Vergleichende Analyse der Gerstmann-Straeussler-Scheinker-Syndrom-assoziierten Mutation A117V mit der neuen pathogenen Mutation G114V des humanen Prion-Proteins in vivo und in vitro

Besides its fully translocated form, the prion protein (PrP) can
exist in two transmembrane forms (NtmPrP and CtmPrP), which span
the lipid bilayer in either direction. Certain mutations in the
membrane-spanning segment of PrP have been shown to increase
synthesis of CtmPrP and result in neurodegeneration. One of these
mutations is A117V, which is associated with
Gerstmann-Sträussler-Scheinker syndrome (GSS). Sequence-analysis of
patients showing neurological disorders revealed a new
point-mutation (G114V) in the central region of PrP. The age of
affected individuals is strikingly low; the clinical symptoms
overlap with GSS as well as Creutzfeldt-Jakob disease. Due to their
close vicinity within the transmembrane domain of PrP and
misincorporation of valine in both cases, PrP G114V and PrP A117V
were investigated in comparative studies. Both mutations caused a
similar cellular phenotype strongly differing from wild type PrP.
Characteristics included reduced expression of surface PrP as well
as increased intracellular accumulation. Besides differences in the
cellular localization, a slowed-down metabolism resulting in
prolonged transit to the cell surface was detectable. Long-term
expression of mutant PrP caused strong agglutination and decline of
human neuroblastoma cells that might be due to the increased
synthesis of transmembrane forms of mutant PrPs as verified using a
cell-free topology assay. When proteasomal degradation was
perturbed, PrP G114V and PrP A117V revealed enhanced proteinase K
resistance and increased detergent insolubility. The close
similarities displayed by both mutations point to a common
pathological mechanism that differs from other prion diseases, thus
arguing for a distinct class of disease.