Apolipoprotein B100 (apoB) is a large (520-kDa) complex secretory protein; its secretion is regulated posttranscriptionally by several degradation pathways. The best described of these degradative processes is cotranslational ubiquitinylation and proteasomal degradation of nascent apoB, involving the 70-and 90-kDa heat shock proteins and the multiple components of the proteasomal pathway. Ubiquitinylation involves several proteins, including ligases called E3s, that coordinate the covalent binding of ubiquitin to target proteins. The recent discovery that tumor autocrine motility factor receptor, also known as gp78, is an endoplasmic reticulum (ER)-associated E3, raised the possibility that this E3 might be involved in the ER-associated degradation of nascent apoB. In a series of experiments in HepG2 cells, we demonstrated that overexpression of gp78 was sufficient for increased ubiquitinylation and proteasomal degradation of apoB, with reduced secretion of apoB-lipoproteins. This action of gp78 was specific: overexpression of the protein did not affect secretion of either albumin or apolipoprotein AI. Furthermore, overexpression of a cytosolic E3, Itch, had no effect on apoB secretion. Finally, using an in vitro translation system, we demonstrated that gp78 led to increased ubiquitinylation and proteasomal degradation of apoB48. Together, these results indicate that an ER-associated protein, gp78, is a bona fide E3 ligase in the apoB ERassociated degradation pathway.Apolipoprotein B100 (apoB) 1 is the essential protein component of atherogenic very low density and low density lipoproteins (1), and overproduction of these lipoproteins is a common feature of human dyslipidemia (2). Extensive studies of cultured primary hepatocytes and hepatoma cells have established that significant control over apoB secretion can be achieved at the post-transcriptional level by degradation. One form of presecretory degradation, namely the ER-associated degradation (ERAD) of apoB, is regulated by the availability of newly synthesized core lipids (triglyceride, cholesterol ester) and microsomal triglyceride transfer protein activity (1, 3, 4). When lipid availability or microsomal triglyceride transfer protein activity is limited, translocation of apoB is incomplete, and apoB is ubiquitinylated co-translationally and degraded by the cytosolic ubiquitin-proteasome pathway (5-9).Cytosolic and nuclear proteins are targeted for proteasomal degradation by the addition of multi-ubiquitin chains. The specificity of this process is largely conferred by ubiquitin (Ub) protein ligases (E3s) (10 -12). E3s interact directly or indirectly with substrate and mediate the transfer of Ub from Ub-conjugating enzymes to target proteins. Two major E3 classes have been identified: HECT domain E3s and RING finger E3s (10 -12). HECT domain E3s are homologous to E6-AP C-terminal domain E3s, which accept Ub from Ub-conjugating enzymes, thereby forming thiol-ester intermediates with Ub. The Ub is then transferred to the target protein. In contrast, RING ...

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Importance: Preliminary reports indicate that acute kidney injury (AKI) is common in coronavirus disease (COVID)-19 patients and is associated with worse outcomes. AKI in hospitalized COVID-19 patients in the United States is not well-described. Objective: To provide information about frequency, outcomes and recovery associated with AKI and dialysis in hospitalized COVID-19 patients. Design: Observational, retrospective study. Setting: Admitted to hospital between February 27 and April 15, 2020. Participants: Patients aged ≥18 years with laboratory confirmed COVID-19 Exposures: AKI (peak serum creatinine increase of 0.3 mg/dL or 50% above baseline). Main Outcomes and Measures: Frequency of AKI and dialysis requirement, AKI recovery, and adjusted odds ratios (aOR) with mortality. We also trained and tested a machine learning model for predicting dialysis requirement with independent validation. Results: A total of 3,235 hospitalized patients were diagnosed with COVID-19. AKI occurred in 1406 (46%) patients overall and 280 (20%) with AKI required renal replacement therapy. The incidence of AKI (admission plus new cases) in patients admitted to the intensive care unit was 68% (553 of 815). In the entire cohort, the proportion with stages 1, 2, and 3 AKI were 35%, 20%, 45%, respectively. In those needing intensive care, the respective proportions were 20%, 17%, 63%, and 34% received acute renal replacement therapy. Independent predictors of severe AKI were chronic kidney disease, systolic blood pressure, and potassium at baseline. In-hospital mortality in patients with AKI was 41% overall and 52% in intensive care. The aOR for mortality associated with AKI was 9.6 (95% CI 7.4-12.3) overall and 20.9 (95% CI 11.7-37.3) in patients receiving intensive care. 56% of patients with AKI who were discharged alive recovered kidney function back to baseline. The area under the curve (AUC) for the machine learned predictive model using baseline features for dialysis requirement was 0.79 in a validation test. Conclusions and Relevance: AKI is common in patients hospitalized with COVID-19, associated with worse mortality, and the majority of patients that survive do not recover kidney function. A machine-learned model using admission features had good performance for dialysis prediction and could be used for resource allocation.

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