Negative regulation of the bovine papillomavirus E5, E6, and E7 oncogenes by the viral E1 and E2 genes

p53 protein was able to block human and bovine papillomavirus DNA amplificational replication while not interfering with Epstein-Barr virus oriP once-per-cell cycle replication. Oligomerization, intact DNA-binding, replication protein A-binding, and proline-rich domains of the p53 protein were essential for efficient inhibition, while the N-terminal transcriptional activation and C-terminal regulatory domains were dispensable for the suppressor activity of the p53 protein. The inhibition of replication was caused neither by the downregulation of expression of the E1 and E2 proteins nor by cell cycle block or apoptosis. Our data suggest that the intrinsic activity of p53 to suppress amplificational replication of the papillomavirus origin may have an important role in the virus life cycle and in virus-cell interactions.

Section: Discussionmentioning

confidence: 99%

p53 Protein Is a Suppressor of Papillomavirus DNA Amplificational Replication

Lepik¹,

Ilves²,

Kristjuhan

et al. 1998

“…In addition to its transcriptional activation function, under some circumstances, full-length E2 can also repress transcription of certain promoters that control expression of the E6 and E7 transforming genes, such as the HPV16 P 97 and HPV18 P 105 promoters (3,41,56). As a repressor, E2 has been shown to function indirectly in the regulation of cell proliferation and transformation phenotypes (40,62,65). Structural studies of the full-length BPV E2 protein have revealed that the E2 transactivator consists of two functional domains linked by a nonconserved hinged region (reviewed in references 18 and 35).…”

mentioning

confidence: 99%

Targeted mutagenesis of the human papillomavirus type 16 E2 transactivation domain reveals separable transcriptional activation and DNA replication functions

Sakai

Yasugi

Benson

et al. 1996

Self Cite

112

The E2 gene products of papillomavirus play key roles in viral replication, both as regulators of viral transcription and as auxiliary factors that act with E1 in viral DNA replication. We have carried out a detailed structure-function analysis of conserved amino acids within the N-terminal domain of the human papillomavirus type 16 (HPV16) E2 protein. These mutants were tested for their transcriptional activation activities as well as transient DNA replication and E1 binding activities. Analysis of the stably expressed mutants revealed that the transcriptional activation and replication activities of HPV16 E2 could be dissociated. The I73A mutant was defective for the transcriptional activation function but retained wild-type DNA replication activity, whereas the E39A mutant had wild-type transcriptional activation function but was defective in transient DNA replication assays. The E39A mutant was also defective for HPV16 E1 binding in vitro, suggesting that the ability of E2 protein to form a complex with E1 appears to be essential for its function as an auxiliary replication factor.

“…These ideas could also explain the curious finding reported here concerning the requirements for repressor proteins in BPV transformation. While wild-type genomes need at least one form of the repressors (24,64), we found that the A3 genome did not display such a requirement. If repressors are normally required to down regulate the activity of E2, certain mutations in E2 itself that destabilize its activity would suppress this requirement.…”

Section: Discussionmentioning

confidence: 58%

“…Study of such a genetic interaction between E2 phosphorylation and the repressors is warranted by the fact that this region of the E2 hinge is also incorporated into the repressor proteins. Furthermore, previously reported observations showed that at least one form of the repressors is required for viral oncogenic transformation of C127 cells (24,64). The A4 and A3 mutations were combined with mutations FIG.…”

Section: Fig 2 Identification Of Phosphorylated Tryptic Fragments Amentioning

confidence: 89%

A papillomavirus E2 phosphorylation mutant exhibits normal transient replication and transcription but is defective in transformation and plasmid retention

Lehman

King

Botchan

1997

Papillomavirus DNA persists in infected cells as a nuclear plasmid, causing epithelial lesions in many hosts, including humans. The viral protein E2 is required for both replication and transcription to facilitate this persistence. Bovine papillomavirus E2 protein is phosphorylated at two predominant sites. Phosphorylation of one of these sites (serine 301) inhibits replication of the genome. Using mass spectrometry and Edman sequencing, we have mapped additional phosphorylation sites in tryptic peptides to positions which lie primarily in the putatively unstructured hinge region of E2. Mutation of the major sites facilitates transformation in the absence of viral repressors and only has a minor effect on transformation when the repressors are present. Mutation of the major phosphorylation sites combined with one additional change at a newly discovered site (serine 235) blocks transformation. Transformation can be restored by mutating this residue to aspartic acid, mimicking a phosphorylated amino acid, suggesting that phosphorylation is key to the regulation. Transformation by the mutant genome can also be rescued by ectopic expression of the E2 enhancer protein, demonstrating a loss of function by the mutant protein and not a toxic defect. In transient assays, phosphorylation site mutants of E2 protein were normal for all viral functions tested, including replication, transcriptional activation and repression (by the overlapping mutant repressors), protein accumulation, and surprisingly, viral oncogene E5 promoter activation. While the mutant genome transiently replicated to high levels, stable replication was defective, suggesting that a function of E2 required for plasmid retention is regulated by phosphorylation.