Heterologous expression of polycystin-1 inhibits endoplasmic reticulum calcium leak in stably transfected MDCK cells.
We previously found that polycystin-1 accelerated the decay of ligand-activated cytoplasmic calcium transients through enhanced reuptake of calcium into the endoplasmic reticulum (ER; Hooper KM, Boletta A, Germino GG, Hu Q, Ziegelstein RC, Sutters M. Am J Physiol Renal Physiol 289: F521-F530, 2005). Calcium flux across the ER membrane is determined by the balance of active uptake and passive leak. In the present study, we show that polycystin-1 inhibited calcium leak across the ER membrane, an effect that would explain the capacity of this protein to accelerate clearance of calcium from the cytoplasm following a calcium release response. Calcium leak was detected by measurement of the accumulation of calcium in the cytoplasm following treatment with thapsigargin. Heterologous polycystin-1, stably expressed in Madin-Darby canine kidney cells, attenuated the thapsigargin-induced calcium peak with no effect on basal calcium stores, mitochondrial calcium uptake, or extrusion of calcium across the plasma membrane. The capacity of polycystin-1 to limit the rate of decay of ER luminal calcium following inhibition of the pump was shown indirectly using the calcium ionophore ionomycin, and directly by loading the ER with a low-affinity calcium indicator. We conclude that disruption of ER luminal calcium homeostasis may contribute to the cyst phenotype in autosomal dominant polycystic kidney disease.
Weber
Kimberly H
KH
Department of Nephrology, John Hopkins University School of Medicine, Baltimore, MD 21224, USA.
Lee
Eun Kyung
EK
Basavanna
Uma
U
Lindley
Sabina
S
Ziegelstein
Roy C
RC
Germino
Gregory G
GG
Sutters
Michael
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D007668:Kidney / Q000166:cytology; D016891:Polycystic Kidney, Autosomal Dominant / Q000235:genetics / Q000378:metabolism*; D050396:TRPP Cation Channels / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection
D002118:Calcium; D004791:Enzyme Inhibitors; D015759:Ionomycin; D007476:Ionophores; D050396:TRPP Cation Channels; D019284:Thapsigargin