COOPERATIVITY BETWEEN THE POLYAMINE PATHWAY AND HER-2NEU IN TRANSFORMATION OF HUMAN MAMMARY EPITHELIAL-CELLS IN CULTURE - ROLE OF THE MAPK PATHWAY

Our experiments were designed to test the cooperativity between the po lyamine pathway and HER-2neu in inducing transformation of human mamma ry epithelial cells in culture. Using the MCF-10A breast epithelial ce ll line, we observed that induction of overexpression of ornithine dec arboxylase (ODC) (the first rate-limiting enzyme in polyamine biosynth esis) markedly potentiated the anchorage-independent growth stimulatin g effect of the beta 2 isoform of neu differentiating factor (NDF) kno wn to activate HER-2neu in MCF-10A cells. ODC overexpression, on the o ther hand, did not enhance growth in liquid culture, thus pointing to a specific effect on transformation rather than proliferation. ODC-ove rexpressing MCF-10A cells exhibited increased MAPK phosphorylation in response to administration of NDF and/or epidermal growth factor (EGF) , In contrast, the phosphorylation of the members of the stress-activa ted protein kinase cascade p38 and SEK were not affected by ODC overex pression. Of note, in the absence of EGF and NDF, ODC overexpression f ailed to induce both clonogenicity and MAPK activation. These results suggest that increased polyamine biosynthetic activity critically inte racts with HER-2neu in promoting human mammary cell transformation in culture and that the MAPK cascade is an important mediator of this int eraction. If confirmed in future in vivo studies, our results may iden tify important new targets for the chemoprevention of human breast can cer. (C) 1998 Wiley-Liss, Inc.