Non-canonical endogenous expression of voltage-gated sodium channel NaV 1.7 subtype by the TE671 rhabdomyosarcoma cell line

Abstract

The human TE671 cell line was originally used as a model of medulloblastoma but has since been reassigned as rhabdomyosarcoma. Despite the characterised endogenous expression of voltage-sensitive sodium currents in these cells, the specific voltage-gated sodium channel (VGSC) subtype underlying these currents remains unknown. To profile the VGSC subtype in undifferentiated TE671 cells, endpoint and quantitative reverse transcription-PCR (qRT-PCR), western blot and whole-cell patch clamp electrophysiology were performed. qRT-PCR profiling revealed that expression of the SCN9A gene was ∼215-fold greater than the SCN4A gene and over 400-fold greater than any of the other VGSC genes, while western blot confirmed that the dominant SCN9A RNA was translated to a protein with a molecular mass of ∼250 kDa. Elicited sodium currents had a mean amplitude of 2.6 ± 0.7 nA with activation and fast inactivation V₅₀ values of -31.9 ± 1.1 and -69.6 ± 1.0 mV, respectively. The currents were completely and reversibly blocked by tetrodotoxin at concentrations greater than 100 nm (IC₅₀ = 22.3 nm). They were also very susceptible to the Na_V 1.7 specific blockers Huwentoxin-IV and Protoxin-II with IC₅₀ values of 14.6 nm and 0.8 nm, respectively, characteristic of those previously determined for Na_V 1.7. Combined, the results revealed the non-canonical and highly dominant expression of Na_V 1.7 in the human TE671 rhabdomyosarcoma cell line. We show that the TE671 cell line is an easy to maintain and cost-effective model for the study of Na_V 1.7, a major target for the development of analgesic drugs and more generally for the study of pain. KEY POINTS: Undifferentiated TE671 cells produce a voltage-sensitive sodium current when depolarised. The voltage-gated sodium channel isoform expressed in undifferentiated TE671 cells was previously unknown. Through qRT-PCR, western blot and toxin pharmacology, it is shown that undifferentiated TE671 cells dominantly (>99.5%) express the Na_V 1.7 isoform that is strongly associated with pain. The TE671 cell line is, therefore, a very easy to maintain and cost-effective model to study Na_V 1.7-targeting drugs.

Keywords: Huwentoxin-IV; NaV1.7; Protoxin-II; TE671 cells; patch-clamp; tetrodotoxin; voltage-gated sodium channel.