Cytotoxic Mechanism of Excess Polyamines Functions through Translational Repression of Specific Proteins Encoded by Polyamine Modulon

Spermidine constitutes a key determinant of motility and attachment of Salmonella Typhimurium through a novel regulatory mechanism

Spermidine is a poly-cationic molecule belonging to the family of polyamines and is ubiquitously present in all organisms. Salmonella synthesizes, and harbours specialized transporters to import spermidine. A group of polyamines have been shown to assist in Salmonella Typhimurium's virulence and regulation of Salmonella pathogenicity Inslad 1 (SPI-1) genes and stress resistance; however, the mechanism remains elusive. The virulence trait of Salmonella depends on its ability to employ multiple surface structures to attach and adhere to the surface of the target cells before invasion and colonization of the host niche. Our study discovers the mechanism by which spermidine assists in the early stages of Salmonella pathogenesis. For the first time, we report that Salmonella Typhimurium regulates spermidine transport and biosynthesis processes in a mutually inclusive manner. Using a mouse model, we show that spermidine is critical for invasion into the murine Peyer's patches, which further validated our in vitro cell line observation. We show that spermidine controls the mRNA expression of fimbrial (fimA) and non-fimbrial adhesins (siiE, pagN) in Salmonella and thereby assists in attachment to host cell surfaces. Spermidine also regulated the motility through the expression of flagellin genes by enhancing the translation of sigma-28, which features an unusual start codon and a poor Shine-Dalgarno sequence. Besides regulating the formation of the adhesive structures, spermidine tunes the expression of the two-component system BarA/SirA to regulate SPI-1 encoded genes. Thus, our study unravels a novel regulatory mechanism by which spermidine exerts critical functions during Salmonella Typhimurium pathogenesis.

Effects of polyamines and indole on the expression of ribosome hibernation factors in Escherichia coli at the translational level

Polyamines and indole are small regulatory molecules that are involved in the adaptation to stress in bacteria, including the regulation of gene expression. Genes, the translation of which is under the regulatory effects of polyamines, form the polyamine modulon. Previously, we showed that polyamines upregulated the transcription of genes encoding the ribosome hibernation factors RMF, RaiA, SRA, EttA and RsfS in Escherichia coli. At the same time, indole affected the expression at the transcriptional level of only the raiA and rmf genes. Ribosome hibernation factors reversibly inhibit translation under stress conditions, including exposure to antibiotics, to avoid resource waste and to conserve ribosomes for a quick restoration of their functions when favorable conditions occur. In this work, we have studied the influence of indole on the expression of the raiA and rmf genes at the translational level and regulatory effects of the polyamines putrescine, cadaverine and spermidine on the translation of the rmf, raiA, sra, ettA and rsfS genes. We have analyzed the mRNA primary structures of the studied genes and the predicted mRNA secondary structures obtained by using the RNAfold program for the availability of polyamine modulon features. We have found that all of the studied genes contain specific features typical of the polyamine modulon. Furthermore, to investigate the influence of polyamines and indole on the translation of the studied genes, we have constructed the translational reporter lacZ-fusions by using the pRS552/λRS45 system. According to the results obtained, polyamines upregulated the expression of the rmf, raiA and sra genes, the highest expression of which was observed at the stationary phase, but did not affect the translation of the ettA and rsfS genes, the highest expression of which took place during the exponential phase. The stimulatory effects were polyamine-specific and observed at the stationary phase, when bacteria are under multiple stresses. In addition, the data obtained demonstrated that indole significantly inhibited translation of the raiA and rmf genes, despite the stimulatory effect on their transcrip- tion. This can suggest the activity of a posttranscriptional regulatory mechanism of indole on gene expression.

