Disassembly of exon junction complexes by PYM.

Exon junction complexes (EJCs) are deposited onto mRNAs during splicing, serve as positional landmarks for the intron exon structure of genes, and direct posttranscriptional processes in the cytoplasm. EJC removal and recycling by translation are ill understood and have been attributed to ribosomal passage. This work identifies the ribosome-associated protein PYM as an EJC disassembly factor and defines its mechanism of function. Whereas EJC assembly intermediates are resistant to PYM, fully assembled EJCs are dissociated from spliced mRNAs by PYM. This disassembly involves PYM binding to the EJC proteins MAGOH-Y14. PYM overexpression in cells disrupts EJC association with spliced mRNA and inhibits nonsense-mediated mRNA decay. In cells depleted of PYM, EJCs accumulate on spliced mRNAs and EJC protein recycling is impaired. Hence, PYM is an EJC disassembly factor that acts both in vitro and in living cells, and that antagonizes important EJC functions.

Incidence, characteristics and predictors of mortality following cardiac arrest in ICUs of a German university hospital: A retrospective cohort study.

BACKGROUND: Cardiac arrest in intensive care is a rarely studied type of in-hospital cardiac arrest. OBJECTIVE: This study examines the incidence, characteristics, risk factors for mortality as well as long-term prognosis following cardiac arrest in intensive care. DESIGN: Retrospective cohort study. SETTING: Five noncardiac surgical ICUs (41 surgical and 37 medical beds) at a German university hospital between 2016 and 2019. PATIENTS: Adults experiencing cardiac arrest defined as the need for chest compressions and/or defibrillation occurring for the first time on the ICU. MAIN OUTCOME MEASURES: Primary endpoint: occurrence of cardiac-arrest in the ICU. Secondary endpoints: diagnostic and therapeutic measures; risk factors and marginal probabilities of no-return of spontaneous circulation; rates of return of spontaneous circulation, hospital discharge, 1-year-survival and 1-year-neurological outcome. RESULTS: A total of 114 cardiac arrests were observed out of 14 264 ICU admissions; incidence 0.8%; 95% confidence interval (CI) 0.7 to 1.0; 45.6% received at least one additional diagnostic test, such as blood gas analysis (36%), echocardiography (19.3%) or chest x-ray (9.9%) with a resulting change in therapy in 52%, (more frequently in those with a return of spontaneous circulation vs none, P  = 0.023). Risk factors for no-return of spontaneous circulation were cardiac comorbidities (OR 5.4; 95% CI, 1.4 to 20.7) and continuous renal replacement therapy (OR 5.9; 95% CI, 1.7 to 20.8). Bicarbonate levels greater than 21 mmol 1 were associated with a higher mortality risk in combination either with cardiac comorbid-ities (bicarbonate <21 mmol I-1: 13%; 21 to 26 mmolI-1 45%; >26mmolI-1:42%)orwithaSOFA at least 2 (bicarbonate <21 mmolI-1 8%; 21 to 26 mmolI-1: 40%; >26mmolI-1: 37%). "In-hospital mortality was 78.1% (n = 89); 1-year-survival-rate was 10.5% (95% CI, 5.5 to 17.7) and survival with a good neurological outcome was 6.1% (95% CI, 2.5 to 12.2). CONCLUSION: Cardiac arrest in ICU is a rare complication with a high mortality and low rate of good neurological outcome. The development of a structured approach to resuscitation should include all available resources of an ICU and adequately consider the complete diagnostic and therapeutic spectra as our results indicate that these are still underused. The development of prediction models of death should take into account cardiac and hepatic comorbidities, continuous renal replacement therapy, SOFA at least 2 before cardiac arrest and bicarbonate level. Further research should concentrate on identifying early predictors and on the prevention of cardiac arrest in ICU.

A comparison of Simplified Acute Physiology Score II and Sepsis-related Organ Failure Assessment Score for prediction of mortality after Intensive Care Unit cardiac arrest.

