GTPase-Mediated Regulation of the Unfolded Protein Response in Caenorhabditis elegans Is Dependent on the AAA⁺ ATPase CDC-48

Abstract

When endoplasmic reticulum (ER) homeostasis is perturbed, an adaptive mechanism is triggered and named the unfolded protein response (UPR). Thus far, three known UPR signaling branches (IRE-1, PERK, and ATF-6) mediate the reestablishment of ER functions but can also lead to apoptosis if ER stress is not alleviated. However, the understanding of the molecular mechanisms integrating the UPR to other ER functions, such as membrane traffic or endomembrane signaling, remains incomplete. We consequently sought to identify new regulators of UPR-dependent transcriptional mechanisms and focused on a family of proteins known to mediate, among other, ER-related functions: the small GTP-binding proteins of the RAS superfamily. To this end, we used transgenic UPR reporter Caenorhabditis elegans strains as a model to specifically silence small-GTPase expression. We show that the Rho subfamily member CRP-1 is an essential component of UPR-induced transcriptional events through its physical and genetic interactions with the AAA ؉ ATPase CDC-48. In addition, we describe a novel signaling module involving CRP-1 and CDC-48 which may directly link the UPR to DNA remodeling and transcription control.The endoplasmic reticulum (ER) is an organelle found in eukaryotic cells, which is mainly involved in calcium sequestration, lipid biosynthesis and translation, folding, and transport of secretory proteins (9). These functions require specialized and integrated molecular machines (7). Most of the proteins distributed in organelles of the secretory pathway, expressed at the cell surface or secreted, transit through the ER before reaching their final destination. Indeed, polypeptide chains, translated on ER membrane-bound ribosomes, are first translocated into the ER lumen via the translocon and then processed through the ER folding machineries, which include a chaperone component (e.g., BiP or GRP94), a posttranslational modification machinery (e.g., N glycosylation with the oligosaccharyl transferase complex, S-S bound formation with the protein disulfide isomerases), and a quality control component (e.g., calnexin, UDP-glucose:glycoprotein glucosyltransferase). Proteins which do not acquire a correct conformation are retained in the ER by ER-specific quality control mechanisms and are consequently granted further folding attempts. If this fails again, terminally misfolded proteins are degraded via the ER-associated degradation (ERAD) machinery (9).Under basal conditions, these integrated mechanisms maintain the ER protein load in equilibrium with ER's folding and export capacities. However, if one of those components is dysfunctional, the entire chain reaction is perturbed and ER homeostasis is disrupted. This leads to an increased amount of improperly folded proteins, which accumulate within the ER. As a mechanism for adaption to this phenomenon, cells have evolved the unfolded protein response (UPR), which aims at restoring ER homeostasis (38, 41) by (i) attenuating protein translation, (ii) increasing ER folding capacity, (iii) incre...

Autocrine control of glioma cells adhesion/migration through Inositol Requiring enzyme 1α (IRE1α)-mediated cleavage of Secreted Protein Acidic Rich in Cysteine (SPARC) mRNA

“…4). This is in agreement with data showing that RhoA is involved in the SPARC-induced migration of U87 cells (Kunigal et al, 2006) and is consistent with our previous work linking Rho GTPase signaling to the Unfolded Protein Response (Bouchecareilh et al, 2011b;Caruso et al, 2008). Moreover, SPARC expression has been previously described to increase U87 cell migration (Rempel et al, 2001).…”

The Caenorhabditis elegans HP1 family protein HPL-2 maintains ER homeostasis through the UPR and hormesis

“…S4), indicating a narrow range of concentrations conferring beneficial effects. Expression of two sensors of UPR induction, hsp-4p::GFP and ckb-2p::GFP (20,24) at TM concentrations as low as 0.1 μg/mL confirmed that preconditioning induces the UPR (Fig. 4C).…”

Cell cycle progression requires the CDC-48 UFD−1/NPL−4 complex for efficient DNA replication

“…At present it is unclear how CDC-48 affects replication but recent studies reported that p97 binds to DNA replication factors (31,32). Interestingly, p97 associates with the human Werner RecQ helicase (33) and C. elegans CDC-48.1 with HIM-6, a Bloom Syndrome helicase homolog (34). As both RecQ helicases are involved in DNA replication to prevent accelerated aging, it is conceivable to speculate about an evolutionarily conserved requirement of CDC-48/p97 in DNA synthesis linked to cancer and longevity.…”