Functional characterization of the partially purified Sac1p independent adenine nucleotide transport system (ANTS) from yeast endoplasmic reticulum

Generation of a Yeast Cell Model Potentially Useful to Identify the Mammalian Mitochondrial N-Acetylglutamate Transporter

The human mitochondrial carrier family (MCF) consists of 53 members. Approximately one-fifth of them are still orphans of a function. Most mitochondrial transporters have been functionally characterized by reconstituting the bacterially expressed protein into liposomes and transport assays with radiolabeled compounds. The efficacy of this experimental approach is constrained to the commercial availability of the radiolabeled substrate to be used in the transport assays. A striking example is that of N-acetylglutamate (NAG), an essential regulator of the carbamoyl synthetase I activity and the entire urea cycle. Mammals cannot modulate mitochondrial NAG synthesis but can regulate the levels of NAG in the matrix by exporting it to the cytosol, where it is degraded. The mitochondrial NAG transporter is still unknown. Here, we report the generation of a yeast cell model suitable for identifying the putative mammalian mitochondrial NAG transporter. In yeast, the arginine biosynthesis starts in the mitochondria from NAG which is converted to ornithine that, once transported into cytosol, is metabolized to arginine. The deletion of ARG8 makes yeast cells unable to grow in the absence of arginine since they cannot synthetize ornithine but can still produce NAG. To make yeast cells dependent on a mitochondrial NAG exporter, we moved most of the yeast mitochondrial biosynthetic pathway to the cytosol by expressing four E. coli enzymes, argB-E, able to convert cytosolic NAG to ornithine. Although argB-E rescued the arginine auxotrophy of arg8∆ strain very poorly, the expression of the bacterial NAG synthase (argA), which would mimic the function of a putative NAG transporter increasing the cytosolic levels of NAG, fully rescued the growth defect of arg8∆ strain in the absence of arginine, demonstrating the potential suitability of the model generated.

A Picrocrocin-Enriched Fraction from a Saffron Extract Affects Lipid Homeostasis in HepG2 Cells through a Non-Statin-like Mode

Dyslipidemia is a lipid metabolism disorder associated with the loss of the physiological homeostasis that ensures safe levels of lipids in the organism. This metabolic disorder can trigger pathological conditions such as atherosclerosis and cardiovascular diseases. In this regard, statins currently represent the main pharmacological therapy, but their contraindications and side effects limit their use. This is stimulating the search for new therapeutic strategies. In this work, we investigated in HepG2 cells the hypolipidemic potential of a picrocrocin-enriched fraction, analyzed by high-resolution ¹H NMR and obtained from a saffron extract, the stigmas of Crocus sativus L., a precious spice that has already displayed interesting biological properties. Spectrophotometric assays, as well as expression level of the main enzymes involved in lipid metabolism, have highlighted the interesting hypolipidemic effects of this natural compound; they seem to be exerted through a non-statin-like mechanism. Overall, this work provides new insights into the metabolic effects of picrocrocin, thus confirming the biological potential of saffron and paving the way for in vivo studies that could validate this spice or its phytocomplexes as useful adjuvants in balancing blood lipid homeostasis.

A new adenine nucleotide transporter located in the ER is essential for maintaining the growth of Toxoplasma gondii

The lumen of the endoplasmic reticulum (ER) is the subcellular site where secretory protein folding, glycosylation and sulfation of membrane-bound proteins, proteoglycans, and lipids occur. The protein folding and degradation in the lumen of the ER require high levels of energy in the form of ATP. Biochemical and genetic approaches show that ATP must first be translocated across ER membrane by particular transporters before serving as substrates and energy sources in the lumenal reactions. Here we describe an ATP/ADP transporter residing in the ER membranes of T.gondii. Immunofluorescence (IFA) assay in transgenic TgANT1-HA tag revealed that TgANT1 is a protein specifically expressed in the ER. In vitro assays, functional integration of TgANT in the cytoplasmic membrane of intact E. coli cells reveals high specificity for an ATP/ADP antiport. The depletion of TgANT leads to fatal growth defects in T.gondii, including a significant slowdown in replication, no visible plaque formation, and reduced ability to invade. We also found that the amino acid mutations in two domains of TgANT lead to the complete loss of its function. Since these two domains are conserved in multiple species, they may share the same transport mechanism. Our results indicate that TgANT is the only ATP/ADP transporter in the ER of T. gondii, and the lack of ATP in the ER is the cause of the death of T. gondii.

