E2F1-3 activate Merkel cell polyomavirus early transcription and replication.

Area of Science:

• Virology
• Oncology
• Molecular Biology

Background:

• Merkel cell polyomavirus (MCPyV) causes Merkel cell carcinoma (MCC).
• MCPyV Large and Small Tumor antigens (LT, ST) drive viral replication and tumorigenesis.
• Control mechanisms for MCPyV LT/ST expression are poorly understood.

Purpose of the Study:

• To elucidate the regulatory mechanisms controlling MCPyV LT/ST expression.
• To investigate the role of E2F transcription factors in MCPyV early gene regulation.
• To understand the implications for viral replication and MCC pathogenesis.

Main Methods:

• Identified E2F1-3/DP1 binding to the MCPyV Non-Coding Control Region (NCCR) using a consensus E2 site.
• Utilized E2 site deletion and small molecule inhibitors to block E2F-NCCR interaction.
• Assessed LT/ST mRNA and protein expression in MCC and transfected cells.

Main Results:

• E2F1-3/DP1 dimers bind the MCPyV NCCR at a specific E2 site.
• Inhibition of E2F-NCCR binding downregulates MCPyV LT/ST expression.
• Identified similar E2 sites in related polyomaviruses, suggesting conserved regulatory mechanisms.

Conclusions:

• Discovered an E2F/LT/RB1 positive feedback loop essential for MCPyV replication and MCC proliferation.
• Challenged the model that PyV LT drives S phase entry; instead, S phase entry stimulates PyV early transcription.
• E2F-mediated regulation is a conserved mechanism in related polyomaviruses.