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Browsing by Author "Yang, Chunlin"
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Item Bromodomains in Protozoan Parasites: Evolution, Function, and Opportunities for Drug Development(American Society for Microbiology, 2017-01-11) Jeffers, Victoria; Yang, Chunlin; Huang, Sherri; Sullivan, William J., Jr.; Pharmacology and Toxicology, School of MedicineParasitic infections remain one of the most pressing global health concerns of our day, affecting billions of people and producing unsustainable economic burdens. The rise of drug-resistant parasites has created an urgent need to study their biology in hopes of uncovering new potential drug targets. It has been established that disrupting gene expression by interfering with lysine acetylation is detrimental to survival of apicomplexan (Toxoplasma gondii and Plasmodium spp.) and kinetoplastid (Leishmania spp. and Trypanosoma spp.) parasites. As "readers" of lysine acetylation, bromodomain proteins have emerged as key gene expression regulators and a promising new class of drug target. Here we review recent studies that demonstrate the essential roles played by bromodomain-containing proteins in parasite viability, invasion, and stage switching and present work showing the efficacy of bromodomain inhibitors as novel antiparasitic agents. In addition, we performed a phylogenetic analysis of bromodomain proteins in representative pathogens, some of which possess unique features that may be specific to parasite processes and useful in future drug development.Item Evolution and expression of core SWI/SNF genes in red algae(Wiley, 2018) Stiller, John W.; Yang, Chunlin; Collén, Jonas; Thompson, Beth E.; Pharmacology and Toxicology, School of MedicineRed algae are the oldest identifiable multicellular eukaryotes, with a fossil record dating back more than a billion years. During that time two major rhodophyte lineages, bangiophytes and florideophytes, have evolved varied levels of morphological complexity. These two groups are distinguished, in part, by different patterns of multicellular development, with florideophytes exhibiting a far greater diversity of morphologies. Interestingly, during their long evolutionary history, there is no record of a rhodophyte achieving the kinds of cellular and tissue‐specific differentiation present in other multicellular algal lineages. To date, the genetic underpinnings of unique aspects of red algal development are largely unexplored; however, they must reflect the complements and patterns of expression of key regulatory genes. Here we report comparative evolutionary and gene expression analyses of core subunits of the SWI/SNF chromatin‐remodeling complex, which is implicated in cell differentiation and developmental regulation in more well studied multicellular groups. Our results suggest that a single, canonical SWI/SNF complex was present in the rhodophyte ancestor, with gene duplications and evolutionary diversification of SWI/SNF subunits accompanying the evolution of multicellularity in the common ancestor of bangiophytes and florideophytes. Differences in how SWI/SNF chromatin remodeling evolved subsequently, in particular gene losses and more rapid divergence of SWI3 and SNF5 in bangiophytes, could help to explain why they exhibit a more limited range of morphological complexity than their florideophyte cousins.Item A plasma membrane localized protein phosphatase in Toxoplasma gondii, PPM5C, regulates attachment to host cells(Springer Nature, 2019-04-11) Yang, Chunlin; Broncel, Malgorzata; Dominicus, Caia; Sampson, Emily; Blakely, William J.; Treeck, Moritz; Arrizabalaga, Gustavo; Pharmacology and Toxicology, School of MedicineThe propagation of Toxoplasma gondii is accomplished by repeated lytic cycles of parasite attachment to a host cell, invasion, replication within a parasitophorous vacuole, and egress from the cell. This lytic cycle is delicately regulated by calcium-dependent reversible phosphorylation of the molecular machinery that drives invasion and egress. While much progress has been made elucidating the protein kinases and substrates central to parasite propagation, little is known about the relevant protein phosphatases. In this study, we focused on the five protein phosphatases that are predicted to be membrane-associated either integrally or peripherally. We have determined that of these only PPM5C, a PP2C family member, localizes to the plasma membrane of Toxoplasma. Disruption of PPM5C results in a slow propagation phenotype in tissue culture. Interestingly, parasites lacking PPM5C divide and undergo egress at a normal rate, but have a deficiency in attaching to host cells. Both membrane localization and phosphatase activity are required for PPM5C's role in attachment. Phosphoproteomic analysis show relatively few phosphorylation sites being affected by PPM5C deletion in extracellular parasites of which several are found on proteins involved in signaling cascades. This implies that PPM5C is part of a wider regulatory network important for attachment to host cells.Item The serine/threonine phosphatases of apicomplexan parasites(Wiley, 2017-10) Yang, Chunlin; Arrizabalaga, Gustavo; Pharmacology and Toxicology, School of MedicineThe balance between phosphorylation and de-phosphorylation, which is delicately regulated by protein kinases and phosphatases, is critical for nearly all biological processes. The Apicomplexa are a large phylum which contains various parasitic protists, including human pathogens, such as Plasmodium, Toxoplasma, Cryptosporidium and Babesia species. The diverse life cycles of these parasites are highly complex and, not surprisingly, many of their key steps are exquisitely regulated by phosphorylation. Interestingly, many of the kinases and phosphatases, as well as the substrates involved in these events are unique to the parasites and therefore phosphorylation constitutes a viable target for antiparasitic intervention. Most progress on this realm has come from studies in Toxoplasma and Plasmodium of their respective kinomes and phosphoproteomes. Nonetheless, given their likely importance, phosphatases have recently become the focus of research within