Intron Retention in mRNA Encoding Ancillary Subunit of Insect Voltage-Gated Sodium Channel Modulates Channel Expression, Gating Regulation and Drug Sensitivity

Insect voltage-gated sodium (Na-v) channels are formed by a well-known pore-forming a-subunit encoded by para-like gene and ancillary subunits related to TipE from the mutation temperature-induced-paralysis locus E. The role of these ancillary subunits in the modulation of biophysical and pharmacological properties of Na+ currents are not enough documented. The unique neuronal ancillary subunit TipE-homologous protein 1 of Drosophila melanogaster (DmTEH1) strongly enhances the expression of insect Na-v channels when heterologously expressed in Xenopus oocytes. Here we report the cloning and functional expression of two neuronal DmTEH1-homologs of the cockroach, Periplaneta americana, PaTEH1A and PaTEH1B, encoded by a single bicistronic gene. In PaTEH1B, the second exon encoding the last 11-amino-acid residues of PaTEH1A is shifted to 3'UTR by the retention of a 96-bp intron-containing coding-message, thus generating a new C-terminal end. We investigated the gating and pharmacological properties of the Drosophila Na-v channel variant (DmNa(v)1-1) co-expressed with DmTEH1, PaTEH1A, PaTEH1B or a truncated mutant PaTEH1 Delta(270-280) in Xenopus oocytes. PaTEH1B caused a 2.2-fold current density decrease, concomitant with an equivalent a-subunit incorporation decrease in the plasma membrane, compared to PaTEH1A and PaTEH1 Delta(270-280). PaTEH1B positively shifted the voltage-dependences of activation and slow inactivation of DmNa(v)1-1 channels to more positive potentials compared to PaTEH1A, suggesting that the C-terminal end of both proteins may influence the function of the voltage-sensor and the pore of Na-v channel. Interestingly, our findings showed that the sensitivity of DmNa(v)1-1 channels to lidocaine and to the pyrazoline-type insecticide metabolite DCJW depends on associated TEH1-like subunits. In conclusion, our work demonstrates for the first time that density, gating and pharmacological properties of Na-v channels expressed in Xenopus oocytes can be modulated by an intron retention process in the transcription of the neuronal TEH1-like ancillary subunits of P. americana.