Increasing the susceptibility of the rat 208F fibroblast cell line to radiation-induced apoptosis does not alter its clonogenic survival dose-response

Abstract

Recent studies have suggested a correlation between the rate and incidence of apoptosis and the radiation response of particular cell lines. However, we found that increasing the rate of induction of apoptosis in the fibroblast line 208F, by transfecting it with human c-myc, did not lead to a change in its clonogenic survival dose-response for either '-?irradiation or "5I-induced DNA damage. It was also found that expression of mutant (T24) Ha-ras in the 208F line appeared to decrease the level of apoptosis per mitosis after irradiation and inhibited the formation of nucleosomal ladders, but did not affect either the onset of the morphological features of apoptosis or the clonogenic survival dose-response of the cells to either '--irradiation or "5I-induced DNA damage. Our findings suggest that it may be incorrect to make predictions about the radiosensitivity of cells based only on knowledge of their mode of death.

Radioresistant MTp53-expressing rat embryo cell transformants exhibit increased DNA-dsb rejoining during exposure to ionizing radiation

“…Other data suggests that the abrogation of the radiationinduced G1 arrest in human colorectal cell lines may be dependent on the actual missense-mutant p53 protein which is expressed (Pocard et al, 1996). In our rodent ®broblast transfection model, di erential clonogenic survival was not explained by the relative level of apoptosis following irradiation using standard morphologic and biochemical end-points, a ®nding supported by a number of studies which have reported a decreased apoptotic response in untransfected, or rastransfected ®broblasts, relative to other cell types (Aldridge et al, 1995;White et al, 1994;Yin and Shimke, 1995).…”

“…Extensive kinetic, and morphologic studies using continuous S-phase labelling will be required on a clone to clone basis in order to correlate permanent cell cycle arrest over multiple cell cycles with relative clonogenic survival (and rejoining of DNA-dsb) over a wide range of doses (Linke et al, 1997). However, similar to the ®ndings by Aldridge et al (1995), Khanna et al (1996) and Yin and Schimke (1995), our REF transfectant data emphasizes the point that cellular radiation survival measured by assays of apoptosis or clonogenicity may be dissimilar.…”

“…Therefore the relative radioresistance of CLASS II clones versus CLASS I clones was not explained by decreased apoptosis compared to CLASS I clones based on a number of morphologic and biochemical end-points. Other groups have reported that the apoptotic response following DNA damage is reduced in ®broblasts which express either activated Hras or mutated p53 proteins (Aldridge et al, 1995;Fernandes et al, 1996 P=0.03 P=0.07 a G1 arrest response was quantitated by the ratio of the fraction of cells in G1 phase to fraction of cells in S phase for irradiated (16 h after 6 Gy) and control cultures. b The SF2 and D10 values for these transformants have been previously reported (see Bristow et al, 1994), and are included for comparative purposes Figure 3 Mean percentages of¯oating and adhered cells with apoptotic nuclei at 36 h following radiation doses of 2 ± 10 Gy for slected CLASS I or II cultures based on 2 ± 3 independent experiments; error bars are ommitted for clarity.…”

“…Although cells derived from haematopoetic cell lineages readily undergo apoptosis following DNA damage, non-apoptotic modes of cellular death may be more important in other cell types, such as ®broblasts (Aldridge et al, 1995;Dewey et al, 1995;Serrano et al, 1997). Of interest, transfection studies by Lowe et al, (1994a,b) have shown that murine embryo ®broblasts (MEF) homozygously de®cient in both p53 alleles and transfected with the adenovirus-E1a and H-ras genes, show reduced levels of apoptosis after exposure to ionizing radiation in comparison to similarly transfected MEF cells containing one or two intact wild type p53 alleles.…”

“…These same authors have argued that di erences in tumour cell sensitivity to radiotherapy or chemotherapy may be explained by the ability of certain oncogenes, such as adenovirus E1a, to induce apoptosis following DNA damage in cells which express a WTp53 genotype. Whether the level of apoptosis and its p53-dependency following irradiation can predict for ultimate tumour clonogen kill is an important issue as local tumour control following chemo-and radiotherapy is ultimately dependent on the number of surviving tumour cells which are capable of clonogenic growth (Aldridge et al, 1995;Bristow et al, 1996b;Hill, 1992;Yin and Schimke, 1995).…”