TULP1 missense mutations induces the endoplasmic reticulum unfolded protein response stress complex (ER-UPR)

Glenn P. Lobo, Lindsey A. Ebke, Adrian Au, Stephanie A. Hagstrom

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

Mutations in the TULP1 gene are associated with early-onset retinitis pigmentosa (RP); however, the molecular mechanisms related to the deleterious effects of TULP1 mutations remains unknown. Several studies have shown that misfolded proteins secondary to genetic mutations can accumulate within the endoplasmic reticulum (ER), causing activation of the unfolded protein response (UPR) complex followed by cellular apoptosis. We hypothesize that TULP1 mutations produce misfolded protein products that accumulate in the ER and induce cellular apoptosis via the UPR. To test our hypothesis, we first performed three in-silico analyses of TULP1 missense mutations (I459K, R420P and F491L), which predicted misfolded protein products. Subsequently, the three mutant TULP1-GFP constructs and wildtype (wt) TULP1-GFP were transiently transfected into hTERT-RPE-1 cells. Staining of cells using ER tracker followed by confocal microscopy showed wt-TULP1 localized predominantly to the cytoplasm and plasma membrane. In contrast, all three mutant TULP1 proteins revealed cytoplasmic punctate staining which colocalized with the ER. Furthermore, western blot analysis of cells expressing mutant TULP1 proteins revealed induction of downstream targets of the ER-UPR complex, including BiP/GPR-78, phosphorylated-PERK (Thr980) and CHOP. Our in-vitro analyses suggest that mutant TULP1 proteins are misfolded and accumulate within the ER leading to induction of the UPR stress response complex.

Original languageEnglish (US)
Title of host publicationAdvances in Experimental Medicine and Biology
PublisherSpringer New York LLC
Pages223-230
Number of pages8
DOIs
StatePublished - Oct 1 2016
Externally publishedYes

Publication series

NameAdvances in Experimental Medicine and Biology
Volume854
ISSN (Print)0065-2598
ISSN (Electronic)2214-8019

Bibliographical note

Funding Information:
This study was supported by NIH Grant EY15638 (SAH), Research to Prevent Blindness Center Grant, Knights Templar Eye Foundation Career-Starter Grant (GPL) and Howard Hughes Medical Institute-Foundation Fighting Blindness Medical Research Fellowship (AA).

Publisher Copyright:
© Springer International Publishing Switzerland 2016.

Keywords

  • Endoplasmic reticulum
  • Photoreceptor
  • Retinal degeneration
  • Tulp1
  • Unfolded protein response

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