TRIM21 promotes ubiquitination of SARS-CoV-2 nucleocapsid protein to regulate innate immunity.

The innate immune response is the first line of host defense against viral infections, but its role in immunity against SARS-CoV-2 remains unclear. By using immunoprecipitation coupled with mass spectroscopy, we observed that the E3 ubiquitin ligase TRIM21 interacted with the SARS-CoV-2 nucleocapsid (N) protein and ubiquitinated it at Lys375 . Upon determining the topology of the TRIM21-mediated polyubiquitination chain on N protein, we then found that polyubiquitination led to tagging of the N protein for degradation by the host cell proteasome. Furthermore, TRIM21 also ubiquitinated the N proteins of SARS-CoV-2 variants of concern, including Alpha, Beta, Gamma, Delta, and Omicron together with SARS-CoV and MERS-CoV variants. Herein, we propose that ubiquitylation and degradation of the SARS-CoV-2 N protein inhibited SARS-CoV-2 viral particle assembly, by which it probably involved in preventing cytokine storm. Eventually, our study has fully revealed the association between the host innate immune system and SARS-CoV-2 N protein, which may aid in developing novel SARS-CoV-2 treatment strategies.

ACE2 Affects the Expression and Function of IFITM3 During SARS-CoV-2 Pseudovirus Infection in Vero E6 Cells.

COVID-19 is a globally infectious viral epidemic of great public health concern caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Angiotensin-converting enzyme 2 (ACE2) plays its role as the receptor for SARS-CoV-2 through binding with S protein and the binding results in ACE2 expression decrease. The change of ACE2 is supposed to elicit a series of cellular and molecular events. Other than as the receptor, ACE2's roles on infection by regulating other molecules need to be further studied during SARS-CoV-2 infection. In the present study, we established the ACE2 knockdown model using Vero E6 cells to study how ACE2 influenced the downstream signaling molecules. Analysis of transcriptome sequencing discovered that ACE2 alteration per se caused the alteration of immune factors, including some related to the viral infection-related signaling pathways. We found that ACE2 silencing induced the reduced interferon-induced transmembrane protein 3 (IFITM3) expression. Overexpression of IFITM3 promoted the SARS-CoV-2 pseudovirus infection of Vero E6 cells lacking the ACE2. It indicates that ACE2 can affect IFITM3 expression and function to affect the SARS-CoV-2 infection. Our results reveal possible mechanisms influencing SARS-CoV-2 infectivity and contribute to explaining the rapid spread and pathogenesis especially in the case of ACE2 low expression.

The pathological autopsy of coronavirus disease 2019 (COVID-2019) in China: a review.

The coronavirus disease 2019 (COVID-2019) that emerged in Wuhan, China, has rapidly spread to many countries across all six WHO regions. However, its pathobiology remains incompletely understood and many efforts are underway to study it worldwide. To clarify its pathogenesis to some extent, it will inevitably require lots of COVID-2019-associated pathological autopsies. Pathologists from all over the world have raised concerns with pathological autopsy relating to COVID-2019. The issue of whether a person died from COVID-2019 infection or not is always an ambiguous problem in some cases, and ongoing epidemiology from China may shed light on it. This review retrospectively summarizes the research status of pathological autopsy for COVID-2019 deaths in China, which will be important for the cause of death, prevention, control and clinical strategies of COVID-2019. Moreover, it points out several challenges at autopsy. We believe pathological studies from China enable to correlate clinical symptoms and pathological features of COVID-2019 for doctors and provide an insight into COVID-2019 disease.