The G215R mutation in the Cl-/H+-antiporter ClC-7 found in ADO II osteopetrosis does not abolish function but causes a severe trafficking defect.
BACKGROUND
ClC-7 is a ubiquitous transporter which is broadly expressed in mammalian tissues. It is implied in the pathogenesis of lysosomal storage disease and osteopetrosis. Because of its endosomal/lysosomal localization it is still poorly characterized.


RESULTS
An electrophysiological characterization of rat ClC-7 using solid-supported membrane-based electrophysiology is presented. The measured currents show the characteristics of ClC-7 and confirm its function as a Cl(-)/H(+)-antiporter. We have used rat ClC-7 in CHO cells as a model system to investigate the functionality and cellular localization of the wt transporter and its variant G213R ClC-7 which is the analogue of human G215R ClC-7 responsible for autosomal dominant osteopetrosis type II. Our study shows that rat G213R ClC-7 is functional but has a localization defect in CHO cells which prevents it from being correctly targeted to the lysosomal membrane. The electrophysiological assay is tested as a tool for drug discovery. The assay is validated with a number of drug candidates. It is shown that ClC-7 is inhibited by DIDS, NPPB and NS5818 at micromolar concentrations.


CONCLUSIONS
It is suggested that the scenario found in the CHO model system also applies to the human transporter and that mislocalization rather than impaired functionality of G215R ClC-7 is the primary cause of the related autosomal dominant osteopetrosis type II. Furthermore, the robust solid-supported membrane-based electrophysiological assay is proposed for rapid screening for potential ClC-7 inhibitors which are discussed for treatment of osteoporosis.
Schulz
Patrick
P
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Frankfurt, Germany.
Werner
Johannes
J
Stauber
Tobias
T
Henriksen
Kim
K
Fendler
Klaus
K
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D018118:Chloride Channels / Q000235:genetics* / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D020125:Mutation, Missense; D010022:Osteopetrosis / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D051381:Rats
C489932:CLCNKA protein, human; D018118:Chloride Channels; C490802:Clcn7 protein, rat