SARS-CoV-2-ORF3a variant Q57H reduces its pro-apoptotic activity in host cells.

Area of Science:

• Virology
• Molecular Biology
• Immunology

Background:

• Mutations in SARS-CoV-2 can alter pathogenicity, affecting transmissibility, disease severity, and mortality.
• The SARS-CoV-2 open reading frame 3a (ORF3a) protein is implicated in viral replication and activating host cell death signaling, contributing to COVID-19 severity.
• The frequent ORF3a-Q57H variant is linked to increased transmissibility and lower mortality, but its precise impact on protein function and cell damage remains unclear.

Purpose of the Study:

• To investigate the functional impact of the SARS-CoV-2 ORF3a-Q57H variant on host cell apoptosis and protein expression.
• To determine if the Q57H mutation affects ORF3a localization and its role in the extrinsic apoptotic pathway.
• To elucidate the molecular mechanisms underlying the observed milder phenotype associated with the ORF3a-Q57H variant.

Main Methods:

• Transient transfection of HEK293T cells with plasmids encoding wild-type (WT) SARS-CoV-2 ORF3a and the Q57H variant.
• Biochemical and cell biological assays to compare protein expression, localization, and apoptosis induction between WT and Q57H ORF3a.
• Analysis of the extrinsic apoptotic pathway activation in response to ORF3a-Q57H expression.

Main Results:

• The SARS-CoV-2 ORF3a-Q57H variant displayed similar whole-cell protein expression to WT but reduced plasma membrane expression.
• Expression of the ORF3a-Q57H variant led to significantly less apoptosis in host cells compared to WT.
• This reduction in apoptosis was associated with lower activation of the extrinsic apoptotic pathway.

Conclusions:

• The SARS-CoV-2 ORF3a-Q57H variant's milder phenotype is likely due to alterations in ORF3a protein function rather than changes in its expression levels.
• The reduced apoptosis observed suggests a modified interaction with the extrinsic apoptotic pathway, contributing to decreased host cell damage.
• These findings provide insights into the molecular basis of SARS-CoV-2 variant evolution and its impact on COVID-19 pathogenesis.