Blockade of PGK1 and ALDOA enhances bilirubin control of Th17 cells in Crohn's disease.

Unconjugated bilirubin (UCB) confers Th17-cells immunosuppressive features by activating aryl-hydrocarbon-receptor, a modulator of toxin and adaptive immune responses. In Crohn's disease, Th17-cells fail to acquire regulatory properties in response to UCB, remaining at an inflammatory/pathogenic state. Here we show that UCB modulates Th17-cell metabolism by limiting glycolysis and through downregulation of glycolysis-related genes, namely phosphoglycerate-kinase-1 (PGK1) and aldolase-A (ALDOA). Th17-cells of Crohn's disease patients display heightened PGK1 and ALDOA and defective response to UCB. Silencing of PGK1 or ALDOA restores Th17-cell response to UCB, as reflected by increase in immunoregulatory markers like FOXP3, IL-10 and CD39. In vivo, PGK1 and ALDOA silencing enhances UCB salutary effects in trinitro-benzene-sulfonic-acid-induced colitis in NOD/scid/gamma humanized mice where control over disease activity and enhanced immunoregulatory phenotypes are achieved. PGK1 and/or ALDOA blockade might have therapeutic effects in Crohn's disease by favoring acquisition of regulatory properties by Th17-cells along with control over their pathogenic potential.

Molecular Docking, QSAR and Microscopic Studies of Anti-trypanosomal Compounds from the Pathogen Box.

BACKGROUND: Trypanosoma brucei (T. brucei) is the cause of the deadly human African trypanosomiasis (HAT) with a case fatality ratio of 10%. OBJECTIVE: Targeting the essential Trypanosomal glucose metabolism pathway through the inhibition of phosphoglycerate kinase (PGK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a valid strategy for anti-T. brucei drug development. METHODS: Here, quantitative structure activity relationship, molecular docking and microscopic studies were used to describe the mode of inhibition of selected compounds from the pathogen box PGK and GAPDH. RESULTS: We identified 4 hit compounds from the pathogen box with optimal binding and chemical interactions. Notably, it was identified that interacting charge surface and atomic mass were key aspects of both PGK and GAPDH inhibition. Also, novel anti-trypanosomal compounds were identified from the pathogen box and their half maximal inhibitory concentrations were described. CONCLUSION: Our study presents new anti-trypanosomal compounds with optimal pharmacological profiles and an optimization strategy for improving target specificity in the rational design of novel anti-trypanosomal compounds.

Pharmacologically inhibiting phosphoglycerate kinase 1 for glioma with NG52.

Inhibition of glycolysis process has been an attractive approach for cancer treatment due to the evidence that tumor cells are more dependent on glycolysis rather than oxidative phosphorylation pathway. Preliminary evidence shows that inhibition of phosphoglycerate kinase 1 (PGK1) kinase activity would reverse the Warburg effect and make tumor cells lose the metabolic advantage for fueling the proliferation through restoration of the pyruvate dehydrogenase (PDH) activity and subsequently promotion of pyruvic acid to enter the Krebs cycle in glioma. However, due to the lack of small molecule inhibitors of PGK1 kinase activity to treat glioma, whether PGK1 could be a therapeutic target of glioma has not been pharmacologically verified yet. In this study we developed a high-throughput screening and discovered that NG52, previously known as a yeast cell cycle-regulating kinase inhibitor, could inhibit the kinase activity of PGK1 (the IC50 = 2.5 ± 0.2 µM). We showed that NG52 dose-dependently inhibited the proliferation of glioma U87 and U251 cell lines with IC50 values of 7.8 ± 1.1 and 5.2 ± 0.2 µM, respectively, meanwhile it potently inhibited the proliferation of primary glioma cells. We further revealed that NG52 (12.5-50 µM) effectively inhibited the phosphorylation of PDHK1 at Thr338 site and the phosphorylation of PDH at Ser293 site in U87 and U251 cells, resulting in more pyruvic acid entering the Krebs cycle with increased production of ATP and ROS. Therefore, NG52 could reverse the Warburg effect by inhibiting PGK1 kinase activity, and switched cellular glucose metabolism from anaerobic mode to aerobic mode. In nude mice bearing patient-derived glioma xenograft, oral administration of NG52 (50, 100, 150 mg· kg-1·d-1, for 13 days) dose-dependently suppressed the growth of glioma xenograft. Together, our results demonstrate that targeting PGK1 kinase activity might be a potential strategy for glioma treatment.