Polyamines and Physical Activity in Musculoskeletal Diseases: A Potential Therapeutic Challenge

Autophagy dysregulation is commonplace in the pathogenesis of several invalidating diseases, such as musculoskeletal diseases. Polyamines, as spermidine and spermine, are small aliphatic cations essential for cell growth and differentiation, with multiple antioxidant, anti-inflammatory, and anti-apoptotic effects. Remarkably, they are emerging as natural autophagy regulators with strong anti-aging effects. Polyamine levels were significantly altered in the skeletal muscles of aged animals. Therefore, supplementation of spermine and spermidine may be important to prevent or treat muscle atrophy. Recent in vitro and in vivo experimental studies indicate that spermidine reverses dysfunctional autophagy and stimulates mitophagy in muscles and heart, preventing senescence. Physical exercise, as polyamines, regulates skeletal muscle mass inducing proper autophagy and mitophagy. This narrative review focuses on the latest evidence regarding the efficacy of polyamines and exercise as autophagy inducers, alone or coupled, in alleviating sarcopenia and aging-dependent musculoskeletal diseases. A comprehensive description of overall autophagic steps in muscle, polyamine metabolic pathways, and effects of the role of autophagy inducers played by both polyamines and exercise has been presented. Although literature shows few data in regard to this controversial topic, interesting effects on muscle atrophy in murine models have emerged when the two "autophagy-inducers" were combined. We hope these findings, with caution, can encourage researchers to continue investigating in this direction. In particular, if these novel insights could be confirmed in further in vivo and clinical studies, and the two synergic treatments could be optimized in terms of dose and duration, then polyamine supplementation and physical exercise might have a clinical potential in sarcopenia, and more importantly, implications for a healthy lifestyle in the elderly population.

ATP13A4 Upregulation Drives the Elevated Polyamine Transport System in the Breast Cancer Cell Line MCF7

Polyamine homeostasis is disturbed in several human diseases, including cancer, which is hallmarked by increased intracellular polyamine levels and an upregulated polyamine transport system (PTS). Thus far, the polyamine transporters contributing to the elevated levels of polyamines in cancer cells have not yet been described, despite the fact that polyamine transport inhibitors are considered for cancer therapy. Here, we tested whether the upregulation of candidate polyamine transporters of the P5B transport ATPase family is responsible for the increased PTS in the well-studied breast cancer cell line MCF7 compared to the non-tumorigenic epithelial breast cell line MCF10A. We found that MCF7 cells presented elevated expression of a previously uncharacterized P5B-ATPase, ATP13A4, which was responsible for the elevated polyamine uptake activity. Furthermore, MCF7 cells were more sensitive to polyamine cytotoxicity, as demonstrated by cell viability, cell death and clonogenic assays. Importantly, the overexpression of ATP13A4 WT in MCF10A cells induced a MCF7 polyamine phenotype, with significantly higher uptake of BODIPY-labeled polyamines and increased sensitivity to polyamine toxicity. In conclusion, we established ATP13A4 as a new polyamine transporter in the human PTS and showed that ATP13A4 may play a major role in the increased polyamine uptake of breast cancer cells. ATP13A4 therefore emerges as a candidate therapeutic target for anticancer drugs that block the PTS.

Conformational cycle of human polyamine transporter ATP13A2

Dysregulation of polyamine homeostasis strongly associates with human diseases. ATP13A2, which is mutated in juvenile-onset Parkinson's disease and autosomal recessive spastic paraplegia 78, is a transporter with a critical role in balancing the polyamine concentration between the lysosome and the cytosol. Here, to better understand human ATP13A2-mediated polyamine transport, we use single-particle cryo-electron microscopy to solve high-resolution structures of human ATP13A2 in six intermediate states, including the putative E2 structure for the P5 subfamily of the P-type ATPases. These structures comprise a nearly complete conformational cycle spanning the polyamine transport process and capture multiple substrate binding sites distributed along the transmembrane regions, suggesting a potential polyamine transport pathway. Integration of high-resolution structures, biochemical assays, and molecular dynamics simulations allows us to obtain a better understanding of the structural basis of how hATP13A2 transports polyamines, providing a mechanistic framework for ATP13A2-related diseases.

