A KCNC3 mutation causes a neurodevelopmental, non-progressive SCA13 subtype associated with dominant negative effects and aberrant EGFR trafficking

Abstract

The autosomal dominant spinocerebellar ataxias (SCAs) are a diverse group of neurological disorders anchored by the phenotypes of motor incoordination and cerebellar atrophy. Disease heterogeneity is appreciated through varying comorbidities: dysarthria, dysphagia, oculomotor and/or retinal abnormalities, motor neuron pathology, epilepsy, cognitive impairment, autonomic dysfunction, and psychiatric manifestations. Our study focuses on SCA13, which is caused by several allelic variants in the voltage-gated potassium channel KCNC3 (Kv3.3). We detail the clinical phenotype of four SCA13 kindreds that confirm causation of the KCNC3R423H allele. The heralding features demonstrate congenital onset with non-progressive, neurodevelopmental cerebellar hypoplasia and lifetime improvement in motor and cognitive function that implicate compensatory neural mechanisms. Targeted expression of human KCNC3R423H in Drosophila triggers aberrant wing veins, maldeveloped eyes, and fused ommatidia consistent with the neurodevelopmental presentation of patients. Furthermore, human KCNC3R423H expression in mammalian cells results in altered glycosylation and aberrant retention of the channel in anterograde and/or endosomal vesicles. Confirmation of the absence of plasma membrane targeting was based on the loss of current conductance in cells expressing the mutant channel. Mechanistically, genetic studies in Drosophila, along with cellular and biophysical studies in mammalian systems, demonstrate the dominant negative effect exerted by the mutant on the wild-type (WT) protein, which explains dominant inheritance. We demonstrate that ocular co-expression of KCNC3R423H with Drosophila epidermal growth factor receptor (dEgfr) results in striking rescue of the eye phenotype, whereas KCNC3R423H expression in mammalian cells results in aberrant intracellular retention of human epidermal growth factor receptor (EGFR). Together, these results indicate that the neurodevelopmental consequences of KCNC3R423H may be mediated through indirect effects on EGFR signaling in the developing cerebellum. Our results therefore confirm the KCNC3R423H allele as causative for SCA13, through a dominant negative effect on KCNC3WT and links with EGFR that account for dominant inheritance, congenital onset, and disease pathology.

CDCP1 overexpression drives prostate cancer progression and can be targeted in vivo

“…CDCP1 Pten -/-MEFs also stained negative for SA-β-gal and exhibited increased cell proliferation with an elongated phenotype when compared with Pten -/-MEFs (Supplemental Figure 6A). a tumor-like phenotype (35,36). We found that overexpression of CDCP1-WT, but not CDCP1-delta, promoted extra macrochaetae formation.…”

“…The frequency of tumors displaying a low level of Table 1. CDCP1-positive samples in BPH, RPE, CRPC, and metastatic PCa in human prostate cancers BPH RPE CRPC Metastasis Total 45 382 102 35 CDCP1-positive 4 65 45 18 For TMA1, n = 564. form of CDCP1 (CDCP1-delta) lacking Src-phosphorylation sites (35,36) in Drosophila melanogaster. The Drosophila larval imaginal discs are a monolayer epithelium that is considered morphologically comparable to mammalian epithelia and therefore constitutes an ideal system in which to model cancer progression in vivo (37).…”

Modeling Neurodegenerative Spinocerebellar Ataxia Type 13 in Zebrafish Using a Purkinje Neuron Specific Tunable Coexpression System

“…Indeed, incorporation of KCNC3 R420H into the channel reduced the excitability of fast-spiking motoneurons and impaired startle reflex in zebrafish (Issa et al, 2011). The design of our PC-specific vector will allow the investigation of the cell biological mechanisms underlying the cytotoxicity of this mutant allele, including the change of electrophysiological properties (Issa et al, 2011) as well as an impaired intracellular trafficking as has been recently suggested (Gallego-Iradi et al, 2014;Khare et al, 2017). A slight drawback of zebrafish cerebellar disease modeling though may arise from only a few differences in cerebellar cytoarchitecture compared with mammals.…”

Novel Features and Abnormal Pattern of Cerebral Glucose Metabolism in Spinocerebellar Ataxia 19

“…Other familial potassium channelopathies associated with cerebellar dysfunction include spinocerebellar ataxia type 13 (SCA13), episodic ataxia type 1 (EA1), and sensorineural deafness, ataxia, mental retardation, and electrolyte imbalance (SESAME syndrome) which are caused by mutations in the KCNC3 , KCNA1 , and KCNJ10 genes, respectively [ 25 – 27 ]. Different to SCA13 in which some patients have a non-progressive course [ 28 ], SCA19/22 is clearly progressive [ 6 , 7 ]. Interestingly, an association between epilepsy and long QT syndrome (LQTS) has been proposed for mutations in KCNQ1 ; however, ataxia is, to the best of our knowledge, not part of the disease spectrum associated with KCNQ1 mutations [ 29 ].…”