title: Characterization of a mutant form of human apolipoprotein B (Thr26_Tyr27del) associated with familial hypobetalipoproteinemia.
abstract: We have previously identified a deletion mutant of human apoB [apoB (Thr26_Tyr27del)] in a subject with primary hypobetalipoproteinemia. The present study determined the effect of Thr26_Tyr27del mutation on apoB secretion using transfected McA-RH7777 cells. Transient or stable transfection of apoB-48 containing the Thr26_Tyr27del mutation showed drastically reduced secretion of the mutant as compared to wild-type apoB-48. No lipoproteins containing the mutant apoB-48 were secreted into the medium. Incubation of transfected cells in a lipid-rich medium in the presence of cycloheximide showed rapid turnover of cell-associated mutant apoB-48 as compared to that of wild-type apoB-48. Immunofluorescence experiments showed that the mutant apoB-48 was mostly localized in the endoplasmic reticulum. Treatment with the proteasomal inhibitor MG132 markedly attenuated the turnover of cell-associated mutant apoB-48, whereas treatment with inhibitors of autophagosomal/lysosomal function (e.g. 3-MA or ammonium chloride) had no effect. Taken together, these results indicated that the defective secretion of the Thr26_Tyr27del mutant was associated with increased intracellular degradation of apoB through the proteasome-dependent pathway.
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Magnolo
authors.affiliation: Department of Internal Medicine and Medical Specialities, University of Palermo, Palermo, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Noto
authors.affiliation: Department of Internal Medicine and Medical Specialities, University of Palermo, Palermo, Italy.
authors.forename: Angelo B
authors.initials: AB
authors.lastname: Cefalù
authors.affiliation: Department of Internal Medicine and Medical Specialities, University of Palermo, Palermo, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Averna
authors.affiliation: Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy.
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Calandra
authors.affiliation: Department of Biochemistry, Microbiology & Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Canada.
authors.forename: Zemin
authors.initials: Z
authors.lastname: Yao
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Tarugi
mesh_terms: D053299:Apolipoprotein B-100 / Q000235:genetics* / Q000378:metabolism; D053283:Apolipoprotein B-48 / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D004252:DNA Mutational Analysis; D004721:Endoplasmic Reticulum / Q000378:metabolism; D020022:Genetic Predisposition to Disease; D006579:Heterozygote; D006801:Humans; D006995:Hypobetalipoproteinemias / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors / Q000494:pharmacology; D059748:Proteolysis; D017384:Sequence Deletion; D013997:Time Factors; D014162:Transfection
chemical_list: C569471:APOB protein, human; D053299:Apolipoprotein B-100; D053283:Apolipoprotein B-48; D061988:Proteasome Inhibitors; D046988:Proteasome Endopeptidase Complex
keywords: Apolipoprotein B mutation; Apolipoprotein B-48 secretion; Hypobetalipoproteinemia; Proteasomal degradation