The secretory protein of T. gondii is essential for its invasion and normal growth in host cells, all the secretory proteins are synthesized in the ER before being destined for these distinct organelles, such as apicoplast, microneme, dense granule and rhoptry. ER ATP is demanded to support secretory protein folding and trafficking, and the level of ER ATP determines which proteins are able to be directed to the distinct organelles. In theory, the supply of ATP in the ER is necessary for T. gondii. However, the transport mechanism and importance of the ER ATP in T. gondii are still unclear. In our study, we identified an ATP/ADP transporter (TgANT) located in the ER and verified its function through various methods. Unlike the ER ATP/ADP transporter in mammals, we proved that TgANT is functionally specific; the deletion of TgANT caused the interruption of the supply of ATP in the ER, which leads to fatal phenotypic defects of T. gondii. Our research further expands the understanding of the growth regulation in T. gondii.

Drosophila melanogaster Uncoupling Protein-4A (UCP4A) Catalyzes a Unidirectional Transport of Aspartate

Uncoupling proteins (UCPs) form a distinct subfamily of the mitochondrial carrier family (MCF) SLC25. Four UCPs, DmUCP4A-C and DmUCP5, have been identified in Drosophila melanogaster on the basis of their sequence homology with mammalian UCP4 and UCP5. In a Parkinson’s disease model, DmUCP4A showed a protective role against mitochondrial dysfunction, by increasing mitochondrial membrane potential and ATP synthesis. To date, DmUCP4A is still an orphan of a biochemical function, although its possible involvement in mitochondrial uncoupling has been ruled out. Here, we show that DmUCP4A expressed in bacteria and reconstituted in phospholipid vesicles catalyzes a unidirectional transport of aspartate, which is saturable and inhibited by mercurials and other mitochondrial carrier inhibitors to various degrees. Swelling experiments carried out in yeast mitochondria have demonstrated that the unidirectional transport of aspartate catalyzed by DmUCP4 is not proton-coupled. The biochemical function of DmUCP4A has been further confirmed in a yeast cell model, in which growth has required an efflux of aspartate from mitochondria. Notably, DmUCP4A is the first UCP4 homolog from any species to be biochemically characterized. In Drosophila melanogaster, DmUCP4A could be involved in the transport of aspartate from mitochondria to the cytosol, in which it could be used for protein and nucleotide synthesis, as well as in the biosynthesis of ß-alanine and N-acetylaspartate, which play key roles in signal transmission in the central nervous system.

An Overview of Mitochondrial Protein Defects in Neuromuscular Diseases

Neuromuscular diseases (NMDs) are dysfunctions that involve skeletal muscle and cause incorrect communication between the nerves and muscles. The specific causes of NMDs are not well known, but most of them are caused by genetic mutations. NMDs are generally progressive and entail muscle weakness and fatigue. Muscular impairments can differ in onset, severity, prognosis, and phenotype. A multitude of possible injury sites can make diagnosis of NMDs difficult. Mitochondria are crucial for cellular homeostasis and are involved in various metabolic pathways; for this reason, their dysfunction can lead to the development of different pathologies, including NMDs. Most NMDs due to mitochondrial dysfunction have been associated with mutations of genes involved in mitochondrial biogenesis and metabolism. This review is focused on some mitochondrial routes such as the TCA cycle, OXPHOS, and β-oxidation, recently found to be altered in NMDs. Particular attention is given to the alterations found in some genes encoding mitochondrial carriers, proteins of the inner mitochondrial membrane able to exchange metabolites between mitochondria and the cytosol. Briefly, we discuss possible strategies used to diagnose NMDs and therapies able to promote patient outcome.

