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Rameh LE, York JD, Blind RD. Multiple inositol phosphate species enhance stability of active mTOR. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.01.592113. [PMID: 38746235 PMCID: PMC11092565 DOI: 10.1101/2024.05.01.592113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
Mechanistic Target of Rapamycin (mTOR) binds the small metabolite inositol hexakisphosphate (IP6) as shown in structures of mTOR, however it remains unclear if IP6, or any other inositol phosphate species, can activate mTOR kinase activity. Here, we show that multiple, exogenously added inositol phosphate species (IP6, IP5, IP4 and IP3) can all enhance the ability of mTOR and mTORC1 to auto-phosphorylate and incorporate radiolabeled phosphate into peptide substrates in in vitro kinase reactions. Although IP6 did not affect the apparent KM of mTORC1 for ATP, monitoring kinase activity over longer reaction times showed increased product formation, suggesting inositol phosphates stabilize an active form of mTORC1 in vitro. The effects of IP6 on mTOR were reversible, suggesting IP6 bound to mTOR can be exchanged dynamically with the free solvent. Interestingly, we also observed that IP6 could alter mTOR solubility and electrophoretic mobility in SDS-PAGE in the presence of manganese, suggesting divalent cations may play a role in inositol phosphate regulation of mTOR. Together, these data suggest for the first time that multiple inositol phosphate species (IP4, IP5 and IP6) can dynamically regulate mTOR and mTORC1 by promoting a stable, active state of the kinase. Our data suggest that studies of the dynamics of inositol phosphate regulation of mTOR are well justified.
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Affiliation(s)
- Lucia E. Rameh
- University of South Alabama, Department of Biochemistry and Molecular Biology, Mobile, AL 36688
- Vanderbilt University School of Medicine, Department of Biochemistry, Nashville, TN 37232
- Vanderbilt University Medical Center, Department of Medicine, Division of Diabetes, Endocrinology and Metabolism, Nashville, TN 37232
| | - John D. York
- Vanderbilt University School of Medicine, Department of Biochemistry, Nashville, TN 37232
| | - Raymond D. Blind
- Vanderbilt University School of Medicine, Department of Biochemistry, Nashville, TN 37232
- Vanderbilt University Medical Center, Department of Medicine, Division of Diabetes, Endocrinology and Metabolism, Nashville, TN 37232
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Authi KS, Khan S, Gibbins JM, Brain SD. Evidence that inositol 1,4,5-trisphosphate 3-kinase and inositol 1,3,4,5-tetrakisphosphate are negative regulators of platelet function. Res Pract Thromb Haemost 2024; 8:102326. [PMID: 38404940 PMCID: PMC10885593 DOI: 10.1016/j.rpth.2024.102326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 12/21/2023] [Accepted: 01/03/2024] [Indexed: 02/27/2024] Open
Abstract
Background Inositol 1,3,4,5-tetrakisphosphate (IP4) is formed from inositol 1,4,5-trisphosphate (IP3) by IP3 3-kinase (ITPK) in most cells. Its function is unknown but has been suggested to be involved in Ca2+ entry, IP3 regulation, and phosphoinositide 3-kinase antagonism. Objectives To better elucidate a function for IP4, we tested a specific inhibitor of ITPK (GNF362) on platelets, the effects of IP4 directly in permeabilized platelets and its effect on phosphatidylinositol 3,4,5-trisphosphate (PIP3) binding to pleckstrin-homology (PH) domain-containing proteins in platelets. Methods Human platelets were utilized in whole blood for thrombus formation, in platelet-rich plasma and washed suspensions for aggregation, and for Ca2+ studies, or resuspended in high K+ and low Na+ buffers for permeabilization experiments. Phosphorylation of AKT-Ser473 and Rap1-GTP formation were measured by Western blotting and PIP3 binding using PIP3 beads. Results GNF362-enhanced platelet aggregation stimulated by low concentrations of ADP, collagen, thrombin, U46619, and thrombus formation in collagen-coated capillaries. GNF362 induced a transient elevation of Ca2+ concentration, elevated basal levels of IP3, and enhanced the peak height of Ca2+ elevated by agonists. In permeabilized platelets, IP4 inhibited GTPγS induced formation of AKT-Ser473 phosphorylation and platelet aggregation. IP4 reduced GTPγS-stimulated Rap1-GTP levels and potently reduced extraction of RASA3 and BTK by PIP3 beads. Conclusion ITPK and IP4 are negative regulators of platelet function. IP4 regulation of PH domain-containing proteins may represent a pathway by which platelet activation may be controlled during thrombosis.
