From tumor rejection antigen to protein chaperone: Exploration of the biochemical basis of tumor-specific immunogenicity of heat shock proteingp96.
Item
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Title
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From tumor rejection antigen to protein chaperone: Exploration of the biochemical basis of tumor-specific immunogenicity of heat shock proteingp96.
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Identifier
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AAI9405550
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identifier
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9405550
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Creator
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Li, Zihai.
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Contributor
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Adviser: Pramod K. Srivastava
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Date
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1993
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Language
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English
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Publisher
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City University of New York.
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Subject
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Health Sciences, Immunology | Chemistry, Biochemistry | Biology, Microbiology
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Abstract
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Immunogenicity of tumors was first demonstrated convincingly in chemically-induced sarcomas of inbred mice. A search for the molecules which mediate this immunity led to the identification of heat shock protein (HSP) gp96 as tumor rejection antigen in methylcholanthrene-induced sarcomas of inbred BALB/c mice. Since gp96 is present in normal tissues as well, it was suggested previously that there were mutations in gp96 genes of tumors. However, sequencing of gp96 cDNAs from tumors as well as normal tissues did not reveal any tumor-specific mutations. These observations raise a question as to the structural basis of tumor-specific immunogenicity of gp96.;As gp96 is a HSP and HSPs are known for their ability to bind a wide array of molecules including peptides, a hypothesis is proposed that gp96 may not be immunogenic per se, but may be a carrier of antigenic peptides. In view of the predominant localization of gp96 in the lumen of the ER, it is further suggested that gp96 acts as a peptide-acceptor in the ER and enables peptide-loading of MHC class I molecules.;Some elements of these hypotheses were tested in the present work. The major observations are: (1) gp96 is a Mg{dollar}\sp{lcub}2+{rcub}{dollar}-dependent ATPase. The activity has a Km of 8 {dollar}\mu{dollar}M and the turn over rate of 0.08 mole/min/mole; (2) The ATPase activity of gp96 is stimulated by misfolded proteins such as dephosphorylated casein but not by peptides: (3) Gp96 associates with MHC class I in human T2 cells as well as murine RMA-S and EL-4 cells; (4) Immunoprecipitation by conformation-dependent antibodies against MHC class I indicates that gp96 binds preferentially unfolded and thus peptide-free MHC class I; (5) Peptides can be extracted from purified gp96, a property of gp96 similar to that of the MHC molecules.;Based on the above results, I propose that gp96 is a protein chaperone for peptides and MHC class I. A model is presented to explain the role of gp96 in the peptide-loading step of the folding/assembly of MHC class I.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