Anticancer potential of novel α,β-unsaturated γ-lactam derivatives targeting the PI3K/AKT signaling pathway

Six recently synthesized alkyl (Z)-2-(2-oxopyrrolidin-3-ylidene)acetates were evaluated for their potential as cytotoxic and anticancer agents. All compounds were tested in the ERα positive MCF-7, triple negative MDA-MB-231, and Her2⁺ SKBR-3 breast cancer cell lines. The most lipophilic derivatives, bearing the 4-isopropylphenyl (2) or 4-tert-butylphenyl (3) group at the γ-lactam nitrogen, proved to be cytotoxic against all the cancer cell lines tested (IC₅₀ values ranging from 18 to 63 μM), exerting their greatest activity in SKBR-3 cells, with IC₅₀ values of 33 and 18 μM, respectively. Biological studies showed that the cytotoxic effects of 2 and 3 are accompanied by apoptotic death in breast cancer cells, and both compounds showed no significant toxicity on healthy cells (e.g., MCF-10A) and red blood cells. An in-depth mechanistic study based on molecular biology, immunoblotting analysis and in silico docking calculations suggested that α,β-unsaturated γ-lactam derivatives could interfere with the functioning of PI3K and PDK-1, two key enzymes in the PI3K/AKT signaling pathway, whose overactivation is related to the regulation of cell growth and survival in several malignancies.

The mitochondrial aspartate/glutamate carrier (AGC or Aralar1) isoforms in D. melanogaster: biochemical characterization, gene structure, and evolutionary analysis

BACKGROUND

In man two mitochondrial aspartate/glutamate carrier (AGC) isoforms, known as aralar and citrin, are required to accomplish several metabolic pathways. In order to fill the existing gap of knowledge in Drosophila melanogaster, we have studied aralar1 gene, orthologue of human AGC-encoding genes in this organism.

METHODS

The blastp algorithm and the "reciprocal best hit" approach have been used to identify the human orthologue of AGCs in Drosophilidae and non-Drosophilidae. Aralar1 proteins have been overexpressed in Escherichia coli and functionally reconstituted into liposomes for transport assays.

RESULTS

The transcriptional organization of aralar1 comprises six isoforms, three constitutively expressed (aralar1-RA, RD and RF), and the remaining three distributed during the development or in different tissues (aralar1-RB, RC and RE). Aralar1-PA and Aralar1-PE, representative of all isoforms, have been biochemically characterized. Recombinant Aralar1-PA and Aralar1-PE proteins share similar efficiency to exchange glutamate against aspartate, and same substrate affinities than the human isoforms. Interestingly, although Aralar1-PA and Aralar1-PE diverge only in their EF-hand 8, they greatly differ in their specific activities and substrate specificity.

CONCLUSIONS

The tight regulation of aralar1 transcripts expression and the high request of aspartate and glutamate during early embryogenesis suggest a crucial role of Aralar1 in this Drosophila developmental stage. Furthermore, biochemical characterization and calcium sensitivity have identified Aralar1-PA and Aralar1-PE as the human aralar and citrin counterparts, respectively.

GENERAL SIGNIFICANCE

The functional characterization of the fruit fly mitochondrial AGC transporter represents a crucial step toward a complete understanding of the metabolic events acting during early embryogenesis.

