Effects of epidermal growth factor on MDA-MB-468 breast cancer cells: Alterations in polyamine biosynthesis and the expression of p21/CIP1/WAF1

We examined the effects of epidermal growth factor (EGF) on MDA-MB-468 cell s to understand its mechanism of action in an EGF receptor-rich breast canc er cell line. EGF inhibited the growth of MDA-MB-468 cells with an IC,, of 1.5 +/- 0.5 nM, as determined by measurements of DNA content of cells in cu lture over a period of 4 to 6 days. This growth inhibition included apoptos is 24 h after EGF addition, as detected by an enzyme-linked immunosorbent a ssay (ELISA) and Hoechst 33342 staining. In EGF-treated cells, peak activit ies of two key enzymes of polyamine biosynthesis, ornithine decarboxylase ( ODC) and S-adenosylmethionine decarboxylase (SAMDC), were reduced by 57% an d 83%, respectively. EGF treatment also caused a 30 to 50% decrease in cell ular putrescine at all time points tested (12 to 48 h). EGF-induced inhibit ion of DNA synthesis was also partially reversed by the addition of putresc ine or spermidine, but not by spermine. Western blot analysis of cell cycle regulatory proteins showed that EGF-mediated growth inhibition was associa ted with the induction of p21, an inhibitor of cyclin-dependent kinases. Ho wever, EGF had no significant effect on the expression of cyclin D1 or cycl in E. Furthermore, putrescine reversal of EGF effects was associated with t he down-regulation of EGF-induced p21. These results suggest that the mecha nism of growth inhibition by EGF in MDA-MB-468 cells include a down-regulat ion of polyamine biosynthesis and the induction of p21. identification of g rowth regulatory pathways in breast cancer cells might be useful in the dev elopment of novel targets for therapeutic intervention. (C) 1999 Wiley-Liss , Inc.