The ring rules the chain - inositol pyrophosphates and the regulation of inorganic polyphosphate.

The maintenance of phosphate homeostasis serves as a foundation for energy metabolism and signal transduction processes in all living organisms. Inositol pyrophosphates (PP-InsPs), composed of an inositol ring decorated with monophosphate and diphosphate moieties, and inorganic polyphosphate (polyP), chains of orthophosphate residues linked by phosphoanhydride bonds, are energy-rich biomolecules that play critical roles in phosphate homeostasis. There is a complex interplay between these two phosphate-rich molecules, and they share an interdependent relationship with cellular adenosine triphosphate (ATP) and inorganic phosphate (Pi). In eukaryotes, the enzymes involved in PP-InsP synthesis show some degree of conservation across species, whereas distinct enzymology exists for polyP synthesis among different organisms. In fact, the mechanism of polyP synthesis in metazoans, including mammals, is still unclear. Early studies on PP-InsP and polyP synthesis were conducted in the slime mould Dictyostelium discoideum, but it is in the budding yeast Saccharomyces cerevisiae that a clear understanding of the interplay between polyP, PP-InsPs, and Pi homeostasis has now been established. Recent research has shed more light on the influence of PP-InsPs on polyP in mammals, and the regulation of both these molecules by cellular ATP and Pi levels. In this review we will discuss the cross-talk between PP-InsPs, polyP, ATP, and Pi in the context of budding yeast, slime mould, and mammals. We will also highlight the similarities and differences in the relationship between these phosphate-rich biomolecules among this group of organisms.

LCN2-Fungal siderophore-iron binding and uptake leads to oxidative stress and cell death in hepatocellular carcinoma cell line HepG2.

Microorganisms produce non-ribosomal peptides called siderophores for the purpose of iron acquisition. Mammalian immune system is well-known for producing small secretory proteins called lipocalins upon bacterial infection. These proteins sequester siderophores produced by invading bacterial pathogens rendering them unable to acquire iron from the host. However, this is not their sole function. In addition to transferrin and lactoferrin, lipocalins are also known to transport siderophore-bound iron to the host cells. While binding of bacterial siderophores with human lipocalin is well studied, binding of the fungal counterpart is still not confirmed and fully understood. Apart from pathogen-affected cells, developing cancerous cells also show varying expression level of different proteins including those involved in iron transport. The possibility of exogenous fungal siderophore-mediated iron transport via lipocalin and its receptor in mammalian cells has not yet been explored much. In present investigation we have checked differential expression of human lipocalin, LCN2 in hepatocellular carcinoma cell lines HepG2 as well as its normal counterpart WRL-68 and computationally determined the feasibility of LCN2 binding with fungal siderophore. Further in case of a stable complex being formed, whether this complex has the ability to transport iron through its specific receptor was assessed. Also, we have tried to explore possible mechanism of fungal-siderophore mediated oxidative stress leading to significant cell death in cancerous cells. This study will thus be useful towards finding a new way of treating hepatocellular carcinoma via inducing siderophore-mediated cell death in cancerous cells.Communicated by Ramaswamy H. Sarma.

In silico analysis of comparative affinity of phytosiderophore and bacillibactin for iron uptake by YSL15 and YSL18 receptors of Oryza sativa.

Iron is an important micronutrient for plant growth and development. In the case of Oryza sativa, iron is made available primarily with the help of iron chelators called phytosiderophores i.e. variants of deoxymugineic acid (DMA). They bind with ferric ions and get internalized through Yellow Stripe Like transporters viz. YSL15 and YSL18. However, due to low amount of secretion of phytosiderophores, rice suffers from iron deficiency. Alternatively, siderophores of plant growth promoting rhizobacteria may support iron uptake and make it available to plants via transporting ferric ions possibly through the same transporters. Present study aims to assess comparative binding of DMA and a xenosiderophore (siderophores used by organisms other than the ones producing them) of rhizobacteria i.e. bacillibactin with Fe3+ ion and subsequent transporters of rice. Protein-protein interaction and gene expression analysis predicts uptake of Fe3+ by YSL15 from the rhizosphere region and further distribution through YSL18 with the help of various predicted functional partners. Docking studies confirm the thermodynamically more favourable structure of bacillibactin-Fe3+ complex than DMA-Fe3+ complex. Molecular modelling of YSL15 and YSL18 was done through ab initio method and their evaluation by Ramachandran plot, ProSA, ERRAT value and verify 3 D score revealed a good quality models. Comparative binding assessment through docking and molecular dynamics simulation suggests better binding energies of YSL transporters with bacillibactin-Fe3+ complex as compared to DMA-Fe3+ complex. The current study suggests possible application of xenosiderophores of PGPR origin in supporting plant growth via iron uptake and distribution in rice.Communicated by Ramaswamy H. Sarma.