Identification of a novel non-ATP-competitive protein kinase inhibitor of PGK1 from marine nature products.

Phosphoglycerate kinase 1 (PGK1) acts as both a glycolytic enzyme and a protein kinase playing critical roles in cancer progression, thereby being regarded as an attractive therapeutic target for cancer treatment. However, no effective inhibitor of PGK1 has been reported. Here, we demonstrate that GQQ-792, a thiodiketopiperazine derivative from marine nature products, is a non-ATP-competitive inhibitor of PGK1 with the disulfide group within the structure of GQQ-792 as a key pharmacophore. The disulfide group of GQQ-792 binds to Cys379 and Cys380 of PGK1, resulting in occlusion of ATP from binding to PGK1. GQQ-792 treatment blocks hypoxic condition- and EGF stimulation-enhanced protein kinase activity of PGK1 that phosphorylates PDHK1 at T338 in glioblastoma cells; this treatment leads to decreased lactate production and glucose uptake, and subsequent apoptosis of glioblastoma cells. Animal studies reveal that GQQ-792 significantly inhibits the growth of tumor derived from glioblastoma cells. These findings underscore the potential of GQQ-792 as a promising anticancer agent and pave an avenue to further optimize the structure of GQQ-792 basing on its target molecule and pharmacophore in future.

Novel Drosophila model for parkinsonism by targeting phosphoglycerate kinase.

Patients with Parkinson's disease (PD) show a common progressive neurodegenerative movement disorder characterized by rigidity, tremors, postural instability, and bradykinesia due to the loss of dopaminergic neurons in the substantia nigra, and is often accompanied by several non-motor symptoms, called parkinsonism. Several lines of recent evidence support the hypothesis that mutations in the gene encoding phosphoglycerate kinase (PGK) play an important role in the PD mechanism. PGK is a key enzyme in the glycolytic pathway that catalyzes the reaction from 1,3-diphosphoglycerate to 3-phosphoglycerate. We herein established a parkinsonism model targeting Drosophila Pgk. Dopaminergic (DA) neuron-specific Pgk knockdown lead to locomotive defects in both young and aged adult flies and was accompanied by progressive DA neuron loss with aging. Pgk knockdown in DA neurons decreased dopamine levels in the central nervous system (CNS) of both young and aged adult flies. These phenotypes are similar to the defects observed in human PD patients, suggesting that the Pgk knockdown flies established herein are a promising model for parkinsonism. Furthermore, pan-neuron-specific Pgk knockdown induced low ATP levels and the accumulation of reactive oxygen species (ROS) in the CNS of third instar larvae. Collectively, these results indicate that a failure in the energy production system of Pgk knockdown flies causes locomotive defects accompanied by neuronal dysfunction and degeneration in DA neurons.

PGK1 inhibitor CBR-470-1 protects neuronal cells from MPP+.

