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Niemann-Pick type C disease: subcellular location and functional characterization of NPC2 proteins with naturally occurring missense mutations.
- Source :
-
Human mutation [Hum Mutat] 2005 Jul; Vol. 26 (1), pp. 20-8. - Publication Year :
- 2005
-
Abstract
- Niemann-Pick disease type C (NPC), a severe neurovisceral lysosomal disorder, is due to mutations on the NPC1 gene or, in a minority of families, the NPC2 gene. Few investigations have been devoted to the NPC2 protein, for which only 13 different disease-causing mutations (including three novel ones in this report) have been described. Among the currently known NPC2 mutant alleles, six resulted in a premature stop codon. Only five missense mutations, c.115G>A (p.V39M), c.140G>T (p.C47F), c.199T>C (p.S67P), c.278G>T (p.C93F), and (this report) c.295T>C (p.C99R) were identified. In the present study, we generated cDNA constructs harboring each of these missense mutations and, upon overexpression in human fibroblasts with a nonsense NPC2 mutation, characterized the mutated proteins by immunoblotting, immunocytofluorescence microscopy, and complementation. Mutation p.V39M, described in the homozygous state in two patients with an adult-onset neurological disease, resulted in the synthesis of apparently functional recombinant proteins correctly targeted to lysosomes. Although a mild functional impact could possibly be overlooked in our overexpression system, comparative studies with NPC1 mutants indicated that mild mutations might not necessarily affect localization of the protein or its quantity in the native state. Conversely, mutations p.C47F, p.C93R, p.C99R but also, less predictably, p.S67P, led to the synthesis of misfolded recombinant proteins that colocalized with an endoplasmic reticulum marker. The four latter proteins were normally secreted but were unable to correct cholesterol storage in NPC2(-/-) cells. Functional characterization of the mutant proteins showed an excellent genotype-phenotype correlation in the three cases for whom a clinical history was available.
- Subjects :
- Adult
Child, Preschool
Female
Fibroblasts
Genetic Complementation Test
Genotype
Humans
Infant
Male
Middle Aged
Phenotype
Protein Transport
Transfection
Vesicular Transport Proteins
Carrier Proteins genetics
Carrier Proteins metabolism
Glycoproteins genetics
Glycoproteins metabolism
Lysosomes metabolism
Mutation, Missense genetics
Niemann-Pick Diseases genetics
Subjects
Details
- Language :
- English
- ISSN :
- 1098-1004
- Volume :
- 26
- Issue :
- 1
- Database :
- MEDLINE
- Journal :
- Human mutation
- Publication Type :
- Academic Journal
- Accession number :
- 15937921
- Full Text :
- https://doi.org/10.1002/humu.20173