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Hawkins LM, Wang C, Chaput D, Batra M, Marsilia C, Awshah D, Suvorova ES. The Crk4-Cyc4 complex regulates G 2/M transition in Toxoplasma gondii. EMBO J 2024:10.1038/s44318-024-00095-4. [PMID: 38600241 DOI: 10.1038/s44318-024-00095-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2024] [Revised: 03/12/2024] [Accepted: 03/26/2024] [Indexed: 04/12/2024] Open
Abstract
A versatile division of apicomplexan parasites and a dearth of conserved regulators have hindered the progress of apicomplexan cell cycle studies. While most apicomplexans divide in a multinuclear fashion, Toxoplasma gondii tachyzoites divide in the traditional binary mode. We previously identified five Toxoplasma CDK-related kinases (Crk). Here, we investigated TgCrk4 and its cyclin partner TgCyc4. We demonstrated that TgCrk4 regulates conventional G2 phase processes, such as repression of chromosome rereplication and centrosome reduplication, and acts upstream of the spindle assembly checkpoint. The spatial TgCyc4 dynamics supported the TgCrk4-TgCyc4 complex role in the coordination of chromosome and centrosome cycles. We also identified a dominant TgCrk4-TgCyc4 complex interactor, TgiRD1 protein, related to DNA replication licensing factor CDT1 but played no role in licensing DNA replication in the G1 phase. Our results showed that TgiRD1 also plays a role in controlling chromosome and centrosome reduplication. Global phosphoproteome analyses identified TgCrk4 substrates, including TgORC4, TgCdc20, TgGCP2, and TgPP2ACA. Importantly, the phylogenetic and structural studies suggest the Crk4-Cyc4 complex is limited to a minor group of the binary dividing apicomplexans.
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Affiliation(s)
- Lauren M Hawkins
- Division of Infectious Diseases, Department of Internal Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL, 33612, USA
| | - Chengqi Wang
- College of Public Health, University of South Florida, Tampa, FL, 33612, USA
| | - Dale Chaput
- Proteomics Core, College of Arts and Sciences, University of South Florida, Tampa, FL, 33612, USA
| | - Mrinalini Batra
- Division of Infectious Diseases, Department of Internal Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL, 33612, USA
| | - Clem Marsilia
- Division of Infectious Diseases, Department of Internal Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL, 33612, USA
| | - Danya Awshah
- Division of Infectious Diseases, Department of Internal Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL, 33612, USA
| | - Elena S Suvorova
- Division of Infectious Diseases, Department of Internal Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL, 33612, USA.
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Marsilia C, Batra M, Pokrovskaya ID, Wang C, Chaput D, Naumova DA, Lupashin VV, Suvorova ES. Essential role of the conserved oligomeric Golgi complex in Toxoplasma gondii. mBio 2023; 14:e0251323. [PMID: 37966241 PMCID: PMC10746232 DOI: 10.1128/mbio.02513-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Accepted: 10/05/2023] [Indexed: 11/16/2023] Open
Abstract
IMPORTANCE The Golgi is an essential eukaryotic organelle and a major place for protein sorting and glycosylation. Among apicomplexan parasites, Toxoplasma gondii retains the most developed Golgi structure and produces many glycosylated factors necessary for parasite survival. Despite its importance, Golgi function received little attention in the past. In the current study, we identified and characterized the conserved oligomeric Golgi complex and its novel partners critical for protein transport in T. gondii tachyzoites. Our results suggest that T. gondii broadened the role of the conserved elements and reinvented the missing components of the trafficking machinery to accommodate the specific needs of the opportunistic parasite T. gondii.