The neurotoxin MPP+ (1-methyl-4-phenylpyridinium ion) disrupts mitochondrial function leading to oxidative stress and neuronal death. Here we examine whether activation of the Keap1-Nrf2 cascade can protect SH-SY5Y neuroblastoma cells from MPP+-induced cytotoxicity. Treatment of SH-SY5Y cells with CBR-470-1, an inhibitor of the glycolytic enzyme phosphoglycerate kinase 1 (PGK1), leads to methylglyoxal modification of Keap1, Keap1-Nrf2 disassociation, and increased expression of Nrf2 responsive genes. Pretreatment with CBR-470-1 potently attenuated MPP+-induced oxidative injury and SH-SY5Y cell apoptosis. CBR-470-1 neuroprotection is dependent upon Nrf2, as Nrf2 shRNA or CRISPR/Cas9-mediated Nrf2 knockout, abolished CBR-470-1-induced SH-SY5Y cytoprotection against MPP+. Consistent with these findings, PGK1 depletion or knockout mimicked CBR-470-1-induced actions and rendered SH-SY5Y cells resistant to MPP+-induced cytotoxicity. Furthermore, activation of the Nrf2 cascade by CRISPR/Cas9-induced Keap1 knockout protected SH-SY5Y cells from MPP+. In Keap1 or PGK1 knockout SH-SY5Y cells,CBR-470-1 failed to offer further cytoprotection against MPP+. Collectively PGK1 inhibition by CBR-470-1 protects SH-SY5Y cells from MPP+ via activation of the Keap1-Nrf2 cascade.

MiRNA-215-5p alleviates the metastasis of prostate cancer by targeting PGK1.

OBJECTIVE: MicroRNAs (miRNAs) are endogenous, non-coding RNAs, which exert crucial functions in regulating biological progressions. Previous studies have demonstrated the anti-tumor effect of miRNA-215-5p. However, its specific role in influencing the progression of prostate cancer (PCa) remains unclear. This study aims to uncover the regulatory effect of miRNA-215-5p on the metastasis and prognosis of PCa. PATIENTS AND METHODS: MiRNA-215-5p levels in collected PCa tissues (n=52) and paracancerous tissues (n=52) were determined by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR). The relationship between miRNA-215-5p level and pathological indexes, as well as overall survival of PCa patients, was analyzed. Regulatory effects of miRNA-215-5p on proliferative and metastatic capacities of LNCaP and DU-145 cells were evaluated through cell counting kit-8 (CCK-8) and transwell assay, respectively. Bioinformatics prediction was performed to search for the target genes of miRNA-215-5p and PGK1 was selected. The biological role of PGK1 in the progression of PCa was finally clarified by a series of rescue experiments. RESULTS: MiRNA-215-5p was lowly expressed in PCa tissues and cell lines. Low level of miRNA-215-5p predicted poor prognosis in PCa patients. The silence of miRNA-215-5p enhanced viability, migratory, and invasive capacities of LNCaP cells, while the overexpression of miRNA-215-5p yielded the opposite trends in DU-145 cells. PGK1 was predicted to be the target of miRNA-215-5p. PGK1 was upregulated in PCa tissues and cell lines and its high level predicted poor prognosis of PCa. Moreover, PGK1 level was negatively correlated to that of miRNA-215-5p in PCa tissues. PGK1 was able to reverse the regulatory effects of miRNA-215-5p on metastatic potentials of PCa cells. CONCLUSIONS: Downregulated miRNA-215-5p in PCa is closely related to distant metastasis and poor prognosis of affected patients. MiRNA-215-5p alleviates the malignant progression of PCa by targeting and downregulating PGK1.

shRNA-mediated inhibition of PhosphoGlycerate Kinase 1 (PGK1) enhances cytotoxicity of intraperitoneal chemotherapy in peritoneal metastasis of gastric origin.

