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Srivastava A, Pati S, Kaushik H, Singh S, Garg LC. Toxin-antitoxin systems and their medical applications: current status and future perspective. Appl Microbiol Biotechnol 2021; 105:1803-1821. [PMID: 33582835 DOI: 10.1007/s00253-021-11134-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2020] [Revised: 01/13/2021] [Accepted: 01/20/2021] [Indexed: 12/11/2022]
Abstract
Almost all bacteria synthesize two types of toxins-one for its survival by regulating different cellular processes and another as a strategy to interact with host cells for pathogenesis. Usually, "bacterial toxins" are contemplated as virulence factors that harm the host organism. However, toxins produced by bacteria, as a survival strategy against the host, also hamper its cellular processes. To overcome this, the bacteria have evolved with the production of a molecule, referred to as antitoxin, to negate the deleterious effect of the toxin against itself. The toxin and antitoxins are encoded by a two-component toxin-antitoxin (TA) system. The antitoxin, a protein or RNA, sequesters the toxins of the TA system for neutralization within the bacterial cell. In this review, we have described different TA systems of bacteria and their potential medical and biotechnological applications. It is of interest to note that while bacterial toxin-antitoxin systems have been well studied, the TA system in unicellular eukaryotes, though predicted by the investigators, have never been paid the desired attention. In the present review, we have also touched upon the TA system of eukaryotes identified to date. KEY POINTS: Bacterial toxins harm the host and also affect the bacterial cellular processes. The antitoxin produced by bacteria protect it from the toxin's harmful effects. The toxin-antitoxin systems can be targeted for various medical applications.
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Affiliation(s)
- Akriti Srivastava
- Department of Life Sciences, Shiv Nadar University, Gautam Buddha Nagar, Greater Noida, Uttar Pradesh, 201314, India
| | - Soumya Pati
- Department of Life Sciences, Shiv Nadar University, Gautam Buddha Nagar, Greater Noida, Uttar Pradesh, 201314, India
| | - Himani Kaushik
- Gene Regulation Laboratory, National Institute of Immunology, New Delhi, 110067, India
| | - Shailja Singh
- Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, 110067, India.
| | - Lalit C Garg
- Gene Regulation Laboratory, National Institute of Immunology, New Delhi, 110067, India.
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Houri H, Ghalavand Z, Faghihloo E, Fallah F, Mohammadi-Yeganeh S. Exploiting yoeB-yefM toxin-antitoxin system of Streptococcus pneumoniae on the selective killing of miR-21 overexpressing breast cancer cell line (MCF-7). J Cell Physiol 2019; 235:2925-2936. [PMID: 31541457 DOI: 10.1002/jcp.29198] [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: 06/11/2019] [Accepted: 09/03/2019] [Indexed: 12/13/2022]
Abstract
Toxin-antitoxin (TA) systems are two-component genetic modules widespread in bacterial and archaeal genomes, in which the toxin module is rendered inactive under resting conditions by its antitoxin counterpart. Under stress conditions, however, the antitoxin is degraded, freeing the toxin to exert its lethal effects. Although not evolved to function in eukaryotes, some studies have established the lethal activity of these bacterial toxins by inducing apoptosis in mammalian cells, an effect that can be neutralized by its cognate antitoxin. Inspired by the way the toxin can become active in eukaryotes cells, we produced an engrained yoeB-yefM TA system to selectively kill human breast cancer cells expressing a high level of miR-21. Accordingly, we generated an engineered yefM antitoxin gene with eight miR-21 target sites placed in its 3'untranslated region. The resulting TA system acts autonomously in human cells, distinguishing those that overexpress miR-21, killed by YoeB, from those that do not, remaining protected by YefM. Thus, we indicated that microRNA-control of the antitoxin protein of bacterial TA systems constitutes a novel strategy to enhance the selective killing of human cancer cells by the toxin module. The present study provides significant insights for developing novel anticancer strategies avoiding off-target effects, a challenge that has been pursued by many investigators over the years.
