A sodium channel variant in Aedes aegypti as a candidate pathogen sensor for viral-associated molecular patterns

Cara Lee,Alexis Jones,Danielle Kainz,Faatima Khan,Michael D Carrithers

doi:10.1016/j.bbrc.2015.06.085

Abstract

Recent work demonstrated that a splice variant of a human macrophage voltage-gated sodium channel expressed on endosomes acts as an intracellular sensor for dsRNA, a viral-associated molecular pattern. Here our goal was to identify a candidate gene in a clinically relevant invertebrate model with related cellular and pattern recognition properties. The para gene in drosophila and other insects encodes voltage-gated sodium channels with similar electrophysiological properties to those found in vertebrate excitable membranes. A database search revealed that the AAEL006019 gene in Aedes aegypti, the yellow fever mosquito, encodes a voltage-gated sodium channel that is distinct from genes that encode para-like sodium channels. As compared to para-like channels, the protein products from this gene have deletions in the N-terminus and in the DII-DIII linker region. When over-expressed in an Aedes aegypti cell line, CCL-125, the AAEL006019 channel demonstrated cytoplasmic expression on vesicular-like organelles. Electrophysiologic analysis revealed that the channel mediates small inward currents that are enhanced by synthetic mimics of viral-derived ssRNA, R848 and ORN02, but not the dsRNA mimic, poly I:C. R848 treatment of CCL-125 cells that express high levels of the channels led to increased expression of RelA and Ago2, two mediators of insect innate immunity. These results suggest that the AAEL006019 channel acts as an intracellular pathogen sensor for ssRNA molecular patterns.

Highlights

Voltage-gated sodium channels mediate evolutionarily conserved signaling mechanisms that are present in organisms as diverse as bacteria and mammals [1]
As compared to the para genes, products of AAEL006019 contain deletions in a portion of the DII-DIII cytoplasmic linker and at the N-terminus (Fig. 1). These deletions are distinct from those in the human macrophage SCN5A variant, which contains a deletion in the DIII S5-S6 extracellular selectivity filter [8]
We here propose that the AAEL006019 gene in Ae. aegypti encodes a voltage-gated sodium channel that acts as an intracellular sensor for virally-derived ssRNA

Summary

Introduction

Voltage-gated sodium channels mediate evolutionarily conserved signaling mechanisms that are present in organisms as diverse as bacteria and mammals [1] In excitable membranes, these channels regulate electrical signaling through the generation of action potentials. A range of non-canonical functions have been described Work from this laboratory has demonstrated that a novel human splice variant, macrophage SCN5A, regulates pathogen recognition and intracellular signaling. Activation of human macrophage SCN5A by cytoplasmic poly I:C, a mimic of viral dsRNA, increases the inward sodium current and leads to increased transcription of antiviral genes through an ATF2-dependent mechanism. Based on these results, we hypothesized that human macrophage SCN5A is a pattern recognition molecule that initiates innate immune signaling

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