title: Retrotranslocation of MHC class I heavy chain from the endoplasmic reticulum to the cytosol is dependent on ATP supply to the ER lumen.
abstract: MHC class I heavy chains (HC) that fail to acquire a mature conformation in the endoplasmic reticulum (ER) as a result of defective folding or assembly with beta2-microglobulin, or lack of appropriate peptide cargo are retrotranslocated through the Sec61 channel to the cytosol for degradation by proteasomes. The mechanisms involved in ER retrotranslocation of HC are as yet incompletely understood. Using a microsomal system, we characterized the molecular requirements for the release of HC into the soluble fraction. Extraction of ubiquitinated HC was facilitated by cytosol, or by addition of proteins that stabilized the membrane association of the cytoplasmic ATPase p97. Functional proteasomes were not needed for HC mobilization. ATP supply to the ER lumen was found to be an essential factor since an inhibitor of the ATP importing pump in the ER membrane blocked HC release. Also non-hydrolyzable ATP analogs delivered to the ER lumen facilitated HC export suggesting that ATP binding by ER chaperones rather than ATP hydrolysis is involved.
authors.affiliation: Division of Molecular Immunology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.
authors.forename: Jörn
authors.initials: J
authors.lastname: Albring
authors.forename: Jens-Oliver
authors.initials: JO
authors.lastname: Koopmann
authors.forename: Günter J
authors.initials: GJ
authors.lastname: Hämmerling
authors.forename: Frank
authors.initials: F
authors.lastname: Momburg
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001693:Biological Transport, Active; D003546:Cysteine Endopeptidases / Q000378:metabolism; D003600:Cytosol / Q000276:immunology / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000276:immunology* / Q000378:metabolism*; D004795:Enzyme Stability; D006031:Glycosylation; D006680:HLA Antigens / Q000737:chemistry / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008861:Microsomes / Q000276:immunology / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex
chemical_list: D006680:HLA Antigens; D015395:Histocompatibility Antigens Class I; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D000255:Adenosine Triphosphate; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C404942:p97 ATPase