Polyomavirus large and small T antigens cooperate in induction of the S phase in serum-starved 3T3 mouse fibroblasts

Abstract

The induction of an S phase in the host cell is a prerequisite for the lytic replication cycle of polyomavirus. This function was attributed to proteins coded for by the early region of the viral DNA, the T antigens. A consideration of the role of the T antigens in the initiation of a mitogenic response of the host cell has to take into account the recent discovery that virus adsorption is sufficient to induce the synthesis of proteins which are known to appear early after quiescent cells are stimulated by the addition of serum, namelyfos, jun, and myc (

Genetic analysis of polyomavirus large T nuclear localization: nuclear localization is required for productive association with pRb family members

“…Activation of the promoter of c-fos ( Fig. 3) is associated with LT's stimulation of the cell cycle (44). The role of pRb-p107 binding in this transactivation has not been previously demonstrated for LT. Figure 3 shows that pCMV-LT.Rb Ϫ can transactivate pfos-CAT as efficiently as the wild type.…”

Binding of Polyomavirus Small T Antigen to Protein Phosphatase 2A Is Required for Elimination of p27 and Support of S-Phase Induction in Concert with Large T Antigen

“…We found that the addition of dexamethasone to 3T3 LT or to 3T3 ST cells causes only a few percent of serum-starved, quiescent cells to move into S phase within 32 h after induction of the T antigen. In contrast, expression of both viral proteins drives about 30% of the cells into S phase (26). We could show that, despite the failure to induce S phase in a sizable fraction of cells, expression of Py LT in quiescent mouse fibroblasts results in efficient transactivation of S-phasespecific enzymes and that this is dependent on the interaction of the T antigen with pocket proteins (23,27).…”

“…Cell culture and transfections. Swiss 3T3 cells and derived cells conditionally expressing the Py T antigens (26) were maintained in Dulbecco's modified Eagle's medium supplemented with 10% fetal calf serum (FCS), penicillin (60 g/ml), and streptomycin (100 g/ml) in a 7.5% CO 2 atmosphere. For growth arrest, asynchronously growing cells were seeded at 5 ϫ 10 5 cells per 100-mmdiameter petri dish; the next day, the serum concentration was reduced to 0.2% for 72 h. Cells were then either growth induced by addition of fresh medium containing 20% FCS or treated with dexamethasone at a concentration of 10 Ϫ6 mol/liter.…”

“…We have previously produced Swiss 3T3 cells carrying the information of Py LT and/or Py ST in hormone-inducible form (26). When dexamethasone at a concentration of 1 mol/liter is added to cultures of such cells, T antigen(s) can be readily detected by immunoblotting about 4 h thereafter.…”

DNA content distribution of mouse cells following infection with polyoma virus

“…Studies with mutant Py virus have suggested that the second phase of c-rnyc and c-fos accumulation may be regulated by the small T either alone or in combination with the large T antigen (20). When Ogris et al (17) transfected plasmids that contained the large or small polyoma T antigens under the control of a dexamethasone inducible mammary tumor virus promoter and a selective marker into 3T3 cells, the isolated cells were induced to express the large or small T antigen. The results demonstrate that neither large or small T antigen alone stimulated DNA synthesis; however, if both T antigens were expressed in the same serum starved 3T3 cell, DNA synthesis was induced.…”