Preneoplastic potential of morphologically distinct transformed foci induced by 3-methylcholanthrene.
Individual variability of scoring foci positive for transformation presents a difficult problem in assessing the transformation assay. In this study, an attempt was made to identify five morphologically distinct types of transformed foci based on size (2-3, 3-4, and > or = 4 mm in diameter), invasiveness (smooth vs. invading margins), and other properties (piling vs. spread) induced by 3-methylcholanthrene in Balb/c-3T3 cells. The transformed focal cells were used in in vitro studies including anchorage-independent analysis, focal reconstruction, gene transfection using NIH-3T3 host cells, and Southern blotting to assess amplification of five proto-oncogenes (K-ras, H-ras, c-fos, c-jun, c-myc) and a tumor suppressor (p53) gene. Results showed that 1) there was a significant increase in anchorage-independent growth of all five types of foci ranging from 7-12%; 2) all five morphological types of transformed foci showed 8-15% focal reconstruction; 3) DNA from all five types of transformed foci induced transformation in NIH-3T3 cells at a level significantly above the control DNA; 4) gene amplification studies indicated amplification in both K-ras and H-ras proto-oncogenes; however, c-fos, c-jun, and c-myc did not show DNA amplification. The tumor suppressor gene (p53) was activated and the increase was up to 3-fold over the normal Balb/c-3T3 DNA. These findings are consistent with our hypothesis that all five morphologically different foci have preneoplastic potential and that any foci of size > or = 2 mm regardless of invasiveness and piling should be scored as positive during the transformation assay.
Keshava
N
N
Genetics and Developmental Biology Program, West Virginia University, Morgantown, USA.
Keshava
C
C
Whong
W Z
WZ
Hubbs
A F
AF
Nath
J
J
Ong
T
T
D016475:3T3 Cells; D000818:Animals; D015139:Blotting, Southern; D002273:Carcinogens / Q000633:toxicity*; D002471:Cell Transformation, Neoplastic / Q000187:drug effects* / Q000235:genetics; D002999:Clone Cells; D008748:Methylcholanthrene / Q000633:toxicity*; D051379:Mice; D008807:Mice, Inbred BALB C; D009153:Mutagens / Q000633:toxicity; D009154:Mutation; D011230:Precancerous Conditions / Q000235:genetics*; D011519:Proto-Oncogenes; D014162:Transfection
D002273:Carcinogens; D009153:Mutagens; D008748:Methylcholanthrene