BACKGROUND: Phosphoglycerate kinase 1 (PGK1) plays metabolic, kinase and translational roles in Peritoneal metastasis (PM) of gastric origin and is associated with chemoresistance. Silencing PGK1 might potentiate the effect of chemotherapy. METHODS: In an orthoptic xenograft nude mice model, human gastric cancer cells (MKN45) were grown in 22 donor animals. Solid tumors were then grafted into the gastric subserosa of 102 recipient animals and allowed to grow for 10 days. Animals were randomized into 7 groups: Five test groups: 1) Mitomycin C (MMC), 2) MMC and small hairpin RNA silencing of PGK1 with an adenoviral vector (Adv-shPGK1), 3) 5-fluorouracil (5-FU), 4) 5-FU and Adv-shPGK1, 5) Adv-shPGK1 alone; two control groups: 1) Sham (NaCl 0.9%), 2) empty viral vector. Intraperitoneal therapy was administered on postoperative day (POD) 11 and 18. Animals were sacrificed at POD 21, analysis was blinded to therapy. RESULTS: Adding Adv-shPGK1 to 5-FU reduced the number (0.23 ± 0.43 vs. 1.36 ± 1.00, p = 0.005) and weight (0,005 ± 0.012 mg vs. 0.05 ± 0.08 mg, p = 0.002) of PM as compared to 5-FU alone. The effect of adding Adv-shPGK1 to MMC did not reach statistical significance. Mortality was not increased by adding Adv-shPGK1 to chemotherapy but was increased by Adv-shPGK1 alone as compared to sham. CONCLUSION: In this experimental model, combined therapy with chemotherapy and Adv-shPGK1 improves control of PM of gastric origin as compared to chemotherapy alone and might counteract chemoresistance of PM. A systemic toxicity of Adv-shPGK1 cannot be excluded.

A metabolite-derived protein modification integrates glycolysis with KEAP1-NRF2 signalling.

Mechanisms that integrate the metabolic state of a cell with regulatory pathways are necessary to maintain cellular homeostasis. Endogenous, intrinsically reactive metabolites can form functional, covalent modifications on proteins without the aid of enzymes1,2, and regulate cellular functions such as metabolism3-5 and transcription6. An important 'sensor' protein that captures specific metabolic information and transforms it into an appropriate response is KEAP1, which contains reactive cysteine residues that collectively act as an electrophile sensor tuned to respond to reactive species resulting from endogenous and xenobiotic molecules. Covalent modification of KEAP1 results in reduced ubiquitination and the accumulation of NRF27,8, which then initiates the transcription of cytoprotective genes at antioxidant-response element loci. Here we identify a small-molecule inhibitor of the glycolytic enzyme PGK1, and reveal a direct link between glycolysis and NRF2 signalling. Inhibition of PGK1 results in accumulation of the reactive metabolite methylglyoxal, which selectively modifies KEAP1 to form a methylimidazole crosslink between proximal cysteine and arginine residues (MICA). This posttranslational modification results in the dimerization of KEAP1, the accumulation of NRF2 and activation of the NRF2 transcriptional program. These results demonstrate the existence of direct inter-pathway communication between glycolysis and the KEAP1-NRF2 transcriptional axis, provide insight into the metabolic regulation of the cellular stress response, and suggest a therapeutic strategy for controlling the cytoprotective antioxidant response in several human diseases.

Glycolysis regulates pollen tube polarity via Rho GTPase signaling.

As a universal energy generation pathway utilizing carbon metabolism, glycolysis plays an important housekeeping role in all organisms. Pollen tubes expand rapidly via a mechanism of polarized growth, known as tip growth, to deliver sperm for fertilization. Here, we report a novel and surprising role of glycolysis in the regulation of growth polarity in Arabidopsis pollen tubes via impingement of Rho GTPase-dependent signaling. We identified a cytosolic phosphoglycerate kinase (pgkc-1) mutant with accelerated pollen germination and compromised pollen tube growth polarity. pgkc-1 mutation greatly diminished apical exocytic vesicular distribution of REN1 RopGAP (Rop GTPase activating protein), leading to ROP1 hyper-activation at the apical plasma membrane. Consequently, pgkc-1 pollen tubes contained higher amounts of exocytic vesicles and actin microfilaments in the apical region, and showed reduced sensitivity to Brefeldin A and Latrunculin B, respectively. While inhibition of mitochondrial respiration could not explain the pgkc-1 phenotype, the glycolytic activity is indeed required for PGKc function in pollen tubes. Moreover, the pgkc-1 pollen tube phenotype was mimicked by the inhibition of another glycolytic enzyme. These findings highlight an unconventional regulatory function for a housekeeping metabolic pathway in the spatial control of a fundamental cellular process.

