Regulation of cellular phenotype and expression of polyomavirus middle T antigen in rat fibroblasts.
Polyoma middle T antigen (mT) was expressed in rat F-111 cells under control of the dexamethasone-regulatable mouse mammary tumor virus promoter. Graded phenotypic responses to levels of mT induction by the hormone were seen, with morphological transformation, focus formation, and anchorage-independent growth requiring increasing levels of mT expression. The ability of different clones to form tumors reflected their maximum level of induction of mT-associated kinase and their ability to grow in soft agar. Expression of transformation parameters and tumorigenicity correlates with the level of mT phosphorylated by pp60c-src in immune complexes and not with the total amount of mT determined by metabolic labeling. We suggest that cellular factors regulate mT activity by forming a kinase-active fraction of mT molecules that controls the transformed state.
D000818:Animals; D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor / Q000235:genetics / Q000502:physiology*; D002448:Cell Adhesion; D002460:Cell Line; D002472:Cell Transformation, Viral; D003907:Dexamethasone / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D005813:Genes, Synthetic; D008297:Male; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics; D009368:Neoplasm Transplantation; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000502:physiology*; D010641:Phenotype; D011120:Polyomavirus / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011494:Protein Kinases / Q000235:genetics / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016392:Proto-Oncogene Proteins pp60(c-src); D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000502:physiology
D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor; D009856:Oncogene Proteins, Viral; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D003907:Dexamethasone; D011494:Protein Kinases; D016392:Proto-Oncogene Proteins pp60(c-src)