Browsing by Subject "Kinase"

Now showing 1 - 7 of 7
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    HUNK Phosphorylates Rubicon to Support Autophagy
    (MDPI, 2019-11-19) Zambrano, Joelle N.; Eblen, Scott T.; Abt, Melissa; Rhett, J. Matthew; Muise-Helmericks, Robin; Yeh, Elizabeth S.; Pharmacology and Toxicology, School of Medicine
    Background: Autophagy is a catabolic cellular recycling pathway that is essential for maintaining intracellular homeostasis. Autophagosome formation is achieved via the coordination of the Beclin-1 protein complex. Rubicon is a Beclin-1 associated protein that suppresses autophagy by impairing the activity of the class III PI3K, Vps34. However, very little is known about the molecular mechanisms that regulate Rubicon function. Methods: In this study, co-immunoprecipitation and kinase assays were used to investigate the ability of Hormonally Upregulated Neu-associated Kinase (HUNK) to bind to and phosphorylate Rubicon. LC3B was monitored by immunofluorescence and immunoblotting to determine whether phosphorylation of Rubicon by HUNK controls the autophagy suppressive function of Rubicon. Results: Findings from this study identify Rubicon as a novel substrate of HUNK and show that phosphorylation of Rubicon inhibits its function, promoting autophagy.
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    Mechanisms and consequences of regulating the spinophilin/NMDA receptor interaction
    (2016-07-12) Beiraghi Salek, Asma; Baucum, Anthony J., II; Belecky-Adams, Teri; Watson, John C.; Cummins, Theodore R.
    Parkinson disease (PD) is the second most common neurodegenerative disease. It is characterized by loss of dopaminergic cells in the substantia nigra, which causes loss of dopaminergic synapses onto striatal medium spiny neurons (MSNs). Dendritic spines that are localized to these striatal MSNs receive synaptic inputs from both the nigral dopamine neurons and cortical glutamate neurons. Signaling downstream of excitatory, glutamatergic drive is modulated by dopamine. This tripartite connection: glutamate, dopamine, and MSN dendritic spine, is important for normal motor function. Glutamate released from presynaptic terminals binds to and activates two classes of inotropic glutamate receptors that are localized to dendritic spines on striatal MSNs: the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) and the N-methyl-D-aspartate receptor (NMDAR). Once these receptors are activated, they allow for Ca2+ influx, which in turn activates Ca2+-dependent processes that underlie neural plasticity, including long-term potentiation (LTP) and long-term depression (LTD). Proper machinery in the pre- and post-synaptic neurons is required for normal signal transduction. Moreover, this signal transduction requires proper organization of synaptic proteins, which is achieved by specific protein-protein interactions. These protein-protein interactions are dynamic and can be modulated under various conditions, including pathological changes in the phosphorylation status of a specific protein. Catalytically active proteins called phosphatases and kinases specifically regulate the phosphorylation status of synaptic proteins. Pathologically, in PD there is increased autophosphorylation and activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII). This increased phosphorylation may be due to changes in the activity of the serine/threonine protein phosphatase 1 (PP1), a highly conserved protein serine/threonine phosphatase that has a diverse set of functions in eukaryotes. Serine/threonine phosphatase substrate specificity is obtained via interactions with targeting and regulatory proteins. One such protein, spinophilin, is a scaffolding protein that targets PP1 to various synaptic substrates to regulate their phosphorylation. Interestingly, the association of PP1 with spinophilin is enhanced in a rat model of PD. The NMDAR is another protein that has altered phosphorylation in animal models of PD. We have found that there is a decrease in the NMDAR-spinophilin interaction in an animal model of PD. Here, we have found that spinophilin and the NMDAR interact in brain tissue and when overexpressed in a mammalian cell system. Moreover, we have identified novel mechanisms that regulate this interaction and have identified putative consequences of altering this association. These studies give us novel insight into mechanisms and consequences underlying pathological changes observed in an animal model of PD. Understanding these changes will inform novel therapeutic targets that may be useful in modulating striatal function.
