Cooperation of middle and small T antigens of polyomavirus in transformation of established fibroblast and epithelial-like cell lines.
We have reported recently that small T antigen of polyomavirus stimulates the growth of NIH 3T3 cells beyond their saturation density and induces weak anchorage-independent growth (T. Noda, M. Satake, T. Robins, and Y. Ito, J. Virol. 60:105-113, 1986). We examined whether small T antigen would cooperate with middle T antigen in the in vitro transformation of NIH 3T3 (fibroblasts) and NRK-52E (epitheliallike) cells. The small-T-antigen gene, when cotransfected with the middle-T-antigen gene, had no additional effect on the efficiency or size of dense foci formation induced by the middle-T-antigen gene on a monolayer of NIH 3T3 cells. However, the small-T-antigen gene dramatically increased the rate of growth of NIH 3T3 cells transformed by middle T antigen in semisolid medium. Introduction of the small-T-antigen gene into middle-T-antigen-transformed cells did not disturb the integrated middle-T gene, alter expression of the middle-T gene, or enhance middle-T-antigen-associated tyrosine protein kinase activity. For NRK-52E cells, the expression of middle T antigen alone resulted in small, slow-growing foci on a monolayer. These cells did not show anchorage-independent growth, despite the fact that middle-T-antigen-associated tyrosine protein kinase activity was clearly detected in these cells. NRK-52E cells expressing both middle and small T antigens formed faster growing foci on a monolayer than middle-T-antigen-expressing cells did and grew in semisolid medium, even when the amounts of middle T antigen and its associated kinase activities were lower than those of middle-T-antigen-expressing cells. We conclude that small T antigen cooperates with middle T antigen in the in vitro transformation of established cell lines of fibroblast and epitheliallike cells, that it does not share the middle-T-antigen function even though they are structurally related, and that it has a significantly more important role in the transformation of NRK-52E cells than that of NIH 3T3 cells.
D000818:Animals; D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor / Q000235:genetics / Q000502:physiology*; D002455:Cell Division; D002460:Cell Line; D002472:Cell Transformation, Viral; D003260:Contact Inhibition; D004848:Epithelium / Q000473:pathology*; D005347:Fibroblasts / Q000473:pathology*; D051379:Mice; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000502:physiology*; D011120:Polyomavirus / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000502:physiology*; D051381:Rats; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology
D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor; D009856:Oncogene Proteins, Viral; D014764:Viral Proteins; D011505:Protein-Tyrosine Kinases