A short sequence in the tail of SARS-CoV-2 envelope protein controls accessibility of its PDZ-binding motif to the cytoplasm

The carboxy-terminal tail of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) envelope protein (E) contains a PDZ-binding motif (PBM) which is crucial for coronavirus pathogenicity. During SARS-CoV-2 infection, the viral E protein is expressed within the Golgi apparatus membrane of host cells with its PBM facing the cytoplasm. In this work, we study the molecular mechanisms controlling the presentation of the PBM to host PDZ (PSD-95/Dlg/ZO-1) domain-containing proteins. We show that at the level of the Golgi apparatus, the PDZ-binding motif of the E protein is not detected by E C-terminal specific antibodies nor by the PDZ domain-containing protein-binding partner. Four alanine substitutions upstream of the PBM in the central region of the E protein tail is sufficient to generate immunodetection by anti-E antibodies and trigger robust recruitment of the PDZ domain-containing protein into the Golgi organelle. Overall, this work suggests that the presentation of the PBM to the cytoplasm is under conformational regulation mediated by the central region of the E protein tail and that PBM presentation probably does not occur at the surface of Golgi cisternae but likely at post-Golgi stages of the viral cycle.

Enhancement of intestinal epithelial barrier function by Weissella confusa F213 and Lactobacillus rhamnosus FBB81 probiotic candidates in an in vitro model of hydrogen peroxide-induced inflammatory bowel disease

OBJECTIVE

Weissella confusa F213 (WCF213) and Lactobacillus rhamnosus FBB81 (LrFBB81) are two probiotic candidates isolated from humans in our previous study. Their functional activity on the mucosal barrier has not yet been adequately investigated. Therefore, the objective of this study was to investigate the effect of these strains on maintaining mucosal integrity in vitro. Caco-2 cell monolayers were pretreated with WCF213 and LrFBB81 before being exposed to hydrogen peroxide. The integrity of mucosal cells was evaluated by measuring the transepithelial resistance (TER), flux of FITC-labelled dextran, and ZO-1 protein distribution with the help of an immunofluorescence method.

RESULTS

WCF213 was found to significantly maintain the TER better than the control hydrogen peroxide-treated cells (p < 0.001), followed by the strain combination, and LrFBB81 alone (p < 0.05). The permeability of mucosa was also successfully maintained by the WCF213 strain. This was illustrated by the significant reduction in the flux of FITC-labelled dextran (p < 0.05), which was larger than that exhibited by the other groups. The ZO-1 distribution of strain-treated cells showed less disruption than hydrogen peroxide-treated cells, consistent with the TER and FITC experimental results. These findings indicate that WCF213 and LrFBB81 plays important roles in the maintenance of mucosal integrity in a strain-dependent manner.

Qihuang decoction promotes the recovery of intestinal immune barrier dysfunction after gastrectomy in rats

OBJECTIVE

This study aims to observe the effect of Qihuang decoction on small intestinal mucosal barrier after gastrectomy in rats.

MATERIALS AND METHODS

A total of 80 Wistar rats were randomly divided into normal group, sham operation group, enteral nutrition group (EN) and Qihuang decoction group (EN+QH), there were 20 rats in each group. Both the EN group and the EN+QH group underwent gastrectomy. Instillation of enteral nutrition in the small intestine was performed after operation in the EN group. Instillation of enteral nutrition and Qihuang decoction in the small intestine was performed after operation in the EN+QH group. Only the abdominal incision and closing was performed in the sham operation group without drug and nutritional intervention. The expression levels of tight junction proteins in intestinal epithelial cells were determined by western blotting method. The sIgA content in different anatomic sites of intestinal mucosa was determined by double antibody-PEG radioimmunoassay technique. The number of IgA+B cells in different anatomic sites of intestinal mucosa was determined by immunohistochemical method.

RESULTS

The sIgA content in the sham operated group was significantly lower than that of normal group (P<0.05). The sIgA content and the number of IgA+B cells in Peyer's patches and lamina propria lym-phocytes in the EN+QH group were significantly higher than that of EN group (P<0.01, P<0.05). The expression levels of RhoA, Rac1 and Cdc42 increased in the EN group, and the phosphorylation levels of occludin, claudin-1, claudin-5, ZO-1 and ZO-2 also increased in the EN group, while the expression levels of non-phosphorylated occluding, claudin-1, claudin-5, ZO-1 and ZO-2 proteins decreased in the EN group (P<0.01, P<0.05). After treatment of Qihuang decoction for 7 days, compared with EN group, the expression levels of RhoA, Rac1 and Cdc42, and the phosphorylation levels of occludin, claudin-1, claudin-5, ZO-1 and ZO-2 significantly decreased in the EN+QH group, while the expression levels of non-phosphorylated occluding, claudin-1, claudin-5, ZO-1 and ZO-2 proteins significantly increased in the EN+QH group (P<0.01, P<0.05).

CONCLUSIONS

Qihuang decoction can promote the proliferation and differentiation of IgA+B lymphocytes and increase the sIgA content in intestinal mucosal immune barrier after gastrectomy in rats, it also can promote the expression of tight junction proteins to improve the permeability of intestinal mucosa and promote the recovery of intestinal immune barrier dysfunction in rats after gastrectomy by inhibiting the tight junction associated proteins' phosphorylation induced by Rho/ROCK signaling pathway.