THE MAMMALIAN METABOLITE, 2-METHOXYESTRADIOL, AFFECTS P53 LEVELS AND APOPTOSIS INDUCTION IN TRANSFORMED-CELLS BUT NOT IN NORMAL-CELLS

The endogenous metabolite, 2-methoxyestradiol (2ME), is an inhibitor o f tubulin polymerization and is therefore toxic to dividing fast-growi ng tumor cells. Transformed cells are not equally susceptible to the e ffects of 2ME. In this study the effects of 1-2 mu M doses of 2ME on c ell cycle progression, apoptosis induction and on p53 levels were eval uated using flow cytometry in cells with different p53 status. No effe ct of 2ME was seen in normal human skin fibroblast strain HSF43 with w ild-type (wt) p53. However, in SV40 T antigen transformed HSF43 cells (line E8T4), 2ME caused a prominent G(2)/M arrest, with subsequent mic ronuclei formation followed by apoptosis. Increased p53 levels were pr esent in the G(2)/M cells. Our results suggest that 2ME, being a micro tubule poison, may release the bound p53 from T antigen, and that this p53 may enhance the apoptotic effects. Two lymphoblast cell lines der ived from the same donor, TK6, expressing low levels of wt p53, and WT K1, expressing high levels of mutant p53, showed similar moderate resp onses to 2ME at 37 degrees C. The effects included enhanced apoptosis and a modest G(2)/M block. No increase in p53 levels was seen. However , at the permissive temperature of 30 degrees C marked increases in ap optosis and a prominent G(2)/M-phase block, similar to that seen in th e E8T4 cells, were present in the WTK1 cells, indicating that the high levels of mutant p53 have now become functional, enhancing the apopto tic effects initiated by 2ME. (C) 1997 Elsevier Science Ltd.