Accumulation of anchorage independent cells showing amplified genes (CAD) during the in vitro propagation of CHEF18 Chinese hamster cells.

Anchorage independence and gene amplification have frequently been associated with a transformed or tumorigenic phenotype in cultured mammalian cells. However, it is unknown whether these two traits occur as related events during transformation, or are independent features of the transformed phenotype. To clarify this point, immortalized, untransformed CHEF18 Chinese hamster cells were propagated in culture until they became transformed and tumorigenic. The frequencies with which CHEF18 cells formed colonies either in soft agar, in medium containing N-phosphonacetyl-L-aspartate or in the two selective media simultaneously, were determined. The results indicate that anchorage independence and CAD gene amplification spontaneously arose during the propagation of the cells and that their concurrent emergence was not the consequence of independent events. However, the kinetics of their appearance suggests that anchorage independence is the early event whereas gene amplification might represent one of the numerous events which can be dynamically selected in anchorage-independent cells.