Disease relevance of CLCN4

• The association of ClC-4 and the Wilson's disease protein (ATP7B) was determined by co-immunoprecipitation [1].

High impact information on CLCN4

• The chloride channel gene, CLCN4, has been previously mapped to the X chromosome in humans [2].
• Overexpression of ClC-4 doubled copper incorporation into ceruloplasmin (P = 0.011), whereas identical overexpression of ClC-3 had no effect [1].
• Involvement of chloride channels in hepatic copper metabolism: ClC-4 promotes copper incorporation into ceruloplasmin [1].
• This gene, termed CICN4 (Chloride Channel 4), contains at least 10 exons spanning 60 to 80 kb on the X chromosome [3].
• Electrophysiological recordings of the heterologously expressed channels in Xenopus oocytes showed that ClC-4 and ClC-4A have opposite sensitivity to pH and unique ion selectivity [4].

Biological context of CLCN4

• Dent disease-like phenotype and the chloride channel ClC-4 (CLCN4) gene [5].
• On the physiological level, the antiport activity of ClC-4/ClC-5 must lead to a review of the role of CLC proteins in intracellular compartments [6].

Anatomical context of CLCN4

• Here we report that ClC-4 and ClC-5 carry a substantial amount of protons across the plasma membrane when activated by positive voltages, as revealed by measurements of pH close to the cell surface [7].
• When heterologously expressed in HEK293 cells and in skeletal muscle fibers, hClC-4 localizes to the endoplasmic/sarcoplasmic reticulum (ER/SR) membranes, in contrast to hClC-3, which localizes to vesicular structures [8].
• This location was confirmed by identification of endogenous ClC-4 in membrane fractions from mouse brain homogenate enriched for the sarco-endoplasmic reticulum ATPase SERCA2, an ER/SR marker [8].
• The human ClC-4 protein, a member of the CLC chloride channel/transporter family, is localized to the endoplasmic reticulum by its N-terminus [8].
• We now show that ClC-4 also gives rise to strongly outwardly rectifying anion currents when expressed in oocytes [9].

Associations of CLCN4 with chemical compounds

• Changing the extracellular (2 mM or nominal Ca(2+)-free) or intracellular Ca(2+) (25 or 250 nM) concentration did not alter hClC-4 currents [10].
• Continuous activity of hClC-4 was sustained to different degrees by internal nucleotides: ATP approximately ATPgammaS >> AMP-PNP approximate GTP > ADP [10].
• In all cells, the expression of hClC-4 generated strongly outward-rectifying Cl(-) currents with the conductance sequence: SCN(-) >> NO(3)(-) >> Cl(-) > Br(-) approximate I(-) >> aspartate [10].
• X-ray crystallographic and electrophysiological studies have identified two glutamate residues required for gated Cl movement and proton permeation in bacterial and two mammalian (ClC-4, ClC-5) ClC transporters [11].

Co-localisations of CLCN4

• We show using confocal and electron microscopy that ClC-4 co-localizes with CFTR in the brush border membrane of the epithelium lining intestinal crypts in mouse and human tissues [12].

Regulatory relationships of CLCN4

• In Caco-2 cells, a cell line thought to model human enterocytes, ClC-4 protein is expressed on the cell surface and also partially co-localizes with EEA1 and transferrin, marker molecules of early and recycling endosomes, respectively [12].

Other interactions of CLCN4

• CLCN5 belongs to a distinct branch of this family, which also includes the recently identified genes CLCN3 and CLCN4 [13].
• IHCEn cultivated on LAM showed stronger expression of VDAC3, CLCN4, and Na+/K+ ATPase mRNA than on plastic culture dish [14].
• Hence, like CFTR, ClC-4 may cycle between the plasma membrane and endosomal compartment [12].

Analytical, diagnostic and therapeutic context of CLCN4

• Here, we used whole-cell recordings to study pore properties of human ClC-4 channels heterologously expressed in tsA201 or HEK293 cells [15].

References