scholarly journals Connexin 32 mutations from X-linked Charcot-Marie-Tooth disease patients: functional defects and dominant negative effects.

1996 ◽  
Vol 7 (6) ◽  
pp. 907-916 ◽  
Author(s):  
Y Omori ◽  
M Mesnil ◽  
H Yamasaki

We have characterized the function of connexin (Cx) 32 gene mutations found in X-linked dominant Charcot-Marie-Tooth disease with respect to their ability to form functional gap junctions among themselves and to inactivate wild-type Cx32 by a dominant negative mechanism. We prepared four types of Cx32 mutant cDNAs and transfected them into HeLa cells, which do not show detectable levels of gap junctional intercellular communication (GJIC), nor expression of any connexins examined. Cells transfected with the wild-type Cx32 gene, but not those transfected with three different base substitution mutations (i.e. Cys 60 to Phe, Val 139 to Met, and Arg 215 to Trp), restored GJIC. Unexpectedly, in cells transfected with a nonsense mutant at codon 220, there was also restored GJIC. When we double-transfected these mutant constructs into the HeLa cells that had already been transfected with the wild-type Cx32 gene and thus were GJIC proficient, three base substitution mutants inhibited GJIC, suggesting that these three mutants can eliminate the function of wild-type Cx32 in a dominant negative manner. The nonsense mutation at codon 220 did not show such a dominant negative effect. Since both mutant and wild-type Cx32 mRNAs were detected, but only poor Cx32 protein expression at cell-cell contact areas was observed in the double transfectants, it is suggested that certain mutants form nonfunctional chimeric connexons with wild-type connexins, which are not properly inserted into the cytoplasmic membrane.

2019 ◽  
Author(s):  
Chao Shen ◽  
Qian Qi ◽  
Yicai Qin ◽  
Dejian Zhou ◽  
Xinyuan Chen ◽  
...  

AbstractCharcot-Marie-Tooth disease is the most common inherited peripheral neuropathy. Dominant mutations in glycyl-tRNA synthetase (GARS) gene cause peripheral nerve degeneration and lead to CMT disease type 2D. Mutations in GARS (GARSCMT2D) show partial loss-of-function features, suggesting that tRNA-charging deficits play a role in disease pathogenesis, but the underlying mechanisms are not fully understood. In this study we report that wild-type GARS tightly binds the NAD+-dependent deacetylase SIRT2 and inhibits its deacetylation activity, resulting in the hyperacetylated α-tubulin, the major substrate of SIRT2. Previous studies showed that acetylation of α-tubulin protects microtubules from mechanical breakage and keep axonal transportation. However, CMT2D mutations in GARS can not inhibit SIRT2 deacetylation, which leads to decrease acetylated α-tubulin and severe axonal transport deficits. Genetic reduction of SIRT2 in the Drosophila model rescues the GARS–induced axonal CMT neuropathy and extends the life span. Our findings demonstrate the pathogenic role of SIRT2-dependent α-tubulin deacetylation in mutant GARS-induced neuropathies and provide new perspectives for targeting SIRT2 as a potential therapy against hereditary axonopathies.


2012 ◽  
Vol 199 (5) ◽  
pp. 799-816 ◽  
Author(s):  
Samuel M. Lee ◽  
Lih-Shen Chin ◽  
Lian Li

Mutations in small integral membrane protein of lysosome/late endosome (SIMPLE) cause autosomal dominant, Charcot-Marie-Tooth disease (CMT) type 1C. The cellular function of SIMPLE is unknown and the pathogenic mechanism of SIMPLE mutations remains elusive. Here, we report that SIMPLE interacted and colocalized with endosomal sorting complex required for transport (ESCRT) components STAM1, Hrs, and TSG101 on early endosomes and functioned with the ESCRT machinery in the control of endosome-to-lysosome trafficking. Our analyses revealed that SIMPLE was required for efficient recruitment of ESCRT components to endosomal membranes and for regulating endosomal trafficking and signaling attenuation of ErbB receptors. We found that the ability of SIMPLE to regulate ErbB trafficking and signaling was impaired by CMT-linked SIMPLE mutations via a loss-of-function, dominant-negative mechanism, resulting in prolonged activation of ERK1/2 signaling. Our findings indicate a function of SIMPLE as a regulator of endosomal trafficking and provide evidence linking dysregulated endosomal trafficking to CMT pathogenesis.


Sign in / Sign up

Export Citation Format

Share Document