This study describes a rounding reaction induced in mammalian cells by the addition of phenylalaninol. In the Chinese hamster ovary tsH1 line the rounding occurred rapidly with a half time of 1 min at 25 mM phenylalaninol. After the removal of phenylalaninol, the rounding was reversed, leading to the reflattening of the cells with a half-time of 3.5 min. Rounding was inhibited by dibutyryl-cAMP and testosterone, and reflattening by cytochalasin B. Either in the case of the tsH1 line and its growth-control revertant GRC+L-73, or in the case of SV40-transformed and untransformed human WI-38 cells, the transformed cells displayed a weakened resistance toward rounding. Likewise rat cells transformed by th highly oncogenic adenovirus-12 were more sensitive to rounding than cells transformed by the poorly oncogenic adenovirus-5, which in turn were more sensitive than untransformed cells. However, drug-resistant cell-surface mutants of the Chinese hamster ovary GAT- line also exhibited an altered sensitivity to rounding. These findings suggest that more than one cellular component determines cellular sensitivity to phenylalaninol-induced rounding. One of these components is specifically altered, giving rise to an enhanced sensitivity, in the course of tumorigenic transformation.
