Temporal control of acute protein aggregate turnover by UBE3C and NRF1-dependent proteasomal pathways.

A hallmark of neurodegenerative diseases is the progressive loss of proteostasis, leading to the accumulation of misfolded proteins or protein aggregates, with subsequent cytotoxicity. To combat this toxicity, cells have evolved degradation pathways (ubiquitin-proteasome system and autophagy) that detect and degrade misfolded proteins. However, studying the underlying cellular pathways and mechanisms has remained a challenge, as formation of many types of protein aggregates is asynchronous, with individual cells displaying distinct kinetics, thereby hindering rigorous time-course studies. Here, we merge a kinetically tractable and synchronous agDD-GFP system for aggregate formation with targeted gene knockdowns, to uncover degradation mechanisms used in response to acute aggregate formation. We find that agDD-GFP forms amorphous aggregates by cryo-electron tomography at both early and late stages of aggregate formation. Aggregate turnover occurs in a proteasome-dependent mechanism in a manner that is dictated by cellular aggregate burden, with no evidence of the involvement of autophagy. Lower levels of misfolded agDD-GFP, enriched in oligomers, utilizes UBE3C-dependent proteasomal degradation in a pathway that is independent of RPN13 ubiquitylation by UBE3C. Higher aggregate burden activates the NRF1 transcription factor to increase proteasome subunit transcription, and subsequent degradation capacity of cells. Loss or gain of NRF1 function alters the turnover of agDD-GFP under conditions of high aggregate burden. Together, these results define the role of UBE3C in degradation of this class of misfolded aggregation-prone proteins and reveals a role for NRF1 in proteostasis control in response to widespread protein aggregation.

Drug Utilization Review of Monitored Parenteral Antimicrobials in a Tertiary Care Private Hospital in Cebu City.

Background: Based on the 2017-2020 annual report of the Department of Health-Antimicrobial Resistance Surveillance Program, significant resistance patterns have been observed for common disease-causing pathogens. In the hospital setting, antimicrobial stewardship programs have been implemented to optimize the use of antimicrobials. Drug utilization review studies provide essential feedback to improve prescribing and use of medications. Objectives: This study aimed to review drug utilization of monitored parenteral antimicrobials among patients admitted from January to December 2019. Methods: The study employed a retrospective, cross-sectional, descriptive research design. A retrospective chart review of drugs administered to patients was conducted. Results: A total of 821 patients charts met the inclusion criteria. The patients' ages ranged from 18 to 98 years old and 52% were females. General Internal Medicine practitioners (28%) were the top prescribers of monitored parenteral antimicrobials primarily for the management of moderate-risk community-acquired pneumonia (39%). They were mostly indicated for empirical treatment of infections (94%) and were given for an average of 5.73 days.Only 58% of the total cases had orders for culture and sensitivity testing. Of which, principally 47% had colony cultures. Blood (29%) and sputum (27%) were the most common specimens taken for culture and sensitivity testing. The microorganisms often isolated were Escherichia coli (19%), Klebsiella pneumoniae (18%), and Staphylococcus aureus (9%). In addition, extended-spectrum beta lactamase-producing gram-negative pathogens (4%) and methicillin-resistant S. aureus (1%) were also isolated. All the microorganisms isolated showed most resistance to ampicillin (81%) and most susceptibility to colistin (100%). There were drug therapy-related problems encountered. There was one case of an adverse drug reaction (0.1%) and two cases of contraindications (0.2%). Therapeutic duplication was also observed in 5% of the cases. Moreover, 39% had instances of drug-drug interactions.Piperacillin-tazobactam had the highest consumption (79.50 defined daily doses/1,000-patient days) among the monitored parenteral antimicrobials.Some prescriptions were deemed inappropriate upon evaluation. 12% of cases were inappropriate based on the justification indicator. As for the critical indicators, duration of therapy (78%) was the main reason. Only four components of the DUE criteria indicators have met or exceeded the established threshold level.The cost analysis indicated that the total actual cost of therapy with the monitored parenteral antimicrobials amounted to ₱17,645,601.73. Considering Department of Health National Antibiotic Guidelines recommendations, ideal total cost of treatment was ₱14,917,214.29. Potential cumulative cost savings of ₱2,728,387.44 could have been achieved for patients admitted last 2019. Conclusion: Consumption of piperacillin-tazobactam was relatively high as compared to the other monitored parenteral antimicrobials covered in this study. Physicians at the study site seldom prescribe monitored parenteral antimicrobials as recommended by the National Antibiotic Guidelines. This is evidenced in the incidence of inappropriate therapy regimens, with inapt duration of therapy as the leading explanation.From the patient's perspective, the main economic implication was on the direct medical costs, particularly the increased cost of the actual antimicrobial therapy prescribed to manage various infections. Adherence of physicians to the established guidelines and selection of the most cost-effective therapy could have resulted in considerable cost savings.

