Ras transformation causes sustained activation of epidermal growth factor receptor and elevation of mitogen-activated protein kinase in human mammaryepithelial cells

Activation of the ms oncogene is an important step in carcinogenesis. Human MCF-10A mammary epithelial cells were transformed with a point-mutated for m of the Ha-ms oncogene, Epidermal growth factor receptor (EGFR) phosphoryl ation levels were chronically elevated after EGF induction and the EGFR lig and-driven internalization rate was slower in Ha-res transformed MCF-10A ce lls, Additionally, basal levels of p42/44 mitogen-activated protein kinase (MAPK) expression and enzyme activity were significantly higher in Ha-res t ransformed cells, localized predominantly in the nucleus. The anti-EGFR mon oclonal antibody (MAb) 225 and the ECFR tyrosine kinase inhibitor PD153035 blocked anchorage-independent growth of Ha-ms transformed cells in soft aga r and were more effective when used in combination, The MEK inhibitor PD980 59 and anti-erbB-2 MAb L26 also suppressed colony formation of Ha-res trans formed cells in soft agar, Therefore, Ha-ms transformation leads to an augm entation in signaling through the EGFR as a result of an increase in ligand -dependent phosphorylation, a decrease in its internalization and an up-reg ulation in basal p44/42 MAPK levels. These effects may contribute to uncont rolled growth of Ha-ms-transformed human mammary epithelial cells. Publishe d 2000 Wiley-Liss, Inc.(dagger)