The Replicative Consequences of Papillomavirus E2 Protein Binding to the Origin Replication Factor ORC2

Area of Science:

• Molecular Biology
• Virology
• Epigenetics

Background:

• The origin recognition complex (ORC) is crucial for DNA replication initiation in eukaryotes.
• Papillomaviruses (PVs) replicate their episomal DNA using viral and host factors, including the E1 helicase and E2 protein.
• The role of ORC in PV replication has not been previously investigated.

Purpose of the Study:

• To investigate the role of ORC, specifically ORC2, in the replication of human and bovine papillomaviruses.
• To determine if ORC2 is recruited to the PV origin of replication.
• To elucidate the interplay between PV E2 protein and ORC2 in regulating viral DNA synthesis.

Main Methods:

• Co-immunoprecipitation to assess binding between PV E2 proteins and ORC2.
• Western blotting to detect ORC2 presence at the PV origin.
• RNA interference (RNAi) to deplete ORC2 and assess its impact on PV replication.
• Analysis of E1 and E2 occupancy at the viral origin using chromatin immunoprecipitation (ChIP).
• Assessment of ORC2 occupation at cellular origins of replication upon HPV E2 overexpression.

Main Results:

• PV E2 proteins (HPV and BPV-1) bind to ORC2, but ORC2 is not detected at the PV origin.
• Depletion of ORC2 significantly enhances PV episomal replication in transient and stable models.
• ORC2 depletion leads to increased occupancy of E1 and E2 at the PV origin.
• Overexpression of HPV E2 reduces ORC2 binding at cellular replication origins.

Conclusions:

• ORC2 is not required for PV origin activation by E1/E2 but acts as a suppressor of PV replication.
• PV E2 likely subverts ORC2 function to promote viral genome amplification during specific replication stages.
• HPV E2 may restrict host replication by limiting ORC assembly at cellular origins, potentially to favor viral replication.