Human cytomegalovirus glycoprotein B variants affect viral entry, cell fusion, and genome stability

Area of Science:

• Virology
• Cell Biology
• Molecular Biology

Background:

• Human cytomegalovirus (HCMV) can induce genome instability and activate DNA damage response (DDR).
• Ataxia-telangiectasia mutated (ATM) kinase activation is a key feature of HCMV-induced DDR.
• Caspase-2 is an initiator caspase activated by DNA damage and supernumerary centrosomes.

Purpose of the Study:

• Investigate the activation of caspase-2 during HCMV infection.
• Identify the viral factors responsible for caspase-2 activation.
• Elucidate the mechanism linking viral entry, cell fusion, and DNA damage signaling.

Main Methods:

• Infection of fibroblasts with different HCMV strains.
• Inhibition of ATM kinase and components of the PIDDosome (PIDD, RAIDD).
• Analysis of chimeric HCMV strains to map genetic determinants.
• Assessment of viral entry mechanisms and syncytia formation.

Main Results:

• Only HCMV strain AD169 activated caspase-2 in infected fibroblasts.
• Caspase-2 activation was dependent on ATM, PIDD, and RAIDD, indicating PIDDosome involvement.
• A single nucleotide polymorphism in the AD169 UL55 gene, leading to D275Y substitution in glycoprotein B (gB), was responsible for caspase-2 activation.
• The gB(275Y) variant enhanced viral entry via direct membrane fusion and induced syncytia formation, unlike the gB(275D) variant.
• gB(275Y)-mediated cell fusion correlated with caspase-2 activation and potential genome instability.

Conclusions:

• Specific HCMV glycoprotein B variants (gB(275Y)) can accelerate viral entry and promote cell fusion.
• This increased fusogenicity triggers the ATM-PIDDosome-caspase-2 signaling axis, indicating a cellular response to potentially dangerous cell fusion events.
• The findings reveal a novel mechanism by which HCMV can compromise genome stability through enhanced cell fusion mediated by specific gB variants.