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Affiliation(s)
- Clem Marsilia
- Division of Infectious Diseases, Department of Internal Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Mrinalini Batra
- Division of Infectious Diseases, Department of Internal Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Irina D. Pokrovskaya
- Department of Physiology and Cell Biology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
| | - Changqi Wang
- College of Public Health, University of South Florida, Tampa, Florida, USA
| | - Dale Chaput
- Proteomics Core, College of Arts and Sciences, University of South Florida, Tampa, Florida, USA
| | - Daria A. Naumova
- Division of Infectious Diseases, Department of Internal Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Vladimir V. Lupashin
- Department of Physiology and Cell Biology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
| | - Elena S. Suvorova
- Division of Infectious Diseases, Department of Internal Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
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Machado M, Klaus S, Klaschka D, Guizetti J, Ganter M. Plasmodium falciparum CRK4 links early mitotic events to the onset of S-phase during schizogony. mBio 2023; 14:e0077923. [PMID: 37345936 PMCID: PMC10470535 DOI: 10.1128/mbio.00779-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Accepted: 05/03/2023] [Indexed: 06/23/2023] Open
Abstract
Plasmodium falciparum proliferates through schizogony in the clinically relevant blood stage of infection. During schizogony, consecutive rounds of DNA replication and nuclear division give rise to multinucleated stages before cellularization occurs. Although these nuclei reside in a shared cytoplasm, DNA replication and nuclear division occur asynchronously. Here, by mapping the proteomic context of the S-phase-promoting kinase PfCRK4, we show that it has a dual role for nuclear-cycle progression: PfCRK4 orchestrates not only DNA replication, but in parallel also the rearrangement of intranuclear microtubules from hemispindles into early mitotic spindles. Live-cell imaging of a reporter parasite showed that these microtubule rearrangements coincide with the onset of DNA replication. Together, our data render PfCRK4 a key factor for nuclear-cycle progression, linking entry into S-phase with the initiation of mitotic events. In part, such links may compensate for the absence of canonical cell cycle checkpoints in P. falciparum. IMPORTANCE The human malaria parasite Plasmodium falciparum proliferates in erythrocytes through schizogony, forming multinucleated stages before cellularization occurs. In marked contrast to the pattern of proliferation seen in most model organisms, P. falciparum nuclei multiply asynchronously despite residing in a shared cytoplasm. This divergent mode of replication is, thus, a good target for therapeutic interventions. To exploit this potential, we investigated a key regulator of the parasite's unusual cell cycle, the kinase PfCRK4 and found that this kinase regulated not only DNA replication but also in parallel the rearrangement of nuclear microtubules into early mitotic spindles. Since canonical cell cycle checkpoints have not been described in P. falciparum parasites, linking entry into S-phase and the initiation of mitotic events via a kinase, may be an alternative means to exert control, which is typically achieved by checkpoints.
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Affiliation(s)
- Marta Machado
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
- Graduate Program in Areas of Basic and Applied Biology, Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal
| | - Severina Klaus
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
| | - Darius Klaschka
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
| | - Julien Guizetti
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
| | - Markus Ganter
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
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Wenz C, Simon CS, Romão TP, Stürmer VS, Machado M, Klages N, Klemmer A, Voß Y, Ganter M, Brochet M, Guizetti J. An Sfi1-like centrin-interacting centriolar plaque protein affects nuclear microtubule homeostasis. PLoS Pathog 2023; 19:e1011325. [PMID: 37130129 PMCID: PMC10180636 DOI: 10.1371/journal.ppat.1011325] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Revised: 05/12/2023] [Accepted: 03/28/2023] [Indexed: 05/03/2023] Open
Abstract
Malaria-causing parasites achieve rapid proliferation in human blood through multiple rounds of asynchronous nuclear division followed by daughter cell formation. Nuclear divisions critically depend on the centriolar plaque, which organizes intranuclear spindle microtubules. The centriolar plaque consists of an extranuclear compartment, which is connected via a nuclear pore-like structure to a chromatin-free intranuclear compartment. Composition and function of this non-canonical centrosome remain largely elusive. Centrins, which reside in the extranuclear part, are among the very few centrosomal proteins conserved in Plasmodium falciparum. Here we identify a novel centrin-interacting centriolar plaque protein. Conditional knock down of this Sfi1-like protein (PfSlp) caused a growth delay in blood stages, which correlated with a reduced number of daughter cells. Surprisingly, intranuclear tubulin abundance was significantly increased, which raises the hypothesis that the centriolar plaque might be implicated in regulating tubulin levels. Disruption of tubulin homeostasis caused excess microtubules and aberrant mitotic spindles. Time-lapse microscopy revealed that this prevented or delayed mitotic spindle extension but did not significantly interfere with DNA replication. Our study thereby identifies a novel extranuclear centriolar plaque factor and establishes a functional link to the intranuclear compartment of this divergent eukaryotic centrosome.
