Efficient induction of focus formation in a subclone of NIH3T3 cells by c-myc and its inhibition by serum and by growth factors.
In both experimental and spontaneous tumors, c-myc expression is often enhanced following its amplification or its rearrangement adjacent to a strong promotor/enhancer. However, c-myc by itself does not induce foci efficiently in fibroblast cultures. The effect of high levels of c-myc expression from a retroviral construct was investigated in several rodent fibroblast cell lines grown in medium containing 10% fetal calf serum or in serum-free PC-1 medium. c-myc-infected NIH3T3 clone 7 cells exhibited efficient quantitative focus formation when grown in PC-1 medium, whereas foci were not detected when grown in serum-supplemented medium. NIH3T3 clone 7 was the only cell line found to be sensitive to c-myc; other clones of NIH3T3 or other rodent fibroblast cell lines proved to be resistant to c-myc focus formation. At least two major types of morphologically distinct c-myc-induced foci were observed; the first was similar to ras-transformed foci induced in NIH3T3 and other fibroblast cell lines, and the second type was composed of adipocyte-like cells similar to NIH3T3 L1 cells. The c-myc infected cells cloned from these two types of foci expressed high levels of retrovirus-derived c-myc RNA and exhibited elevated levels of immunoreactive myc protein, as detected by immunofluorescent staining with an anti-myc polyclonal antibody. c-myc-transformed clones displayed only a limited ability to grow in soft-agar in the presence of serum and were not tumorigenic in nude mice. Focus formation by c-myc was quantitatively inhibited by the addition of interferon alpha + beta (INF alpha, beta), tumor necrosis factor alpha (TNF alpha) or transforming growth factor beta 1 (TGF beta 1) to the serum-free PC-1 medium, and, in correlation, NIH3T3 clone 7 cells produced the lowest level of endogenous TGF beta of the various cell lines tested.
Laboratory of Tumor Immunology and Biology, National Cancer Institute, NIH, Bethesda, Maryland 20892.
B
B
Blondel
N
N
Talbot
G R
GR
Merlo
C
C
Wychowski
H
H
Yokozaki
E M
EM
Valverius
D S
DS
Salomon
R H
RH
Bassin
D000818:Animals; D001798:Blood Proteins / Q000494:pharmacology*; D002460:Cell Line; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D006133:Growth Substances / Q000494:pharmacology*; D007370:Interferon Type I / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology*; D016271:Proto-Oncogene Proteins c-myc; D011519:Proto-Oncogenes; D051381:Rats; D015291:Transforming Growth Factors / Q000378:metabolism / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D001798:Blood Proteins; D006133:Growth Substances; D007370:Interferon Type I; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D014409:Tumor Necrosis Factor-alpha; D015291:Transforming Growth Factors