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Affiliation(s)
- Hamidreza Houri
- Infectious Diseases and Tropical Medicine Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.,Department of Microbiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Zohreh Ghalavand
- Department of Microbiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Ebrahim Faghihloo
- Department of Microbiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Fatemeh Fallah
- Infectious Diseases and Tropical Medicine Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.,Department of Microbiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Samira Mohammadi-Yeganeh
- Cellular and Molecular Biology Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.,Department of Biotechnology, School of Advanced Technologies in Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
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Slayden RA, Dawson CC, Cummings JE. Toxin-antitoxin systems and regulatory mechanisms in Mycobacterium tuberculosis. Pathog Dis 2018; 76:4969681. [PMID: 29788125 DOI: 10.1093/femspd/fty039] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 05/01/2018] [Indexed: 11/14/2022] Open
Abstract
There has been a significant reduction in annual tuberculosis incidence since the World Health Organization declared tuberculosis a global health threat. However, treatment of M. tuberculosis infections requires lengthy multidrug therapeutic regimens to achieve a durable cure. The development of new drugs that are active against resistant strains and phenotypically diverse organisms continues to present the greatest challenge in the future. Numerous phylogenomic analyses have revealed that the Mtb genome encodes a significantly expanded repertoire of toxin-antitoxin (TA) loci that makes up the Mtb TA system. A TA loci is a two-gene operon encoding a 'toxin' protein that inhibits bacterial growth and an interacting 'antitoxin' partner that neutralizes the inhibitory activity of the toxin. The presence of multiple chromosomally encoded TA loci in Mtb raises important questions in regard to expansion, regulation and function. Thus, the functional roles of TA loci in Mtb pathogenesis have received considerable attention over the last decade. The cumulative results indicate that they are involved in regulating adaptive responses to stresses associated with the host environment and drug treatment. Here we review the TA families encoded in Mtb, discuss the duplication of TA loci in Mtb, regulatory mechanism of TA loci, and phenotypic heterogeneity and pathogenesis.
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Affiliation(s)
- Richard A Slayden
- Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO 80523-0922, USA
| | - Clinton C Dawson
- Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO 80523-0922, USA
| | - Jason E Cummings
- Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO 80523-0922, USA
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Chan WT, Espinosa M, Yeo CC. Keeping the Wolves at Bay: Antitoxins of Prokaryotic Type II Toxin-Antitoxin Systems. Front Mol Biosci 2016; 3:9. [PMID: 27047942 PMCID: PMC4803016 DOI: 10.3389/fmolb.2016.00009] [Citation(s) in RCA: 96] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Accepted: 03/04/2016] [Indexed: 12/21/2022] Open
Abstract
In their initial stages of discovery, prokaryotic toxin-antitoxin (TA) systems were confined to bacterial plasmids where they function to mediate the maintenance and stability of usually low- to medium-copy number plasmids through the post-segregational killing of any plasmid-free daughter cells that developed. Their eventual discovery as nearly ubiquitous and repetitive elements in bacterial chromosomes led to a wealth of knowledge and scientific debate as to their diversity and functionality in the prokaryotic lifestyle. Currently categorized into six different types designated types I–VI, type II TA systems are the best characterized. These generally comprised of two genes encoding a proteic toxin and its corresponding proteic antitoxin, respectively. Under normal growth conditions, the stable toxin is prevented from exerting its lethal effect through tight binding with the less stable antitoxin partner, forming a non-lethal TA protein complex. Besides binding with its cognate toxin, the antitoxin also plays a role in regulating the expression of the type II TA operon by binding to the operator site, thereby repressing transcription from the TA promoter. In most cases, full repression is observed in the presence of the TA complex as binding of the toxin enhances the DNA binding capability of the antitoxin. TA systems have been implicated in a gamut of prokaryotic cellular functions such as being mediators of programmed cell death as well as persistence or dormancy, biofilm formation, as defensive weapons against bacteriophage infections and as virulence factors in pathogenic bacteria. It is thus apparent that these antitoxins, as DNA-binding proteins, play an essential role in modulating the prokaryotic lifestyle whilst at the same time preventing the lethal action of the toxins under normal growth conditions, i.e., keeping the proverbial wolves at bay. In this review, we will cover the diversity and characteristics of various type II TA antitoxins. We shall also look into some interesting deviations from the canonical type II TA systems such as tripartite TA systems where the regulatory role is played by a third party protein and not the antitoxin, and a unique TA system encoding a single protein with both toxin as well as antitoxin domains.
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Affiliation(s)
- Wai Ting Chan
- Molecular Microbiology and Infection Biology, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas Madrid, Spain
| | - Manuel Espinosa
- Molecular Microbiology and Infection Biology, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas Madrid, Spain
| | - Chew Chieng Yeo
- Faculty of Medicine, Biomedical Research Centre, Universiti Sultan Zainal Abidin Kuala Terengganu, Malaysia
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Heterologous Expression of Toxins from Bacterial Toxin-Antitoxin Systems in Eukaryotic Cells: Strategies and Applications. Toxins (Basel) 2016; 8:49. [PMID: 26907343 PMCID: PMC4773802 DOI: 10.3390/toxins8020049] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2016] [Revised: 02/03/2016] [Accepted: 02/15/2016] [Indexed: 11/21/2022] Open
Abstract
Toxin-antitoxin (TA) systems are found in nearly all prokaryotic genomes and usually consist of a pair of co-transcribed genes, one of which encodes a stable toxin and the other, its cognate labile antitoxin. Certain environmental and physiological cues trigger the degradation of the antitoxin, causing activation of the toxin, leading either to the death or stasis of the host cell. TA systems have a variety of functions in the bacterial cell, including acting as mediators of programmed cell death, the induction of a dormant state known as persistence and the stable maintenance of plasmids and other mobile genetic elements. Some bacterial TA systems are functional when expressed in eukaryotic cells and this has led to several innovative applications, which are the subject of this review. Here, we look at how bacterial TA systems have been utilized for the genetic manipulation of yeasts and other eukaryotes, for the containment of genetically modified organisms, and for the engineering of high expression eukaryotic cell lines. We also examine how TA systems have been adopted as an important tool in developmental biology research for the ablation of specific cells and the potential for utility of TA systems in antiviral and anticancer gene therapies.
