Transformation of rat cells by an altered polyoma virus genome expressing only the middle-T protein

Abstract

A modified polyoma virus genome has been constructed which can encode the middle-T protein, but not the large-T or small-T proteins. This was achieved, starting with the full length viral DNA inserted into a plasmid vector, by replacing a small genomic restriction fragment spanning the middle-T intervening sequence with the equivalent fragment from a cloned partial cDNA copy of the middle-T protein mRNA. Transfection of the modified viral DNA into cultured rat cells efficiently induced the formation of transformed cell foci which gave rise to cell lines that grew as tumours after injection into Fisher rats. The only viral early-region antigen synthesized by the cell lines was the middle-T protein. Expression of the middle-t protein is therefore sufficient to establish and maintain a transformed state. The viral mRNA produced by two of the transformed cell lines was structurally indistinguishable from the normal middle-T mRNA found in productively infected cells, suggesting that RNA splicing is not an essential step in the biogenesis of this messenger.

Association between src-kinases and the polyoma virus oncogene middle T-antigen requires PP2A and a specific sequence motif

“…Expression of the polyoma virus encoded middle Tantigen (MT) in established rodent ®broblasts alters the cell's properties to a fully transformed phenotype (Treisman et al, 1981). MT does not appear to express any enzymatic activity of its own.…”

Protein kinase B/Akt is activated by polyomavirus middle-T antigen via a phosphatidylinositol 3-kinase-dependent mechanism

“…Mouse polyomavirus induces a broad spectrum of tumors in mice and transforms cells in culture (Treisman et al, 1981;Rassoulzadegan et al, 1982). The viral proteins mediating this function are the tumor antigens, in particular the middle-T antigen.…”

At the onset of transformation polyomavirus middle-T recruits shc and src to a perinuclear compartment coincident with condensation of endosomes

“…The middle-T antigen (mT) of polyomavirus is su cient to transform a wide variety of cell lines as well as produce tumours in transgenic animals (Aguzzi et al, 1991;Gri n and Dilworth, 1983;Rassoulzadegan et al, 1990;Treisman et al, 1981) and is a model system for studying many aspects of transformation (reviewed in Dilworth, 1995). However, the role of mT in transformation has been determined almost exclusively in transformed or lytically infected cells and at a single time point (Andrews et al, 1993;Carmichael et al, 1982;Dilworth et al, 1986;Krauzewicz et al, 1994;Segawa and Ito, 1982;Zhu et al, 1984).…”