Combinatorial Effect of Arsenic and Herbal Compounds in Telomerase-Mediated Apoptosis Induction in Liver Cancer.

Tumour illness and its resistance against existing anticancer therapies pose a serious health concern globally despite the progressive advancement of therapeutic options. The prevailing treatment of HCC using numerous antitumor agents has inflated long-lived complete remissions, but a percentage of individuals still die due to disease recurrence, indicating a need for further exploration of possible anti-tumour regimes. We aim to boost the effectiveness of the HCC treatment by conducting current investigations evaluating the effect of arsenic trioxide (ATO) with different herbal compounds like quercetin and aloe-emodin against liver tumour via inhibition of telomerase, a pro-cancer enzyme. The anticancer activity of ATO with herbal compounds was investigated in human control liver cell line (Wrl-68) and cancer liver cell line (HepG2) at different time intervals. Viability and cytotoxicity in response to combinatorial drugs were assessed in vitro by trypan blue dye exclusion assay and MTT and WST assay. Apoptosis was analysed by annexin V/PI assay, and the expression of telomerase and apoptosis-regulating proteins was evaluated by immunoblotting and qRT-PCR. Arsenic trioxide in combination with quercetin and aloe-emodin reduced cell viability in cancerous cells compared to normal cells by inducing apoptosis, downregulating telomerase and Bcl-2 (anti-apoptotic protein) and upregulating the expression of Bax (pro-apoptotic protein). ATO exhibited significant anticancer effects due to the synergistic effects of quercetin and aloe-emodin in liver tumour cells. The current study data collectively suggest that a successful inhibition of cancer growth by the combination of ATO and tested herbal medicines against liver tumour growth is via the inhibition of telomerase activity.

Induction of Iron Stress in Hepatocellular Carcinoma Cell Lines by Siderophore of Aspergillus nidulans Towards Promising Anticancer Effect.

Hepatocellular carcinoma is among the leading causes of cancer-related deaths worldwide and needs efficient and feasible approach of treatment. Present study focuses on exploring the anticancer activity of a secondary metabolite called siderophore of Aspergillus nidulans against hepatocellular carcinoma cell line HepG2. These small peptides are produced by microorganisms including fungi for scavenging iron from its surroundings. Fungi including Aspergillus spp. are known to produce siderophores under iron-limited conditions. Siderophores have high affinity towards iron and are classified into various types. In the present study, siderophore isolated and purified from fungal cultures was confirmed to be of hydroxamate type by chrome azurol sulfonate and Atkin's assay. HPLC analysis confirmed purity while LC-ESI-MS revealed that the siderophore is triacetyl fusigen. Cancerous cells, HepG2, grown under siderophore treatment showed inhibition in growth and proliferation in a dose- and time-dependent manner. Reduction in viability and metabolic activity was evident upon treatment as seen in trypan blue, MTT and WST assay. Fluorescent staining using PI and DAPI confirmed the same while DCFDA staining revealed increased reactive oxygen species production which might have led to cell death and deterioration. Such increase in ROS has been correlated with iron accumulation by assessing intracellular iron level through ICP-MS. To assess the effect of siderophore treatment on normal cells, WRL-68, same assays were carried out but the effect was mostly non-significant up to 48 h. Thus, present work suggests that an optimum dose of siderophore purified from A. nidulans culture might prove a useful anticancer agent.

Antifungal Activity of Siderophore Isolated From Escherichia coli Against Aspergillus nidulans via Iron-Mediated Oxidative Stress.

