Abnormalities of parathyroid hormone-mediated signal transduction mechanisms in opossum kidney cells.
The second-messengers cAMP, diacylglycerol and inositol 1,4,5-trisphosphate (IP3)-Ca2+ ([Ca2+]i) have been implicated in parathyroid hormone (PTH) receptor-mediated inhibition of sodium/phosphate (Na/P(i)) cotransport across the apical membrane of the proximal tubule. Studies on opossum kidney (OK) cells have been used to study regulatory cascades involved in these PTH actions. In the present study, we further characterized PTH regulatory pathways in two stable mutant cell sublines (J01 and J141) compared to control OK (J09) cells. In J09 cells, addition of PTH resulted in a dose-dependent decrease in Na/P(i) uptake which was associated with an increase in cAMP and cytosolic Ca2+ concentration as well as with activation of protein kinase A, protein kinase C, and MAP kinase. Activation of protein kinase C and of MAP kinase can be detected at PTH concentrations lower than those required for protein kinase A activity. PTH led to similar changes in J01 cells except for the absence of PTH-induced Ca2+ transients. These data confirm the important role of protein kinase C and suggest further that [Ca2+]i transients are not necessary for PTH-mediated inhibition of Na/P(i) cotransport. The J141 subline possessed all of the measured PTH signal pathways but PTH was without effect on Na/P(i) cotransport. The absence of PTH response on Na/P(i) cotransport in J141 cells is likely beyond the PTH-dependent activation of protein kinase A and/or protein kinase C. These studies suggest that Na/P(i) cotransport may be uncoupled from the normal regulatory process. These defined OK cell sublines may be useful in further characterization of PTH action on Na/P(i) cotransport.
Quamme
G
G
Department of Medicine and Biomedical Research Centre, University of British Columbia, University Hospital, Vancouver, Canada.
Pelech
S
S
Biber
J
J
Murer
H
H
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D002999:Clone Cells; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D008969:Molecular Sequence Data; D009893:Opossums; D010281:Parathyroid Hormone / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D018016:Receptors, Parathyroid Hormone / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters
D002352:Carrier Proteins; D010281:Parathyroid Hormone; D018016:Receptors, Parathyroid Hormone; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D002118:Calcium