A single point mutation in the low-density lipoprotein receptor switches the degradation of its mature protein from the proteasome to the lysosome.
Pathogenic mutations in the low-density lipoprotein receptor prevent cholesterol uptake and cause familial hypercholesterolemia. In comparison to the biogenesis and endocytic trafficking of this receptor and some of its mutants, their degradation mechanisms are not well understood. Therefore, to gain some insights into this aspect, we analyzed the effects of proteasomal and lysosomal inhibitors on the levels of the wild type low-density lipoprotein receptor and a mutant form, C358Y, which was prevalent in a sample of Spanish familial hypercholesterolemia patients. In transfected cells, the mutant C358Y exhibited lower activity than the wild type receptor, as well as retarded post-translational processing of its precursor to the mature form. Interestingly, about 30% of the mutant precursor was degraded by a lysosomal pathway. Moreover, its mature form was more rapidly degraded than the wild type receptor (half lives of 5.3 and 10.9 h, respectively) and its degradation was exclusively dependent on a lysosomal pathway. In contrast, the mature form of the wild type receptor was mainly degraded by proteasomes and, to a minor extent (30%), by lysosomes. We conclude that a single mutation in the low-density lipoprotein receptor switches the degradation of the mature receptor from a proteasomal to a lysosomal pathway which degrades the protein at a faster rate. This suggests cooperation of proteasomes and lysosomes in the degradation of the low-density lipoprotein receptor and adds an intriguing new aspect to our understanding of receptor-mediated endocytosis.
Martín de Llano
José Javier
JJ
Laboratorio de Biología Celular, Centro de Investigación Príncipe Felipe, Avda. Autopista del Saler 16, 46013 Valencia, Spain.
Fuertes
Graciela
G
Andreu
Enrique José
EJ
Puig
Oscar
O
Chaves
F Javier
FJ
Soutar
Anne K
AK
Armengod
María-Eugenia
ME
Knecht
Erwin
E
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001692:Biological Transport / Q000187:drug effects; D016466:CHO Cells; D019556:COS Cells; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism / Q000493:pharmacokinetics; D008247:Lysosomes / Q000378:metabolism*; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D011499:Protein Processing, Post-Translational; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
D015853:Cysteine Proteinase Inhibitors; D008077:Lipoproteins, LDL; D050505:Mutant Proteins; D061988:Proteasome Inhibitors; D011973:Receptors, LDL; C067713:lactacystin; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine