Epidermal growth factor receptor transactivation mediates substance P-induced mitogenic responses in U-373 MG cells

Ligand-induced activation of G protein-coupled receptors is emerging as an important pathway leading to the activation of certain receptors with intri nsic tyrosine kinase activity, such as the epidermal growth factor receptor (EGFR). Substance P (SP) exerts many effects via activation of its G prote in-coupled receptor (neurokinin-l, NIF-l). SP participates in acute inflamm ation and activates hey proteins involved in mitogenic pathways, such mitog en-activated protein kinases (MAPKs), stimulating DNA synthesis. We tested the hypothesis that SP-induced MAPK activation and DNA synthesis require ac tivation of the EGFR. In U-373 MG cells, which express functional NK-1, SP induced tyrosine phosphorylation of several proteins including EGFR. SP ind uced formation of an activated EGFR complex containing the adapter proteins SHC and Grb2, but not c-Src. SP activated the MAPK pathway as shown by inc reased Erk2 kinase activity. SP induced Erk2 activation, and DNA synthesis was inhibited in cells transfected with a dominant negative EGFR plasmid la cking kinase activity, as well as in cells treated with a specific EGFR inh ibitor. In addition, pertussis toxin, an inhibitor of G alpha(i) protein su bunits, prevented SP-induced EGFR transactivation and subsequent DNA synthe sis. Our results implicate EGFR as an essential regulator in SP/NK-1-induce d activation of the MAPK pathway and cell proliferation in U-373 MG cells, and these events are mediated by a pertussis toxin-sensitive G alpha protei n. We suggest that this mechanism by which SP controls cell proliferation i s an important pathway in tissue restoration and healing.