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Affiliation(s)
- Kalwant S. Authi
- School of Cardiovascular and Metabolic Medicine and Sciences, BHF Centre for Research Excellence, London, UK
| | - Sabeeya Khan
- Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK
| | - Jonathan M. Gibbins
- Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK
| | - Susan D. Brain
- School of Cardiovascular and Metabolic Medicine and Sciences, BHF Centre for Research Excellence, London, UK
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Dilworth L, Stennett D, Omoruyi F. Cellular and Molecular Activities of IP6 in Disease Prevention and Therapy. Biomolecules 2023; 13:972. [PMID: 37371552 DOI: 10.3390/biom13060972] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Revised: 06/02/2023] [Accepted: 06/05/2023] [Indexed: 06/29/2023] Open
Abstract
IP6 (phytic acid) is a naturally occurring compound in plant seeds and grains. It is a poly-phosphorylated inositol derivative that has been shown to exhibit many biological activities that accrue benefits in health and diseases (cancer, diabetes, renal lithiasis, cardiovascular diseases, etc.). IP6 has been shown to have several cellular and molecular activities associated with its potential role in disease prevention. These activities include anti-oxidant properties, chelation of metal ions, inhibition of inflammation, modulation of cell signaling pathways, and modulation of the activities of enzymes and hormones that are involved in carbohydrate and lipid metabolism. Studies have shown that IP6 has anti-oxidant properties and can scavenge free radicals known to cause cellular damage and contribute to the development of chronic diseases such as cancers and cardiovascular diseases, as well as diabetes mellitus. It has also been shown to possess anti-inflammatory properties that may modulate immune responses geared towards the prevention of inflammatory conditions. Moreover, IP6 exhibits anti-cancer properties through the induction of cell cycle arrest, promoting apoptosis and inhibiting cancer cell growth. Additionally, it has been shown to have anti-mutagenic properties, which reduce the risk of malignancies by preventing DNA damage and mutations. IP6 has also been reported to have a potential role in bone health. It inhibits bone resorption and promotes bone formation, which may help in the prevention of bone diseases such as osteoporosis. Overall, IP6's cellular and molecular activities make it a promising candidate for disease prevention. As reported in many studies, its anti-inflammatory, anti-oxidant, and anti-cancer properties support its inclusion as a dietary supplement that may protect against the development of chronic diseases. However, further studies are needed to understand the mechanisms of action of this dynamic molecule and its derivatives and determine the optimal doses and appropriate delivery methods for effective therapeutic use.
