Characterization of a human cytomegalovirus with phosphorylation site mutations in the immediate-early 2 protein

Area of Science:

• Virology
• Molecular Biology
• Cellular Biology

Background:

• Human cytomegalovirus (HCMV) immediate-early 2 (IE2) protein plays a crucial role in viral gene regulation.
• Phosphorylation of IE2 protein residues is known to influence its function.
• Understanding IE2 protein modifications is key to deciphering HCMV replication and pathogenesis.

Purpose of the Study:

• To investigate the functional impact of specific IE2 protein phosphorylation sites on HCMV replication and promoter transactivation.
• To characterize a novel HCMV mutant (TNsubIE2P) with alanine substitutions at four key phosphorylation sites in the IE2 protein.
• To assess the effect of these modifications on viral growth, viral promoter activation, and heterologous promoter transactivation.

Main Methods:

• Construction of a recombinant HCMV mutant (TNsubIE2P) by site-directed mutagenesis, replacing four phosphorylated residues in the IE2 protein with alanine.
• Assessment of viral growth kinetics at various multiplicities of infection (MOI).
• Analysis of viral promoter activation (major immediate-early, UL4, UL44) and transactivation of an endogenous simian virus 40 early promoter in infected human fibroblasts.
• Examination of IE2 protein modification, specifically sumoylation.

Main Results:

• The TNsubIE2P mutant exhibited growth kinetics comparable to wild-type HCMV at both low and high MOI.
• Mutant virus demonstrated similar activation levels and kinetics for HCMV major immediate-early, UL4, and UL44 promoters compared to wild-type.
• The TNsubIE2P mutant showed accelerated and enhanced transactivation of the simian virus 40 early promoter in infected human fibroblasts.
• The study also explored the sumoylated state of the modified IE2 protein.

Conclusions:

• Specific phosphorylation sites in the HCMV IE2 protein are not essential for viral replication or the activation of viral promoters.
• Modification of these phosphorylation sites can enhance the IE2 protein's ability to transactivate heterologous promoters, suggesting a regulatory role in viral gene expression.
• These findings provide insights into the complex post-translational modifications of the IE2 protein and their impact on HCMV transcriptional regulation.