Metalloprotease-mediated ligand release regulates autocrine signaling through the epidermal growth factor receptor

Ligands that activate the epidermal growth factor receptor (EGFR) are synth esized as membrane-anchored precursors that appear to be proteolytically re leased by members of the ADAM family of metalloproteases. Because membrane- anchored EGFR ligands are thought to be biologically active, the role of li gand release in the regulation of EGFR signaling is unclear. To investigate this question, we used metalloprotease inhibitors to block EGFR ligand rel ease from human mammary epithelial cells. These cells express both transfor ming growth factor a and amphiregulin and require autocrine signaling throu gh the EGFR for proliferation and migration. We found that metalloprotease inhibitors reduced cell proliferation in direct proportion to their effect on transforming growth factor a release. Metalloprotease inhibitors also re duced growth of EGF-responsive tumorigenic cell lines and were synergistic with the inhibitory effects of antagonistic EGFR antibodies. Blocking relea se of EGFR ligands also strongly inhibited autocrine activation of the EGFR and reduced both the rate and persistence of cell migration. The effects o f metalloprotease inhibitors could be reversed by either adding exogenous E GF or by expressing an artificial gene for EGF that lacked a membrane-ancho ring domain. Our results indicate that soluble rather than mem brane-anchor ed forms of the ligands mediate most of the biological effects of EGFR liga nds. Metalloprotease inhibitors have shown promise in preventing spread of metastatic disease. Many of their antimetastatic effects could be the resul t of their ability to inhibit autocrine signaling through the EGFR.