Virtual Screening against Phosphoglycerate Kinase 1 in Quest of Novel Apoptosis Inhibitors.

Inhibition of apoptosis is a potential therapy to treat human diseases such as neurodegenerative disorders (e.g., Parkinson's disease), stroke, and sepsis. Due to the lack of druggable targets, it remains a major challenge to discover apoptosis inhibitors. The recent repositioning of a marketed drug (i.e., terazosin) as an anti-apoptotic agent uncovered a novel target (i.e., human phosphoglycerate kinase 1 (hPgk1)). In this study, we developed a virtual screening (VS) pipeline based on the X-ray structure of Pgk1/terazosin complex and applied it to a screening campaign for potential anti-apoptotic agents. The hierarchical filters in the pipeline (i.e., similarity search, a pharmacophore model, a shape-based model, and molecular docking) rendered 13 potential hits from Specs chemical library. By using PC12 cells (exposed to rotenone) as a cell model for bioassay, we first identified that AK-918/42829299, AN-465/41520984, and AT-051/43421517 were able to protect PC12 cells from rotenone-induced cell death. Molecular docking suggested these hit compounds were likely to bind to hPgk1 in a similar mode to terazosin. In summary, we not only present a versatile VS pipeline for potential apoptosis inhibitors discovery, but also provide three novel-scaffold hit compounds that are worthy of further development and biological study.

Bioenergetic status modulates motor neuron vulnerability and pathogenesis in a zebrafish model of spinal muscular atrophy.

Degeneration and loss of lower motor neurons is the major pathological hallmark of spinal muscular atrophy (SMA), resulting from low levels of ubiquitously-expressed survival motor neuron (SMN) protein. One remarkable, yet unresolved, feature of SMA is that not all motor neurons are equally affected, with some populations displaying a robust resistance to the disease. Here, we demonstrate that selective vulnerability of distinct motor neuron pools arises from fundamental modifications to their basal molecular profiles. Comparative gene expression profiling of motor neurons innervating the extensor digitorum longus (disease-resistant), gastrocnemius (intermediate vulnerability), and tibialis anterior (vulnerable) muscles in mice revealed that disease susceptibility correlates strongly with a modified bioenergetic profile. Targeting of identified bioenergetic pathways by enhancing mitochondrial biogenesis rescued motor axon defects in SMA zebrafish. Moreover, targeting of a single bioenergetic protein, phosphoglycerate kinase 1 (Pgk1), was found to modulate motor neuron vulnerability in vivo. Knockdown of pgk1 alone was sufficient to partially mimic the SMA phenotype in wild-type zebrafish. Conversely, Pgk1 overexpression, or treatment with terazosin (an FDA-approved small molecule that binds and activates Pgk1), rescued motor axon phenotypes in SMA zebrafish. We conclude that global bioenergetics pathways can be therapeutically manipulated to ameliorate SMA motor neuron phenotypes in vivo.

Metabolic alteration--Overcoming therapy resistance in gastric cancer via PGK-1 inhibition in a combined therapy with standard chemotherapeutics.

