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Parathyroid hormone leads to the lysosomal degradation of the renal type II Na/Pi cotransporter
1Institute of, University of Zurich, CH-8057 Zurich, Switzerland.
Abstract:
We have studied the involvement of proteolytic pathways in the regulation of the Na/Pi cotransporter type II by parathyroid hormone (PTH) in opossum kidney cells. Inhibition of lysosomal degradation (by leupeptin, ammonium chloride, methylamine, chloroquine, L-methionine methyl ester) prevented the PTH-mediated degradation of the transporter, whereas inhibition of the proteasomal pathway (by lactacystin) did not. Moreover it was found (i) that whereas lysosomal inhibitors prevented the PTH-mediated degradation of the transporter they did not prevent the PTH-mediated inhibition of the Na/Pi cotransport and (ii) that treating opossum kidney cells with lysosomal inhibitors led to an increased expression of the transporter without any concomitant increase in the Na/Pi cotransport. Further analysis by subcellular fractionation and morphological techniques showed (i) that the Na/Pi cotransporter is constitutively transported to and degraded within late endosomes/lysosomes and (ii) that PTH leads to the increased degradation of the transporter in late endosomes/lysosomes.
Insights
Parathyroid hormone (PTH) regulates the Na/Pi cotransporter in kidney cells. Lysosomal degradation, not proteasomal, is key to PTH-mediated transporter breakdown and function.
Area of Science:
- Cell biology
- Renal physiology
- Molecular mechanisms
Background:
- The Na/Pi cotransporter type II is crucial for phosphate reabsorption in the kidneys.
- Parathyroid hormone (PTH) is a key regulator of phosphate homeostasis.
- The precise mechanisms by which PTH regulates Na/Pi cotransporter type II activity and stability are not fully understood.
Purpose of the Study:
- To investigate the role of proteolytic pathways in parathyroid hormone (PTH)-mediated regulation of the Na/Pi cotransporter type II in opossum kidney cells.
- To determine whether lysosomal or proteasomal pathways are involved in the degradation of the Na/Pi cotransporter type II in response to PTH.
Main Methods:
- Opossum kidney cells were treated with inhibitors of lysosomal degradation (leupeptin, ammonium chloride, methylamine, chloroquine, L-methionine methyl ester) and proteasomal pathways (lactacystin).
- PTH-mediated degradation of the Na/Pi cotransporter and Na/Pi cotransport activity were assessed.
- Subcellular fractionation and morphological techniques were employed to localize the transporter and its degradation sites.
Main Results:
- Inhibition of lysosomal degradation prevented PTH-mediated degradation of the Na/Pi cotransporter, while proteasomal inhibition did not.
- Lysosomal inhibitors blocked PTH-mediated transporter degradation but not the inhibition of Na/Pi cotransport.
- Treatment with lysosomal inhibitors increased transporter expression without a corresponding increase in Na/Pi cotransport.
- The Na/Pi cotransporter is constitutively degraded in late endosomes/lysosomes, a process enhanced by PTH.
Conclusions:
- Lysosomal degradation is the primary proteolytic pathway involved in the regulation of the Na/Pi cotransporter type II by PTH.
- PTH accelerates the degradation of the Na/Pi cotransporter within late endosomes/lysosomes.
- While lysosomal degradation affects transporter stability, it does not solely account for the PTH-induced inhibition of Na/Pi cotransport.