Escrt proteins in physiology and diseases

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necessity of eukaryotes for viability

Transcript of Escrt proteins in physiology and diseases

  • Credit seminar on ESCRT proteins in physiology and disease Speaker: Sandeep Kumar Guide : Dr. S. K. Sood Animal Biochemistry
  • Contents Introduction Roles in physiology and Diseases Multivesicular bodies formation Cytokinesis HIV budding Development Signal attenuation and Cancer Autophagy and Neurodegeneration
  • Introduction ESCRT: Endosomal sorting complex required for transport ESCRT first discovered in yeast that were defective in formation of MVB and called as Vps E complex Originally identified as regulators of protein targeting to lysosomes. ESCRTs work by mediating cargo recruitment and the formation of intraluminal vesicles during the maturation of MVBs ESCRTs are actually four distinct complexes: ESCRT-0, -I, -II, -III.
  • Multivesicular Bodies Formation (Daniel P. Nickerson,2009) GLUE Multivesicular bodies (MVBs): The endocytic organelle, mediates either the lysosomal degradation or recycling of proteins. The formation and scission of these intraluminal vesicles are mediated by the ESCRT complexes.
  • Multivesicular Bodies Formation (Oliver Schmidt,2008)
  • ESCRT in Cytokinesis (Bethan McDonald,2009) 3 Steps in cytokinesis Assembly of central spindles Formation of cleavage Furrow Final abscission at mid body
  • ESCRT in Cytokinesis (Anna Caballe,2011)
  • HIV Budding (Bo Meng,2013)
  • HIV Budding (Carlton,2009)
  • ESCRT Proteins in Development bicoid mRNA is coupled to the microtubule-dependent transport pathway by binding Staufen, which forms a complex with three ESCRT-II proteins, Vps22, Vps25 and Vps36. A mutant form of any of these ESCRT-II proteins abolishes the bicoid mRNA gradient. Bicoid Nanog Anterior Posterior Bicoid protein Gradient Nanog protein Gradient (Irion U & St Johnston D. ,2007) Drosophila egg
  • ESCRT in Cell Signalling (Wegner,2009)
  • Cancer Signaling Endosomes: Early endosomes containing activated receptors are in the on state in terms of signaling. EGFR: best studied receptor tyrosine kinases excessive signaling Cancer Tsg101: Tumor Susceptibility gene Mdm2 DNA damage ATM serine kinase p53 p Arrest cell Cycle in G1 phase p53 Ub Degradation of p53 Tsg101 Cancer (Nobuyuki Tanaka,2008) Mdm2 p53
  • ESCRT in Autophagy Phagophore closure require ESCRT as in cytokinesis & Budding. Formation of autolysosomes is inhibited in cells depleted of Tsg101 or Vps24(Fig E) ESCRT-III dysfunction caused by loss of mSnf7-2 or CHMP2BIntron5 expression leads to the accumulation of autophagosomes in neurons (Fig F) (Lee,2007)(Filimonenko et. al.,2008)
  • Jin-A Lee, Anne Beigneux, S. Tariq Ahmad, Stephen G. Young,2,4 and Fen-Biao Gao Gladstone Institute of Neurological Disease and Department of Neurology Gladstone Institute of Cardiovascular Disease and Department of Medicine University of California,San Francisco, California 94158 Summary Defect in the endosomal-lysosomal pathway have been implicated in a number of neurodegenerative disorders[1]. A key step in the endocytic regulation of transmembrane proteins occurs in a subset of late endosomal compartments known as multivesicular bodies (MVBs), whose formation is controlled by endosomal sorting complex required for transport (ESCRT) [2, 3]. The roles of ESCRT in dendritic maintenance and neurodegeneration remain unknown. Here, we show that mSnf7-2, a key component of ESCRT-III, is highly expressed in most mammalian neurons. Loss of mSnf7-2 in mature cortical neurons caused retraction of dendrites and neuronal cell loss. mSnf7-2 binds to CHMP2B, another ESCRT-III subunit, in which a rare dominant mutation is associated with frontotemporal dementia linked to chromosome 3 (FTD3). Ectopic expression of the mutant protein CHMP2BIntron5 also caused dendritic retraction prior to neurodegeneration. CHMP2BIntron5 was associated more avidly than with mSnf7-2, resulting in sequestration CHMP2BWT of mSnf7-2 in ubiquitin-positive late-endosomal vesicles in cortical neurons. Moreover, loss of mSnf7-2 or CHMP2BIntron5 expression caused the accumulation of autophagosomes in cortical neurons and flies. These findings indicate that ESCRT-III dysfunction is associated with the autophagy pathway, suggesting a novel neurodegeneration mechanism that may have important implications for understanding FTD and other age-dependent neurodegenerative diseases.