BACKGROUND AND OBJECTIVES: It can be assumed that PGK1 is involved in metastatic spread of gastric carcinomas. Furthermore PGK1 has a proven influence on the characteristics of tumor stem cells. The presence of malignant stem cells, regarding treatment resistance and recurrence, is of considerable importance. We hypothesized that inhibition of PGK1 makes these cells more sensitive to chemotherapeutic agents and therefore mediates an overcome of the existing therapy resistance. METHODS: All investigations were performed with human gastric adenocarcinoma cell lines. Small hairpin RNA knockdown of PGK1 via adenovirus-shPGK1 was used for PGK1-inhibition. Chemotherapeutic agents were 5-FU and mitomycin. FACS, qRT-PCR, and xCELLigence were performed. RESULTS: Using the medium-sole-control indicating the highest cell viability and Triton indicating the lowest, mitomycin and 5-FU alone showed a significant decrease in cell viability. The treatment with AdvshPGK1 alone already showed a better decrease. The simultaneous application of chemotherapeutics and adenovirus showed the strongest effect and is comparable to the effect of Triton. CONCLUSIONS: We showed a significant decrease in cell viability after the simultaneous application of chemotherapeutics and adenovirus. These results suggest that PGK1-inhibition is able to increase the vulnerability of gastric cancer cells and tumor stem cells to overcome the chemotherapeutic therapy resistance.

The phosphoglycerate kinase isoenzymes have distinct roles in the regulation of carbohydrate metabolism in Trypanosoma cruzi.

The glycolytic enzyme phosphoglycerate kinase (PGK) is present in Trypanosoma cruzi as three isoenzymes, two of them located inside glycosomes (PGKA and PGKC) and another one in the cytosol (PGKB). The three isoenzymes are expressed at all stages of the life cycle of the parasite. A heterologous expression system for PGKA (rPGKA) was developed and the substrate affinities of the natural and recombinant PGKA isoenzyme were determined. Km values measured for 3-phosphoglycerate (3PGA) were 174 and 850 µM, and for ATP 217 and 236 µM, for the natural and recombinant enzyme, respectively. No significant differences were found between the two forms of the enzyme. The rPGKA was inhibited by Suramin with Ki values of 10.08 µM and 12.11 µM for ATP and 3PGA, respectively, and the natural enzyme was inhibited at similar values. A site-directed mutant was created in which the 80 amino acids PGKA sequence, present as a distinctive insertion in the N-terminal domain, was deleted. This internally truncated PGKA showed the same Km values and specific activity as the full-length rPGKA. The natural PGKC isoenzyme was purified from epimastigotes and separated from PGKA through molecular exclusion chromatography and its kinetic characteristics were determined. The Km value obtained for 3PGA was 192 µM, and 10 µM for ATP. Contrary to PGKA, the activity of PGKC is tightly regulated by ATP (substrate inhibition) with a Ki of 270 µM, suggesting a role for this isoenzyme in regulating metabolic fluxes inside the glycosomes.

Induction of tumor stem cell differentiation--novel strategy to overcome therapy resistance in gastric cancer.

PURPOSE: Metastases are a frequent finding in gastric cancer and are associated with poor prognosis. A recently discovered link between metabolic changes, differentiation, and therapy resistance due to tumor stem cells could depict a novel approach in cancer research and therapy. Phosphoglycerate kinase 1 (PGK1) is a metabolic enzyme and is known to be involved in enabling gastric cancer cells to be invasive and to disseminate. In this study, we investigated if PGK1 is a promising candidate in inducing stem cell differentiation in gastric cancer. MATERIALS AND METHODS: MKN45 gastric cancer cells were used due to their known cancer stem cell population, which is defined by the surface marker CD44. MKN45 cells were separated between CD44+ and CD44- cells and, in equal parts, incubated with shRNA anti-PGK1 using fluorescence-activated cell sorting (FACS) analysis; they were then injected into nude mice to evaluate their tumor growth behavior in vivo. Further, the invasive potential of gastric cancer cells was evaluated in vitro using the xCelligence analyzing system. RESULTS: CD44+ gastric cancer cells treated with and without shRNA anti-PGK1 were capable to cause tumor growth in vivo, whereas tumor growth in CD44+ cells treated with shRNA anti-PGK1 was considerably smaller in comparison with that in CD44+ cells without treatment. CD44- cells did not show any noticeable tumor growth in vivo. By targeting PGK1, the invasive potential of gastric cancer cells was impressively reduced in vitro. In all our cells, which were targeted with shRNA anti-PGK1, we did not find any change that is in accordance with the phenotype of the cells using FACS analysis. CONCLUSIONS: Our findings suggest that targeting the key metabolic enzyme PGK1 in gastric cancer cells may open a new chapter in cancer treatment, which is well worth for further exploration in combination with recent chemotherapy, and might be a promising possibility to overcome therapy resistance in gastric cancer.