Cation Homeostasis: Coordinate Regulation of Polyamine and Magnesium Levels in Salmonella

Polyamines are organic cations that are important in all domains of life. Here, we show that in Salmonella, polyamine levels and Mg²⁺ levels are coordinately regulated and that this regulation is critical for viability under both low and high concentrations of polyamines. Upon Mg²⁺ starvation, polyamine synthesis is induced, as is the production of the high-affinity Mg²⁺ transporters MgtA and MgtB. Either polyamine synthesis or Mg²⁺ transport is required to maintain viability. Mutants lacking the polyamine exporter PaeA, the expression of which is induced by PhoPQ in response to low Mg²⁺, lose viability in the stationary phase. This lethality is suppressed by blocking either polyamine synthesis or Mg²⁺ transport, suggesting that once Mg²⁺ levels are reestablished, the excess polyamines must be excreted. Thus, it is the relative levels of both Mg²⁺ and polyamines that are regulated to maintain viability. Indeed, sensitivity to high concentrations of polyamines is proportional to the Mg²⁺ levels in the medium. These results are recapitulated during infection. Polyamine synthesis mutants are attenuated in a mouse model of systemic infection, as are strains lacking the MgtB Mg²⁺ transporter. The loss of MgtB in the synthesis mutant background confers a synthetic phenotype, confirming that Mg²⁺ and polyamines are required for the same process(es). Mutants lacking PaeA are also attenuated, but deleting paeA has no phenotype in a polyamine synthesis mutant background. These data support the idea that the cell coordinately controls both the polyamine and Mg²⁺ concentrations to maintain overall cation homeostasis, which is critical for survival in the macrophage phagosome. IMPORTANCE Polyamines are organic cations that are important in all life forms and are essential in plants and animals. However, their physiological functions and regulation remain poorly understood. We show that polyamines are critical for the adaptation of Salmonella to low Mg²⁺ conditions, including those found in the macrophage phagosome. Polyamines are synthesized upon low Mg²⁺ stress and partially replace Mg²⁺ until cytoplasmic Mg²⁺ levels are restored. Indeed, it is the sum of Mg²⁺ and polyamines in the cell that is critical for viability. While Mg²⁺ and polyamines compensate for one another, too little of both or too much of both is lethal. After cytoplasmic Mg²⁺ levels are reestablished, polyamines must be exported to avoid the toxic effects of excess divalent cations.

Polyamine and Ethanolamine Metabolism in Bacteria as an Important Component of Nitrogen Assimilation for Survival and Pathogenicity

Nitrogen is an essential element required for bacterial growth. It serves as a building block for the biosynthesis of macromolecules and provides precursors for secondary metabolites. Bacteria have developed the ability to use various nitrogen sources and possess two enzyme systems for nitrogen assimilation involving glutamine synthetase/glutamate synthase and glutamate dehydrogenase. Microorganisms living in habitats with changeable availability of nutrients have developed strategies to survive under nitrogen limitation. One adaptation is the ability to acquire nitrogen from alternative sources including the polyamines putrescine, cadaverine, spermidine and spermine, as well as the monoamine ethanolamine. Bacterial polyamine and monoamine metabolism is not only important under low nitrogen availability, but it is also required to survive under high concentrations of these compounds. Such conditions can occur in diverse habitats such as soil, plant tissues and human cells. Strategies of pathogenic and non-pathogenic bacteria to survive in the presence of poly- and monoamines offer the possibility to combat pathogens by using their capability to metabolize polyamines as an antibiotic drug target. This work aims to summarize the knowledge on poly- and monoamine metabolism in bacteria and its role in nitrogen metabolism.

The interaction mechanism of nickel ions with L929 cells based on integrative analysis of proteomics and metabolomics data

