Molecular targets for papillomavirus therapy.

Papillomaviruses are infectious agents for human and animal epithelial tissue, and nearly 100 distinct human types (HPVs) have been identified. When these viruses infect cutaneous or mucosal skin they can initially cause clinical warts or persistent infection with little or no visible manifestations. Warts, while usually benign, can be painful or cosmetically unacceptable and often require medical treatment. Furthermore, infection with certain specific HPV types, such as 16 or 18 (as well as several others), is the major risk factor for a woman's development of cervical cancer. In addition to cervical cancer, papillomaviruses have also been implicated in cancers of the skin and respiratory track though the evidence is not yet as conclusive. It is clear that prevention or elimination of papillomavirus infections would ultimately reduce the incidence of cervical cancer and possibly other epithelial cancers as well. Unfortunately, progress in vaccine development has been slow and no specific anti-papillomavirus agents are available. The rational development of effective anti-papillomaviral treatments will require a detailed understanding of how these viruses replicate and interact with the host cell, and much progress has been made in this area over the last 10 years. These viruses have small DNA genomes with limited coding capacity, and their complete array of viral protein products is known. This review will discuss the known functions of the viral proteins with a focus on strategies to interdict their biological activities as a possible means of specific therapy.

Determination of the protein composition of the occlusion-derived virus of Autographa californica nucleopolyhedrovirus.

The occlusion derived form of baculovirus is specially adapted for primary infection of the host midgut epithelium. As such, the virion must contain the proteins essential for host range determination and initiation of infection. Because knowledge of virion composition is a prerequisite for functional investigation, this study used a combination of techniques to identify the proteins present within or associated with the occlusion-derived virus (ODV) virion. Thirty-one proteins, including proteins known to be essential for viral DNA replication, were identified with confidence. An additional 13 proteins were identified by using one of the three techniques. A comparison of gene conservation among the ODV proteins encoded in the 16 sequenced baculoviridae genomes is presented. With knowledge of the composition of ODV, it is now possible to target proteins and study their role(s) during primary infection.

Identification of BV/ODV-C42, an Autographa californica nucleopolyhedrovirus orf101-encoded structural protein detected in infected-cell complexes with ODV-EC27 and p78/83.

orf101 is a late gene of Autographa californica nucleopolyhedrovirus (AcMNPV). It encodes a protein of 42 kDa which is a component of the nucleocapsid of budded virus (BV) and occlusion-derived virus (ODV). To reflect this viral localization, the product of orf101 was named BV/ODV-C42 (C42). C42 is predominantly detected within the infected-cell nucleus: at 24 h postinfection (p.i.), it is coincident with the virogenic stroma, but by 72 h p.i., the stroma is minimally labeled while C42 is more uniformly located throughout the nucleus. Yeast two-hybrid screens indicate that C42 is capable of directly interacting with the viral proteins p78/83 (1629K) and ODV-EC27 (orf144). These interactions were confirmed using blue native gels and Western blot analyses. At 28 h p.i., C42 and p78/83 are detected in two complexes: one at approximately 180 kDa and a high-molecular-mass complex (500 to 600 kDa) which also contains EC27.

Effects of deletion and overexpression of the Autographa californica nuclear polyhedrosis virus FP25K gene on synthesis of two occlusion-derived virus envelope proteins and their transport into virus-induced intranuclear membranes.

Partial deletions within Autographa californica open reading frame 61 (FP25K) alter the expression and accumulation profile of several viral proteins and the transport of occlusion-derived virus (ODV)-E66 to intranuclear membranes during infection (S. C. Braunagel et al., J. Virol. 73:8559-8570, 1999). Here we show the effects of a full deletion and overexpression of FP25K on the transport and expression of two ODV envelope proteins, ODV-E66 (E66) and ODV-E25 (E25). Deletion and overexpression of FP25K substantially altered the levels of expression of E66 during infection. Compared with cells infected with wild-type (wt) virus, the levels of E66 were reduced fivefold in cells infected with a viral mutant lacking FP25K (DeltaFP25K) and were slightly increased in cells infected with a viral mutant overexpressing FP25K (FP25K(polh)). In contrast, no significant changes were observed in the levels of E25 among wt-, DeltaFP25K-, and FP25K(polh)-infected cells. The changes observed in the levels of E66 among the different viral mutants were not accompanied by changes in either the time of synthesis, membrane association, protein turnover, or steady-state transcript abundance. Deletion of FP25K also substantially altered the transport and localization of E66 during infection. In cells infected with the DeltaFP25K mutant virus, E66 accumulated in localized regions at the nuclear periphery and the outer nuclear membrane and did not traffic to intranuclear membranes. In contrast, in cells infected with the FP25K(polh) mutant virus E66 trafficked to intranuclear membranes. For comparison, E25 was normally transported to intranuclear membranes in both DeltaFP25K- and FP25K(polh)-infected cells. Altogether these studies suggest that FP25K affects the synthesis of E66 at a posttranscriptional level, probably by altering the translation of E66; additionally, the block in transport of E66 at the nuclear envelope in DeltaFP25K-infected cells suggests that the pathway of E66 trafficking to the inner nuclear membrane and intranuclear microvesicles is specifically regulated and must be influenced by factors that do not control the traffic of E25.

Mutations within the Autographa californica nucleopolyhedrovirus FP25K gene decrease the accumulation of ODV-E66 and alter its intranuclear transport.

Previous reports indicate that mutations within the Autographa californica nucleopolyhedrosis virus FP25K gene (open reading frame 61) significantly reduce incorporation of enveloped nucleocapsids into viral occlusions. We report that FP25K is a nucleocapsid protein of both the budded virus (BV) and occluded virus (ODV), and we describe the effects of two FP25K mutations (480-1 [N-terminal truncation] and FP-betagal [C-terminal fusion]) on the expression and cellular localization of ODV-E66 and ODV-E25. Significantly decreased amounts of ODV-E66 are detected in cells infected with 480-1 or FP-betagal viral mutants, even though during FP-betagal infection, steady-state levels of ODV-E66 transcripts remain unchanged. While ODV-E66 is normally detected in intranuclear microvesicles and ODV envelopes by 24 h postinfection (p.i.), ODV-E66 remains cytosolic throughout infection in cells infected with 480-1 virus (up to 96 h p.i.), and its intranuclear localization is not detected until 96 h p.i. in cells infected with the FP-betagal mutant virus. The nuclear localization of ODV-E25 is not affected during infection by the FP-betagal mutant; however, its trafficking is significantly delayed during infection by the 480-1 mutant. Temporal Western blot analyses of cell lysates show that both 480-1 and FP-betagal mutant virus infections result in altered accumulation patterns of several structural proteins, including gp67, BV/ODV-E26, and the major capsid protein p39. In addition to BV/ODV-E26, ODV-E66 and gp67 may interact with FP25K, and ODV-E25 and p39 may also be components of a protein complex containing ODV-E66 and FP25K. Together, these data suggest that FP25K and its associated protein complex(es) may play an important role in the targeting and intracellular transport of viral proteins during infection.