The ND10 Component Promyelocytic Leukemia Protein Relocates to Human Papillomavirus Type 1 E4 Intranuclear Inclusion Bodies in Cultured Keratinocytes and in Warts

Human papillomavirus type 1 (HPV1) E4 protein is associated with cytoplasmic and nuclear inclusions in
productively infected keratinocytes. Here we have used transient expression of HPV1 E4 (also known as
E1^E4) protein in keratinocytes to reproduce formation of E4 inclusions. Immunofluorescence analysis
showed that progressive formation of inclusions correlated with diminished colocalization between E4 and
keratin intermediate filaments (IFs). Our results support a model in which the HPV1 E4-keratin IF association
is transient, occurring only at an early stage of inclusion formation. We also demonstrate that E4 induces
relocation of the promyelocytic leukemia protein (PML) from multiple intranuclear speckles (ND10 bodies) to
the periphery of nuclear E4 inclusions and that this activity is specific to full-length E4 protein. Analysis of
HPV1-induced warts demonstrated that nuclear PML-E4 inclusions were present in productively infected
keratinocytes, indicating that reorganization of PML occurs during the virus’s replication cycle. It has been
suggested that ND10 bodies are the sites for papillomavirus genome replication and virion assembly. Our
finding that E4 induces reorganization of ND10 bodies in vitro and in vivo is further strong evidence that these
domains play an important role in the papillomavirus life cycle. This study indicates that HPV1 is analogous
to other DNA viruses that disrupt or reorganize ND10 domains, possibly to increase efficiency of virus
infection. We hypothesize that HPV1 E4-induced reorganization of PML is necessary for efficient replication
of the virus during the virus-producing phase.