The aim of this paper was to study the toxicity mechanism of nickel ions (Ni2+) on L929 cells by combining proteomics and metabolomics. First, iTRAQ-based proteomics and LC/MS metabolomics analyses were used to determine the protein and metabolite expression profiles in L929 cells after treatment with 100 μM Ni2+ for 12, 24 and 48 h. A total of 177, 2191 and 2109 proteins and 40, 60 and 74 metabolites were found to be differentially expressed. Then, the metabolic pathways in which both differentially expressed proteins and metabolites were involved were identified, and three pathways with proteins and metabolites showing upstream and downstream relationships were affected at all three time points. Furthermore, the protein-metabolite-metabolic pathway network was constructed, and two important metabolic pathways involving 4 metabolites and 17 proteins were identified. Finally, the functions of the important screened metabolic pathways, metabolites and proteins were investigated and experimentally verified. Ni2+ mainly affected the expression of upstream proteins in the glutathione metabolic pathway and the arginine and proline metabolic pathway, which further regulated the synthesis of downstream metabolites, reduced the antioxidant capacity of cells, increased the level of superoxide anions and the ratio of GSSG to GSH, led to oxidative stress, affected energy metabolism and induced apoptosis.

PaeA (YtfL) protects from cadaverine and putrescine stress in Salmonella Typhimurium and E. coli

Salmonella and E. coli synthesize, import, and export cadaverine, putrescine, and spermidine to maintain physiological levels and provide pH homeostasis. Both low and high intracellular levels of polyamines confer pleiotropic phenotypes or lethality. Here, we demonstrate that the previously uncharacterized inner membrane protein PaeA (YtfL) is required for reducing cytoplasmic cadaverine and putrescine concentrations. We identified paeA as a gene involved in stationary phase survival when cells were initially grown in acidic medium, in which they produce cadaverine. The paeA mutant is also sensitive to putrescine, but not to spermidine or spermine. Sensitivity to external cadaverine in stationary phase is only observed at pH > 8, suggesting that the polyamines need to be deprotonated to passively diffuse into the cell cytoplasm. In the absence of PaeA, intracellular polyamine levels increase and the cells lose viability. Degradation or modification of the polyamines is not relevant. Ectopic expression of the known cadaverine exporter, CadB, in stationary phase partially suppresses the paeA phenotype, and overexpression of PaeA in exponential phase partially complements a cadB mutant grown in acidic medium. These data support the hypothesis that PaeA is a cadaverine/putrescine exporter, reducing potentially toxic levels under certain stress conditions.

Effect of Spermidine on Biofilm Formation in Escherichia coli K-12

Polyamines are essential for biofilm formation in Escherichia coli, but it is still unclear which polyamines are primarily responsible for this phenomenon. To address this issue, we constructed a series of E. coli K-12 strains with mutations in genes required for the synthesis and metabolism of polyamines. Disruption of the spermidine synthase gene (speE) caused a severe defect in biofilm formation. This defect was rescued by the addition of spermidine to the medium but not by putrescine or cadaverine. A multidrug/spermidine efflux pump membrane subunit (MdtJ)-deficient strain was anticipated to accumulate more spermidine and result in enhanced biofilm formation compared to the MdtJ⁺ strain. However, the mdtJ mutation did not affect intracellular spermidine or biofilm concentrations. E. coli has the spermidine acetyltransferase (SpeG) and glutathionylspermidine synthetase/amidase (Gss) to metabolize intracellular spermidine. Under biofilm-forming conditions, not Gss but SpeG plays a major role in decreasing the too-high intracellular spermidine concentrations. Additionally, PotFGHI can function as a compensatory importer of spermidine when PotABCD is absent under biofilm-forming conditions. Last, we report here that, in addition to intracellular spermidine, the periplasmic binding protein (PotD) of the spermidine preferential ABC transporter is essential for stimulating biofilm formation.IMPORTANCE Previous reports have speculated on the effect of polyamines on bacterial biofilm formation. However, the regulation of biofilm formation by polyamines in Escherichia coli has not yet been assessed. The identification of polyamines that stimulate biofilm formation is important for developing novel therapies for biofilm-forming pathogens. This study sheds light on biofilm regulation in E. coli Our findings provide conclusive evidence that only spermidine can stimulate biofilm formation in E. coli cells, not putrescine or cadaverine. Last, ΔpotD inhibits biofilm formation even though the spermidine is synthesized inside the cells from putrescine. Since PotD is significant for biofilm formation and there is no ortholog of the PotABCD transporter in humans, PotD could be a target for the development of biofilm inhibitors.