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Affiliation(s)
- Lowell Dilworth
- Department of Pathology, The University of the West Indies, Mona Campus, Kingston 7, Jamaica
| | - Dewayne Stennett
- The Transitional Year Programme, University of Toronto, Toronto, ON M5S 2E8, Canada
| | - Felix Omoruyi
- Department of Life Sciences, Texas A&M University, Corpus Christi, TX 78412, USA
- Department of Health Sciences, Texas A&M University, Corpus Christi, TX 78412, USA
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Melnikova N, Malygina D, Balakireva A, Peretyagin P, Revin V, Devyataeva A, Malafeeva K, Revin V. The Effect of Betulin Diphosphate in Wound Dressings of Bacterial Cellulose-ZnO NPs on Platelet Aggregation and the Activity of Oxidoreductases Regulated by NAD(P)+/NAD(P)H-Balance in Burns on Rats. Molecules 2021; 26:5478. [PMID: 34576949 PMCID: PMC8469126 DOI: 10.3390/molecules26185478] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Revised: 09/04/2021] [Accepted: 09/06/2021] [Indexed: 11/21/2022] Open
Abstract
The inhibition of platelet aggregation, and the activity of oxidoreductases and microhemocirculation in a burn wound on the treatment of burns with wound dressings based on bacterial nanocellulose (BC)-zinc oxide nanoparticles (ZnO NPs)-betulin diphosphate (BDP) were studied. The control of the treatment by BC-ZnO NPs-BDP on burned rats by the noninvasive DLF method showed an increase in perfusion and the respiratory component in wavelet spectra, characterizing an improvement in oxygen saturation in the wound. The study on the volunteers' blood found the inhibition of ADP-induced platelet aggregation by 30-90%. Disaggregation depends on the dose under the action of the ionized form of BDP and ZnO NPs-BDP in a phosphate buffer; it was reversible and had two waves. It was shown on rats that the specific activity of LDHreverse and LDHdirect (control-intact animals) on day 21 of treatment increased by 11-38% and 23%, respectively. The LDHreverse/LDHdirect ratio increased at BC-ZnO NPs-BDP treatment, which characterizes efficient NAD+ regeneration. AlDH activity increased significantly in the first 10 days by 70-170%, reflecting the effectiveness of the enzyme and NAD+ in utilizing toxic aldehydes at this stage of burn disease. The activities of GR and G6PDH using NADP(H) were increased with BC-ZnO NPs-BDP treatment.
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Affiliation(s)
- Nina Melnikova
- Faculty of Chemistry, Lobachevsky University, 23/5 Gagarin Av., 603950 Nizhny Novgorod, Russia
| | - Darina Malygina
- Department of Pharmaceutical Chemistry, Privolzhsky Research Medical University, 10/1 Minin Sq., 603950 Nizhny Novgorod, Russia;
| | - Alyona Balakireva
- Central Research Laboratory, Privolzhsky Research Medical University, 10/1 Minin Sq., 603950 Nizhny Novgorod, Russia; (A.B.); (P.P.)
| | - Peter Peretyagin
- Central Research Laboratory, Privolzhsky Research Medical University, 10/1 Minin Sq., 603950 Nizhny Novgorod, Russia; (A.B.); (P.P.)
| | - Vadim Revin
- Department of Biotechnology, Bioengineering and Biochemistry, National Research Ogarev Mordovia State University, 68 Bolshevistskaya Str., 430005 Saransk, Russia; (V.R.); (A.D.); (K.M.); (V.R.)
| | - Anna Devyataeva
- Department of Biotechnology, Bioengineering and Biochemistry, National Research Ogarev Mordovia State University, 68 Bolshevistskaya Str., 430005 Saransk, Russia; (V.R.); (A.D.); (K.M.); (V.R.)
| | - Kseniya Malafeeva
- Department of Biotechnology, Bioengineering and Biochemistry, National Research Ogarev Mordovia State University, 68 Bolshevistskaya Str., 430005 Saransk, Russia; (V.R.); (A.D.); (K.M.); (V.R.)
| | - Viktor Revin
- Department of Biotechnology, Bioengineering and Biochemistry, National Research Ogarev Mordovia State University, 68 Bolshevistskaya Str., 430005 Saransk, Russia; (V.R.); (A.D.); (K.M.); (V.R.)
