Abstract 17307: Pre-Existing Endoplasmic Reticulum (ER) Stress Inhibits Sars-Co-V2 Entry Into Host Cells Through Modulation of AKT Signaling and Unfolded Protein Response (UPR)

Introduction: It is well known that SARS-Co-V2 infection can induce ER stress-associated activation of unfolded protein response (UPR) in various host cells which may contribute to the pathogenesis of COVID-19. However, the interplay between SARS-Co-V2 infection and UPR signaling in pre-existing ER stress associated pathological conditions has not been well elucidated. Hypothesis: We hypothesized that modulation of a pre-existing ER stress in host cells could attenuate susceptibility to SARS-CoV-2 infection by activating a range of cellular defense.

Methods: Increasing concentrations of Tunicamycin (Tm) and Thapsigargin (Tg) have been used to induce ER stress in Huh-7 cells. After 6h treatment, cells were infected with SARS-CoV-2 pseudotyped particles (SARS-CoV-2pp) for 48 p.i. SARS-Co-V2-2pp entry was measured using Bright Glo ^TM luciferase assay. Cell viability was measured by cell titer Glo ^® luminescent cell viability assay. The mRNA and protein expression of UPR markers were evaluated using RT-qPCR and Western blot methods.

Results: Tm (5 μg/ml) and Tg (1 μM) efficiently inhibited SARS-CoV-2pp entry into cells without any cytotoxic effect. Chemical ER stress-induced inhibition of SARS-CoV-2pp entry was associated with significant reduction of ACE2 expression in Tg-infected cells but not with Tm. Strikingly, Tm and Tg revealed differential effects in modulating the expression of ER stress genes in infected cells. Both Tm and Tg significantly reduced the expression of stress-inducible ER chaperone GRP78/BIP in infected cells. In contrast, the IRE1-XBP1s and PERK-eIF2α-ATF4-CHOP signaling pathways were downregulated in Tg-infected cells only. Additionally, insulin-mediated glucose uptake, phosphorylation of Ser ³⁰⁷ IRS-1 and downstream p-AKT were enhanced in Tg-infected cells without any change in ERK phosphorylation.

Conclusions: These findings suggest that pre-existing ER stress could modulate a specific UPR response in infected cells capable of counteracting the stress-inducible elements signaling, thereby depriving SARS-Co-V2 of essential components for their entry and replication. Pharmacological manipulation of ER stress in host cells might provide new therapeutic strategies to alleviate SARS-CoV-2 infection.