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Affiliation(s)
- Christoph Wenz
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
| | | | | | | | - Marta Machado
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
- Graduate Program in Areas of Basic and Applied Biology, Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal
| | - Natacha Klages
- Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Anja Klemmer
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
| | - Yannik Voß
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
| | - Markus Ganter
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
| | - Mathieu Brochet
- Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Julien Guizetti
- Center for Infectious Diseases, Heidelberg University Hospital, Heidelberg, Germany
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Wang QQ, He K, Aleem MT, Long S. Prenyl Transferases Regulate Secretory Protein Sorting and Parasite Morphology in Toxoplasma gondii. Int J Mol Sci 2023; 24:ijms24087172. [PMID: 37108334 PMCID: PMC10138696 DOI: 10.3390/ijms24087172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2023] [Revised: 04/01/2023] [Accepted: 04/07/2023] [Indexed: 04/29/2023] Open
Abstract
Protein prenylation is an important protein modification that is responsible for diverse physiological activities in eukaryotic cells. This modification is generally catalyzed by three types of prenyl transferases, which include farnesyl transferase (FT), geranylgeranyl transferase (GGT-1) and Rab geranylgeranyl transferase (GGT-2). Studies in malaria parasites showed that these parasites contain prenylated proteins, which are proposed to play multiple functions in parasites. However, the prenyl transferases have not been functionally characterized in parasites of subphylum Apicomplexa. Here, we functionally dissected functions of three of the prenyl transferases in the Apicomplexa model organism Toxoplasma gondii (T. gondii) using a plant auxin-inducible degron system. The homologous genes of the beta subunit of FT, GGT-1 and GGT-2 were endogenously tagged with AID at the C-terminus in the TIR1 parental line using a CRISPR-Cas9 approach. Upon depletion of these prenyl transferases, GGT-1 and GGT-2 had a strong defect on parasite replication. Fluorescent assay using diverse protein markers showed that the protein markers ROP5 and GRA7 were diffused in the parasites depleted with GGT-1 and GGT-2, while the mitochondrion was strongly affected in parasites depleted with GGT-1. Importantly, depletion of GGT-2 caused the stronger defect to the sorting of rhoptry protein and the parasite morphology. Furthermore, parasite motility was observed to be affected in parasites depleted with GGT-2. Taken together, this study functionally characterized the prenyl transferases, which contributed to an overall understanding of protein prenylation in T. gondii and potentially in other related parasites.
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Affiliation(s)
- Qiang-Qiang Wang
- National Key Laboratory of Veterinary Public Health Security, School of Veterinary Medicine, China Agricultural University, Beijing 100193, China
| | - Kai He
- National Key Laboratory of Veterinary Public Health Security, School of Veterinary Medicine, China Agricultural University, Beijing 100193, China
| | - Muhammad-Tahir Aleem
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, Cleveland, OH 44115, USA
| | - Shaojun Long
- National Key Laboratory of Veterinary Public Health Security, School of Veterinary Medicine, China Agricultural University, Beijing 100193, China
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Tomasina R, Gonzalez FC, Martins-Duarte ÉS, Bastin P, Gissot M, Francia ME. Separate To Operate: the Centriole-Free Inner Core of the Centrosome Regulates the Assembly of the Intranuclear Spindle in Toxoplasma gondii. mBio 2022;:e0185922. [PMID: 36069445 DOI: 10.1128/mbio.01859-22] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Centrosomes are the main microtubule-organizing center of the cell. They are normally formed by two centrioles, embedded in a cloud of proteins known as pericentriolar material (PCM). The PCM ascribes centrioles with their microtubule nucleation capacity. Toxoplasma gondii, the causative agent of toxoplasmosis, divides by endodyogeny. Successful cell division is critical for pathogenesis. The centrosome, one of the microtubule organizing centers of the cell, plays central roles in orchestrating the temporal and physical coordination of major organelle segregation and daughter cell formation during endodyogeny. The Toxoplasma centrosome is constituted by multiple domains: an outer core, distal from the nucleus; a middle core; and an inner core, proximal to the nucleus. This modular organization has been proposed to underlie T. gondii's cell division plasticity. However, the role of the inner core remains undeciphered. Here, we focus on understanding the function of the inner core by finely studying the localization and role of its only known molecular marker; TgCep250L1. We show that upon conditional degradation of TgCep250L1 parasites are unable to survive. Mutants exhibit severe nuclear segregation defects. In addition, the rest of the centrosome, defined by the position of the centrioles, disconnects from the nucleus. We explore the structural defects underlying these phenotypes by ultrastructure expansion microscopy. We show that TgCep250L1's location changes with respect to other markers, and these changes encompass the formation of the mitotic spindle. Moreover, we show that in the absence of TgCep250L1, the microtubule binding protein TgEB1, fails to localize at the mitotic spindle, while unsegregated nuclei accumulate at the residual body. Overall, our data support a model in which the inner core of the T. gondii centrosome critically participates in cell division by directly impacting the formation or stability of the mitotic spindle. IMPORTANCE Toxoplasma gondii parasites cause toxoplasmosis, arguably the most widespread and prevalent parasitosis of humans and animals. During the clinically relevant stage of its life cycle, the parasites divide by endodyogeny. In this mode of division, the nucleus, containing loosely packed chromatin and a virtually intact nuclear envelope, parcels into two daughter cells generated within a common mother cell cytoplasm. The centrosome is a microtubule-organizing center critical for orchestrating the multiple simultaneously occurring events of endodyogeny. It is organized in two distinct domains: the outer and inner cores. We demonstrate here that the inner core protein TgCEP250L1 is required for replication of T. gondii. Lack of TgCEP250L1 renders parasites able to form daughter cells, while unable to segregate their nuclei. We determine that, in the absence of TgCEP250L1, the mitotic spindle, which is responsible for karyokinesis, does not assemble. Our results support a role for the inner core in nucleation or stabilization of the mitotic spindle in T. gondii.
