Cell transformation induced by Rous sarcoma virus: analysis of density dependence

Trypsinized chick embryo cells will divide at least once when seeded onto stationary, preexisting cultures of chick cells, but not when seeded onto stationary mouse cells. It is suggested that the mouse cells reconstitute a surface component for the trypsinized chick cells. These findings explain why crowded mouse cell layers, but not chick cell layers, suppress the transformation of chick cells infected with Rous sarcoma virus (RSV), since the infected cells must proceed through one cell cycle before transformation is expressed. Density-dependent suppression of cell transformation by RSV is not related to the susceptibility of the inhibiting cell layer to infection with RSV. High cell density does not affect the adsorption and penetration of RSV but does affect the development of morphologically distinct foci of Rous cells. In cultures which are dense, aged, or maintained without agar overlay, morphological conversion is suppressed without concomitant suppression of transformed growth characteristics. In these conditions, therefore, morphological conversion is considered a poor index of neoplastic transformation induced by RSV.