Dominant protein interactions that influence the pathogenesis of conformational diseases
Jordan Wright, … , Ming Liu, Peter Arvan
Jordan Wright, … , Ming Liu, Peter Arvan
Published June 3, 2013
Citation Information: J Clin Invest. 2013;123(7):3124-3134. https://doi.org/10.1172/JCI67260.
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Research Article Endocrinology

Dominant protein interactions that influence the pathogenesis of conformational diseases

Abstract

Misfolding of exportable proteins can trigger endocrinopathies. For example, misfolding of insulin can result in autosomal dominant mutant INS gene–induced diabetes of youth, and misfolding of thyroglobulin can result in autosomal recessive congenital hypothyroidism with deficient thyroglobulin. Both proinsulin and thyroglobulin normally form homodimers; the mutant versions of both proteins misfold in the ER, triggering ER stress, and, in both cases, heterozygosity creates potential for cross-dimerization between mutant and WT gene products. Here, we investigated these two ER-retained mutant secretory proteins and the selectivity of their interactions with their respective WT counterparts. In both cases and in animal models of these diseases, we found that conditions favoring an increased stoichiometry of mutant gene product dominantly inhibited export of the WT partner, while increased relative level of the WT gene product helped to rescue secretion of the mutant partner. Surprisingly, the bidirectional consequences of secretory blockade and rescue occur simultaneously in the same cells. Thus, in the context of heterozygosity, expression level and stability of WT subunits may be a critical factor influencing the effect of protein misfolding on clinical phenotype. These results offer new insight into dominant as well as recessive inheritance of conformational diseases and offer opportunities for the development of new therapies.

Authors

Jordan Wright, Xiaofan Wang, Leena Haataja, Aaron P. Kellogg, Jaemin Lee, Ming Liu, Peter Arvan

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Figure 3

Intracellular distribution of mutant proinsulins in regulated secretory cells coexpressing or not coexpressing WT proinsulin.

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Intracellular distribution of mutant proinsulins in regulated secretory ...
(A) Cultured INS1 pancreatic β cells (that express endogenous proinsulin) were transiently transfected to express WT or mutant hPro-CpepSfGFP, as indicated. Fixed cells (counterstained with DAPI) were examined by confocal microscopy for the distribution of SfGFP-containing peptides (scale bar: 20 μm). The cell lysates and overnight bathing media were collected, immunoprecipitated with anti-GFP, and analyzed by immunoblotting with anti-GFP to examine secretion efficiency. Noncontiguous lanes from the same gel are shown. The media/cell ratio for WT, G(B23)V, and C(A7)Y hPro-CpepSfGFP bands was 14.8 ± 3.8, 0.74 ± 0.04, and 0.16 ± 0.06, respectively (P < 0.05 for all groups, n = 4). (B) Cultured AtT20 pituitary corticotroph cells (that do not express endogenous proinsulin) were transiently cotransfected with one of three different plasmid combinations, as indicated. Fixed cells were examined by confocal fluorescence for the distribution of SfGFP-containing peptides (green) and immunofluorescence to localize ACTH-containing secretory granules (red) at the tips of cell (arrowheads; scale bar: 20 μm). Cell boundaries were defined from phase-contrast images (data not shown). Enrichment of average GFP intensity in the secretory granule region was compared with average GFP intensity in nongranule regions. Data represent mean ± SEM from 30 to 38 separately imaged cells for each of the 3 respective transfection conditions. *P < 0.05.