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    The mTOR Substrate S6 Kinase 1 (S6K1) Is a Negative Regulator of Axon Regeneration and a Potential Drug Target for Central Nervous System Injury
    (Society for Neuroscience, 2017-07-26) Al-Ali, Hassan; Ding, Ying; Slepak, Tatiana; Wu, Wei; Sun, Yan; Martinez, Yania; Xu, Xiao-Ming; Lemmon, Vance P.; Bixby, John L.; Neurological Surgery, School of Medicine
    The mammalian target of rapamycin (mTOR) positively regulates axon growth in the mammalian central nervous system (CNS). Although axon regeneration and functional recovery from CNS injuries are typically limited, knockdown or deletion of PTEN, a negative regulator of mTOR, increases mTOR activity and induces robust axon growth and regeneration. It has been suggested that inhibition of S6 kinase 1 (S6K1, gene symbol: RPS6KB1), a prominent mTOR target, would blunt mTOR's positive effect on axon growth. In contrast to this expectation, we demonstrate that inhibition of S6K1 in CNS neurons promotes neurite outgrowth in vitro by twofold to threefold. Biochemical analysis revealed that an mTOR-dependent induction of PI3K signaling is involved in mediating this effect of S6K1 inhibition. Importantly, treating female mice in vivo with PF-4708671, a selective S6K1 inhibitor, stimulated corticospinal tract regeneration across a dorsal spinal hemisection between the cervical 5 and 6 cord segments (C5/C6), increasing axon counts for at least 3 mm beyond the injury site at 8 weeks after injury. Concomitantly, treatment with PF-4708671 produced significant locomotor recovery. Pharmacological targeting of S6K1 may therefore constitute an attractive strategy for promoting axon regeneration following CNS injury, especially given that S6K1 inhibitors are being assessed in clinical trials for nononcological indications.SIGNIFICANCE STATEMENT Despite mTOR's well-established function in promoting axon regeneration, the role of its downstream target, S6 kinase 1 (S6K1), has been unclear. We used cellular assays with primary neurons to demonstrate that S6K1 is a negative regulator of neurite outgrowth, and a spinal cord injury model to show that it is a viable pharmacological target for inducing axon regeneration. We provide mechanistic evidence that S6K1's negative feedback to PI3K signaling is involved in axon growth inhibition, and show that phosphorylation of S6K1 is a more appropriate regeneration indicator than is S6 phosphorylation.
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    De Novo and Inherited Loss-of-Function Variants in TLK2: Clinical and Genotype-Phenotype Evaluation of a Distinct Neurodevelopmental Disorder
    (Elsevier, 2018-06-07) Reijnders, Margot R.F.; Miller, Kerry A.; Alvi, Mohsan; Goos, Jacqueline A.C.; Lees, Melissa M.; de Burca, Anna; Henderson, Alex; Kraus, Alison; Mikat, Barbara; de Vries, Bert B.A.; Isidor, Bertrand; Kerr, Bronwyn; Marcelis, Carlo; Schluth-Bolard, Caroline; Deshpande, Charu; Ruivenkamp, Claudia A.L.; Wieczorek, Dagmar; Baralle, Diana; Blair, Edward M.; Engels, Hartmut; Lüdecke, Hermann-Josef; Eason, Jacqueline; Santen, Gijs W.E.; Clayton-Smith, Jill; Chandler, Kate; Tatton-Brown, Katrina; Payne, Katelyn; Helbig, Katherine; Radtke, Kelly; Nugent, Kimberly M.; Cremer, Kirsten; Strom, Tim M.; Bird, Lynne M.; Sinnema, Margje; Bitner-Glindzicz, Maria; van Dooren, Marieke F.; Alders, Marielle; Koopmans, Marije; Brick, Lauren; Kozenko, Mariya; Harline, Megan L.; Klaassens, Merel; Steinraths, Michelle; Cooper, Nicola S.; Edery, Patrick; Yap, Patrick; Terhal, Paulien A.; van der Spek, Peter J.; Lakeman, Phillis; Taylor, Rachel L.; Littlejohn, Rebecca O.; Pfundt, Rolph; Mercimek-Andrews, Saadet; Stegmann, Alexander P.A.; Kant, Sarina G.; McLean, Scott; Joss, Shelagh; Swagemakers, Sigrid M.A.; Douzgou, Sofia; Wall, Steven A.; Küry, Sebastian; Calpena, Eduardo; Koelling, Nils; McGowan, Simon J.; Twigg, Stephen R.F.; Mathijssen, Irene M.J.; Nellaker, Christoffer; Brunner, Han G.; Wilkie, Andrew O.M.; Medical and Molecular Genetics, School of Medicine
    Next-generation sequencing is a powerful tool for the discovery of genes related to neurodevelopmental disorders (NDDs). Here, we report the identification of a distinct syndrome due to de novo or inherited heterozygous mutations in Tousled-like kinase 2 (TLK2) in 38 unrelated individuals and two affected mothers, using whole-exome and whole-genome sequencing technologies, matchmaker databases, and international collaborations. Affected individuals had a consistent phenotype, characterized by mild-borderline neurodevelopmental delay (86%), behavioral disorders (68%), severe gastro-intestinal problems (63%), and facial dysmorphism including blepharophimosis (82%), telecanthus (74%), prominent nasal bridge (68%), broad nasal tip (66%), thin vermilion of the upper lip (62%), and upslanting palpebral fissures (55%). Analysis of cell lines from three affected individuals showed that mutations act through a loss-of-function mechanism in at least two case subjects. Genotype-phenotype analysis and comparison of computationally modeled faces showed that phenotypes of these and other individuals with loss-of-function variants significantly overlapped with phenotypes of individuals with other variant types (missense and C-terminal truncating). This suggests that haploinsufficiency of TLK2 is the most likely underlying disease mechanism, leading to a consistent neurodevelopmental phenotype. This work illustrates the power of international data sharing, by the identification of 40 individuals from 26 different centers in 7 different countries, allowing the identification, clinical delineation, and genotype-phenotype evaluation of a distinct NDD caused by mutations in TLK2.