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Brusini L, Dos Santos Pacheco N, Tromer EC, Soldati-Favre D, Brochet M. Composition and organization of kinetochores show plasticity in apicomplexan chromosome segregation. J Cell Biol 2022; 221:213421. [PMID: 36006241 PMCID: PMC9418836 DOI: 10.1083/jcb.202111084] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Revised: 05/31/2022] [Accepted: 07/15/2022] [Indexed: 01/01/2023] Open
Abstract
Kinetochores are multiprotein assemblies directing mitotic spindle attachment and chromosome segregation. In apicomplexan parasites, most known kinetochore components and associated regulators are apparently missing, suggesting a minimal structure with limited control over chromosome segregation. In this study, we use interactomics combined with deep homology searches to identify 13 previously unknown components of kinetochores in Apicomplexa. Apicomplexan kinetochores are highly divergent in sequence and composition from animal and fungal models. The nanoscale organization includes at least four discrete compartments, each displaying different biochemical interactions, subkinetochore localizations and evolutionary rates across the phylum. We reveal alignment of kinetochores at the metaphase plate in both Plasmodium berghei and Toxoplasma gondii, suggestive of a conserved "hold signal" that prevents precocious entry into anaphase. Finally, we show unexpected plasticity in kinetochore composition and segregation between apicomplexan lifecycle stages, suggestive of diverse requirements to maintain fidelity of chromosome segregation across parasite modes of division.
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Affiliation(s)
- Lorenzo Brusini
- Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland,Correspondence to Lorenzo Brusini:
| | - Nicolas Dos Santos Pacheco
- Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Eelco C. Tromer
- Cell Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Faculty of Science and Engineering, University of Groningen, Groningen, Netherlands
| | - Dominique Soldati-Favre
- Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Mathieu Brochet
- Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland,Mathieu Brochet:
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Zhu X, Li S, Wang C, Yu Y, Wang J, He L, Siddiqui FA, Chen L, Zhu L, Zhou D, Qin J, Miao J, Cui L, Cao Y. The Plasmodium falciparum Nuclear Protein Phosphatase NIF4 Is Required for Efficient Merozoite Invasion and Regulates Artemisinin Sensitivity. mBio 2022;:e0189722. [PMID: 35938722 DOI: 10.1128/mbio.01897-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Artemisinin resistance in Plasmodium falciparum has been associated with a mutation in the NLI-interacting factor-like phosphatase PfNIF4, in addition to the mutations in the Kelch13 protein as the major determinant. We found that PfNIF4 was predominantly expressed at the schizont stage and localized in the nuclei of the parasite. To elucidate the functions of PfNIF4 in P. falciparum, we performed PfNIF4 knockdown (KD) using the inducible ribozyme system. PfNIF4 KD attenuated merozoite invasion and affected gametocytogenesis. PfNIF4 KD parasites also showed significantly increased in vitro susceptibility to artemisinins. Transcriptomic and proteomic analysis revealed that PfNIF4 KD led to the downregulation of gene categories involved in invasion and artemisinin resistance (e.g., mitochondrial function, membrane, and Kelch13 interactome) at the trophozoite and/or schizont stage. Consistent with PfNIF4 being a protein phosphatase, PfNIF4 KD resulted in an overall upregulation of the phosphoproteome of infected erythrocytes. Quantitative phosphoproteomic profiling identified a set of PfNIF4-regulated phosphoproteins with functional similarity to FCP1 substrates, particularly proteins involved in chromatin organization and transcriptional regulation. Specifically, we observed increased phosphorylation of Ser2/5 of the tandem repeats in the C-terminal domain (CTD) of RNA polymerase II (RNAPII) upon PfNIF4 KD. Furthermore, using the TurboID-based proteomic approach, we identified that PfNIF4 interacted with the RNAPII components, AP2-domain transcription factors, and chromatin-modifiers and binders. These findings suggest that PfNIF4 may act as the RNAPII CTD phosphatase, regulating the expression of general and parasite-specific cellular pathways during the blood-stage development.