KRAS-regulated glutamine metabolism requires UCP2-mediated aspartate transport to support pancreatic cancer growth

The oncogenic KRAS mutation has a critical role in the initiation of human pancreatic ductal adenocarcinoma (PDAC) since it rewires glutamine metabolism to increase reduced nicotinamide adenine dinucleotide phosphate (NADPH) production, balancing cellular redox homeostasis with macromolecular synthesis^1,2. Mitochondrial glutamine-derived aspartate must be transported into the cytosol to generate metabolic precursors for NADPH production². The mitochondrial transporter responsible for this aspartate efflux has remained elusive. Here, we show that mitochondrial uncoupling protein 2 (UCP2) catalyses this transport and promotes tumour growth. UCP2-silenced KRAS^mut cell lines display decreased glutaminolysis, lower NADPH/NADP⁺ and glutathione/glutathione disulfide ratios and higher reactive oxygen species levels compared to wild-type counterparts. UCP2 silencing reduces glutaminolysis also in KRAS^WT PDAC cells but does not affect their redox homeostasis or proliferation rates. In vitro and in vivo, UCP2 silencing strongly suppresses KRAS^mut PDAC cell growth. Collectively, these results demonstrate that UCP2 plays a vital role in PDAC, since its aspartate transport activity connects the mitochondrial and cytosolic reactions necessary for KRAS^mut rewired glutamine metabolism², and thus it should be considered a key metabolic target for the treatment of this refractory tumour.

Drosophila melanogaster Mitochondrial Carriers: Similarities and Differences with the Human Carriers

Mitochondrial carriers are a family of structurally related proteins responsible for the exchange of metabolites, cofactors and nucleotides between the cytoplasm and mitochondrial matrix. The in silico analysis of the Drosophila melanogaster genome has highlighted the presence of 48 genes encoding putative mitochondrial carriers, but only 20 have been functionally characterized. Despite most Drosophila mitochondrial carrier genes having human homologs and sharing with them 50% or higher sequence identity, D. melanogaster genes display peculiar differences from their human counterparts: (1) in the fruit fly, many genes encode more transcript isoforms or are duplicated, resulting in the presence of numerous subfamilies in the genome; (2) the expression of the energy-producing genes in D. melanogaster is coordinated from a motif known as Nuclear Respiratory Gene (NRG), a palindromic 8-bp sequence; (3) fruit-fly duplicated genes encoding mitochondrial carriers show a testis-biased expression pattern, probably in order to keep a duplicate copy in the genome. Here, we review the main features, biological activities and role in the metabolism of the D. melanogaster mitochondrial carriers characterized to date, highlighting similarities and differences with their human counterparts. Such knowledge is very important for obtaining an integrated view of mitochondrial function in D. melanogaster metabolism.

5-(Carbamoylmethylene)-oxazolidin-2-ones as a Promising Class of Heterocycles Inducing Apoptosis Triggered by Increased ROS Levels and Mitochondrial Dysfunction in Breast and Cervical Cancer

Oxazolidinones are antibiotics that inhibit protein synthesis by binding the 50S ribosomal subunit. Recently, numerous worldwide researches focused on their properties and possible involvement in cancer therapy have been conducted. Here, we evaluated in vitro the antiproliferative activity of some 5-(carbamoylmethylene)-oxazolidin-2-ones on MCF-7 and HeLa cells. The tested compounds displayed a wide range of cytotoxicity on these cancer cell lines, measured by MTT assay, exhibiting no cytotoxicity on non-tumorigenic MCF-10A cells. Among the nine tested derivatives, four displayed a good anticancer potential. Remarkably, OI compound showed IC₅₀ values of 17.66 and 31.10 µM for MCF-7 and HeLa cancer cells, respectively. Furthermore, we assessed OI effect on the cell cycle by FACS analysis, highlighting a G1 phase arrest after 72 h, supported by a low expression level of Cyclin D1 protein. Moreover, mitochondrial membrane potential was reduced after OI treatment driven by high levels of ROS. These findings demonstrate that OI treatment can inhibit MCF-7 and HeLa cell proliferation and induce apoptosis by caspase-9 activation and cytochrome c release in the cytosol. Hence, 5-(carbamoylmethylene)-oxazolidin-2-ones have a promising anticancer activity, in particular, OI derivative could represent a good candidate for in vivo further studies and potential clinical use.