BACKGROUND: This study investigates the predictive value and suitable cutoff values of the Sepsis-related Organ Failure Assessment Score (SOFA) and Simplified Acute Physiology Score II (SAPS-II) to predict mortality during or after Intensive Care Unit Cardiac Arrest (ICU-CA). METHODS: In this secondary analysis the ICU database of a German university hospital with five ICU was screened for all ICU-CA between 2016-2019. SOFA and SAPS-II were used for prediction of mortality during ICU-CA, hospital-stay and one-year-mortality. Receiver operating characteristic curves (ROC), area under the ROC (AUROC) and its confidence intervals were calculated. If the AUROC was significant and considered "acceptable," cutoff values were determined for SOFA and SAPS-II by Youden Index. Odds ratios and sensitivity, specificity, positive and negative predictive values were calculated for the cutoff values. RESULTS: A total of 114 (78 male; mean age: 72.8±12.5 years) ICU-CA were observed out of 14,264 ICU-admissions (incidence: 0.8%; 95% CI: 0.7-1.0%). 29.8% (N.=34; 95% CI: 21.6-39.1%) died during ICU-CA. SOFA and SAPS-II were not predictive for mortality during ICU-CA (P>0.05). Hospital-mortality was 78.1% (N.=89; 95% CI: 69.3-85.3%). SAPS-II (recorded within 24 hours before and after ICU-CA) indicated a better discrimination between survival and death during hospital stay than SOFA (AUROC: 0.81 [95% CI: 0.70-0.92] vs. 0.70 [95% CI: 0.58-0.83]). A SAPS-II-cutoff-value of 43.5 seems to be suitable for prognosis of hospital mortality after ICU-CA (specificity: 87.5%, sensitivity: 65.6%; SAPS-II>43.5: 87.5% died in hospital; SAPS-II<43.5: 65.6% survived; odds ratio:13.4 [95% CI: 3.25-54.9]). Also for 1-year-mortality (89.5%; 95% CI: 82.3-94.4) SAPS-II showed a better discrimination between survival and death than SOFA: AUROC: 0.78 (95% CI: 0.65-0.91) vs. 0.69 (95% CI: 0.52-0.87) with a cutoff value of the SAPS-II of 40.5 (specificity: 91.7%, sensitivity: 64.3%; SAPS-II>40.5: 96.4% died; SAPS-II<40.5: 42.3% survived; odd ratio: 19.8 [95% CI: 2.3-168.7]). CONCLUSIONS: Compared to SOFA, SAPS-II seems to be more suitable for prediction of hospital and 1-year-mortality after ICU-CA.

The hierarchy of exon-junction complex assembly by the spliceosome explains key features of mammalian nonsense-mediated mRNA decay.

Exon junction complexes (EJCs) link nuclear splicing to key features of mRNA function including mRNA stability, translation, and localization. We analyzed the formation of EJCs by the spliceosome, the physiological EJC assembly machinery. We studied a comprehensive set of eIF4A3, MAGOH, and BTZ mutants in complete or C-complex-arrested splicing reactions and identified essential interactions of EJC proteins during and after EJC assembly. These data establish that EJC deposition proceeds through a defined intermediate, the pre-EJC, as an ordered, sequential process that is coordinated by splicing. The pre-EJC consists of eIF4A3 and MAGOH-Y14, is formed before exon ligation, and provides a binding platform for peripheral EJC components that join after release from the spliceosome and connect the core structure with function. Specifically, we identified BTZ to bridge the EJC to the nonsense-mediated messenger RNA (mRNA) decay protein UPF1, uncovering a critical link between mRNP architecture and mRNA stability. Based on this systematic analysis of EJC assembly by the spliceosome, we propose a model of how a functional EJC is assembled in a strictly sequential and hierarchical fashion, including nuclear splicing-dependent and cytoplasmic steps.

An mRNA m7G cap binding-like motif within human Ago2 represses translation.

microRNAs (miRNAs) bind to Argonaute (Ago) proteins and inhibit translation or promote degradation of mRNA targets. Human let-7 miRNA inhibits translation initiation of mRNA targets in an m(7)G cap-dependent manner and also appears to block protein production, but the molecular mechanism(s) involved is unknown and the role of Ago proteins in translational regulation remains elusive. Here we identify a motif (MC) within the Mid domain of Ago proteins, which bears significant similarity to the m(7)G cap-binding domain of eIF4E, an essential translation initiation factor. We identify conserved aromatic residues within the MC motif of human Ago2 that are required for binding to the m(7)G cap and for translational repression but do not affect the assembly of Ago2 with miRNA or its catalytic activity. We propose that Ago2 represses the initiation of mRNA translation by binding to the m(7)G cap of mRNA targets, thus likely precluding the recruitment of eIF4E.