Effect of epidermal growth factor on phosphate uptake in renal proximal tubule cells: involvement of PKC, MAPK, and cPLA2.
OBJECTIVE
The present study was conducted to examine the effect of epidermal growth factor (EGF) on Pi uptake and its related signal pathways in the primary cultured renal proximal tubule cells (PTCs).


RESULTS
EGF (50 ng/ml) inhibited Pi uptake, a typical marker of Na(+)/phosphate cotransporter, in a time- and dose-dependent manner. EGF-induced inhibition of Pi uptake was blocked by AG1478 (an EGF receptor antagonist), genistein or herbimycin A (tyrosine kinase inhibitors) and also blocked by mepacrine (a phospholipase A(2) (PLA(2)) inhibitor) and AACOCF(3 )(a cPLA(2) inhibitor). EGF increased [(3)H]-arachidonic acid (AA) release, which was also blocked by AG1478, genistein or herbimycin. Furthermore, EGF-induced inhibition of Pi uptake was blocked by indomethacin (a cyclooxygenase inhibitor) and econazole (a cytochrome P-450 epoxygenase inhibitor), but not by NDGA (a lipoxygenase inhibitor). On the other hand, EGF-induced inhibition of Pi uptake was blocked by staurosporine, H-7, or bisindolylmaleimide I (PKC inhibitors), PD 98059 (a p44/42 MAPK inhibitor), but not by SB 203580 (a p38 MAPK inhibitor). EGF-induced increase of [(3)H]-AA release was blocked by PKC inhibitors and a p44/42 mitogen-activated protein kinase (MAPK) inhibitor, but not by a p38 MAPK inhibitor. In addition, a PKC inhibitor blocked EGF-induced phosphorylation of p44/42 MAPK.


CONCLUSIONS
EGF inhibits Pi uptake via PKC-p44/42 MAPK-cPLA(2) pathway in the PTCs.
Han
Ho Jae
HJ
Department of Veterinary Physiology, College of Veterinary Medicine, Hormone Research Center, Chonnam National University, Gwangju, Korea.
Park
Ji Yeong
JY
Lee
Yun Jung
YJ
Park
Soo Hyun
SH
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D054513:Group IV Phospholipases A2; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008297:Male; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D011817:Rabbits; D015398:Signal Transduction
D004791:Enzyme Inhibitors; D010710:Phosphates; D016718:Arachidonic Acid; D004815:Epidermal Growth Factor; D011493:Protein Kinase C; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D010741:Phospholipases A; D054513:Group IV Phospholipases A2