IFN-γ‒Induced APOBEC3B Contributes to Merkel Cell Polyomavirus Genome Mutagenesis in Merkel Cell Carcinoma

Area of Science:

• Virology
• Oncology
• Molecular Biology

Background:

• Merkel cell polyomavirus (MCPyV) causes an aggressive skin cancer, Merkel cell carcinoma.
• The viral genome integrates into tumor DNA, featuring mutations in the large T antigen helicase domain.
• The mechanisms generating these tumor-specific mutations are not fully understood.

Purpose of the Study:

• To investigate the role of host cytosine deaminases, specifically APOBEC3 enzymes, in MCPyV genome mutation.
• To elucidate the molecular mechanisms driving tumor-specific mutations in MCPyV during Merkel cell carcinoma development.

Main Methods:

• In vitro experiments using MCPyV-replicating 293-derivative cells to assess APOBEC3A, APOBEC3B, and APOBEC3G activity.
• Bioinformatic analysis of MCPyV genomes from the NCBI database and tumor samples.
• Microarray data analysis to correlate immune marker expression with APOBEC3 levels in tumors.
• In vitro IFN-γ treatment of MCPyV-positive Merkel cell carcinoma cell lines.

Main Results:

• APOBEC3A, APOBEC3B, and APOBEC3G were found to introduce specific mutations into episomal MCPyV genomes.
• Sequence analysis revealed a depletion of TpC dinucleotides in the large T antigen gene, a known target for APOBEC3A/B.
• MCPyV genomes from tumors showed cytosine mutations with a bias towards TpC dinucleotides.
• Expression of IFN-γ and cytotoxic T lymphocyte markers correlated positively with APOBEC3 levels in MCPyV-positive tumors.
• IFN-γ treatment upregulated APOBEC3B and APOBEC3G expression in a Merkel cell carcinoma cell line.

Conclusions:

• The IFN-γ-APOBEC3B axis plays a significant role in shaping MCPyV genomic sequences.
• This pathway contributes to the generation of tumor-specific large T antigen mutations during Merkel cell carcinoma development.