Nuclear organization of herpes simplex virus type 1 infection: A study of replication compartments

Herpes Simplex Virus Type I (HSV-1) infection results in the disruption of nuclear matrix domains ND10 (also called nuclear bodies, PODs or PML-associated bodies. After ND10 disruption, viral transcription and DNA replication occur in globular nuclear domains called replication compartments. We defined four stages of infection using antibodies to the major viral DNA binding protein ICP8 (SSB, UL29) and the ND10 antigen PML. Immediately after infection, cells contain FD10 detected by staining for PML (stage 1); within one hour ND10 are disrupted and cells exhibit diffuse staining for ICP8 (stage 11). After all ND10 have been disrupted, foci containing both PML and ICP8 appear (stage 111); these foci resemble but are not equivalent to ND10 found before infection. Formation of stage III foci requires viral helicase/primase and origin binding proteins. However, cells infected with a mutant that lacks the polymerase catalytic subunit, UL30, form stage III-like ICP8 foci which do not contain PML. We find that recruitment of PML requires the localization of UL30 to stage III foci but not its catalytic activity. The polymerase processivity unit, UL42, is not required for the recruitment of PML to viral foci. Wild type infection quickly progresses through stage III to stage IV, in which cells contain replication compartments that stain for both ICP8 and PML. We showed that replication compartments contain only some isoforms of PML. ICPO is a viral protein known to cause FD10 disruption, and ICPO mutants are more defective at low than high multiplicities of infection (MOI). We showed that FD10 disruption is also MOI dependent: an ICPO mutant virus disrupted ND10 at high but not low MOI. A delay in replication compartment formation correlated well with a delay in ND10 disruption at high MOI, suggesting ND10 disruption must precede formation of replication compartments. Furthermore, treatment with factors that increase the stability of FD10 arsenic trioxide and the proteasome inhibitor MG132, inhibited viral disruption of ND10, replication compartment formation, and virus production. These results further define the viral factors that carry out ND10 disruption, and strengthen the correlation between ND10 disruption and productive viral infection.