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Analysis of gap junction assembly using mutated connexins detected in Charcot-Marie-Tooth X-linked disease
P E Martin1, E T Mambetisaeva, D A Archer
1Department of Medical Biochemistry, University of Wales College of Medicine, Cardiff, UK. wmbpem@cardiff.ac.uk
Abstract:
The assembly of gap junction intercellular communication channels was studied by analysis of the molecular basis of the dysfunction of connexin 32 mutations associated with the X-linked form of Charcot-Marie-Tooth disease in which peripheral nervous transmission is impaired. A cell-free translation system showed that six recombinant connexin 32 mutated proteins-four point mutations at the cytoplasmic amino terminus, one at the membrane aspect of the cytoplasmic carboxyl terminus, and a deletion in the intracellular loop-were inserted into microsomal membranes and oligomerised into connexon hemichannels with varying efficiencies. The functionality of the connexons was determined by the ability of HeLa cells expressing the respective connexin cDNAs to transfer Lucifer yellow. The intracellular trafficking properties of the mutated connexins were determined by immunocytochemistry. The results show a relationship between intracellular interruption of connexin trafficking, the efficiency of intercellular communication, and the severity of the disease phenotype. Intracellular retention was explained either by deficiencies in the ability of connexins to oligomerise or by mutational changes at two targeting motifs. The results point to dominance of two specific targeting motifs: one at the amino terminus and one at the membrane aspect of the cytoplasmically located carboxyl tail. An intracellular loop deletion of six amino acids, associated with a mild phenotype, showed partial oligomerisation and low intercellular dye transfer compared with wild-type connexin 32. The results show that modifications in trafficking and assembly of gap junction channels emerge as a major feature of Charcot-Marie-Tooth X-linked disease.
Insights
Connexin 32 mutations disrupt gap junction assembly and trafficking, impairing nerve cell communication in Charcot-Marie-Tooth disease. These molecular defects explain the disease
Area of Science:
- Neuroscience
- Molecular Biology
- Genetics
Background:
- Charcot-Marie-Tooth disease (CMT) is a group of inherited disorders affecting peripheral nerves.
- X-linked CMT (CMT-X) is often caused by mutations in the connexin 32 (CX32) gene, leading to impaired peripheral nerve transmission.
- Understanding the molecular basis of CX32 dysfunction is crucial for developing therapeutic strategies.
Purpose of the Study:
- To investigate the molecular mechanisms underlying connexin 32 (CX32) mutations in X-linked Charcot-Marie-Tooth disease.
- To analyze how CX32 mutations affect the assembly, trafficking, and function of gap junction channels.
- To identify specific domains or motifs critical for CX32 trafficking and connexon formation.
Main Methods:
- Utilized a cell-free translation system to assess the membrane insertion and oligomerization of mutated CX32 proteins.
- Employed HeLa cells expressing CX32 cDNAs to evaluate connexon functionality via Lucifer yellow dye transfer assays.
- Applied immunocytochemistry to determine the intracellular trafficking properties of wild-type and mutated CX32.
Main Results:
- Six recombinant CX32 mutations exhibited varying efficiencies in membrane insertion and oligomerization into connexon hemichannels.
- Defective intracellular trafficking and impaired connexon assembly correlated with reduced intercellular communication and disease severity.
- Identified specific targeting motifs at the amino terminus and carboxyl tail critical for proper CX32 trafficking; an intracellular loop deletion resulted in partial oligomerization and mild phenotype.
Conclusions:
- Intracellular retention and impaired assembly of connexin 32 are key features of X-linked Charcot-Marie-Tooth disease.
- The efficiency of connexin trafficking and oligomerization directly impacts intercellular communication and disease phenotype.
- Targeting motifs within connexin 32 play a dominant role in regulating gap junction channel assembly and function.