Oncogenic transformation increases the sensitivity for apoptosis inductionby inhibitors of macromolecular synthesis

Inhibition of RNA or protein synthesis causes apoptosis in fibroblasts. Thi s points to the constitutive expression of a longlived apoptosis machinery which is controlled by shortlived negative regulatory proteins, termed endo genous survival factors. The length of time between addition of the inhibit or of macromolecular synthesis and the onset of apoptosis can be used as an estimation of the effective survival factor concentration. Transformation of rat fibroblasts by a constitutively expressed src oncogene or an inducib le ms oncogene increases the sensitivity for apoptosis induction by inhibit ors of macromolecular synthesis, indicating that their endogenous survival factor pool has been decreased.