Dominant protein interactions that influence the pathogenesis of conformational diseases
Jordan Wright, Xiaofan Wang, Leena Haataja, Aaron P. Kellogg, Jaemin Lee, Ming Liu, Peter Arvan
Jordan Wright, Xiaofan Wang, Leena Haataja, Aaron P. Kellogg, Jaemin Lee, Ming Liu, Peter Arvan
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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 6

Rescue of mutant Tg and blockade of WT proinsulin in primary tissue from animal models of disease.

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Rescue of mutant Tg and blockade of WT proinsulin in primary tissue from...
(A) Lobules of thyroid glands were freshly prepared from mice of the indicated genotypes. Secretory proteins delivered for posttranslational iodination were labeled by incubation of thyroid lobules with 1.0 μCi/μl Na125I for 30 minutes, as described in Methods. The thyroid lobules were then lysed and immunoprecipitated with anti-Myc. The immunoprecipitates were either mock-digested or digested with EndoH, as in Figure 2B, and then analyzed by SDS-PAGE and autoradiography. *P < 0.05. (B) Pancreata from 6-week-old mice, with the genotypes indicated, were fixed in paraffin, sectioned, deparaffinized, and immunostained with antibodies specific to mPro (red) and calnexin to mark the ER (green). From confocal microscope images (scale bar: 10 μm), a blinded reader scored the localization of WT mPro in each β cell as either a predominant juxtanuclear crescent of increased intensity (Golgi, consistent with previous reports, refs. 20, 23; e.g., see arrows) or mainly colocalized with calnexin (ER; e.g., see arrowheads). Quantitation of these data is shown as mean ± SEM from n = 5 mice with 5 islets per mouse. BG, blood glucose. *P < 0.05.