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Subcellular Localization of Thioredoxin/Thioredoxin Reductase System-A Missing Link in Endoplasmic Reticulum Redox
Krisztina Veszelyi1, Ibolya Czegle2, Viola Varga1
1Institute of Translational Medicine, Semmelweis University, H-1085 Budapest, Hungary.
International Journal of Molecular Sciences
|June 27, 2024
Summary
The endoplasmic reticulum (ER) lumen lacks thioredoxin (Trx)/thioredoxin reductase (TrxR) proteins, crucial for redox balance. Their absence explains the parallel presence of oxidized and reduced molecules, vital for cell survival.
Area of Science:
- Cellular biology
- Redox biology
- Endoplasmic reticulum (ER) function
Background:
- The ER lumen is generally considered oxidative, yet contains both oxidized thiol-disulfides and reduced pyridine nucleotides.
- This suggests a missing link connecting these redox systems within the ER lumen.
Purpose of the Study:
- To investigate the presence and function of thioredoxin (Trx)/thioredoxin reductase (TrxR) proteins in the ER lumen.
- To understand the implications of Trx/TrxR absence on ER redox homeostasis.
Main Methods:
- Western blot analysis to detect Trx/TrxR isoforms in the ER.
- Immunofluorescent co-localization studies with ER marker Grp94.
- In silico analysis to predict protein localization.
- Cell viability assays following ER-targeted transfection.
Main Results:
- Specific activity of TrxR in the ER lumen was undetectable; higher activities were found in cytoplasm and mitochondria.
- Western blot and co-localization studies confirmed the absence of Trx/TrxR isoforms from the ER lumen.
- In silico tools predicted a very low probability of luminal localization for Trx/TrxR isoforms.
- ER-targeted expression of Trx1 and TrxR1 in HeLa cells reduced cell viability and induced apoptosis.
Conclusions:
- The absence of the Trx/TrxR system in the ER lumen likely explains the uncoupling of its redox systems.
- This uncoupling allows the simultaneous presence of reduced pyridine nucleotides and an oxidized protein pool, which is essential for cellular viability.
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