Inhibition of phosphatidylinositide 3-kinase in OK-cells reduces Na/Pi-cotransport but does not interfere with its regulation by parathyroid hormone.
The importance of phosphatidylinositide 3- kinase(s) [PI 3-kinase(s)] in membrane trafficking processes led us to examine its/their possible role in parathyroid-hormone- (PTH-) induced endocytosis and lysosomal degradation of the type IIa Na/Pi-cotransporter in opossum kidney cells (OK-cells). We used wortmannin, a potent inhibitor of several mammalian PI 3-kinase isoforms, and measured Na/Pi-cotransporter activity and type IIa Na/Pi-cotransporter protein expression; also the induction of a negative dominant subunit (Deltap85) was used to reduce PI 3-kinase activity. Wortmannin and Deltap85 led to a reduction of Na/Pi-cotransport activity but were unable to prevent its inhibition by PTH. Wortmannin led in a dose- and time-dependent manner to a reduction of Na/Pi-cotransport activity and transporter protein expression, and retarded their recovery from PTH-induced inhibition/degradation. The data suggest that a PI 3-kinase "controlled" mechanism is involved in the synthesis (and/or routing) of the apical type IIa Na/Pi-cotransporter in OK-cells.
Pfister
M F
MF
Institute of Physiology, University of Zurich-Irchel, CH-8057 Zurich, Switzerland.
Brunskill
N J
NJ
Forgo
J
J
Stange
G
G
Biber
J
J
Murer
H
H
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002460:Cell Line; D004705:Endocytosis / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D008247:Lysosomes / Q000378:metabolism; D009893:Opossums; D010281:Parathyroid Hormone / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D000077191:Wortmannin
D000730:Androstadienes; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D010281:Parathyroid Hormone; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D000077191:Wortmannin