pRb suppresses camptothecin-induced apoptosis in human osteosarcoma Saos-2cells by inhibiting c-Jun N-terminal kinase

This paper studies the cytotoxic effect induced by the topoisomerase I inhi bitor camptothecin in human osteosarcoma Saos-2 cells, which lack p53 and c ontain a non-functional form of the product of the retinoblastoma gene, pRb , Cytotoxicity induced by camptothecin was dose- and time-dependent; the tr eatment with 100 nM camptothecin reduced cell viability by 50% at 32 h and by 75% at 72 h of exposure, The cytotoxic effect was caused by apoptosis, a s ascertained by morphological evidence, acridine orange-ethidium bromide s taining and flow cytometric analysis. Apoptosis was accompanied by both the activation of caspase-3 and the fragmentation of poly(ADP-ribose) polymera se, Treatment with camptothecin caused a threefold increase in the activity of c-Jun N-terminal kinase (JNK) and an eightfold increase in the level of phosphorylated c-Jun, The introduction of the RE gene into Saos-2 cells re duced the rate of cell growth. Moreover, stable clones of transfected cells were resistant to camptothecin, Exposure to 100 nM camptothecin for 72 h r educed the viability of transfected cells by only 10% moreover, very modest effects were observed on the activity of JNK as well as on the level of ph osphorylated c-Jun, The results reported in this paper support the conclusi on that the expression of wild-type pRb in Saos-2 cells exerts an antiapopt otic Influence through the control of JNK activity. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B,V. All righ ts reserved,