INVESTIGATIONS INTO THE MECHANISMS OF CARCINOGEN-INDUCED NUCLEAR ENLARGEMENT IN HELA S3 CELLS IN-VITRO

Carcinogen-induced nuclear enlargement has been reported both in vitro and in vivo, but the mechanism, and whether it is causally related to carcinogenesis, has not yet been established. This study was designed to investigate the role of increased DNA content, such as might occur in polyploidy, in induction of nuclear enlargement. The effects of tw o genotoxic carcinogens, N-methyl-N-nitrosourea and adriamycin, were c ompared with the effects induced by diethylstilboestrol, which is argu ably a nongenotoxic carcinogen but is known to induce polyploidy. HeLa S3 cells were used as the model system for comparison with previous s tudies. N-methyl-N-nitrosourea and adriamycin both induced a concentra tion-related increase in nuclear size 24 to 72 hr after a 30 min pulse -treatment. This was accompanied by an increase in the proportions of cells in the G(2) + M stage of the cell cycle, possibly due to a G(2) block. There was some evidence of polyploidy with adriamycin but not w ith N-methyl-N-nitrosourea. The distributions of nuclear areas indicat ed that increases in ploidy contributed to, but did not totally accoun t for, the nuclear enlargement. In contrast, diethylstilboestrol incre ased the range of nuclear areas and DNA content, to both less than and greater than that of control cells, but only after a prolonged exposu re period of 48 hr. These data were consistent with diethylstilboestro l inducing spindle damage. These results demonstrate that carcinogen-i nduced nuclear enlargement is only partially explained by increased nu clear DNA content, and that certain classes of non-genotoxic carcinoge n may produce a completely different pattern to that from genotoxic ca rcinogens.