Mutations linked to interstitial lung disease can abrogate anti-amyloid function of prosurfactant protein C.
The newly synthesized proSP-C (surfactant protein C precursor) is an integral ER (endoplasmic reticulum) membrane protein with a single metastable polyvaline alpha-helical transmembrane domain that comprises two-thirds of the mature peptide. More than 20 mutations in the ER-lumenal CTC (C-terminal domain of proSP-C), are associated with ILD (interstitial lung disease), and some of the mutations cause intracellular accumulation of cytotoxic protein aggregates and a corresponding decrease in mature SP-C. In the present study, we showed that: (i) human embryonic kidney cells expressing the ILD-associated mutants proSP-C(L188Q) and proSP-C(DeltaExon4) accumulate Congo Red-positive amyloid-like inclusions, whereas cells transfected with the mutant proSP-C(I73T) do not; (ii) transfection of CTC into cells expressing proSP-C(L188Q) results in a stable CTC-proSP-C(L188Q) complex, increased proSP-C(L188Q) half-life and reduced formation of Congo Red-positive deposits; (iii) replacement of the metastable polyvaline transmembrane segment with a stable polyleucine transmembrane segment likewise prevents formation of amyloid-like proSP-C(L188Q) aggregates; and (iv) binding of recombinant CTC to non-helical SP-C blocks SP-C amyloid fibril formation. These results suggest that CTC can prevent the polyvaline segment of proSP-C from promoting formation of amyloid-like deposits during biosynthesis, by binding to non-helical conformations. Mutations in the Brichos domain of proSP-C may lead to ILD via loss of CTC chaperone function.
Nerelius
Charlotte
C
Department of Anatomy, Physiology and Biochemistry, Swedish University of Agricultural Sciences, The Biomedical Centre, S-75123 Uppsala, Sweden.
Martin
Emily
E
Peng
Siwei
S
Gustafsson
Magnus
M
Nordling
Kerstin
K
Weaver
Timothy
T
Johansson
Jan
J
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000682:Amyloid / Q000037:antagonists & inhibitors / Q000502:physiology*; D002449:Cell Aggregation / Q000502:physiology; D002460:Cell Line; D005091:Exons; D006801:Humans; D007668:Kidney; D017563:Lung Diseases, Interstitial / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D037721:Pulmonary Surfactant-Associated Protein C / Q000737:chemistry / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D000682:Amyloid; D037721:Pulmonary Surfactant-Associated Protein C; C489679:SFTPC protein, human