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Naumov AV, Wang C, Chaput D, Ting LM, Alvarez CA, Keller T, Ramadan A, White MW, Kim K, Suvorova ES. Restriction Checkpoint Controls Bradyzoite Development in Toxoplasma gondii. Microbiol Spectr 2022; 10:e0070222. [PMID: 35652638 PMCID: PMC9241953 DOI: 10.1128/spectrum.00702-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 05/04/2022] [Indexed: 11/21/2022] Open
Abstract
Human toxoplasmosis is a life-threatening disease caused by the apicomplexan parasite Toxoplasma gondii. Rapid replication of the tachyzoite is associated with symptomatic disease, while suppressed division of the bradyzoite is responsible for chronic disease. Here, we identified the T. gondii cell cycle mechanism, the G1 restriction checkpoint (R-point), that operates the switch between parasite growth and differentiation. Apicomplexans lack conventional R-point regulators, suggesting adaptation of alternative factors. We showed that Cdk-related G1 kinase TgCrk2 forms alternative complexes with atypical cyclins (TgCycP1, TgCycP2, and TgCyc5) in the rapidly dividing developmentally incompetent RH and slower dividing developmentally competent ME49 tachyzoites and bradyzoites. Examination of cyclins verified the correlation of cyclin expression with growth dependence and development capacity of RH and ME49 strains. We demonstrated that rapidly dividing RH tachyzoites were dependent on TgCycP1 expression, which interfered with bradyzoite differentiation. Using the conditional knockdown model, we established that TgCycP2 regulated G1 duration in the developmentally competent ME49 tachyzoites but not in the developmentally incompetent RH tachyzoites. We tested the functions of TgCycP2 and TgCyc5 in alkaline induced and spontaneous bradyzoite differentiation (rat embryonic brain cells) models. Based on functional and global gene expression analyses, we determined that TgCycP2 also regulated bradyzoite replication, while signal-induced TgCyc5 was critical for efficient tissue cyst maturation. In conclusion, we identified the central machinery of the T. gondii restriction checkpoint comprised of TgCrk2 kinase and three atypical T. gondii cyclins and demonstrated the independent roles of TgCycP1, TgCycP2, and TgCyc5 in parasite growth and development. IMPORTANCE Toxoplasma gondii is a virulent and abundant human pathogen that puts millions of silently infected people at risk of reactivation of the chronic disease. Encysted bradyzoites formed during the chronic stage are resistant to current therapies. Therefore, insights into the mechanism of tissue cyst formation and reactivation are major areas of investigation. The fact that rapidly dividing parasites differentiate poorly strongly suggests that there is a threshold of replication rate that must be crossed to be considered for differentiation. We discovered a cell cycle mechanism that controls the T. gondii growth-rest switch involved in the conversion of dividing tachyzoites into largely quiescent bradyzoites. This switch operates the T. gondii restriction checkpoint using a set of atypical and parasite-specific regulators. Importantly, the novel T. gondii R-point network was not present in the parasite's human and animal hosts, offering a wealth of new and parasite-specific drug targets to explore in the future.
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Affiliation(s)
- Anatoli V. Naumov
- Department of Internal Medicine, Division of Infectious Diseases and International Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Chengqi Wang
- Center for Global Health and Infectious Diseases Research and USF Genomics Program, College of Public Health, University of South Florida, Tampa, Florida, USA
| | - Dale Chaput
- Proteomics Core, College of Arts and Sciences, University of South Florida, Tampa, Florida, USA
| | - Li-Min Ting
- Department of Internal Medicine, Division of Infectious Diseases and International Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Carmelo A. Alvarez
- Department of Internal Medicine, Division of Infectious Diseases and International Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Thomas Keller
- Department of Internal Medicine, Division of Infectious Diseases and International Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Ahmed Ramadan
- Department of Molecular Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Michael W. White
- Department of Internal Medicine, Division of Infectious Diseases and International Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Kami Kim
- Department of Internal Medicine, Division of Infectious Diseases and International Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
| | - Elena S. Suvorova
- Department of Internal Medicine, Division of Infectious Diseases and International Medicine, Morsani College of Medicine, University of South Florida, Tampa, Florida, USA
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