Suppression of transformation by and growth adaptation to low concentrations of glutamine in NIH-3T3 cells

Abstract

NIH-3T3 cells, commonly used as targets for oncogene-mediated neoplastic transformation, undergo high rates of spontaneous transformation. When the glutamine concentration in the medium was reduced from 5 to 1 mM or less, the transformation rate was reduced. This effect was not dependent upon a reduction in the growth rate, which remained unaffected by reduction of glutamine even to 0.6 mM. Upon trypsinization and transfer to 5 mM glutamine-containing medium, cells exposed to 0.2 mM glutamine for as little as 4 days formed fewer foci than control cells exposed over a similar period to 5 mM glutamine. This indicates that short term changes in the supply of this polyfunctional metabolite have heritable consequences in later cell generations. If populations containing highly transformed cells were passaged weekly for 1-3 weeks in 0.2 mM glutamine, resultant populations were better adapted to grow in low-glutamine medium and formed fewer transformed foci upon re-transfer to 5 mM glutamine medium, suggesting that the transformed state is at least partially reversible. If similar cell populations were exposed to low-glutamine medium but were not passaged, growth adaptation occurred but there was no reduction in focus formation, indicating that maintenance of a moderate rate of cell division may be required in addition to the lowered glutamine for reversal of transformation. Transformed and non-transformed cells originating from foci and from nonfocal areas of the same culture dishes multiplied at the same reduced rate in 0.2 mM glutamine. This indicates that suppression of spontaneous transformation in low-glutamine medium was not the result of selecting pre-existing variants but was itself an adaptive response of the population.