Glycolytic enzymes PGK1 and PKM2 as novel transcriptional targets of PPARγ in breast cancer pathophysiology.

Peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor and plays important roles in breast cancer cell proliferation. The complexity of the underlying biochemical and molecular mechanisms of breast cancer and the involvement of PPARγ in breast cancer pathophysiology are unclear. In this study, we carried out prediction of the peroxisome proliferator response element (PPRE) motifs in 2332 genes reported to be involved in breast cancer in literature. A total of 178 genes were found to have PPRE (DR1/DR2) and/or PPAR-associated conserved motif (PACM) motifs. We further constructed protein-protein interaction network, disease gene network and gene ontology (GO) analyses to identify novel key genes for experimental validation. We identified two genes in the glycolytic pathway (phosphoglycerate kinase 1 (PGK1) and pyruvate kinase M2 (PKM2)) at the ATP production steps and experimentally validated their repression by PPARγ in two breast cancer cell lines MDA-MB-231 and MCF-7. Further analysis suggested that this repression leads to decrease in ATP levels and apoptosis. These investigations will help us in understanding the molecular mechanisms by which PPARγ regulates the cellular energy pathway and the use of its ligands in human breast cancer therapeutics.

siPGK1 sensitizes chemoresistant human ovarian cancer cell lines to cisplatin.

Enhanced glycolysis provides essential intermediates for cancer cell proliferation. Its inhibition could be a promising approach for destroying tumors, especially those developing in hypoxic conditions, which are presumably the most chemoresistant. In hypoxic cells, glycolysis provides the main part of ATP. Phosphoglycerate kinase-1 (PGK1) catalyzes a crucial reaction of glycolysis that reconstitutes the two molecules of ATP previously consumed. PGK1 inhibition could arrest growth or kill hypoxic and/or chemoresistant cells. We tested siPGK1 transfection in two human ovarian cancer cells lines of increasing chemoresistance, and showed that: Expression of PGK1 was significantly reduced and associated with blockade of cell growth in the G(1) phase; siPGK1 associated with cisplatin was more effective than cisplatin-alone at inhibiting proliferation of chemoresistant cells; siPGK1 -alone and -associated with cisplatin strongly increased expression of the BH3-only pro-apoptotic protein BCL-2 Interacting Mediator of cell death (BIM). PGK1 might be a key target for sensitizing chemoresistant cells to cisplatin.

The application of selective reaction monitoring confirms dysregulation of glycolysis in a preclinical model of schizophrenia.

BACKGROUND: Establishing preclinical models is essential for novel drug discovery in schizophrenia. Most existing models are characterized by abnormalities in behavioral readouts, which are informative, but do not necessarily translate to the symptoms of the human disease. Therefore, there is a necessity of characterizing the preclinical models from a molecular point of view. Selective reaction monitoring (SRM) has already shown promise in preclinical and clinical studies for multiplex measurement of diagnostic, prognostic and treatment-related biomarkers. METHODS: We have established an SRM assay for multiplex analysis of 7 enzymes of the glycolysis pathway which is already known to be affected in human schizophrenia and in the widely-used acute PCP rat model of schizophrenia. The selected enzymes were hexokinase 1 (Hk1), aldolase C (Aldoc), triosephosphate isomerase (Tpi1), glyceraldehyde-3-phosphate dehydrogenase (Gapdh), phosphoglycerate mutase 1 (Pgam1), phosphoglycerate kinase 1 (Pgk1) and enolase 2 (Eno2). The levels of these enzymes were analyzed using SRM in frontal cortex from brain tissue of PCP treated rats. RESULTS: Univariate analyses showed statistically significant altered levels of Tpi1 and alteration of Hk1, Aldoc, Pgam1 and Gapdh with borderline significance in PCP rats compared to controls. Most interestingly, multivariate analysis which considered the levels of all 7 enzymes simultaneously resulted in generation of a bi-dimensional chart that can distinguish the PCP rats from the controls. CONCLUSIONS: This study not only supports PCP treated rats as a useful preclinical model of schizophrenia, but it also establishes that SRM mass spectrometry could be used in the development of multiplex classification tools for complex psychiatric disorders such as schizophrenia.

