title: Amyloidogenic lysozymes accumulate in the endoplasmic reticulum accompanied by the augmentation of ER stress signals.
abstract: BACKGROUND
  Naturally occurring single mutants, I56T, F57I, W64R and D67H of lysozyme in human, have been known to form abnormal protein aggregates (amyloid fibrils) and to accumulate in several organs, including the liver, spleen and kidney, resulting in familial systemic amyloidosis. These human pathogenic lysozyme variants are considered to raise subtle conformational changes compared to the wild type.
  
  
  METHODS
  Here we examined the effects of the aberrant mutant lysozymes I56T, F57I, W64R and D67H, each of which possesses a point mutation in its molecule, on a cultured human cell line, HEK293, in which the genes were individually integrated and overexpressed.
  
  
  RESULTS
  Western blot analyses showed lesser amounts of these variant proteins in the medium compared to the wild type, but they were abundant in the cell pellets, indicating that the modified lysozyme proteins were scarcely secreted into the medium but were retained in the cells. Immunocytochemistry revealed that these proteins resided in restricted regions which were stained by an endoplasmic reticulum (ER) marker. Moreover, the overexpression of the mutant lysozymes were accompanied by marked increases in XBP-1s and GRP78/BiP, which are downstream agents of the IRE1α signaling pathway responding to the unfolded protein response (UPR) upon ER stress. RNAi for the mutant lysozymes' expression greatly suppressed the increases of these agents.
  
  
  CONCLUSIONS
  Our results suggest that the accumulation of pathogenic lysozymes in the ER caused ER stress and the UPR response mainly via the IRE1α pathway.
authors: Laboratory of Biochemistry and Bioscience, The United Graduate School of Agricultural Sciences, Kagoshima University, Kagoshima 890-0065, Japan.
authors: Yoshiki
authors: Y
authors: Kamada
authors: Laboratory of Sericultural Science, Graduate School of Agricultural Sciences, Kyushu University, Fukuoka 812-8581, Japan.
authors: Takahiro
authors: T
authors: Kusakabe
authors: Laboratory of Biochemistry and Bioscience, The United Graduate School of Agricultural Sciences, Kagoshima University, Kagoshima 890-0065, Japan. Electronic address: yasushi@chem.agri.kagoshima-u.ac.jp.
authors: Yasushi
authors: Y
authors: Sugimoto
mesh_terms: D028226:Amyloidosis, Familial / Q000201:enzymology* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress; D004722:Endoribonucleases / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D005838:Genotype; D057809:HEK293 Cells; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010641:Phenotype; D011487:Protein Conformation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection; D056811:Unfolded Protein Response; D000071717:X-Box Binding Protein 1
chemical_list: D004268:DNA-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D012333:RNA, Messenger; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C528229:ERN1 protein, human; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases; D009113:Muramidase
keywords: Amyloidosis; ER stress; Endoplasmic reticulum; Lysozyme; Mutants