Transit Defect of Potassium-Chloride Co-transporter 3 Is a Major Pathogenic Mechanism in Hereditary Motor and Sensory Neuropathy with Agenesis of the Corpus Callosum

Abstract

Missense and protein-truncating mutations of the human potassium-chloride co-transporter 3 gene (KCC3) cause hereditary motor and sensory neuropathy with agenesis of the corpus callosum (HMSN/ACC), which is a severe neurodegenerative disease characterized by axonal dysfunction and neurodevelopmental defects. We previously reported that KCC3-truncating mutations disrupt brain-type creatine kinase-dependent activation of the co-transporter through the loss of its last 140 amino acids. Here, we report a novel and more distal HMSN/ACCtruncating mutation (3402C3 T; R1134X) that eliminates only the last 17 residues of the protein. This small truncation disrupts the interaction with brain-type creatine kinase in mammalian cells but also affects plasma membrane localization of the mutant transporter. Although it is not truncated, the previously reported HMSN/ACC-causing 619C3 T (R207C) missense mutation also leads to KCC3 loss of function in Xenopus oocyte flux assay. Immunodetection in Xenopus oocytes and in mammalian cultured cells revealed a decreased amount of R207C at the plasma membrane, with significant retention of the mutant proteins in the endoplasmic reticulum. In mammalian cells, curcumin partially corrected these mutant protein mislocalizations, with more protein reaching the plasma membrane. These findings suggest that mis-trafficking of mutant protein is an important pathophysiological feature of HMSN/ACC causative KCC3 mutations.

WNK1/HSN2 Mutation in Human Peripheral Neuropathy Deregulates KCC2 Expression and Posterior Lateral Line Development in Zebrafish (Danio rerio)

“…This cotransporter has been studied in the context of hereditary motor and sensory neuropathy with agenesis of the corpus callosum (HMSN/ACC), where causative mutations have been identified in SC12A6 (coding for KCC3) 52. Truncating as well as loss-of-function mutations have been reported to cause mis-trafficking of proteins, decreasing their plasma membrane expression 53. This neuropathy is characterized by progressive sensory-motor deficits, where axonal swelling can be observed in patients.…”

Molecular evidence for a role for K+-Cl− cotransporters in the kidney

“…Additionally, inactivation mutations of KCC3 result in Anderman's syndrome, a severe inherited neurological disease with peripheral neuropathy associated with agenesis of the corpus callosum (12,25,45). Because of this, a tremendous amount of information (10,14,22,36,45) has been produced in this area since the molecular identification of KCCs (5,27). A third fundamental role for KCCs is transepithelial K ϩ and Cl Ϫ transport.…”

K-Cl cotransporters, cell volume homeostasis, and neurological disease

“…One ACCPN mutation, KCC3 R207C, significantly decreases plasma membrane localization of KCC3. This misfolding mutation results in KCC3 retention in the endoplasmic reticulum [77]. Curcumin, which has been shown to stimulate the release of misfolded transmembrane proteins from the endoplasmic reticulum, partially rescues this transport deficit in cells expressing the R207C mutant [77].…”