Epidermal growth factor‐induced proliferation of renal cells from a mouse model of polycystic kidney disease involves multiple signaling pathways

Abstract

Epidermal growth factor (EGF) is linked to the pathogenesis of cyst formation in polycystic kidney disease (PKD). We explored the effects of EGF in the orpk cilia (−) collecting duct cell line, derived from a mouse model of PKD, and in a control, orpk cilia (+) cell line to determine signaling pathways activated by EGF. RT‐PCR demonstrated mRNAs for EGF receptor subunits ErbB1, ErbB2, ErbB3, ErbB4, and mRNAs for Na+/H+ exchangers, NHE‐1, NHE‐2, and NHE‐3 in both cell lines. We measured changes in extracellular pH as a reflection of NHE activity with a Cytosensor microphysiometer, assessed extracellular signal regulated kinase (ERK) activation by Western blotting, and cell proliferation by a bromodeoxyuridine uptake. Exposure to 10 ng/ml of EGF caused ≥20% increase in NHE activity, ≥70% increase in ERK phosphorylation, and ~ 30% increase in proliferation in orpk cilia (+) cells. All effects were more pronounced in orpk cilia (−) cells: ≥30% increase in NHE activity, ≥200% increase in ERK phosphorylation, and ~43% increase in proliferation. The amiloride analog, MIA, blocked NHE activation and inhibited ERK phosphorylation suggesting that NHE is critical for ERK activation by EGF. EGF‐induced proliferation was significantly decreased by MIA and by the ERK inhibitor PD98059, suggesting roles for NHE and ERK in EGF mitogenic activity. These studies are important because of the emerging role of EGF in the pathogenesis of PKD.