway inhibitors indirectly affect HIF but there have been no clinically approved direct HIF inhibitors. This can be attributed to the complexity of the HIF pathway, as well as to the challenges of inhibiting protein-protein interactions.

Recent advances in the heterologous expression of microbial natural product biosynthetic pathways

The heterologous expression of microbial natural product biosynthetic pathways coupled with advanced DNA engineering enables optimisation of product yields, functional elucidation of cryptic gene clusters, and generation of novel derivatives. This review summarises the recent advances in cloning and maintenance of natural product biosynthetic gene clusters for heterologous expression and the efforts fundamental for discovering novel natural products in the post-genomics era, with a focus on polyketide synthases (PKSs) and non-ribosomal polypeptide synthetases (NRPS).

Negative regulation of human growth hormone gene expression by insulin is dependent on hypoxia-inducible factor binding in primary non-tumor pituitary cells

Insulin controls growth hormone (GH) production at multiple levels, including via a direct effect on pituitary somatotrophs. There are no data, however, on the regulation of the intact human (h) GH gene (hGH1) by insulin in non-tumor pituitary cells, but the proximal promoter region (nucleotides -496/+1) responds negatively to insulin in transfected pituitary tumor cells. A DNA-protein interaction was also induced by insulin at nucleotides -308/-235. Here, we confirmed the presence of a hypoxia-inducible factor 1 (HIF-1) binding site within these sequences (-264/-259) and investigated whether HIF-1 is associated with insulin regulation of "endogenous" hGH1. In the absence of primary human pituitary cells, transgenic mice expressing the intact hGH locus in a somatotroph-specific manner were generated. A significant and dose-dependent decrease in hGH and mouse GH RNA levels was detected in primary pituitary cell cultures from these mice with insulin treatment. Increasing HIF-1α availability with a hypoxia mimetic significantly decreased hGH RNA levels and was accompanied by recruitment of HIF-1α to the hGH1 promoter in situ as seen with insulin. Both inhibition of HIF-1 DNA binding by echinomycin and RNA interference of HIF-1α synthesis blunted the negative effect of insulin on hGH1 but not mGH. The insulin response is also sensitive to histone deacetylase inhibition/trichostatin A and associated with a decrease in H3/H4 hyperacetylation in the proximal hGH1 promoter region. These data are consistent with HIF-1-dependent down-regulation of hGH1 by insulin via chromatin remodeling specifically in the proximal promoter region.

Dual effect of echinomycin on hypoxia-inducible factor-1 activity under normoxic and hypoxic conditions

Hypoxia-inducible factor-1 (HIF-1) is now recognized as a possible target for cancer treatment. This transcription factor is responsible for the overexpression of several genes favouring cancer cell survival and inducing neo-angiogenesis. Echinomycin has recently been described to inhibit HIF-1 DNA binding and transcriptional activity. In this work, it is shown that echinomycin strongly inhibits the activity of HIF-1 under hypoxic conditions, and also interferes with the activity of other transcription factors. These results demonstrate the lack of specificity of this molecule. Moreover, it is demonstrated that echinomycin induces an increase in HIF-1 activity under normoxic conditions, parallel to an increase in the expression of HIF-1 target genes. This effect is caused by an increase in HIF-1alpha protein level, resulting from an increase in the transcription of the HIF-1A gene in the presence of a low concentration of echinomycin. Transfection experiments with HIF-1alpha promoter constructs revealed the presence of an Sp1 binding element responsive to echinomycin. Furthermore, echinomycin enhanced Sp1 activity, as measured by the use of a specific reporter system. These findings show, for the first time, that echinomycin has a dual effect on HIF-1 activity under normoxic and hypoxic conditions, demonstrating that this molecule cannot be used in cancer treatment.

Echinomycin, a small-molecule inhibitor of hypoxia-inducible factor-1 DNA-binding activity

The identification of small molecules that inhibit the sequence-specific binding of transcription factors to DNA is an attractive approach for regulation of gene expression. Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that controls genes involved in glycolysis, angiogenesis, migration, and invasion, all of which are important for tumor progression and metastasis. To identify inhibitors of HIF-1 DNA-binding activity, we expressed truncated HIF-1alpha and HIF-1beta proteins containing the basic-helix-loop-helix and PAS domains. Expressed recombinant HIF-1alpha and HIF-1beta proteins induced a specific DNA-binding activity to a double-stranded oligonucleotide containing a canonical hypoxia-responsive element (HRE). One hundred twenty-eight compounds previously identified in a HIF-1-targeted cell-based high-throughput screen of the National Cancer Institute 140,000 small-molecule library were tested in a 96-well plate ELISA for inhibition of HIF-1 DNA-binding activity. One of the most potent compounds identified, echinomycin (NSC-13502), a small-molecule known to bind DNA in a sequence-specific fashion, was further investigated. Electrophoretic mobility shift assay experiments showed that NSC-13502 inhibited binding of HIF-1alpha and HIF-1beta proteins to a HRE sequence but not binding of the corresponding proteins to activator protein-1 (AP-1) or nuclear factor-kappaB (NF-kappaB) consensus sequences. Interestingly, chromatin immunoprecipitation experiments showed that NSC-13502 specifically inhibited binding of HIF-1 to the HRE sequence contained in the vascular endothelial growth factor (VEGF) promoter but not binding of AP-1 or NF-kappaB to promoter regions of corresponding target genes. Accordingly, NSC-13502 inhibited hypoxic induction of luciferase in U251-HRE cells and VEGF mRNA expression in U251 cells. Our results indicate that it is possible to identify small molecules that inhibit HIF-1 DNA binding to endogenous promoters.