3-Amino-alkylated indoles: unexplored green products acting as anti-inflammatory agents

Aim: Over the years, indole has proved to be a versatile scaffold for the design of molecules acting as anti-inflammatory agents. Materials & Methods: A small library of 3-amino-alkylated indoles has been obtained by an optimized Mannich green approach. The anti-inflammatory activity of the new 3-amino-alkylated indoles, GLYC 0–10, was evaluated in RAW 264.7 macrophages. Results: The anti-inflammatory activity of the new 3-amino-alkylated indoles, GLYC 0–10, was evaluatedn and, among them, GLYC 4, 5 and 9 displayed the greatest inhibitory effects on nitric oxide production, with IC50 values of 5.41, 4.22 and 6.3 μM, respectively. Conclusion: Our outcomes, overall, highlight the importance of the indole substitution in the anti-inflammatory activity of these compounds, exerted by acting on the interlinked NF-κB/ERK1/2 pathways.

Thioalbamide, A Thioamidated Peptide from Amycolatopsis alba, Affects Tumor Growth and Stemness by Inducing Metabolic Dysfunction and Oxidative Stress

Thioalbamide, a thioamidated peptide biosynthesized by Amycolatopsis alba, is a thioviridamide-like molecule, and is part of a family of natural products representing a focus of biotechnological and pharmaceutical research in recent years due to their potent anti-proliferative and cytotoxic activities on malignant cells. Despite the high antitumor potential observed at nanomolar concentrations, the mechanisms underlying thioalbamide activity are still not known. In this work, the cellular effects induced by thioalbamide treatment on breast cancer cell lines were evaluated for the first time, highlighting the ability of this microbial natural peptide to induce mitochondrial dysfunction, oxidative stress, and apoptotic cell death. Furthermore, we demonstrate that thioalbamide can inhibit the propagation of cancer stem-like cells, which are strongly dependent on mitochondrial function and are responsible for chemotherapy resistance, metastasis, and tumor recurrence.

Antioxidant and Anti-Inflammatory Activities of Flavanones from Glycyrrhiza glabra L. (licorice) Leaf Phytocomplexes: Identification of Licoflavanone as a Modulator of NF-kB/MAPK Pathway

Inflammation represents an adaptive response generated by injuries or harmful stimuli. Natural remedies represent an interesting alternative to traditional therapies, involving several biochemical pathways. Besides, the valorization of agrochemical wastes nowadays seems to be a feasible way to reduce the health spending and improve the accessibility at bioactive natural compounds. In this context, the chemical composition of three Glycyrrhiza glabra L. (licorice) leaf extracts, obtained through maceration or ultrasound-assisted method (fresh and dried leaves) was investigated. A guided fractionation obtained three main components: pinocembrin, glabranin and licoflavanone. All the extracts showed similar antioxidant properties, evaluated by 2,2′-diphenyl-1-picrylhydrazyl (DPPH) or 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) Diammonium Salt (ABTS) assay, while, among the isolated compounds, licoflavanone exhibited the best antioxidant activity. The anti-inflammatory activity of the extracts and the purified compounds was investigated in lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophages. Extract C and licoflavanone showed a good anti-inflammatory activity without affecting cell viability, as they decreased nitrite levels even when used at 12.5 μg/mL (p < 0.005) and 50 μM concentration (p < 0.001), respectively. Interestingly, licoflavanone markedly decreased pro-inflammatory cytokines and cyclooxygenase 2/inducible nitric oxide synthase (COX-2/iNOS) expression levels (p < 0.001). A modulation of nuclear factor kappa B/mitogen-activated protein kinases (NF-kB/MAPK) pathway underlay such behavior, highlighting the potential of this natural compound as a new scaffold in anti-inflammatory drug research.