Control of PERK eIF2α kinase activity by the endoplasmic reticulum stress-induced molecular chaperone P58 ^IPK

Abstract

P58 IPK is an Hsp40 family member known to inhibit the interferon (IFN)-induced, double-stranded RNA-activated, eukaryotic initiation factor 2␣ (eIF2␣) protein kinase R (PKR) by binding to its kinase domain. We find that the stress of unfolded proteins in the endoplasmic reticulum (ER) activates P58 IPK gene transcription through an ER stress-response element in its promoter region. P58 IPK interacts with and inhibits the PKR-like ER-localized eIF2␣ kinase PERK, which is normally activated during the ER-stress response to protect cells from ER stress by attenuating protein synthesis and reducing ER client protein load. Levels of phosphorylated eIF2␣ were lower in ER-stressed P58 IPK -overexpressing cells and were enhanced in P58 IPK mutant cells. In the ER-stress response, PKR-like ER kinase (PERK)-mediated translational repression is transient and is followed by translational recovery and enhanced expression of genes that increase the capacity of the ER to process client proteins. The absence of P58 IPK resulted in increased expression levels of two ER stress-inducible genes, BiP and Chop, consistent with the enhanced eIF2␣ phosphorylation in the P58 IPK deletion cells. Our studies suggest that P58 IPK induction during the ER-stress response represses PERK activity and plays a functional role in the expression of downstream markers of PERK activity in the later phase of the ER-stress response.

The Role of p58IPK in Protecting the Stressed Endoplasmic Reticulum

“…The glycans on both p58 CHO and Prl/p58 CHO were fully sensitive to digestion by endoglycosidase H, whereas those of the plasma membrane-resident transferrin receptor were resistant ( Figure 2E). This result suggests that p58 IPK is retained in the ER, consistent with previous immunofluorescence localization studies (Yan et al, 2002), proteomic analysis of the secretory pathway (Gilchrist et al, 2006), and our own observations using green fluorescent protein (GFP)-tagged p58 IPK constructs (data not shown). Based on these analyses with chimeric constructs and exogenously expressed protein, we conclude that p58 IPK can be targeted to and translocated across the ER membrane in vitro and in vivo, where it may be a resident of the ER lumen.…”

“…We therefore reexamined the subcellular localization of p58 IPK , which had previously been proposed to be a peripheral protein of the ER membrane (Yan et al, 2002;Oyadomari et al, 2006). p58 IPK from all species tested, including human, rodent, nematode, and plant, contains a hydrophobic N-terminal region predicted to be a cleavable ER signal sequence (Figure 2A; data not shown).…”

“…Although the mechanism of this release is poorly understood, it might involve the DnaJ family protein p58 IPK . Best known as an inhibitor of the eIF2␣ protein kinases PKR and PERK (Yan et al, 2002;van Huizen et al, 2003), p58 IPK was recently proposed to have an independent function in protection from ER stress (Oyadomari et al, 2006). In that study, p58 IPK was proposed to interact with both ER translocons and cytosolic HSP70, thereby recruiting cytosolic chaperone and degradation machinery to the translocon for the clearance of translocationally stalled nascent proteins.…”

Cluster analysis of rat pancreatic islet gene mRNA levels after culture in low-, intermediate- and high-glucose concentrations

“…4). Among these putative XBP1-target genes [35], Dnajc3 could mediate a negative feedback of the UPR on ISR activation by inhibiting PERK (EIF2AK3) activity [48]. Such feedback Fig.…”

Stress du réticulum endoplasmique

“…D'autre part, des travaux ont montré que les protéines ATF6 et XBP1 co-immunopré-cipitent, ce qui suggère que ces deux facteurs de transcription peuvent former un hétérodimère in vivo [24]. De plus certains gènes induits par XBP1 régulent de façon négative l'activité de PERK [25]. Il en est de même pour la protéine adaptatrice NCK1 : non seulement celle-ci interagit avec IRE1, mais elle est impliquée dans l'atténuation de la voie PERK en favorisant la phosphorylation d'eIF2α [26].…”