bims-cemest 2024-12-15 papers

Elife. 2024 Dec 10. pii: RP93117. [Epub ahead of print]12

UGGT1-mediated reglucosylation of N-glycan competes with ER-associated degradation of unstable and misfolded glycoproteins.

Satoshi Ninagawa, Masaki Matsuo, Deng Ying, Shuichiro Oshita, Shinya Aso, Kazutoshi Matsushita, Mai Taniguchi, Akane Fueki, Moe Yamashiro, Kaoru Sugasawa, Shunsuke Saito, Koshi Imami, Yasuhiko Kizuka, Tetsushi Sakuma, Takashi Yamamoto, Hirokazu Yagi, Koichi Kato, Kazutoshi Mori.

How the fate (folding versus degradation) of glycoproteins is determined in the endoplasmic reticulum (ER) is an intriguing question. Monoglucosylated glycoproteins are recognized by lectin chaperones to facilitate their folding, whereas glycoproteins exposing well-trimmed mannoses are subjected to glycoprotein ER-associated degradation (gpERAD); we have elucidated how mannoses are sequentially trimmed by EDEM family members (George et al., 2020; 2021 eLife). Although reglucosylation by UGGT was previously reported to have no effect on substrate degradation, here we directly tested this notion using cells with genetically disrupted UGGT1/2. Strikingly, the results showed that UGGT1 delayed the degradation of misfolded substrates and unstable glycoproteins including ATF6α. An experiment with a point mutant of UGGT1 indicated that the glucosylation activity of UGGT1 was required for the inhibition of early glycoprotein degradation. These and overexpression-based competition experiments suggested that the fate of glycoproteins is determined by a tug-of-war between structure formation by UGGT1 and degradation by EDEMs. We further demonstrated the physiological importance of UGGT1, since ATF6α cannot function properly without UGGT1. Thus, our work strongly suggests that UGGT1 is a central factor in ER protein quality control via the regulation of both glycoprotein folding and degradation.

Keywords: EDEM; ER protein quality control; UGGT1; cell biology; human; protein degradation; protein folding

DOI: https://doi.org/10.7554/eLife.93117

bioRxiv. 2024 Nov 28. pii: 2024.11.27.625751. [Epub ahead of print]

Loss of FIC-1-mediated AMPylation activates the UPR ER and upregulates cytosolic HSP70 chaperones to suppress polyglutamine toxicity.

Kate M Van Pelt, Matthias C Truttmann.

Targeted regulation of cellular proteostasis machinery represents a promising strategy for the attenuation of pathological protein aggregation. Recent work suggests that the unfolded protein response in the endoplasmic reticulum (UPR ER ) directly regulates the aggregation and toxicity of expanded polyglutamine (polyQ) proteins. However, the mechanisms underlying this phenomenon remain poorly understood. In this study, we report that perturbing ER homeostasis in Caenorhabditis elegans through the depletion of either BiP ortholog, hsp-3 or hsp-4, causes developmental arrest in worms expressing aggregation-prone polyQ proteins. This phenotype is rescued by the genetic deletion of the conserved UPR ER regulator, FIC-1. We demonstrate that the beneficial effects of fic-1 knock-out (KO) extend into adulthood, where the loss of FIC-1-mediated protein AMPylation in polyQ-expressing animals is sufficient to prevent declines in fitness and lifespan. We further show that loss of hsp-3 and hsp-4 leads to distinct, but complementary transcriptomic responses to ER stress involving all three UPR ER stress sensors (IRE-1, PEK-1, and ATF-6). We identify the cytosolic HSP70 family chaperone F44E5.4 , whose expression is increased in fic-1 -deficient animals upon ER dysregulation, as a key effector suppressing polyQ toxicity. Over-expression of F44E5.4 , but not other HSP70 family chaperones, is sufficient to rescue developmental arrest in polyQ-expressing embryos upon hsp-3 knock-down. Finally, we show that knock-down of ire-1 , pek-1 , or atf-6 blocks the upregulation of F44E5.4 in fic-1 -deficient worms. Taken together, our findings support a model in which the loss of FIC-1-mediated AMPylation engages UPR ER signaling to upregulate cytosolic chaperone activity in response to polyQ toxicity.

