BCL-2 OVER-EXPRESSION DELAYS RADIATION-INDUCED APOPTOSIS WITHOUT AFFECTING THE CLONOGENIC SURVIVAL OF HUMAN PROSTATE-CANCER CELLS

In this study we evaluated the effect of over-expression of the bcl-2 gene, a potent apoptosis suppressor, on radiation-induced apoptotic ce ll death in 2 human prostate cancer cell lines, androgen-independent P C-3 cells and androgen-sensitive LNCaP cells. Cells were transfected w ith the bcl-2 gene and bcl-2 transfectant clones isolated under neomyc in selection; bcl-2 gene integration and level of mRNA and protein exp ression in the cloned transfectants were examined by Southern, Norther n and Western blot analyses, respectively. Parental, neo control and b cl-2-expressing cells were exposed to single or fractionated doses of ionizing irradiation, and the cellular response to radiation was deter mined at 24, 48 and 72 hr post-irradiation, on the basis of: (i) loss of cell viability, (ii) clonogenic survival and (iii) induction of apo ptotic DNA fragmentation. At 24 hr post-irradiation all cell lines, i. e., parental and bcl-2 transfectants, failed to form colonies, though the majority of bcl-2-expressing cells did not exhibit apoptotic morph ology; bcl-2 over-expression in both cell lines reduced apoptosis 48 h r post-irradiation from 20-25% to 5% at a dose of 2,000 cGy. By 72 hr, bcl-2 over-expression afforded a 3-fold protection from radiation-ind uced apoptosis. There was no significant difference, however, in the c lonogenic survival of the parental and bcl-2-expressing cells. Further more, there was a 24 hr delay in induction of the apoptosis marker gen e SCP-2/TRPM-2 in the bcl-2-expressing cells, co incidental with the d elay in apoptotic DNA fragmentation. (C) 1997 Wiley-Liss, Inc.