Mutations in the VP1 coding region of polyomavirus determine differentiating stage specificity

PARP-1 interaction with VP1 capsid protein regulates polyomavirus early gene expression

Poly(ADP-ribose)polymerases are involved in fundamental cellular events as well as they seem to be associated to some viral infection process. In this work, the poly(ADP-ribose)polymerase-1 (PARP-1) role in the polyomavirus life cycle has been investigated. Early viral transcription was reduced by competitive inhibitors of PARPs in Swiss 3T3 cells and almost abolished in PARP-1 knockout fibroblasts and in wild-type fibroblasts when PARP-1 was silenced by RNA interference. In vivo chromatin immunoprecipitation assays showed that poly(ADP-ribosyl)ation (poly(ADP-ribose)) facilitates the release of the capsid protein viral protein 1 (VP1) from the chromatin of infecting virions. In vitro experiments demonstrated that VP1 stimulates the enzymatic activity of PARP-1 and binds non-covalently both protein-free and PARP-1-bound poly(ADP-ribose). Our studies suggest that PARP-1 promotes the complete VP1 displacement from viral DNA favouring the viral early transcription.

Chromosome-protein interactions in polyomavirus virions

In this work, we sought to determine whether the components of the murine polyomavirus capsid establish specific interactions with the minichromosome encapsidated into the mature viral particles by using the cis-diamminedichloroplatinum(II) cross-linking reagent. Our data indicated that VP1, but not minor capsid proteins, interacts with the viral genome in vivo. In addition, semiquantitative PCR assays performed on cross-linked DNA complexes revealed that VP1 binds to all regions of the viral genome but significantly more to the regulatory region. The implications of such an interaction for viral infectivity are discussed.

Formation of polyomavirus-like particles with different VP1 molecules that bind the urokinase plasminogen activator receptor

Icosahedral virus-like particles formed by the self-assembly of polyomavirus capsid proteins (Py-VLPs) can serve as useful nanostructures for delivering nucleic acids, proteins, and pharmaceuticals into animal cells and tissues. Four predominant surface-exposed loops in the VP1 structure offer potential sites to display sequences that might contribute new targeting specificities. Introduction into each of these loops of sequences derived from the amino-terminal fragment of urokinase plasminogen activator (uPA) or a related phage display peptide reduced the solubility of VP1 molecules when expressed in insect cells, and insertions into the EF loop reduced VP1 solubility least. Coexpression in insect cells of the uPA-VP1 molecules and VP1 containing a FLAG epitope in the HI loop permitted the formation of heterotypic Py-VLPs containing uPA-VP1 and FLAG-VP1. These heterotypic VLPs bound to uPAR on the surfaces of animal cells. Heterotypic Py-VLPs containing ligands for multiple cell surface receptors should be useful for targeting specific cells and tissues.

A mutation in the DE loop of the VP1 protein that prevents polyomavirus transcription and replication

Natural mutants of the DE loop of the Polyomavirus (Py) major coat protein VP1 have been previously shown to display an altered host specificity (L. Ricci, R. Maione, C. Passananti, A. Felsani, and P. Amati, 1992, J. Virol. 66, 7153-7158). To better understand the role of this outfacing loop of the VP1 protein in Py infectivity, we constructed and characterized a Py mutant (Py M17) harboring a deletion of 7 AA within the tip of the DE loop. The mutant virions obtained after DNA transfection were unable to replicate and initiate early transcription in fibroblast cells. Complementation experiments performed to rescue the deficient M17 replication by means of wt functions revealed the cis-dominance of the mutation. In situ cell fractionation experiments demonstrated that the Py mutant, like the Py wt, enters the cells, reaches the nucleus and that both the viral DNA and VP1 protein are found tightly bound to the nuclear matrix. These data suggest that the VP1 protein, associated to the viral DNA, conditions early viral gene expression and that the DE loop of the protein must be involved in this process.

The polyomavirus major capsid protein VP1 interacts with the nuclear matrix regulatory protein YY1

Polyomavirus reaches the nucleus in a still encapsidated form, and the viral genome is readily found in association with the nuclear matrix. This association is thought to be essential for viral replication. In order to identify the protein(s) involved in the virus-nuclear matrix interaction, we focused on the possible roles exerted by the multifunctional cellular nuclear matrix protein Yin Yang 1 (YY1) and by the viral major capsid protein VP1. In the present work we report on the in vivo association between YY1 and VP1. Using the yeast two-hybrid system we demonstrate that the VP1 and YY1 proteins physically interact through the D-E region of VP1 and the activation domain of YY1.

Mutations of polyomavirus VP1 allow in vitro growth in undifferentiated cells and modify in vivo tissue replication specificity

Mutants of polyomavirus with altered host specificities were isolated in undifferentiated C2 myoblast cells (L. Ricci, R. Maione, C. Passananti, A. Felsani, and P. Amati, J. Virol. 66:7153-7158, 1992). The mutations responsible for this phenotype belonged to either of the two classes: a large duplication of the enhancer region or a 6-bp deletion in the VP1 coding region. Since both classes of mutations enabled the virus to grow in undifferentiated myoblast cells, we investigated their ability to replicate in embryonal carcinoma cells and in various tissues in newborn mice. Our results show that both kinds of mutations confer the ability to replicate in vitro in embryonal carcinoma F9 cells; the VP1 mutants acquired an in vivo host range of replication which is different from that of their original wild-type strain, whereas the mutation in the regulatory region did not alter the in vivo growth spectrum.