Protein release through nonlethal oncotic pores as an alternative nonclassical secretory pathway.

BACKGROUND: Nonclassical (unconventional) protein secretion is thought to represent the primary secretion mechanism for several cytosolic proteins, such as HIV-Tat, galectin 1, interleukin-1ß, and several proteins that shuttle between the nucleus and cytosol, such as fibroblast growth factor 1 (FGF1), FGF2, and nucleolin. Four nonclassical secretory pathways have been described including direct transport (presumably through transporters in the plasma membrane), secretion via exosomes, lysosomal secretion, and blebbing. The purpose of this study was to gain mechanistic insight into nonclassical protein secretion using phosphoglycerate kinase 1 (PGK1), a previously identified nonclassical secretory protein, as a reporter protein. RESULTS: Upon shifting HeLa cells into serum-free media PGK1 was released as a free soluble protein without cell loss. Release occurred in two phases: a rapid early phase and a slow late phase. Using a repertory of inhibitors, PGK1 release was shown not to rely on the classical secretory pathway. However, components of the cytoskeleton partially contributed to its release. Significantly, the presence of serum or bovine serum albumin in the media inhibited PGK1 release. CONCLUSIONS: These results are consistent with a novel model of protein release termed oncotic release, in which a change in the colloidal osmotic pressure (oncotic pressure) upon serum withdrawal creates nonlethal oncotic pores in the plasma membrane through which PGK1 - and likely other nearby proteins - are released before the pores are rapidly resealed. These findings identify an alternative mechanism of release for FGF1, HIV-Tat, and galectin 1 whose reported nonclassical secretion is induced by serum withdrawal. Oncotic release may occur in routine cell biological experiments during which cells are washed with serum-free buffers or media and in pathophysiological conditions, such as edema, during which extracellular protein concentrations change.

The association of glycolytic enzymes from yeast confers resistance against inhibition by trehalose.

During stress, many organisms accumulate compatible solutes. These solutes must be eliminated upon return to optimal conditions as they inhibit cell metabolism and growth. In contrast, enzyme interactions optimize metabolism through mechanisms such as channeling of substrates. It was decided to test the (compatible solute) trehalose-mediated inhibition of some yeast glycolytic pathway enzymes known to associate and whether inhibition is prevented when enzymes are allowed to associate. Trehalose inhibited the isolated glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and hexokinase (HXK), but not aldolase (ALD) nor phosphoglycerate kinase (PGK). When these enzymes were mixed in pairs, both GAPDH and HXK were protected by either ALD or PGK acquiring the inhibition behavior of the resistant enzyme. GAPDH was not protected by HXK, albumin or lactate dehydrogenase (LDH). Also, ALD did not protect glucose 6-phosphate dehydrogenase (G6PDH), suggesting that protection is specific. In yeast cell extracts, fermentation was resistant to trehalose inhibition, suggesting all enzymes involved in the glucose-dependent production of ethanol were stabilized. It is suggested that during the yeast stress response, enzyme association protects some metabolic pathways against trehalose-mediated inhibition.