the apicomplexan parasites. In this review, we concentrate on serine/threonine phosphatases in apicomplexan parasites, with the focus on comprehensively identifying and naming protein phosphatases in available apicomplexan genomes, and summarizing the progress of their functional analyses in recent years.Item The protein phosphatase PPKL is a key regulator of daughter parasite development in Toxoplasma gondii(American Society for Microbiology, 2023-10-25) Yang, Chunlin; Doud, Emma H.; Sampson, Emily; Arrizabalaga, Gustavo; Pharmacology and Toxicology, School of MedicineApicomplexan parasites, including Toxoplasma gondii, encode many plant-like proteins, which play significant roles and present attractive targets for drug development. In this study, we have characterized the plant-like protein phosphatase PPKL, which is unique to the parasite and absent in its mammalian host. We have shown that its localization changes as the parasite divides. In non-dividing parasites, it is present in the cytoplasm, nucleus, and preconoidal region. As the parasite begins division, PPKL is enriched in the preconoidal region and the cortical cytoskeleton of nascent parasites. Later in the division, PPKL is present in the basal complex ring. Conditional knockdown of PPKL showed that it is essential for parasite propagation. Moreover, parasites lacking PPKL exhibit uncoupling of division, with normal DNA duplication but severe defects in forming daughter parasites. While PPKL depletion does not impair the duplication of centrosomes, it affects the stability of cortical microtubules. Both co-immunoprecipitation and proximity labeling identified the kinase DYRK1 as a potential functional partner of PPKL. Complete knockout of DYRK1 causes parasites to exhibit division defects with predominantly asynchronous divisions. Global phosphoproteomics analysis revealed a significant increase in phosphorylation of the microtubule-associated protein SPM1 in PPKL-depleted parasites, suggesting that PPKL regulates cortical microtubules by mediating the phosphorylation state of SPM1. More importantly, the phosphorylation of cell cycle-associated kinase Crk1, a known regulator of daughter cell assembly, is altered in PPKL-depleted parasites. Thus, we propose that PPKL regulates daughter parasite development by influencing the Crk1-dependent signaling pathway. IMPORTANCE: Toxoplasma gondii can cause severe disease in immunocompromised or immunosuppressed patients and during congenital infections. Treating toxoplasmosis presents enormous challenges since the parasite shares many biological processes with its mammalian hosts, which results in significant side effects with current therapies. Consequently, proteins that are essential and unique to the parasite represent favorable targets for drug development. Interestingly, Toxoplasma, like other members of the phylum Apicomplexa, has numerous plant-like proteins, many of which play crucial roles and do not have equivalents in the mammalian host. In this study, we found that the plant-like protein phosphatase PPKL appears to be a key regulator of daughter parasite development. With the depletion of PPKL, the parasite shows severe defects in forming daughter parasites. This study provides novel insights into the understanding of parasite division and offers a new potential target for the development of antiparasitic drugs.Item The Tyrosine Phosphatase PRL Regulates Attachment of Toxoplasma gondii to Host Cells and Is Essential for Virulence(American Society for Microbiology, 2022) Yang, Chunlin; Blakely, William J.; Arrizabalaga, Gustavo; Pharmacology and Toxicology, School of MedicineThe pathogenesis of Toxoplasma gondii is mainly due to tissue damage caused by the repeating lytic cycles of the parasite. Many proteins localized to the pellicle of the parasite, particularly kinases, have been identified as critical regulators of the Toxoplasma lytic cycle. However, little is known about the associated protein phosphatases. Phosphatase of regenerating liver (PRL), a highly conserved tyrosine phosphatase, is an oncoprotein that plays pivotal roles in mammalian cells and typically associates with membranes via a conserved prenylation site. PRL in Toxoplasma has a predicted prenylation motif in the C terminus, like other homologs. We have determined that T. gondii PRL (TgPRL) localizes to the plasma membrane and that disruption of TgPRL results in a defect in the parasite's ability to attach to host cells. This function is dependent on both TgPRL's membrane localization and phosphatase activity. Importantly, in vivo experiments have shown that while mice infected with parental strain parasites die within days of infection, those infected with parasites lacking TgPRL not only survive but also develop immunity that confers protection against subsequent infection with wild-type parasites. Immunoprecipitation experiments revealed that the PRL-CNNM (cyclin M) complex, which regulates intracellular Mg2+ homeostasis in mammalian cells, is also present in Toxoplasma. Consistent with this interaction, parasites lacking TgPRL had higher intracellular Mg2+ levels than the parental or complemented strains, suggesting TgPRL is involved in regulating intracellular Mg2+ homeostasis. Thus, TgPRL is a vital regulator of the Toxoplasma lytic cycle and virulence, showing its potential as a target of therapeutic intervention. IMPORTANCE: Infection with Toxoplasma gondii can lead to severe and even life-threatening diseases in people with compromised or suppressed immune systems. Unfortunately, drugs to combat the parasite are limited, highly toxic, and ineffective against the chronic stage of the parasite. Consequently, there is a strong demand for the discovery of new treatments. A comprehensive understanding of how the parasite propagates in the host cells and which proteins contribute to the parasite's virulence will facilitate the discovery of new drug targets. Our study meets this objective and adds new insights to understanding the lytic cycle regulation and virulence of Toxoplasma by determining that the protein phosphatase TgPRL plays a vital role in the parasite's ability to attach to host cells and that it is essential for parasite virulence.