Parathyroid hormone stimulates extracellular signal-regulated kinase (ERK) activity through two independent signal transduction pathways: role of ERK in sodium-phosphate cotransport.
Parathyroid hormone (PTH), a major physiologic regulator of proximal renal tubule cell sodium-phosphate cotransport, stimulates several signal transduction pathways including extracellular signal-regulated kinases (ERK). The physiologic role of PTH-stimulated ERK is unknown. The purpose of the present study was to identify signaling components involved in PTH-stimulated ERK activity and to determine the role of PTH-stimulated ERK activity in regulation of phosphate transport. PTH-stimulated ERK activity was measured in opossum kidney (OK) cell lysates as phosphorylation of myelin basic protein by an in vitro kinase assay. PTH stimulated a dose-dependent increase in ERK activity with a peak at 10(-7) M. The time course was biphasic with an early peak at 10 min and a later peak at 20 min. Pretreatment of OK cells with the nonreceptor tyrosine kinase inhibitors genistein and herbimycin A or with the phosphatidylinositol 3-kinase (PI-3K) inhibitors wortmannin and LY294002 blocked the early and late peaks of PTH-stimulated ERK activity. Pretreatment with the protein kinase C inhibitor calphostin C blocked only the later phase of PTH-stimulated ERK. To determine the role of ERK in regulation of phosphate transport, PTH inhibition of phosphate uptake and PTH regulation of sodium-phosphate cotransporter (NaPi-4) expression were measured in OK cells pretreated with the MEK inhibitor PD098059. PD098059 significantly attenuated PTH inhibition of phosphate uptake but did not prevent PTH downregulation of NaPi-4. It is concluded that PTH stimulates ERK through two signal transduction pathways: an early pathway dependent on tyrosine kinase and PI-3K and a late pathway dependent on protein kinase C. PTH-stimulated ERK regulates phosphate transport by a mechanism other than downregulation of NaPi-4 expression.
Lederer
Eleanor D
ED
Department of Medicine University of Louisville School of Medicine, Louisville, Kentucky.|Veterans Affairs Medical Center, Louisville, Kentucky.
Sohi
Sameet S
SS
Department of Biochemistry, University of Louisville School of Medicine, Louisville, Kentucky.
McLeish
Kenneth R
KR
Department of Medicine University of Louisville School of Medicine, Louisville, Kentucky.|Department of Molecular Biology, University of Louisville School of Medicine, Louisville, Kentucky.|Veterans Affairs Medical Center, Louisville, Kentucky.
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009893:Opossums; D009994:Osmolar Concentration; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010710:Phosphates / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D013997:Time Factors
D002352:Carrier Proteins; D010281:Parathyroid Hormone; D010710:Phosphates; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D020928:Mitogen-Activated Protein Kinases