title: Nijmegen breakage syndrome: the clearance pathway for mutant nibrin protein is allele specific.
abstract: The autosomal recessive disorder Nijmegen breakage syndrome (NBS) is caused by mutations in the NBN gene which codes for the protein nibrin (NBS1; p95). In the majority of cases, a 5bp deletion, a founder mutation, leads to a hypomorphic 70kD protein, p70-nibrin, after alternative initiation of translation. Protein levels are of relevance for the clinical course of the disease, particularly with regard to malignancy. Here, mechanisms and efficiency of mutant protein clearance were examined in order to establish whether these have an impact on nibrin abundance. Cell lines from NBS patients and retroviral transductants were treated with proteasome and lysosome inhibitors and examined by semi-quantitative immunoblotting for p70-nibrin and p95-nibrin levels. The results show that p70-nibrin is degraded by the proteasome with varying efficiency in cell lines from different NBS patients leading to lower or higher steady state levels of this partially active protein fragment. In contrast, a previously described NBN missense mutation, which disturbs protein folding due to the substitution of a critical arginine by tryptophan, was found to be cleared by lysosomal microautophagy leading also to lower cellular levels. The data show that truncated nibrin and misfolded nibrin have different clearance pathways.
authors: Charité-Universitätsmedizin Berlin, Institute of Medical and Human Genetics, Augustenburger Platz 1, 13353 Berlin, Germany.
authors: Bastian
authors: B
authors: Salewsky
authors: Petra
authors: P
authors: Wessendorf
authors: Daniel
authors: D
authors: Hirsch
authors: Harald
authors: H
authors: Krenzlin
authors: Martin
authors: M
authors: Digweed
mesh_terms: D000483:Alleles; D019943:Amino Acid Substitution; D001343:Autophagy / Q000235:genetics; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D005819:Genetic Markers; D005822:Genetic Vectors; D006801:Humans; D007700:Kinetics; D050505:Mutant Proteins / Q000235:genetics*; D020125:Mutation, Missense; D049932:Nijmegen Breakage Syndrome / Q000235:genetics* / Q000473:pathology; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D012190:Retroviridae / Q000235:genetics / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D005819:Genetic Markers; D050505:Mutant Proteins; C112156:NBN protein, human; D009687:Nuclear Proteins; D061988:Proteasome Inhibitors; D046988:Proteasome Endopeptidase Complex