Microorganisms produce various secondary metabolites for growth and survival. During iron stress, they produce secondary metabolites termed siderophores. In the current investigation, antifungal activity of catecholate siderophore produced by Escherichia coli has been assessed against Aspergillus nidulans. Exogenous application of the bacterial siderophore to fungal cultures resulted in decreased colony size, increased filament length, and changes in hyphal branching pattern. Growth inhibition was accompanied with increased intracellular iron content. Scanning electron microscopy revealed dose-dependent alteration in fungal morphology. Fluorescent staining by propidium iodide revealed cell death in concert with growth inhibition with increasing siderophore concentration. Antioxidative enzyme activity was also compromised with significant increase in catalase activity and decrease in ascorbate peroxidase activity. Siderophore-treated cultures showed increased accumulation of reactive oxygen species as observed by fluorescence microscopy and enhanced membrane damage in terms of malondialdehyde content. Antifungal property might thus be attributed to xenosiderophore-mediated iron uptake leading to cell death. STRING analysis showed interaction of MirB (involved in transport of hydroxamate siderophore) and MirA (involved in transport of catecholate siderophore), confirming the possibility of uptake of iron-xenosiderophore complex through fungal transporters. MirA structure was modeled and validated with 95% residues occurring in the allowed region. In silico analysis revealed MirA-Enterobactin-Fe3+ complex formation. Thus, the present study reveals a promising antifungal agent in the form of catecholate siderophore and supports involvement of MirA fungal receptors in xenosiderophore uptake.

Iron: Key player in cancer and cell cycle?

BACKGROUND: Iron is an essential element for growth and metabolic activities of all living organisms but remains in its oxyhydroxide ferric ion form in the surrounding. Unavailability of iron in soluble ferrous form led to development of specific pathways and machinery in different organisms to make it available for use and maintain its homeostasis. Iron homeostasis is essential as under different circumstances iron in excess as well as deprivation leads to different pathological conditions in human. OBJECTIVE: This review highlights the current findings related to iron excess as well as deprivation with regards to cellular proliferation. CONCLUSIONS: Iron excess is extensively associated with different types of cancers viz. colorectal cancer, breast cancer etc. by producing an oxidative stressed condition and alteration of immune system. Ironically its deprivation also results in anaemic conditions and leads to cell cycle arrest at different phases with mechanism yet to be explored. Iron deprivation arrests cell cycle at G1/S and in some cases at G2/M checkpoints resulting in growth arrest. However, in some cases iron overload arrests cell cycle at G1 phase by blocking certain signalling pathways. Certain natural and synthetic iron chelators are being explored from few decades to combat diseases caused by alteration in iron homeostasis.

Siderophore-assisted cadmium hyperaccumulation in Bacillus subtilis.

Siderophores (Gk iron carriers) are low molecular weight secondary metabolites produced by bacteria, fungi, and plants that have strong binding affinity for iron. Owing to their iron-chelating ability, they are produced mainly when the organism faces iron scarcity. The present study empirically investigated the importance of applying hydroxamate siderophore extracted from Aspergillus nidulans to the cells of Bacillus subtilis for bioremediation of cadmium salt. This investigation deals with siderophore-mediated intracellular Cd accumulation by bacterial cells, growth estimation, biochemical assays like lipid peroxidation, total protein content, carbohydrate content, and iron content estimation. In silico docking and STRING analyses revealed specific interaction between Aspergillus siderophore and receptors present on B. subtilis. Estimation of intracellular Cd by atomic absorption spectroscopy showed more accumulation of Cd ions by B. subtilis in the presence of hydroxamate siderophore. This suggests a possibility of confiscating environmental Cd2+ by utilizing metal chelation property of siderophores and hence can lead to emerging bioremediation mechanisms for heavy metals. In silico studies support experimental investigation and suggest higher affinity of siderophore for Cd ions as compared with ferric ions.

Synthesis, nature and utility of universal iron chelator - Siderophore: A review.

Siderophores, the secondary metabolite of various microorganisms are ferric ion specific chelators secreted under iron stressed condition. These non-ribosomal peptides have been classified as catecholate, hydroxamate, carboxylate and mixed types. Recent studies focus on discovery of possible mammalian siderophores. The biosynthesis pathway including non-ribosomal dependent as well as non-ribosomal independent pathways are of great interest now a days. Many significant roles of siderophores such as virulence in pathogens, oxidative stress tolerance, classification of organisms etc. are being discovered. Studies on siderophore utilization in bioremediation and other heavy metal chelation have increased in past decade. The iron chelation ability of siderophores is being recently studied with regards to malignant cancerous cells. Not only this, it has been found that they possess antimicrobial properties which can be utilized against number of microbes. This review covers all recent aspects of siderophore and its applications.