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Shi M, Liu B, Liu G, Wang P, Yang M, Li Y, Zhou J. Low intensity-pulsed ultrasound induced apoptosis of human hepatocellular carcinoma cells in vitro. ULTRASONICS 2016; 64:43-53. [PMID: 26231998 DOI: 10.1016/j.ultras.2015.07.011] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2015] [Revised: 07/18/2015] [Accepted: 07/21/2015] [Indexed: 05/15/2023]
Abstract
The present study was conducted to determine whether low intensity-pulsed ultrasound (LIPUS) could induce apoptosis of human hepatocellular carcinoma cells, SMMC-7721, and to define the mechanism of ultrasound-induced apoptosis, in vitro. MTT assay was used to measure cell proliferation. Apoptosis was investigated by multiple methods such as flow cytometry, DNA fragmentation, Ca(2+) mobilizations, pro- and anti-apoptotic protein expression, and light as well as ultramicroscopic morphology. The results provide evidence that LIPUS induced a dose-dependent effect on cell viability and apoptosis of SMMC-7721 cells. Specifically, exposure of cells to >0.5 W/cm(2) intensity significantly increased cell apoptosis, caused shifts in cell cycle phase, and induced structural changes. Ultrasound significantly increased intracellular Ca(2+) concentrations and modulated expression of caspase-3, Bcl-2 and Bax. The findings suggest that this novel technology can be used to induce SMMC-7721 apoptosis via the Ca(2+)/mitochondrial pathway and could potentially be of clinical use for the treatment of hepatocellular carcinoma (SMMC-7721 cell line) and other cancers.
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Affiliation(s)
- Mingfang Shi
- Department of Rehabilitation, Zhongshan Hospital, Fudan University, Shanghai 200032, China
| | - Bangzhong Liu
- Department of Rehabilitation, Zhongshan Hospital, Fudan University, Shanghai 200032, China.
| | - Guanghua Liu
- Department of Rehabilitation, Zhongshan Hospital, Fudan University, Shanghai 200032, China
| | - Ping Wang
- Department of Rehabilitation, Zhongshan Hospital, Fudan University, Shanghai 200032, China
| | - Mingzhen Yang
- Department of Rehabilitation, Zhongshan Hospital, Fudan University, Shanghai 200032, China
| | - Yun Li
- Department of Rehabilitation, Zhongshan Hospital, Fudan University, Shanghai 200032, China
| | - Jian Zhou
- Liver Cancer Institute, Zhongshan Hospital, Fudan University, Shanghai 200032, China
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Chan WT, Balsa D, Espinosa M. One cannot rule them all: Are bacterial toxins-antitoxins druggable? FEMS Microbiol Rev 2015; 39:522-40. [PMID: 25796610 PMCID: PMC4487406 DOI: 10.1093/femsre/fuv002] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/02/2015] [Indexed: 01/31/2023] Open
Abstract
Type II (proteic) toxin–antitoxin (TA) operons are widely spread in bacteria and archaea. They are organized as operons in which, usually, the antitoxin gene precedes the cognate toxin gene. The antitoxin generally acts as a transcriptional self-repressor, whereas the toxin acts as a co-repressor, both proteins constituting a harmless complex. When bacteria encounter a stressful environment, TAs are triggered. The antitoxin protein is unstable and will be degraded by host proteases, releasing the free toxin to halt essential processes. The result is a cessation of cell growth or even death. Because of their ubiquity and the essential processes targeted, TAs have been proposed as good candidates for development of novel antimicrobials. We discuss here the possible druggability of TAs as antivirals and antibacterials, with focus on the potentials and the challenges that their use may find in the ‘real’ world. We present strategies to develop TAs as antibacterials in view of novel technologies, such as the use of very small molecules (fragments) as inhibitors of protein–protein interactions. Appropriate fragments could disrupt the T:A interfaces leading to the release of the targeted TA pair. Possible ways of delivery and formulation of Tas are also discussed. We consider various approaches to develop the toxins of the type II family as possible candidates to drug discovery; druggability of toxins-antitoxins could be possible as antivirals. As antibacterials, they might be considered as druggable but delivery and formulation may not be simple so far.
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Affiliation(s)
- Wai Ting Chan
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu, 9, 28006-Madrid, Spain
| | - Dolors Balsa
- Immunology & Vaccines, Laboratorios LETI, Gran Via de les Corts Catalanes 184. 08034-Barcelona, Spain
| | - Manuel Espinosa
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu, 9, 28006-Madrid, Spain
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