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Vucenik I, Druzijanic A, Druzijanic N. Inositol Hexaphosphate (IP6) and Colon Cancer: From Concepts and First Experiments to Clinical Application. Molecules 2020; 25:E5931. [PMID: 33333775 PMCID: PMC7765177 DOI: 10.3390/molecules25245931] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 12/07/2020] [Accepted: 12/12/2020] [Indexed: 12/14/2022] Open
Abstract
Multiple human health-beneficial effects have been related to highly phosphorylated inositol hexaphosphate (IP6). This naturally occurring carbohydrate and its parent compound, myo-inositol (Ins), are abundantly present in plants, particularly in certain high-fiber diets, but also in mammalian cells, where they regulate important cellular functions. However, the striking and broad-spectrum anticancer activity of IP6, consistently demonstrated in different experimental models, has been in a spotlight of the scientific community dealing with the nutrition and cancer during the last several decades. First experiments were performed in colon cancer 30 years ago. Since then, it has been shown that IP6 reduces cell proliferation, induces apoptosis and differentiation of malignant cells with reversion to normal phenotype, affecting several critical molecular targets. Enhanced immunity and antioxidant properties also contribute to the tumor cell destruction. Although Ins possesses a modest anticancer potential, the best anticancer results were obtained from the combination of IP6 + Ins. Here we review the first experimental steps in colon cancer, when concepts and hypotheses were put together almost without real knowledge and present clinical studies, that were initiated in colon cancer patients. Available as a dietary supplement, IP6 + Ins has been shown to enhance the anticancer effect of conventional chemotherapy, controls cancer metastases, and improves quality of life in cancer patients. Emerging clinical and still vast amount of experimental data suggest its role either as an adjuvant or as an "alternative" to current chemotherapy for cancer.
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Affiliation(s)
- Ivana Vucenik
- Department of Medical and Research Technology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
- Department of Pathology, School of Medicine, University of Maryland, Baltimore, MD 21201, USA
| | - Ana Druzijanic
- Department of Oral Medicine and Periodontology, School of Medicine, Dental Medicine, University of Split, 21000 Split, Croatia;
| | - Nikica Druzijanic
- Department of Surgery, University Hospital Split, School of Medicine, University of Split, 21000 Split, Croatia;
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The Host Cell Metabolite Inositol Hexakisphosphate Promotes Efficient Endogenous HIV-1 Reverse Transcription by Stabilizing the Viral Capsid. mBio 2020; 11:mBio.02820-20. [PMID: 33262260 PMCID: PMC7733946 DOI: 10.1128/mbio.02820-20] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
HIV-1 infection requires reverse transcription of the viral genome. While much is known about the biochemistry of reverse transcription from simplified biochemical reactions, reverse transcription during infection takes place within a viral core. However, endogenous reverse transcription reactions using permeabilized HIV-1 virions or purified viral cores have been inefficient. Using viral cores purified from infectious HIV-1 particles, we show that efficient reverse transcription is achieved in vitro by addition of the capsid-stabilizing metabolite inositol hexakisphosphate. The enhancement of reverse transcription was linked to the capsid-stabilizing effect of the compound, consistent with the known requirement for an intact or semi-intact viral capsid for HIV-1 infection. Our results establish a biologically relevant system for dissecting the function of the viral capsid and its disassembly during reverse transcription. The system should also prove useful for mechanistic studies of capsid-targeting antiviral drugs. A defining activity of retroviruses is reverse transcription, the process by which the viral genomic RNA is converted into the double-stranded DNA required for virus replication. Reverse transcriptase (RT), the viral enzyme responsible for this process, was identified in 1970 by assaying permeabilized retrovirus particles for DNA synthesis in vitro. Such reactions are inefficient, with only a small fraction of viral genomes being converted to full-length double-stranded DNA molecules, possibly owing to disruption of the structure of the viral core. Here, we show that reverse transcription in purified HIV-1 cores is enhanced by the addition of the capsid-binding host cell metabolite inositol hexakisphosphate (IP6). IP6 potently enhanced full-length minus-strand synthesis, as did hexacarboxybenzene (HCB), which also stabilizes the HIV-1 capsid. Both IP6 and HCB stabilized the association of the viral CA and RT proteins with HIV-1 cores. In contrast to the wild type, cores isolated from mutant HIV-1 particles containing intrinsically hyperstable capsids exhibited relatively efficient reverse transcription in the absence of IP6, further indicating that the compound promotes reverse transcription by stabilizing the viral capsid. We also observed that the capsid-destabilizing antiviral compound PF74 inhibited endogenous reverse transcription with a potency that mirrors its ability to inhibit reverse transcription during infection. Our results show that the stabilization of the HIV-1 capsid permits efficient reverse transcription in HIV-1 cores, providing a sensitive experimental system for analyzing the functions of viral and host cell molecules and the role of capsid disassembly (uncoating) in the process.