Microplastics in Hong Kong's marine waters: Impact of rainfall and Pearl River discharge.

This study provided a systematic investigation of microplastics in Hong Kong's surface marine waters during the pandemic from 2019 to 2021. Microplastics (2.07 ± 4.00 particles/m3) exhibited significant temporal variations with higher abundance in the wet season, without a consistent trend after the mandatory mask-wearing requirement was announced. The impact of pandemic restrictions on microplastic distribution was found to be relatively minor. However, significant correlations between microplastic abundances and rainfall highlighted the substantial contribution of local emissions through surface runoff. Notably, sites in closer proximity to the Pearl River Delta exhibited higher microplastic abundances, indicating their association with emission sources. The influence of rainfall and adverse weather on marine microplastic loads demonstrated different sensitivities among various locations but can generally last for one month. These results revealed the impact of seasonal rainfall on coastal microplastics and emphasized the need for efforts to reduce microplastic discharge from land-based sources.

Pain Assessment Following Opioid Administration in Aneurysmal Subarachnoid Hemorrhage Associated Headache.

Background: Headache is a debilitating complication following an aneurysmal subarachnoid hemorrhage (aSAH). Despite its impact on morbidity and quality of life, limited evidence characterizes the effectiveness of opioids. Objective: The aim of this study was to evaluate opioid associated reduction in pain scores in patients with aSAH-associated headache. Methods: This is a retrospective study of adult patients with an aSAH, Hunt and Hess grades I - III, admitted to a neurosciences intensive care unit. Descriptive and inferential statistics were used to characterize headache treatment strategies and opioid associated reduction in pain scores. Results: Opioids were used in up to 97.6% of patients for the management of aSAH-associated headache. Median reduction in pain after opioid administration was -1 (IQR: -3-0). Correlation between opioid dose and change in pain scores was negligible (rs = .01). Overall, 68.8% of patients were discharged on an opioid analgesic with predictive factors being severe headache (OR 2.52; 1.04 - 6.14) and oral morphine milligram equivalents ≥60 mg per day during the hospital stay (OR 3.02; 1.22 - 7.47). Conclusions: Opioids were associated with a small reduction in pain when assessed via the NRS. An increased opioid dose did not correlate with a greater reduction in assessed pain scores. A high percentage of patients remained on opioids throughout hospitalization and were eventually discharged on an opioid. The impact of discharge opioid prescriptions and risk of opioid persistence creates a cause for concern. It is imperative that we seek improved pain management strategies for aSAH-associated headache.

Tools of clinical Photodynamic Therapy (PDT): A Mini Compendium.

Unlike surgical instruments and endoscopic equipment, Photodynamic Therapy (PDT) devices are not readily available or accessible to the clinicians who may like to add this form of treatment modality for selected patients and on an ad hock basis. There is in fact a vacuum in finding the "tools" of PDT for those clinicians who are not part of a "Centre" with a built-in knowledge base and contacts for manufacturers. In this compendium the Yorkshire Laser Centre /YLC in the UK, (the Project of the Moghissi Laser Trust - (Charity number 326689) requested three experienced clinicians (RA, ZH, KM) to produce essential information on the use of and equipment for PDT in the clinic. The YLC also sponsored a researcher (ID) to search and compile a detailed but non-exhaustive list of approved photosensitizing agents, pharmaceutical companies, light sources and laser manufacturers with appropriate delivery devices for PDT. Thus, this Mini -Compendium is the end result of what is hoped to be a useful adjunct for practitioners, scientists and students of PDT.

