Impairment of Human KV4.3 Protein Biosynthesis and Channel Gating by Novel SCA19/22-associated Mutations

Abstract

The autosomal dominant neurodegenerative disorder spinocerebellar ataxia types 19 and 22 (SCA19/22) is associated with mutations in the human voltage-gated K+ channel subunit KV4.3. The precise mechanism underlying the dominant inheritance pattern of SCA19/22 remains unclear. Using in vitro heterologous expression systems, we employed biophysical and biochemical analyses to characterize several novel SCA19/22-causing mutant human KV4.3 channels. Compared to the wild-type (WT) counterpart, the peak current amplitudes of these KV4.3 mutant channels are notably smaller, consistent with the presence of loss-of-function phenotype. Electrophysiological analyses further reveal that these SCA19/22-associated KV4.3 mutant channels manifest altered voltage-dependent activation and inactivation properties. Upon co-expression with the WT channel, the KV4.3 mutants exert considerable dominant-negative effects on both voltage-dependent gating and effective K+ current level of human KV4.3 channel. Protein chemistry analyses demonstrate that the KV4.3 mutants are associated with significantly lower total protein levels, reduced protein half-life values, and defective membrane trafficking. Moreover, co-expression with the mutants substantially decreases the total and cell surface levels of KV4.3 WT protein. Taken together, we propose that the dominant inheritance pattern of SCA19/22 may be explained by the aberrant effects of the mutants on protein biosynthesis and voltage-dependent gating of KV4.3 WT channel.