title: Mmi1, the yeast homologue of mammalian TCTP, associates with stress granules in heat-shocked cells and modulates proteasome activity.
abstract: As we have shown previously, yeast Mmi1 protein translocates from the cytoplasm to the outer surface of mitochondria when vegetatively growing yeast cells are exposed to oxidative stress. Here we analyzed the effect of heat stress on Mmi1 distribution. We performed domain analyses and found that binding of Mmi1 to mitochondria is mediated by its central alpha-helical domain (V-domain) under all conditions tested. In contrast, the isolated N-terminal flexible loop domain of the protein always displays nuclear localization. Using immunoelectron microscopy we confirmed re-location of Mmi1 to the nucleus and showed association of Mmi1 with intact and heat shock-altered mitochondria. We also show here that mmi1Δ mutant strains are resistant to robust heat shock with respect to clonogenicity of the cells. To elucidate this phenotype we found that the cytosolic Mmi1 holoprotein re-localized to the nucleus even in cells heat-shocked at 40°C. Upon robust heat shock at 46°C, Mmi1 partly co-localized with the proteasome marker Rpn1 in the nuclear region as well as with the cytoplasmic stress granules defined by Rpg1 (eIF3a). We co-localized Mmi1 also with Bre5, Ubp3 and Cdc48 which are involved in the protein de-ubiquitination machinery, protecting protein substrates from proteasomal degradation. A comparison of proteolytic activities of wild type and mmi1Δ cells revealed that Mmi1 appears to be an inhibitor of the proteasome. We conclude that one of the physiological functions of the multifunctional protein module, Mmi1, is likely in regulating degradation and/or protection of proteins thereby indirectly regulating the pathways leading to cell death in stressed cells.
authors.affiliation: Department Cell Biology, Division Genetics, University of Salzburg, Salzburg, Austria.
authors.forename: Mark
authors.initials: M
authors.lastname: Rinnerthaler
authors.forename: Renata
authors.initials: R
authors.lastname: Lejskova
authors.forename: Tomas
authors.initials: T
authors.lastname: Grousl
authors.forename: Vendula
authors.initials: V
authors.lastname: Stradalova
authors.forename: Gino
authors.initials: G
authors.lastname: Heeren
authors.forename: Klaus
authors.initials: K
authors.lastname: Richter
authors.forename: Lore
authors.initials: L
authors.lastname: Breitenbach-Koller
authors.forename: Jan
authors.initials: J
authors.lastname: Malinsky
authors.forename: Jiri
authors.initials: J
authors.lastname: Hasek
authors.forename: Michael
authors.initials: M
authors.lastname: Breitenbach
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000378:metabolism*; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism*; D018869:Heat-Shock Response; D006358:Hot Temperature; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D000074405:Valosin Containing Protein
chemical_list: D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D029701:Saccharomyces cerevisiae Proteins; C513776:TMA19 protein, S cerevisiae; D025801:Ubiquitin; D010450:Endopeptidases; D046988:Proteasome Endopeptidase Complex; C503886:Bre5 protein, S cerevisiae; C101111:UBP3 protein, S cerevisiae; D000251:Adenosine Triphosphatases; C000614177:CDC48 protein, S cerevisiae; D000074405:Valosin Containing Protein