School of Biomedical Sciences - Research Publications
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ItemPrion-like domains in RNA binding proteins are essential for building subnuclear paraspeckles(ROCKEFELLER UNIV PRESS, 2015-08-17)Prion-like domains (PLDs) are low complexity sequences found in RNA binding proteins associated with the neurodegenerative disorder amyotrophic lateral sclerosis. Recently, PLDs have been implicated in mediating gene regulation via liquid-phase transitions that drive ribonucleoprotein granule assembly. In this paper, we report many PLDs in proteins associated with paraspeckles, subnuclear bodies that form around long noncoding RNA. We mapped the interactome network of paraspeckle proteins, finding enrichment of PLDs. We show that one protein, RBM14, connects key paraspeckle subcomplexes via interactions mediated by its PLD. We further show that the RBM14 PLD, as well as the PLD of another essential paraspeckle protein, FUS, is required to rescue paraspeckle formation in cells in which their endogenous counterpart has been knocked down. Similar to FUS, the RBM14 PLD also forms hydrogels with amyloid-like properties. These results suggest a role for PLD-mediated liquid-phase transitions in paraspeckle formation, highlighting this nuclear body as an excellent model system for understanding the perturbation of such processes in neurodegeneration.
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ItemPOLYGLUTAMINE AGGREGATION IN HUNTINGTON AND RELATED DISEASES(SPRINGER-VERLAG BERLIN, 2012)Polyglutamine (polyQ)-expansions in different proteins cause nine neurodegenerative diseases. While polyQ aggregation is a key pathological hallmark of these diseases, how aggregation relates to pathogenesis remains contentious. In this chapter, we review what is known about the aggregation process and how cells respond and interact with the polyQ-expanded proteins. We cover detailed biophysical and structural studies to uncover the intrinsic features of polyQ aggregates and concomitant effects in the cellular environment. We also examine the functional consequences ofpolyQ aggregation and how cells may attempt to intervene and guide the aggregation process.
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ItemTracking protein aggregation and mislocalization in cells with flow cytometry(NATURE PUBLISHING GROUP, 2012-05)We applied pulse-shape analysis (PulSA) to monitor protein localization changes in mammalian cells by flow cytometry. PulSA enabled high-throughput tracking of protein aggregation, translocation from the cytoplasm to the nucleus and trafficking from the plasma membrane to the Golgi as well as stress-granule formation. Combining PulSA with tetracysteine-based oligomer sensors in a cell model of Huntington's disease enabled further separation of cells enriched with monomers, oligomers and inclusion bodies.
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ItemPutting Huntingtin "Aggregation" in View with Windows into the Cellular Milieu(BENTHAM SCIENCE PUBL LTD, 2012-11)Huntington's disease arises from CAG codon-repeat expansions in the Htt gene, which leads to a Htt gene product with an expanded polyglutamine (polyQ) sequence. The length of the polyQ expansion correlates with an increased tendency to form aggregates and clustering into micrometer-plus sized inclusion bodies in neurons and other cell types. Yet after nearly 20 years since the genetic basis for HD was identified, our knowledge of how polyQ-expanded Htt fragment aggregation relates to disease mechanisms remains fragmentary and controversial. Challenges remain in defining the aggregation process at the molecular level and how this process is influenced by, or influences cellular activities. Insight is further confounded by the term "aggregation" being used to describe a composite of distinct processes that may have opposing consequences to cell health and survival. This review discusses these issues in light of a historic summary of Htt aggregation in the cellular milieu and the intrinsic attributes of polyQ-expanded Htt that lead to aggregation. Finally, discussion centers on strategies forward to improve our knowledge for how aggregation relates to cellular dysfunction.
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ItemSOD1 protein aggregates stimulate macropinocytosis in neurons to facilitate their propagation(BIOMED CENTRAL LTD, 2015-10-31)BACKGROUND: Amyotrophic Lateral Sclerosis is characterized by a focal onset of symptoms followed by a progressive spread of pathology that has been likened to transmission of infectious prions. Cell-to-cell transmission of SOD1 protein aggregates is dependent on fluid-phase endocytosis pathways, although the precise molecular mechanisms remain to be elucidated. RESULTS: We demonstrate in this paper that SOD1 aggregates interact with the cell surface triggering activation of Rac1 and subsequent membrane ruffling permitting aggregate uptake via stimulated macropinocytosis. In addition, other protein aggregates, including those associated with neurodegenerative diseases (TDP-43, Httex146Q, α-synuclein) also trigger membrane ruffling to gain entry into the cell. Aggregates are able to rupture unstructured macropinosomes to enter the cytosol allowing propagation of aggregation to proceed. CONCLUSION: Thus, we conclude that in addition to basic proteostasis mechanisms, pathways involved in the activation of macropinocytosis are key determinants in the spread of pathology in these misfolding diseases.
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ItemSerpinB2 (PAI-2) Modulates Proteostasis via Binding Misfolded Proteins and Promotion of Cytoprotective Inclusion Formation(PUBLIC LIBRARY SCIENCE, 2015-06-17)SerpinB2 (PAI-2), a member of the clade B family of serine protease inhibitors, is one of the most upregulated proteins following cellular stress. Originally described as an inhibitor of urokinase plasminogen activator, its predominant cytoplasmic localisation suggests an intracellular function. SerpinB2 has been reported to display cytoprotective properties in neurons and to interact with intracellular proteins including components of the ubiquitin-proteasome system (UPS). In the current study we explored the potential role of SerpinB2 as a modulator of proteotoxic stress. Initially, we transiently transfected wild-type SerpinB2 and SerpinB2-/- murine embryonic fibroblasts (MEFs) with Huntingtin exon1-polyglutamine (fused C-terminally to mCherry). Inclusion body formation as result of Huntingtin aggregation was evident in the SerpinB2 expressing cells but significantly impaired in the SerpinB2-/- cells, the latter concomitant with loss in cell viability. Importantly, recovery of the wild-type phenotype and cell viability was rescued by retroviral transduction of SerpinB2 expression. SerpinB2 modestly attenuated Huntingtin and amyloid beta fibril formation in vitro and was able to bind preferentially to misfolded proteins. Given the modest chaperone-like activity of SerpinB2 we tested the ability of SerpinB2 to modulate UPS and autophagy activity using a GFP reporter system and autophagy reporter, respectively. Activity of the UPS was reduced and autophagy was dysregulated in SerpinB2-/- compared to wild-type MEFs. Moreover, we observed a non-covalent interaction between ubiquitin and SerpinB2 in cells using GFP-pulldown assays and bimolecular fluorescence complementation. We conclude that SerpinB2 plays an important role in proteostasis as its loss leads to a proteotoxic phenotype associated with an inability to compartmentalize aggregating proteins and a reduced capacity of the UPS.