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Maffucci T, Falasca M. Signalling Properties of Inositol Polyphosphates. Molecules 2020; 25:molecules25225281. [PMID: 33198256 PMCID: PMC7696153 DOI: 10.3390/molecules25225281] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 11/02/2020] [Accepted: 11/04/2020] [Indexed: 12/16/2022] Open
Abstract
Several studies have identified specific signalling functions for inositol polyphosphates (IPs) in different cell types and have led to the accumulation of new information regarding their cellular roles as well as new insights into their cellular production. These studies have revealed that interaction of IPs with several proteins is critical for stabilization of protein complexes and for modulation of enzymatic activity. This has not only revealed their importance in regulation of several cellular processes but it has also highlighted the possibility of new pharmacological interventions in multiple diseases, including cancer. In this review, we describe some of the intracellular roles of IPs and we discuss the pharmacological opportunities that modulation of IPs levels can provide.
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Affiliation(s)
- Tania Maffucci
- Centre for Cell Biology and Cutaneous Research, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London E1 2AT, UK
- Correspondence: (T.M.); (M.F.); Tel.: +61-08-92669712 (M.F.)
| | - Marco Falasca
- School of Pharmacy and Biomedical Sciences, CHIRI, Curtin University, Perth 6102, Australia
- Correspondence: (T.M.); (M.F.); Tel.: +61-08-92669712 (M.F.)
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Brehm MA, Windhorst S. New options of cancer treatment employing InsP 6. Biochem Pharmacol 2019; 163:206-214. [PMID: 30797871 DOI: 10.1016/j.bcp.2019.02.024] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2019] [Accepted: 02/19/2019] [Indexed: 12/21/2022]
Abstract
Many mechanistic studies have been performed to analyze the cellular functions of the highly phosphorylated molecule inositol hexakisphosphate (InsP6) in health and disease. While the physiological intracellular functions are well described, the mechanism of potential pharmacological effects on cancer cell proliferation is still controversial. There are numerous studies demonstrating that a high InsP6 concentration (≥75 µM) inhibits growth of cancer cells in vitro and in vivo. Thus, there is no doubt that InsP6 exhibits anticancer activity but the mechanism underlying the cellular effects of extracellular InsP6 on cancer cells is far from being understood. In addition, studies on the inhibitory effect of InsP6 on cancer progression in animal models ignore aspects of its bioavailability. Here, we review and critically discuss the uptake mechanism and the intracellular involvement in signaling pathways of InsP6 in cancer cells. We take into account the controversial findings on InsP6 plasma concentration, which is a critical aspect of pharmacological accessibility of InsP6 for cancer treatment. Further, we discuss novel findings with respect to the effect of InsP6 on normal and immune cells as well as on platelet aggregate size. Our goal is to stimulate further mechanistic studies into novel directions considering previously disregarded aspects of InsP6. Only when we fully understand the mechanism underlying the anticancer activity of InsP6 novel and more efficient treatment options can be developed.
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Affiliation(s)
- Maria A Brehm
- Department of Pediatric Hematology and Oncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Sabine Windhorst
- Department of Biochemistry and Signal Transduction, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany.
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