Loss of bovine papillomavirus DNA replication control in growth-arrested transformed cells.
The bovine papillomavirus type 1 (BPV-1) genome replicates as a plasmid within the nuclei of BPV-1-transformed murine C127 cells at a constant multiple copy number, and spontaneous amplification of the viral DNA is rarely observed. We report here that a mutant BPV-1 plasmid within a contact-inhibited C127 cell line replicated as a stable multicopy plasmid in exponentially growing cells but amplified to a high level in confluent cell culture. In situ hybridization analysis revealed that most of the mutant viral DNA amplification occurred in a minor subpopulation of cells within the culture. These consisted of giant nondividing cells with greatly enlarged nuclei, a cell form which was specifically induced in stationary-phase cultures. These observations indicated that expression of a viral DNA replication factor was cell growth stage specific. Consistent with this hypothesis, considerable amplification of wild-type BPV-1 DNA associated with characteristic giant cell formation was observed in typical wild-type virus-transformed C127 cultures following a period of growth arrest achieved by serum deprivation. Further observations indicated that induction of the giant-cell phenotype was dependent on BPV-1 gene expression and implicated a viral E1 replication factor in this process. Moreover, heterogeneity in virus genome copy numbers within the giant-cell population suggested a complex regulation of induction of DNA synthesis in these cells. It appears that this process represents a mechanism employed by the virus to ensure maximal viral DNA synthesis within a growth-arrested cell. Fundamental questions concerning the integration of the virus-cell control circuitry in proliferating and resting cells are discussed.
Burnett
S
S
Department of Medical Genetics, University of Uppsala, Sweden.
Kiessling
U
U
Pettersson
U
U
D000818:Animals; D052688:Bovine papillomavirus 1 / Q000235:genetics*; D002453:Cell Cycle; D002454:Cell Differentiation; D002461:Cell Line, Transformed / Q000166:cytology / Q000382:microbiology; D002471:Cell Transformation, Neoplastic / Q000473:pathology*; D002472:Cell Transformation, Viral; D003470:Culture Media; D004261:DNA Replication; D004279:DNA, Viral / Q000235:genetics*; D005784:Gene Amplification; D051379:Mice; D027383:Papillomaviridae / Q000235:genetics*; D014779:Virus Replication
D003470:Culture Media; D004279:DNA, Viral