DOI: https://doi.org/10.1101/2024.11.27.625751

Protein Sci. 2025 Jan;34(1): e5255

Ordered ATP hydrolysis in the Hsp90 chaperone is regulated by Aha1 and a conserved post-translational modification.

Desmond Prah Amoah, Solomon K Hussein, Jill L Johnson, Paul LaPointe.

Hsp90 is a dimeric molecular chaperone that is important for the folding, stabilization, activation, and maturation of hundreds of protein substrates called "clients" in cells. Dozens of co-chaperones and hundreds of post-translational modifications (PTMs) regulate the ATP-dependent client activation cycle. The Aha1 co-chaperone is the most potent stimulator of the ATPase cycle of Hsp90 and phosphorylation of threonine 22 in Hsp90 can regulate the recruitment of Aha1 in cells. We report here that phosphorylation of threonine 22 regulates specific aspects of Aha1 function after recruitment occurs. The phosphomimetic substitution, T22E, neutralizes the action of the Aha1 NxNNWHW motif. Moreover, this substitution can exert this effect from only one protomer of the Hsp90 dimer. This work sheds light on how asymmetric modifications in the Hsp90 dimer can functionalize individual protomers and fine-tune the Hsp90 cycle.

Keywords: ATPase; Aha1; Hsp90; chaperones; protein folding; yeast genetics

DOI: https://doi.org/10.1002/pro.5255

Bioessays. 2024 Dec 12. e202300158

Circadian Control of Protein Synthesis.

Nathan R James, John S O'Neill.

Daily rhythms in the rate and specificity of protein synthesis occur in most mammalian cells through an interaction between cell-autonomous circadian regulation and daily cycles of systemic cues. However, the overall protein content of a typical cell changes little over 24 h. For most proteins, translation appears to be coordinated with protein degradation, producing phases of proteomic renewal that maximize energy efficiency while broadly maintaining proteostasis across the solar cycle. We propose that a major function of this temporal compartmentalization-and of circadian rhythmicity in general-is to optimize the energy efficiency of protein synthesis and associated processes such as complex assembly. We further propose that much of this temporal compartmentalization is achieved at the level of translational initiation, such that the translational machinery alternates between distinct translational mechanisms, each using a distinct toolkit of phosphoproteins to preferentially recognize and translate different classes of mRNA.

Keywords: biphasic model; circadian rhythms; protein synthesis; temporal compartmentalization; translational initiation

DOI: https://doi.org/10.1002/bies.202300158

Eur J Pharmacol. 2024 Dec 05. pii: S0014-2999(24)00877-X. [Epub ahead of print] 177187

Therapeutic targeting of the oxidative stress generated by pathological molecular pathways in the neurodegenerative diseases, ALS and Huntington's.

Akarsh Bajpai, Vidhya Bharathi, Basant K Patel.

Neurodegenerative disorders are characterized by a progressive decline of specific neuronal populations in the brain and spinal cord, typically containing aggregates of one or more proteins. They can result in behavioral alterations, memory loss and a decline in cognitive and motor abilities. Various pathways and mechanisms have been outlined for the potential treatment of these diseases, where redox regulation is considered as one of the most common druggable targets. For example, in amyotrophic lateral sclerosis (ALS) with superoxide dismutase-1 (SOD1) pathology, there is a downregulation of the antioxidant response nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. TDP-43 proteinopathy in ALS is associated with elevated levels of reactive oxygen species and mitochondrial dyshomeostasis. In ALS with mutant FUS, poly ADP ribose polymerase-dependent X ray repair cross complementing 1/DNA-ligase recruitment to the sites of oxidative DNA damage is affected, thereby causing defects in DNA damage repair. Oxidative stress in Huntington's disease (HD) with mutant huntingtin accumulation manifests as protein oxidation, metabolic energetics dysfunction, metal ion dyshomeostasis, DNA damage and mitochondrial dysfunction. The impact of oxidative stress in the progression of these diseases further warrants studies into the role of antioxidants in their treatment. While an antioxidant, edaravone, has been approved for therapeutics of ALS, numerous antioxidant molecules failed to pass the clinical trials despite promising initial studies. In this review, we summarize the oxidative stress pathways and redox modulators that are investigated in ALS and HD using various models.

Keywords: Amyotrophic lateral sclerosis; Huntington's disease; Oxidative stress; ROS; mitochondria

DOI: https://doi.org/10.1016/j.ejphar.2024.177187