Abstract
Endoplasmic reticulum (ER) maintains within, an oxidative redox state suitable for disulfide bond formation. We monitored the ER redox dynamics subsequent to proteasome inhibition using an ER redox probe ERroGFP S4. Proteasomal inhibition initially led to oxidation of the ER, but gradually the normal redox state was recovered that further led to a reductive state. These events were found to be concomitant with the increase in the both oxidized and reduced glutathione in the microsomal fraction, with a decrease of total intracellular glutathione. The ER reduction was suppressed by pretreatment of a glutathione synthesis inhibitor or by knockdown of ATF4, which induces glutathione-related genes. These results suggested cellular adaptation of ER redox homeostasis: (1) inhibition of proteasome led to accumulation of misfolded proteins and oxidative state in the ER, and (2) the oxidative ER was then reduced by ATF4 activation, followed by influx of glutathione into the ER.
Highlights
Endoplasmic reticulum (ER) maintains within, an oxidative redox state suitable for disulfide bond formation
When stresses exceed the capacity of ER protein quality control system, misfolded proteins accumulate in the ER, a condition referred to as ER stress
The unfolded protein response (UPR) is activated by three ER stress sensors, PERK, ATF6 and IRE19, which are successively activated; PERK is first dimerized and phosphorylated, inducing phosphorylation of eIF2α to suppress the general mRNA translation except for the translation of transcriptional factors such as ATF410,11
Summary
Endoplasmic reticulum (ER) maintains within, an oxidative redox state suitable for disulfide bond formation. Proteasomal inhibition initially led to oxidation of the ER, but gradually the normal redox state was recovered that further led to a reductive state These events were found to be concomitant with the increase in the both oxidized and reduced glutathione in the microsomal fraction, with a decrease of total intracellular glutathione. The ER reduction was suppressed by pretreatment of a glutathione synthesis inhibitor or by knockdown of ATF4, which induces glutathione-related genes These results suggested cellular adaptation of ER redox homeostasis: (1) inhibition of proteasome led to accumulation of misfolded proteins and oxidative state in the ER, and (2) the oxidative ER was reduced by ATF4 activation, followed by influx of glutathione into the ER. IRE1 is subsequently phosphorylated by oligomerization, activating endoribonuclease functions required to generate the active form of transcriptional factor XBP1s13 When these adaptation mechanisms cannot remove the accumulated misfolded proteins sufficiently, cells undergo apoptosis. Proteasome activity decline by aging and the resulting accumulation of abnormal proteins are known to be associated with the pathogenesis of a variety of diseases
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