The herpesvirus UL49.5 protein hijacks a cellular C-degron pathway to drive TAP transporter degradation.

The transporter associated with antigen processing (TAP) is a key player in the major histocompatibility class I-restricted antigen presentation and an attractive target for immune evasion by viruses. Bovine herpesvirus 1 impairs TAP-dependent antigenic peptide transport through a two-pronged mechanism in which binding of the UL49.5 gene product to TAP both inhibits peptide transport and triggers its proteasomal degradation. How UL49.5 promotes TAP degradation has, so far, remained unknown. Here, we use high-content siRNA and genome-wide CRISPR-Cas9 screening to identify CLR2KLHDC3 as the E3 ligase responsible for UL49.5-triggered TAP disposal. We propose that the C terminus of UL49.5 mimics a C-end rule degron that recruits the E3 to TAP and engages the cullin-RING E3 ligase in endoplasmic reticulum-associated degradation.

UFM1 E3 ligase promotes recycling of 60S ribosomal subunits from the ER.

Reversible modification of target proteins by ubiquitin and ubiquitin-like proteins (UBLs) is widely used by eukaryotic cells to control protein fate and cell behaviour1. UFM1 is a UBL that predominantly modifies a single lysine residue on a single ribosomal protein, uL24 (also called RPL26), on ribosomes at the cytoplasmic surface of the endoplasmic reticulum (ER)2,3. UFM1 conjugation (UFMylation) facilitates the rescue of 60S ribosomal subunits (60S) that are released after ribosome-associated quality-control-mediated splitting of ribosomes that stall during co-translational translocation of secretory proteins into the ER3,4. Neither the molecular mechanism by which the UFMylation machinery achieves such precise target selection nor how this ribosomal modification promotes 60S rescue is known. Here we show that ribosome UFMylation in vivo occurs on free 60S and we present sequential cryo-electron microscopy snapshots of the heterotrimeric UFM1 E3 ligase (E3(UFM1)) engaging its substrate uL24. E3(UFM1) binds the L1 stalk, empty transfer RNA-binding sites and the peptidyl transferase centre through carboxy-terminal domains of UFL1, which results in uL24 modification more than 150 Å away. After catalysing UFM1 transfer, E3(UFM1) remains stably bound to its product, UFMylated 60S, forming a C-shaped clamp that extends all the way around the 60S from the transfer RNA-binding sites to the polypeptide tunnel exit. Our structural and biochemical analyses suggest a role for E3(UFM1) in post-termination release and recycling of the large ribosomal subunit from the ER membrane.

Small-molecule correctors divert CFTR-F508del from ERAD by stabilizing sequential folding states.

Over 80% of people with cystic fibrosis (CF) carry the F508del mutation in the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride ion channel at the apical plasma membrane (PM) of epithelial cells. F508del impairs CFTR folding causing it to be destroyed by endoplasmic reticulum associated degradation (ERAD). Small-molecule correctors, which act as pharmacological chaperones to divert CFTR-F508del from ERAD, are the primary strategy for treating CF, yet corrector development continues with only a rudimentary understanding of how ERAD targets CFTR-F508del. We conducted genome-wide CRISPR/Cas9 knockout screens to systematically identify the molecular machinery that underlies CFTR-F508del ERAD. Although the ER-resident ubiquitin ligase, RNF5 was the top E3 hit, knocking out RNF5 only modestly reduced CFTR-F508del degradation. Sublibrary screens in an RNF5 knockout background identified RNF185 as a redundant ligase and demonstrated that CFTR-F508del ERAD is robust. Gene-drug interaction experiments illustrated that correctors tezacaftor (VX-661) and elexacaftor (VX-445) stabilize sequential, RNF5-resistant folding states. We propose that binding of correctors to nascent CFTR-F508del alters its folding landscape by stabilizing folding states that are not substrates for RNF5-mediated ubiquitylation.

