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

Abstract

Polyomavirus mutants capable of replicating in undifferentiated murine C2 myoblasts were selected and characterized. These mutants grow normally in 3T6 mouse fibroblast cells, and they do not complement the wild-type virus in coinfection experiments of C2 myoblasts. Of 12 isolates, 10 possess duplications of the regulatory region including the enhancer A domain. On the bases of the regulatory region structure and the presence and length of the enhancer duplication, the mutant viruses could be grouped into three classes. One mutant class (e.g., PyMB3) possesses an enhancer duplication of 91 bp identical to that of a previously characterized polyomavirus mutant, PyNB11/1. We have demonstrated that this enhancer duplication gives rise at its junction to a novel recognition motif for the transcriptional factor NF-1 (M. Caruso, C. Iacobini, C.

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

“…Conclusions. These results confirmed our previous report (24) claiming that in vitro host specificity can be determined by both enhancer constitution and VP1 type. We found that the two VP1 mutations selected in undifferentiated myoblast cells also confer to the virus the ability to replicate in undifferentiated embryonal carcinoma F9 cells, strongly indicating that VP1, directly or indirectly, plays a role in viral replication.…”

“…In recent years, several laboratories have investigated the relationship between the genomic variations of mouse polyomavirus (Py) and the tissue specificity of in vitro and in vivo viral replication and oncogenic transformation. In in vitro studies, it was found that host range alteration of replication was due to mutations of the regulatory region (for reviews, see references 2 and 30) except for the two mutants that we isolated in undifferentiated myoblast cells (24). On the other hand, in in vivo studies, both the regulatory region and the major capsid protein VP1 were shown to determine different tissue specificities of replication (1,4,6,9,11,25,31).…”

“…Py mutants MB3, MB40, and MB27 were isolated for their capacity to grow in undifferentiated C2 myoblast cells (24). Their broader host range was determined by a 91-bp duplication (nucleotides 5047 to 5138) in the enhancer region that encompasses the A and D domains (29) in the case of Py MB3 or, in the cases of Py MB27 and Py MB40, by a 6-bp deletion in the VP1 coding region (nucleotides 3627 to 3632 and 3636 to 3641, respectively).…”

“…Only these genomic modifications were shown to cause the altered phenotype. The viruses used in the present work are Py MB3.1, a reconstructed virus in which the regulatory region of Py MB3 has been recombined into the wild-type (wt) genomic context, Py MB40.2, a reconstructed genome in which the regulatory region of Py MB40 has been substituted with the wt homologous region in order to eliminate the concomitant 30-bp duplication in the enhancer A domain that by itself did not determine growth in undifferentiated myoblast cells, and PyMB27, which displayed only the 6-bp deletion and a wt enhancer (24).…”

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

“…Results from our and other laboratories [16–21] had suggested the possibility that VP1, the major capsid protein, could determine alterations in the host specificity of growth and tumorigenicity. In order to determine the possible mechanisms that allow the encapsidated polyomaviruses that reach the cell nucleus to associate with the NM, we investigated the possible role of YY1 in this necessary step of viral function.…”