Epidermal Growth Factor Inhibits ¹⁴C-α -Methyl-D-Glucopyranoside Uptake in Renal Proximal Tubule Cells: Involvement of PLC/PKC, p44/42 MAPK, and cPLA₂

The effect of EGF on ¹⁴C-α-methyl-D-glucopyranoside (α-MG) uptake and its related signaling pathways were examined in primary cultured rabbit renal proximal tubule cells (PTCs). Epidermal growth factor (EGF) (50 ng/ml) was found to inhibit α-MG uptake, a distinctive proximal tubule marker. The EGF effect was blocked by AG1478 (an EGF receptor antagonist) or genistein and herbimycin (tyrosine kinase inhibitors), respectively. In addition, the EGF-induced inhibition of α-MG uptake was blocked by neomycin and U73122 (phospholipase C inhibitors) as well as staurosporine, H-7, and bisindolylmaleimide I (protein kinase C inhibitors). EGF was also observed to increase inositol phosphate formation. Furthermore, both the EGF-induced inhibition of α-MG uptake and increase of arachidonic acid (AA) release were blocked by AACOCF₃ (a cytosolic phospholipase A₂ inhibitor), indomethacin (a cyclooxygenase inhibitor), and econazole (a cytochrome P-450 epoxygenase inhibitor). We examined the involvement of mitogen-activated protein kinases (MAPKs) in mediating the effect of EGF on α-MG uptake. Indeed, EGF increased phosphorylation of p44/p42 MAPK and the EGF-induced inhibition of α-MG uptake as well as the stimulatory effect of EGF on AA release was blocked by PD 98059 (a p44/42 MAPK inhibitor), suggesting a causal relationship. However, inhibitors of PKC also prevented the EGF-induced increase of AA release. In conclusion, EGF partially inhibited α-MG uptake via PLC/PKC, p44/42 MAPK, and PLA₂ signaling pathways.