Drug utilization review of monitored parenteral antimicrobials in a Tertiary Care Private Hospital in Cebu City

Background@#Based on the 2017-2020 annual report of the Department of Health-Antimicrobial Resistance Surveillance Program, significant resistance patterns have been observed for common disease-causing pathogens. In the hospital setting, antimicrobial stewardship programs have been implemented to optimize the use of antimicrobials. Drug utilization review studies provide essential feedback to improve prescribing and use of medications.@*Objectives@#This study aimed to review drug utilization of monitored parenteral antimicrobials among patients admitted from January to December 2019.@*Methods@#The study employed a retrospective, cross-sectional, descriptive research design. A retrospective chart review of drugs administered to patients was conducted.@*@#Results. A total of 821 patients charts met the inclusion criteria. The patients’ ages ranged from 18 to 98 years old and 52% were females. General Internal Medicine practitioners (28%) were the top prescribers of monitored parenteral antimicrobials primarily for the management of moderate-risk community-acquired pneumonia (39%). They were mostly indicated for empirical treatment of infections (94%) and were given for an average of 5.73 days. Only 58% of the total cases had orders for culture and sensitivity testing. Of which, principally 47% had colony cultures. Blood (29%) and sputum (27%) were the most common specimens taken for culture and sensitivity testing. The microorganisms often isolated were Escherichia coli (19%), Klebsiella pneumoniae (18%), and Staphylococcus aureus (9%). In addition, extended-spectrum beta lactamase-producing gram-negative pathogens (4%) and methicillin-resistant S. aureus (1%) were also isolated. All the microorganisms isolated showed most resistance to ampicillin (81%) and most susceptibility to colistin (100%). There were drug therapy-related problems encountered. There was one case of an adverse drug reaction (0.1%) and two cases of contraindications (0.2%). Therapeutic duplication was also observed in 5% of the cases. Moreover, 39% had instances of drug-drug interactions.Piperacillin-tazobactam had the highest consumption (79.50 defined daily doses/1,000-patient days) among the monitored parenteral antimicrobials. Some prescriptions were deemed inappropriate upon evaluation. 12% of cases were inappropriate based on the justification indicator. As for the critical indicators, duration of therapy (78%) was the main reason. Only four components of the DUE criteria indicators have met or exceeded the established threshold level.The cost analysis indicated that the total actual cost of therapy with the monitored parenteral antimicrobials amounted to ₱17,645,601.73. Considering Department of Health National Antibiotic Guidelines recommenda-tions, ideal total cost of treatment was ₱14,917,214.29. Potential cumulative cost savings of ₱2,728,387.44 could have been achieved for patients admitted last 2019.@*Conclusion@#Consumption of piperacillin-tazobactam was relatively high as compared to the other monitored parenteral antimicrobials covered in this study. Physicians at the study site seldom prescribe monitored parenteral antimicrobials as recommended by the National Antibiotic Guidelines. This is evidenced in the incidence of inappropriate therapy regimens, with inapt duration of therapy as the leading explanation.From the patient’s perspective, the main economic implication was on the direct medical costs, particularly the increased cost of the actual antimicrobial therapy prescribed to manage various infections. Adherence of physicians to the established guidelines and selection of the most cost-effective therapy could have resulted in considerable cost savings.

Safety and efficacy of fixed versus variable-dose prothrombin complex concentrate for emergent reversal of vitamin K antagonists: A systematic review and meta-analysis.