  • Neurodegeneration mSnf7-2 and CHMP2B is Required for Dendritic Integrity. CHMP2BIntron5 bind more stronger with mSnf7-2 than CHMP2BWT so CHMP2BIntron5 fails to dissociate from ESCRT-III properly and aberrant MVB formation occur Ubiqitinated P62 and Htt PolyQ aggeregate- FTD And Huntington (Filimonenko et. al.,2007) mSnf7-2 CHMP2B (Lee,2007)
  • Summary ESCRT: necessity of eukaryotes for viability The ESCRT machinery has evolved as a conserved device for abscission of narrow membrane tubes filled with cytosol, mediating inward budding of vesicles into MVEs as well as cell separation during cytokinesis. Enveloped RNA viruses have acquired the ability to hijack this machinery to facilitate their budding from the plasma membrane. The functions of ESCRT subunits as tumour suppressors in Drosophila models can be correlated to their ability to mediate receptor downregulation and cancer. The ESCRT machinery is important for neuronal function. Even though the neurodegeneration in CHMP2B mutant cells has been attributed to impaired autophagy
  • Unanswered Questions How are MVBs that fuse with the lysosome different from MVBs that fuse with the plasma membrane to release exosomes? Why only ESCRT subunit CHMP2B and Snf7-2 found to be mutated in neurodegenerative diseases. Why.? It is possible that one gene copy of the ESCRT subunits is sufficient for normal development, but that both alleles are required under certain conditions of physiologic stress. Why.? There is no role of ESCRT II in cytokinesis but if there is mutation in ESCRT II it block cytokinesis. Why.? Which tumors over-express ESCRT and reduce.? why depletion of the vpsE genes is lethal in multicellular organisms but not in yeast. ..?????
  • The yeast and human ESCRT proteins
  • Abbreviations AAA ATPases associated with diverse cellular activities AIP1 ALG-2 interacting protein 1, synonym for Alix Bro BCK1-like resistance to osmotic shock CC Coiled-coil CHMP Chromatin modifying protein (human orthologs of ESCRT-III subunits) Doa Degradation of alpha2 DUB De-ubiquitinating enzyme EAP ELL associated protein (human orthologs of ESCRT-II subunits) EEA1 Early endosomal antigen 1 EGF Epidermal growth factor receptor EGFR EGF receptor ESCRT Endosomal sorting complex required for transport FYVE Fab1, YOTB, Vac1, EEA1 GAT GGA and TOM GLUE GRAM-like ubiquitin binding in EAP45 GRAM Glucosyltransferases, Rab-like GTPase activators and myotubularins HIV Human immunodeficiency virus
  • Hrs Hepatocyte growth factor receptor substrate Hse Has symptoms of class E mutants; resembles Hrs, STAM, East MIT Microtubule interacting and trafficking MVB Multivesicular body NZF Npl4 zinc finger PI(3)P phosphatidylinositol 3-phosphate Snf Sucrose non-fermenting STAM Signal transducing adaptor molecule Tsg101 Tumor susceptibility gene 101, the human ortholog of vps23 Vps Vacuolar protein sorting Ub Ubiquitin UEV Unusual E2 variant UIM Ubiquitin interacting motif VHS Vps27, Hrs, STAM WW Tryptophan-Tryptophan FTD3 frontotemporal dementia linked to chromosome 3 Abbreviations
  • References Henne,W.M., Buchkovich,N.J. & Emr,E. The ESCRT Pathway. Developmental Cell 21, 71-91 (2011) Williams,R.L. & Urbe,S. The emerging shape of the ESCRT machinery. Nat. Rev. Mol. Cell Biol. 8, 355368 (2007) Schiel,J.A., Childs,C. & Prekeris,R. Endocytic transport and cytokinesis: From regulation of the cytoskeleton to midbody inheritance. Trends in Cell Biology 23:7 319-327 (2013) Hanson,P.I., Shim,S. & Merrill,S.A. Cell biology of the ESCRT machinery. Current Opinion in Cell Biology 21,568574 (2009) Nickerson,D.P., Russell,R.G. & Odorizzi,G. A concentric circle model of multivesicular body cargo sorting. EMBO reports 8, 644650 (2007) Rusten,T.E. & Stenmark,H. How do ESCRT proteins control autophagy? J. Cell Sci. 122, 2179-2183 (2009) Lee,J.A., Beigneux, A., Ahmad,S.T., Young,S.G. & Gao,F.B. ESCRT-III dysfunction causes autophagosome accumulation and neurodegeneration. Curr. Biol. 17, 1561-1567 (2007) Schmidt,O. & Teis,D. The ESCRT machinery. Current Biology 22 No 4 R116 Michelet,X., Djeddi,A. & Legouis,R. Developmental and cellular functions of the ESCRT machinery in pluricellular organisms. Biol. Cell 102, 191202 (2010) Roxrud,I., Stenma