Shedding of c-Met is regulated by crosstalk between a G-protein coupled receptor and the EGF receptor and is mediated by a TIMP-3 sensitive metalloproteinase

A wide repertoire of transmembrane proteins are proteolytically released fr om the cell surface by a process known as 'ectodomain shedding' under both normal and pathophysiological conditions. Little is known about the physiol ogical mechanisms that regulate this process. As a model system, we have in vestigated the metalloproteinase-mediated cleavage of the hepatocyte growth factor receptor, Met. We show that epidermal growth factor (EGF) receptor activation, either directly by EGF or indirectly via the G-protein coupled receptor (GPCR) agonist lysophosphatidic acid (LPA), induces cleavage of Me t through activation of the Erk MAP kinase signalling cascade. The tyrosine kinase activity of the EGFR was a prerequisite for this stimulation, since treatment of cells with a synthetic inhibitor of this receptor, AG1478, co mpletely abrogated shedding. The metalloproteinase mediating Met cleavage w as specifically inhibited by the tissue inhibitor of metalloproteinases (TI MP)-3, but not by TIMP-1 or TIMP-2. Furthermore, the level of Met shedding could be modulated by different cell-matrix interactions. Our results indic ate that ectodomain shedding is a highly regulated process that can be stim ulated by EGFR signalling pathways and integrin ligation.