STUDY OBJECTIVE: Four-factor prothrombin complex concentrate (4F-PCC) is standard of care for emergent vitamin K antagonist (VKA) reversal but optimal dosing is uncertain. This meta-analysis estimated the proportion of patients treated with fixed dose (FD) 4F-PCC who achieved adequate reversal and compared safety and efficacy of FD versus weight-based dose (WB) strategies. METHODS: This review was conducted according to PRISMA guidelines. Medline and Scopus were searched and included studies evaluating FD regimens and comparing FD and WB for emergent VKA reversal. Data was pooled using random effects. Subgroup analyses examined heterogeneity. Risk of bias was assessed with Newcastle-Ottawa Scale and RoB2 score. RESULTS: Twenty-three studies (n = 2055) were included with twelve (n = 1143) comparing FD versus WB. The proportion of patients achieving goal INR with FD varied depending on the INR target, being significantly higher for INR <2 (90.9%, 95% Confidence Interval (CI) 87.2, 94.06) compared to INR <1.6 (70.97%, 95%CI 65.33, 76.31). Compared to WB, FD was less likely to achieve a goal INR <1.6 (Risk Difference (RD) -13%, 95% CI -21, -4) but achieved similar reversal for a goal INR <2.0, (RD -1%, 95%CI -7, 4). There was no difference in hospital mortality (RD 4%, 95%CI -2, 9) or thrombosis (RD 0.0%, 95%CI -3, 3). CONCLUSION: FD VKA reversal was associated with significantly lower attainment of goal INR compared to WB with lower INR targets. This did not translate to differences in hospital mortality, but these results should be interpreted cautiously in light of the observational nature of the included studies.

The herpesvirus UL49.5 protein hijacks a cellular C-degron pathway to drive TAP transporter degradation.

The transporter associated with antigen processing (TAP) is a key player in the MHC class I-restricted antigen presentation and an attractive target for immune evasion by viruses. Bovine herpesvirus 1 (BoHV-1) impairs TAP-dependent antigenic peptide transport through a two-pronged mechanism in which binding of the UL49.5 gene product to TAP both inhibits peptide transport and promotes its proteasomal degradation. How UL49.5 promotes TAP degradation is unknown. Here, we use high-content siRNA and genome-wide CRISPR-Cas9 screening to identify CLR2KLHDC3 as the E3 ligase responsible for UL49.5-triggered TAP disposal in human cells. We propose that the C-terminus of UL49.5 mimics a C-end rule degron that recruits the E3 to TAP and engages the CRL2 E3 in ER-associated degradation.

Evaluating SWAG and Its Validity When Compared to 3D Imagery of Secondarily Grafted Cleft Sites.

OBJECTIVE: To test validity of 2D Standardized Way to Assess Grafts (SWAG) ratings to assess 3D outcomes of bone grafting (ABG). PATIENTS: 43 patients (34 UCLP, 9 BCLP) with non-syndromic complete clefts, bone-grafted at mean age 9yrs/3mos, with available post-graft occlusal radiographs and cone beam computed tomography (CBCT) (taken mean 4yrs/9mos post-ABG). MAIN OUTCOME MEASURES: 2D occlusal radiographs rated twice using SWAG by 6 calibrated raters. 12 scores were averaged and converted to a percentage reflecting bone-fill. Weighted Kappas were assessed for SWAG reliability. 3D cleft-site bone volume was calculated by 1 rater using ITK-SNAP. 13 cleft sites were re-measured by the 'one rater' for 3D reliability using Intraclass Correlation Coefficient (ICC). 2D versus 3D ratings were compared using paired t-test, independent samples t-test, Bland-Altman and Linear Regression. Significance level was P = .5. RESULTS: 2D reliability was 0.724 (intra-rater) and 0.546 (inter-rater). 3D reliability was 0.986. Bland-Altman plot comparing 2D vs 3D showed for 45 of 47 graft-sites were within 2 SD's. Mean % bone-fill was 64.11% with 2D and 69.06% with 3D (mean difference = 4.95%) that was a non-significant difference in both t-tests. Regression showed a statistically significant relation between the two methods (r2 = 0.46; P = .0001). CONCLUSION: 2D SWAG systematically and non-significantly underestimated bone-fill. There was a significant correlation between 2D/3D methods. Bland-Altman analysis illustrated the similarity of the two methods. For comparisons of group (cleft treatment Centers') bone grafting outcomes, the 2D method may suffice as a proxy for the 3D method. However, with individual variation up to 40% in 2D estimates of actual 3D volume, 2D SWAG method cannot be used in place of 3D images.