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    Parkinson's disease-associated mutations in the GTPase domain of LRRK2 impair its nucleotide-dependent conformational dynamics
    (American Society for Biochemistry and Molecular Biology, 2019-04-12) Wu, Chun-Xiang; Liao, Jingling; Park, Yangshin; Reed, Xylena; Engel, Victoria A.; Hoang, Neo C.; Takagi, Yuichiro; Johnson, Steven M.; Wang, Mu; Federici, Mark; Nichols, R. Jeremy; Sanishvili, Ruslan; Cookson, Mark R.; Hoang, Quyen Q.; Biochemistry and Molecular Biology, School of Medicine
    Mutation in leucine-rich repeat kinase 2 (LRRK2) is a common cause of familial Parkinson's disease (PD). Recently, we showed that a disease-associated mutation R1441H rendered the GTPase domain of LRRK2 catalytically less active and thereby trapping it in a more persistently “on” conformation. However, the mechanism involved and characteristics of this on conformation remained unknown. Here, we report that the Ras of complex protein (ROC) domain of LRRK2 exists in a dynamic dimer–monomer equilibrium that is oppositely driven by GDP and GTP binding. We also observed that the PD-associated mutations at residue 1441 impair this dynamic and shift the conformation of ROC to a GTP-bound–like monomeric conformation. Moreover, we show that residue Arg-1441 is critical for regulating the conformational dynamics of ROC. In summary, our results reveal that the PD-associated substitutions at Arg-1441 of LRRK2 alter monomer–dimer dynamics and thereby trap its GTPase domain in an activated state.
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    Phosphorylation of a Conserved Tyrosine in the Papillomavirus E2 Protein Regulates Brd4 Binding and Viral Replication
    (American Society for Microbiology, 2019-05-01) DeSmet, Marsha; Jose, Leny; Isaq, Nasro; Androphy, Elliot J.; Dermatology, School of Medicine
    The papillomavirus (PV) E2 protein coordinates viral transcription and genome replication. Following a strategy to identify amino acids in E2 that are posttranslationally modified, we reported that tyrosine kinase fibroblast growth factor receptor 3 (FGFR3) complexes with and phosphorylates E2, which inhibits viral DNA replication. Here, we present several lines of evidence indicating that tyrosine (Y) 138 of HPV-31 E2 is a substrate of FGFR3. The active form of FGFR3 bound to and phosphorylated the region of amino acids (aa) 107 to 175 in HPV-31 E2. The E2 phenylalanine (F) mutant Y138F displayed reduced FGFR3-induced phosphotyrosine. A constitutive kinase-active FGFR3 inhibited wild-type (WT) E2-induced E1-dependent DNA replication, while the 138F mutant retained activity. The tyrosine to glutamic acid (E) mutant Y138E, which can mimic phosphotyrosine, failed to induce transient DNA replication, although it maintained the ability to bind and localize the viral DNA helicase E1 to the viral origin. The bromodomain-containing protein 4 (Brd4) binds to E2 and is necessary for initiation of viral DNA synthesis. Interestingly, the Y138E protein coimmunoprecipitated with full-length Brd4 but was defective for association with its C-terminal domain (CTD). These results imply that the activity of the FGFR3 kinase in the infected epithelial cell restricts the HPV replication program through phosphorylation of E2 at Y138, which interferes with E2 binding to the Brd4 CTD, and that this interaction is required for initiation of viral DNA synthesis.IMPORTANCE Human papillomaviruses (HPVs) are highly infectious pathogens that commonly infect the oropharynx and uterine cervix. The idea that posttranslational modifications of viral proteins coordinates viral genome replication is less explored. We recently discovered that fibroblast growth factor receptor 3 (FGFR3) phosphorylates the viral E2 protein. The current study demonstrates that FGFR3 phosphorylates E2 at tyrosine 138, which inhibits association with the C-terminal peptide of Brd4. This study illustrates a novel regulatory mechanism of virus-host interaction and provides insight into the role of Brd4 in viral replication.
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    Roc, the G-domain of the Parkinson’s disease-associated protein LRRK2
    (Elsevier, 2022) Park, Yangshin; Liao, Jingling; Hoang, Quyen Q.; Biochemistry and Molecular Biology, School of Medicine
    Mutation in LRRK2 (Leucine-rich repeat kinase 2) is a common cause of Parkinson’s disease. Aberrant LRRK2 kinase activity is associated with disease pathogenesis, and thus it is an attractive drug target for combating PD. Intense efforts in the past nearly two decades have focused on developing small-molecule inhibitors of the kinase domain of LRRK2, which have identified potent kinase inhibitors. However, most LRRK2 kinase inhibitors have shown adverse effects; therefore, alternative mechanism-based strategies are desperately needed. In this review, we will discuss the new insights gleaned from recent cryo-EM structures of LRRK2 towards understanding the mechanisms of actions of LRRK2 and explore the potential new therapeutic avenues.