The beta-glucuronidase klotho exclusively activates the epithelial Ca2+ channels TRPV5 and TRPV6.
BACKGROUND
Active Ca(2+) reabsorption in the kidney is facilitated by the epithelial transient receptor potential vanilloid Ca(2+) channel subtype 5 (TRPV5). The complex-glycosylated TRPV5 is expressed at the apical membrane of the renal distal convoluted tubule (DCT) cells where the pro-urine hormone klotho can stimulate its activity by N-oligosaccharide hydrolysis. This study investigates whether klotho and its closely related analogue, beta-glucuronidase, can activate other renal ion channels than TRPV5 expressed by DCT cells.


METHODS
To determine the specificity of this stimulatory effect of klotho and beta-glucuronidase, a selection of ion channels and transporters expressed in the kidney (TRPV4, TRPV5, TRPV6 and TRPM6) was screened in transfected HEK293 cells by using Ca(2+)-influx measurements.


RESULTS
Klotho and beta-glucuronidase have been found to significantly increase the activity of TRPV5 and TRPV6, but had no effect on TRPV4 and TRPM6. Furthermore, deglycosylation by endoglycosidase-F also stimulated the activity of TRPV4, TRPV5 and TRPV6, but not of TRPM6.


CONCLUSIONS
These results suggest a modulating effect for klotho primarily restricted to the epithelial Ca(2+) channels TRPV5 and TRPV6.
Lu
Peng
P
Department of Physiology, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
Boros
Sandor
S
Chang
Qing
Q
Bindels
René J
RJ
Hoenderop
Joost G
JG
D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002460:Cell Line; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism*; D005966:Glucuronidase / Q000494:pharmacology*; D006801:Humans; D007686:Kidney Tubules, Distal / Q000187:drug effects* / Q000378:metabolism*; D000090265:Klotho Proteins; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase / Q000494:pharmacology; D050916:TRPV Cation Channels / Q000187:drug effects / Q000378:metabolism*; D014162:Transfection
D015220:Calcium Channels; D050916:TRPV Cation Channels; C416986:TRPV4 protein, human; C492239:TRPV5 protein, human; C422827:TRPV6 protein, human; D005966:Glucuronidase; D000090265:Klotho Proteins; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D002118:Calcium