Disease relevance of CLCN5

• Idiopathic low molecular weight proteinuria associated with hypercalciuric nephrocalcinosis in Japanese children is due to mutations of the renal chloride channel (CLCN5) [1].
• Characterisation of renal chloride channel, CLCN5, mutations in hypercalciuric nephrolithiasis (kidney stones) disorders [2].
• These results clarified four novel mutations in the CLCN5 genes, and additionally suggested that the loss-of-function mutation of the CLCN5 does not necessarily lead to hypercalciuria and nephrocalcinosis in the early stage of the disease, and that LMWP is an early and essential manifestation of disorders of the CLC-5 chloride channel [3].
• One genomic deletion including exons 5 to 8 in the CLCN5 gene was found in a patient with hypophosphatemic rickets, and a nonsense mutation (R347X) was found in one patient with LMWP and slight hypercalciuria [3].
• No mutations of the exons and exon-intron boundaries in the CLCN5 gene were found in one patient with LMWP, aminoaciduria, and hypokalemia [3].

High impact information on CLCN5

• A microdeletion in one Dent's disease kindred allowed the identification of a candidate gene, CLCN5 (refs 8,9) which encodes a putative renal chloride channel [4].
• Heterologous expression of wild-type CLCN5 in Xenopus oocytes yielded outwardly rectifying chloride currents, which were either abolished or markedly reduced by the mutations [4].
• Three disorders of hypercalciuric nephrolithiasis (Dent's disease, X-linked recessive nephrolithiasis (XRN), and X-linked recessive hypophosphataemic rickets (XLRH)) have been mapped to Xp11.22 (refs 5-7) [4].
• Thus, the results of our study expand the spectrum of clinical phenotypes associated with CLCN5 mutations to include this proximal renal tubular disorder of Japanese children [1].
• In addition, the mutational screening of CLCN5 by SSCP will help to supplement the clinical evaluation of the annual urinary screening program for this disorder [1].

Chemical compound and disease context of CLCN5

• A possible approach to this problem is to search for CLCN5 mutations in patients who may have a high prevalence of mutations: end-stage renal disease (ESRD) patients with previous calcium, struvite, or radio-opaque (CSR) stones [5].
• All patients had mild increases in lactate dehydrogenase and/or creatine kinase levels, which rarely is observed in CLCN5-positive patients, but frequently found in patients with Lowe syndrome [6].

Biological context of CLCN5

• Mutations of the renal-specific chloride channel (CLCN5) gene, which is located on chromosome Xp11.22, are associated with hypercalciuric nephrolithiasis (kidney stones) in the Northern European and Japanese populations [2].
• In this study, an additional six unrelated patients with Dent's disease were identified and investigated for CLCN5 mutations by DNA sequence analysis of the 11 coding exons of CLCN5 [7].
• In one three-generation family, the absence of mutation was confirmed by sequencing in two additional affected family members, and in this family haplotype analysis excluded linkage to the region of the CLCN5 gene [8].
• In these 13 patients, we also sequenced two regions of the CLCN5 promoter (626 and 586 bp, respectively, 2.1 and 1 kb upstream of exon 2) containing regulatory sites [activating protein-1 (AP-1)-like, AP-4, and cyclic adenosine monophosphate (cAMP)-receptor element binding protein (CREB)] and primary and secondary transcription start sites [8].
• We report a missense mutation in exon 6 of the CLCN5 gene [9].

Anatomical context of CLCN5

• These are predicted to lead to a loss of chloride channel function, and heterologous expression of the missense CLCN5 mutation in Xenopus oocytes demonstrated a 70% reduction in channel activity when compared with the wild-type [1].
• Leukocyte genomic DNA from patients and their relatives was used with CLCN5-specific primers for polymerase chain reaction amplification of the coding region and exon-intron boundaries [10].
• ClC-5 has been proposed to be an electrically shunting Cl- channel in early endosomes, facilitating intraluminal acidification [11].
• 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 [11].
• ClC-5 was expressed in all cell lines, while it was observed in only T and B cells but not in neutrophils from normal subjects [12].

Associations of CLCN5 with chemical compounds

• Here we describe the isolation and characterization of the complete open reading frame of the human CLCN5 gene, which is predicted to encode a protein of 746 amino acids, with significant homology to all known members of the ClC family of voltage-gated chloride channels [13].
• CONCLUSIONS: Neither urinary low-molecular-weight-proteins, urinary calcium to creatinine ratio, nor renal ultrasonography was predictive of carrier state in the 3 families with this disease, although each carrier mother had CLCN5 mutation [14].
• Defective protein sorting/targeting of Ocrl might be the reason for mildly elevated creatine kinase and lactate dehydrogenase serum concentrations in these patients and a clue to suspect Dent disease unrelated to CLCN5 mutations [6].
• Thus, CLC-5 is expressed at multiple sites in the human nephron and is likely to have a role in the receptor-mediated endocytic pathway [15].
• We determined whether the functional activity of ClC-5 could be restored by coexpression of the truncated protein (containing the NH2-terminal region) with its complementary "missing" COOH-terminal region [16].

Physical interactions of CLCN5

• Nedd4-2 functionally interacts with ClC-5: involvement in constitutive albumin endocytosis in proximal tubule cells [17].

Regulatory relationships of CLCN5

• To test whether the inhibitory effects of ClC-5 were specific for ENaC, ClC-5 was also co-expressed with CFTR [18].

Other interactions of CLCN5

• CLCN5 belongs to a distinct branch of this family, which also includes the recently identified genes CLCN3 and CLCN4 [13].
• RESULTS: RT-PCR analysis gave positive bands at the predicted size for CLC-3 and CLC-5 from fresh human, rabbit and bovine as well as CBCEC [19].
• RECENT FINDINGS: Hypercalciuria is discussed relative to mutations in the renal chloride genes CLCN5 and CLCNKB, WNK kinases, ATPB61, and NPT2 [20].
• Cloning and characterization of CLCN5, the human kidney chloride channel gene implicated in Dent disease (an X-linked hereditary nephrolithiasis) [13].
• We studied a Spanish patient with Dent's disease and found, by polymerase chain reaction amplification of the CLCN5 exons, an abnormally large exon 11 [21].

Analytical, diagnostic and therapeutic context of CLCN5

• Here, we found, by RT-PCR amplification of RNA extracted from the patient's blood and subsequent DNA sequencing, that the Alu insertion led to an aberrant splicing of the CLCN5 pre-mRNA that skipped exon 11 [22].
• To establish more efficient screening for CLCN5 abnormalities, we developed a new diagnostic method using reverse transcription and polymerase chain reaction (RT-PCR) of cultured renal tubular cells from the urine of patients [23].
• Sequence analysis of the henceforward 17 CLCN5 exons revealed no mutation in the patients with a phenotype resembling Dent's disease [24].
• Mutant CLCN5 cDNAs were generated by site directed mutagenesis for two premature stop codon variants (R347X and M517IfsX528), and several missense mutations (C221R, L324R, G462 V, and R516 W) [25].
• As the presence of hypercalciuria may affect the decision to consider a CLCN5 mutation in the differential diagnosis, the phenotypic spectrum and the relative frequency of hypercalciuria in patients with CLCN5 mutations was determined [26].

References