leupeptins and Astrocytoma

Human cytomegalovirus (HCMV) down-regulates expression of MHC class I products by selective proteolysis. A single HCMV gene, US11, which encodes an endoplasmic reticulum (ER) resident type-I transmembrane glycoprotein, is sufficient to cause this effect. In US11+cells, MHC class I molecules are core-glycosylated and therefore inserted into the ER. They are degraded with a half-time of less than 1 min. A full length breakdown intermediate that has lost the single N-linked glycan in an N-glycanase-catalyzed reaction transiently accumulates in cells exposed to the protease inhibitors LLnL, Cbz-LLL, and lactacystin, identifying the proteasome as a key protease. Subcellular fractionation experiments show this intermediate to be cytosolic. Thus, US11 dislocates newly synthesized class I molecules from the ER to the cytosol, where they are acted upon by an N-glycanase and the proteasome.

Topics: Astrocytoma; Cell Line; Cysteine Endopeptidases; Cytomegalovirus; Cytosol; Endoplasmic Reticulum; Gene Expression Regulation, Viral; Genes, MHC Class I; Genes, Viral; Glycosylation; Histocompatibility Antigens Class I; Humans; Leupeptins; Microscopy, Immunoelectron; Multienzyme Complexes; Protease Inhibitors; Proteasome Endopeptidase Complex; Recombinant Proteins; RNA-Binding Proteins; Transfection; Tumor Cells, Cultured; Viral Proteins