Analysis of polyomavirus middle-T-antigen-transformed rat cell variants expressing different levels of pp60c-src.
We characterize two independent variant cellular clones which arose following in vitro passage of polyomavirus middle-T-antigen (MTAg)-transformed FR3T3 cells expressing RNA complementary to c-src mRNA. These clones were initially flat and underwent morphologic transformation at a high frequency to a phenotype indistinguishable from that of parental MTAg-transformed FR3T3 cells. Biochemical analysis of the flat clones prior to phenotypic conversion revealed that these cells synthesized little detectable pp60c-src and had correspondingly low levels of pp60c-src protein kinase activity and MTAg-associated protein kinase activity. The flat cell clones did not possess detectable focus-forming activity, were not capable of detectable anchorage-independent growth, and had saturation densities and doubling times below those normally observed for FR3T3 cells. Following conversion of the flat clones to a shape resembling that of typical MTAg-transformed cells, the abundance of pp60c-src, pp60c-src kinase activity, and MTAg-associated in vitro protein kinase activity were all restored to the levels found in the parental MTAg transformants. These cells had growth rates, focus-forming activities, anchorage-independent growth rates, and saturation densities similar to those of the parental MTAg-transformed rat cells. These data provide additional evidence that maintenance of a transformed phenotype by polyomavirus MTAg in established rat cell lines depends, at least in part, on a minimal threshold level of pp60c-src.
D000818:Animals; D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor / Q000235:genetics*; D002455:Cell Division; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D002999:Clone Cells; D014644:Genetic Variation; D009856:Oncogene Proteins, Viral / Q000235:genetics*; D011120:Polyomavirus / Q000201:enzymology / Q000235:genetics*; D011494:Protein Kinases / Q000235:genetics*; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016392:Proto-Oncogene Proteins pp60(c-src); D051381:Rats
D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor; D009856:Oncogene Proteins, Viral; D011518:Proto-Oncogene Proteins; D011494:Protein Kinases; D016392:Proto-Oncogene Proteins pp60(c-src)