Region-specific changes in brain activity and memory after continuous positive airway pressure therapy in obstructive sleep apnea: a pilot high-density electroencephalography study.

STUDY OBJECTIVES: Limited channel electroencephalography (EEG) investigations in obstructive sleep apnea (OSA) have revealed deficits in slow wave activity (SWA) and spindles during sleep and increased EEG slowing during resting wakefulness. High-density EEG (Hd-EEG) has also detected local parietal deficits in SWA (delta power) during NREM. It is unclear whether effective continuous positive airway pressure (CPAP) treatment reverses regional SWA deficits, and other regional sleep and wake EEG abnormalities, and whether any recovery relates to improved overnight memory consolidation. METHODS: A clinical sample of men with moderate-severe OSA underwent sleep and resting wake recordings with 256-channel Hd-EEG before and after 3 months of CPAP. Declarative and procedural memory tasks were administered pre- and post-sleep. Topographical spectral power maps and differences between baseline and treatment were compared using t-tests and statistical nonparametric mapping (SnPM). RESULTS: In 11 compliant CPAP users (5.2 ±â€…1.1 hours/night), total sleep time did not differ after CPAP but N1 and N2 sleep were lower and N3 was higher. Centro-parietal gamma power during N3 increased and fronto-central slow spindle activity during N2 decreased (SnPM < 0.05). No other significant differences in EEG power were observed. When averaged specifically within the parietal region, N3 delta power increased after CPAP (p = 0.0029) and was correlated with the change in overnight procedural memory consolidation (rho = 0.79, p = 0.03). During resting wakefulness, there were trends for reduced delta and theta power. CONCLUSIONS: Effective CPAP treatment of OSA may correct regional EEG abnormalities, and regional recovery of SWA may relate to procedural memory improvements in the short term.

Small molecule correctors divert CFTR-F508del from ERAD by stabilizing sequential folding states.

Over 80% of people with cystic fibrosis (CF) carry the F508del mutation in the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride ion channel at the apical plasma membrane (PM) of epithelial cells. F508del impairs CFTR folding causing it to be destroyed by endoplasmic reticulum associated degradation (ERAD). Small molecule correctors, which act as pharmacological chaperones to divert CFTR-F508del from ERAD, are the primary strategy for treating CF, yet corrector development continues with only a rudimentary understanding of how ERAD targets CFTR-F508del. We conducted genome-wide CRISPR/Cas9 knockout screens to systematically identify the molecular machinery that underlies CFTR-F508del ERAD. Although the ER-resident ubiquitin ligase, RNF5 was the top E3 hit, knocking out RNF5 only modestly reduced CFTR-F508del degradation. Sublibrary screens in an RNF5 knockout background identified RNF185 as a redundant ligase, demonstrating that CFTR-F508del ERAD is highly buffered. Gene-drug interaction experiments demonstrated that correctors tezacaftor (VX-661) and elexacaftor (VX-445) stabilize sequential, RNF5-resistant folding states. We propose that binding of correctors to nascent CFTR-F508del alters its folding landscape by stabilizing folding states that are not substrates for RNF5-mediated ubiquitylation.

Parallel CRISPR-Cas9 screens identify mechanisms of PLIN2 and lipid droplet regulation.

Despite the key roles of perilipin-2 (PLIN2) in governing lipid droplet (LD) metabolism, the mechanisms that regulate PLIN2 levels remain incompletely understood. Here, we leverage a set of genome-edited human PLIN2 reporter cell lines in a series of CRISPR-Cas9 loss-of-function screens, identifying genetic modifiers that influence PLIN2 expression and post-translational stability under different metabolic conditions and in different cell types. These regulators include canonical genes that control lipid metabolism as well as genes involved in ubiquitination, transcription, and mitochondrial function. We further demonstrate a role for the E3 ligase MARCH6 in regulating triacylglycerol biosynthesis, thereby influencing LD abundance and PLIN2 stability. Finally, our CRISPR screens and several published screens provide the foundation for CRISPRlipid (http://crisprlipid.org), an online data commons for lipid-related functional genomics data. Our study identifies mechanisms of PLIN2 and LD regulation and provides an extensive resource for the exploration of LD biology and lipid metabolism.

