Subcellular localisation of the middle and large T-antigens of polyoma virus.

Abstract

The distribution of two of the polyoma virus early proteins (the large and middle T‐antigens) in lytically infected mouse cells and transformed rat cells has been investigated by indirect immunofluorescence and immuno‐electron microscopy using well‐characterised monoclonal antibodies. By these techniques, the viral large T‐antigen was found almost exclusively in the nucleus, sometimes in association with nuclear pores, but never in the nucleolus. In lytically infected, but not transformed cells, fluorescence was detected in discrete areas (‘hot spots’) within the nucleus and, in a minor population of lytically infected cells, cytoplasmic immunoreactive material was observed. The viral middle T‐antigen was found in association with most cytoplasmic membranes and in the majority of cells mainly in the endoplasmic reticulum. Only a fraction of the staining was observed in the plasma membrane and no staining in the nucleoplasm was observed. The data suggest that the site of action of the major transforming activity of polyoma virus need not be at the plasma membrane. Functions associated with the viral antigens are discussed in terms of their subcellular distributions within cells.

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

“…Localization of mT within the cell interior has been observed previously (Dilworth et al, 1986;Zhu et al, 1984;Messerschmidt et al, 1996). However, in these studies cellular morphology with respect to the early events in transformation and the site of initial sub-cellular location of mT were not analysed in detail.…”

“…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). As a result, little is known about the initial changes that occur in cells expressing mT.…”

“…Although extensively studied, the site of mT membrane localization remains unresolved with morphologic studies favouring intracellular membranes (Dilworth et al, 1986;Templeton et al, 1984;Zhu et al, 1984) while biochemical analyses continue to be interpreted as suggesting that kinase active mT containing complexes are located at the plasma membrane (Ballmer-Hofer and Benjamin, 1985;Ito et al, 1977;Scha hausen et al, 1982;Segawa and Ito, 1982). Recently, we have demonstrated a role for cytoskeletal proteins, particularly actin, in the localization of mT (Andrews et al, 1993).…”

Cell transformation by the middle T-antigen of polyoma virus

“…MT is associated with most cellular membranes (Dilworth et al, 1986), though localization to a precise perinuclear membrane site may be an initial step (Zhu et al, 1998). MT is probably synthesized on free polysomes, and then attaches to membranes via a 22 residue stretch of hydrophobic amino acids found near its C-terminal end.…”

Modeling variation in tumors in vivo

“…These mice carry a transgene that causes expression of the polyoma virus middle T antigen in mammary cells. Middle T antigen is located at the cell membrane, where it binds and activates kinases that ultimately activate the Ras signal transduction pathway (29,30). It was reasonable to anticipate that cells in the polyoma virus middle T antigen tumor model might exhibit reduced genetic stability, because Ras pathway activation has been linked to genetic instability (31)(32)(33).…”