The Role of EGF Receptor Negative Regulatory Components in Breast Cell Growth

Previous results showed that MDA-MB-468 cells, with 1.9 x 10(exp 6) EGF-R per cell, did not rapidly eliminate activated EGF-R. The variant cell lines S1 and S11 possessing 1.6 x 10(exp 4) and 6.6 x 10(exp 4) EGF-R per cell respectively, did rapidly eliminate activated EGF-R. S1 and S11 lines transduced with EGF-R express EGF-R levels intermediate to the S variants and the 468 cells and eliminate their activated EGF-R at an intermediate rate. We show that phosphatase activity is not limiting following receptor amplification and that all phosphotyrosine can be removed within 30 seconds. Our data suggests that PY is prolonged following receptor amplification because the amplified cell lines cannot rapidly segregate ligand and receptor during trafficking. Further, we show that receptor amplification does not increase ligand capture efficiency or increase expression of autocrine ligands. Because basal PY increases following EGF-R amplification increases in a linear fashion this data further supports our model. Lastly, basal phosphotyrosine increases following EGF-R amplification appear to be ligand dependent whereas increases in EGF-R basal PY due to Her2 amplification appear to be ligand independent.