Rapid evolutionary repair by secondary perturbation of a primary disrupted transcriptional network.

The discrete steps of transcriptional rewiring have been proposed to occur neutrally to ensure steady gene expression under stabilizing selection. A conflict-free switch of a regulon between regulators may require an immediate compensatory evolution to minimize deleterious effects. Here, we perform an evolutionary repair experiment on the Lachancea kluyveri yeast sef1Δ mutant using a suppressor development strategy. Complete loss of SEF1 forces cells to initiate a compensatory process for the pleiotropic defects arising from misexpression of TCA cycle genes. Using different selective conditions, we identify two adaptive loss-of-function mutations of IRA1 and AZF1. Subsequent analyses show that Azf1 is a weak transcriptional activator regulated by the Ras1-PKA pathway. Azf1 loss-of-function triggers extensive gene expression changes responsible for compensatory, beneficial, and trade-off phenotypes. The trade-offs can be alleviated by higher cell density. Our results not only indicate that secondary transcriptional perturbation provides rapid and adaptive mechanisms potentially stabilizing the initial stage of transcriptional rewiring but also suggest how genetic polymorphisms of pleiotropic mutations could be maintained in the population.

RPL26/uL24 UFMylation is essential for ribosome-associated quality control at the endoplasmic reticulum.

Ribosomes that stall while translating cytosolic proteins are incapacitated by incomplete nascent chains, termed "arrest peptides" (APs) that are destroyed by the ubiquitin proteasome system (UPS) via a process known as the ribosome-associated quality control (RQC) pathway. By contrast, APs on ribosomes that stall while translocating secretory proteins into the endoplasmic reticulum (ER-APs) are shielded from cytosol by the ER membrane and the tightly sealed ribosome-translocon junction (RTJ). How this junction is breached to enable access of cytosolic UPS machinery and 26S proteasomes to translocon- and ribosome-obstructing ER-APs is not known. Here, we show that UPS and RQC-dependent degradation of ER-APs strictly requires conjugation of the ubiquitin-like (Ubl) protein UFM1 to 60S ribosomal subunits at the RTJ. Therefore, UFMylation of translocon-bound 60S subunits modulates the RTJ to promote access of proteasomes and RQC machinery to ER-APs.

RPL26/uL24 UFMylation is essential for ribosome-associated quality control at the endoplasmic reticulum.

Ribosomes that stall while translating cytosolic proteins are incapacitated by incomplete nascent chains, termed "arrest peptides" (APs) that are destroyed by the ubiquitin proteasome system (UPS) via a process known as the ribosome-associated quality control (RQC) pathway. By contrast, APs on ribosomes that stall while translocating secretory proteins into the endoplasmic reticulum (ER-APs) are shielded from cytosol by the ER membrane and the tightly sealed ribosome-translocon junction (RTJ). How this junction is breached to enable access of cytosolic UPS machinery and 26S proteasomes to translocon- and ribosome-obstructing ER-APs is not known. Here, we show that UPS and RQC-dependent degradation of ER-APs strictly requires conjugation of the ubiquitin-like (Ubl) protein UFM1 to 60S ribosomal subunits at the RTJ. Therefore, UFMylation of translocon-bound 60S subunits modulates the RTJ to promote access of proteasomes and RQC machinery to ER-APs. Significance Statement: UFM1 is a ubiquitin-like protein that is selectively conjugated to the large (60S) subunit of ribosomes bound to the endoplasmic reticulum (ER), but the specific biological function of this modification is unclear. Here, we show that UFMylation facilitates proteasome-mediated degradation of arrest polypeptides (APs) which are generated following splitting of ribosomes that stall during co-translational translocation of secretory proteins into the ER. We propose that UFMylation weakens the tightly sealed ribosome-translocon junction, thereby allowing the cytosolic ubiquitin-proteasome and ribosome-associated quality control machineries to access ER-APs.