Differential MAPK pathways utilized for HGF- and EGF- dependent renal epithelial morphogenesis

Cells derived from the inner medullary collecting duct undergo in vitro bra nching tubulogenesis to both the c-met receptor ligand hepatocyte growth fa ctor (HGF) as well as epidermal growth factor (EGF) receptor ligands. In co ntrast, many other cultured renal epithelial cells respond in this manner o nly to HGF, suggesting that these two receptors may use independent signali ng pathways during morphogenesis. We have therefore compared the signaling pathways for mIMCD-3 cell morphogenesis in response to EGF and HGF, Inhibit ion of the p42/44 mitogen-activated protein kinase (MAPK) pathway with the mitogen-activated protein kinase kinase (MKK1) inhibitor PD98059 (50 muM) m arkedly inhibits HGF-induced cell migration with only partial inhibition of EGF-induced cell motility. Similarly, HGF-dependent, but not EGF-dependent , branching morphogenesis was more greatly inhibited by the MKK1 inhibitor. Examination of EGF-stimulated cells demonstrated that extracellular-regula ted kinase 5 (ERK5) was activated in response to EGF but not HGF, and that activation of ERK5 was only 60% inhibited by 50 muM PD98059. In contrast, t he MKK inhibitor U0126 markedly inhibited both ERK1/2 and ERK5 activation a nd completely prevented HGF- and EGF-dependent migration and branching proc ess formation. Expression of dominant negative ERK5 (dn-BMK1) likewise inhi bited EGF-dependent-branching process formation, but did not affect HGF-dep endent branching process formation. Our results indicate that activation of the ERK1/ERK2 signaling pathway is critical for HGF-induced cell motility/ morphogenesis in mIMCD-3 cells, whereas ERK5 appears to be required for EGF -dependent morphogenesis.