Agonist- and Ca2+-dependent Desensitization of TRPV1 Channel Targets the Receptor to Lysosomes for Degradation

Lucía Sanz-Salvador,Amparo Andrés-Borderia,Antonio Ferrer-Montiel,Rosa Planells-Cases

doi:10.1074/jbc.m111.289751

Abstract

TRPV1 receptor agonists such as the vanilloid capsaicin and the potent analog resiniferatoxin are well known potent analgesics. Depending on the vanilloid, dose, and administration site, nociceptor refractoriness may last from minutes up to months, suggesting the contribution of different cellular mechanisms ranging from channel receptor desensitization to Ca(2+) cytotoxicity of TRPV1-expressing neurons. The molecular mechanisms underlying agonist-induced TRPV1 desensitization and/or tachyphylaxis are still incompletely understood. Here, we report that prolonged exposure of TRPV1 to agonists induces rapid receptor endocytosis and lysosomal degradation in both sensory neurons and recombinant systems. Agonist-induced receptor internalization followed a clathrin- and dynamin-independent endocytic route, triggered by TRPV1 channel activation and Ca(2+) influx through the receptor. This process appears strongly modulated by PKA-dependent phosphorylation. Taken together, these findings indicate that TRPV1 agonists induce long-term receptor down-regulation by modulating the expression level of the channel through a mechanism that promotes receptor endocytosis and degradation and lend support to the notion that cAMP signaling sensitizes nociceptors through several mechanisms.

Highlights

The contribution of TRPV1 trafficking to vanilloid-induced desensitization and tachyphylaxis remains unexplored
At 4 °C labeled TRPV1 remained at the plasma membrane, incubation at 37 °C led to a partial internalization of receptors from the plasma membrane, as evident from a clear intracellular staining pattern (Fig. 1A)
Because different cell-specific factors/pathways might shift the EC50 for capsaicin and heterologously expressed TRPV1 may not be as sensitive as the native receptor in neurons, TRPV1ϩ HEK293 cells were exposed to 1 ␮M capsaicin (Fig. 1B)

Summary

Introduction

The contribution of TRPV1 trafficking to vanilloid-induced desensitization and tachyphylaxis remains unexplored. Dose, and administration site, nociceptor refractoriness may last from minutes up to months, suggesting the contribution of different cellular mechanisms ranging from channel receptor desensitization to Ca2؉ cytotoxicity of TRPV1-expressing neurons. Agonist-induced receptor internalization followed a clathrin- and dynamin-independent endocytic route, triggered by TRPV1 channel activation and Ca2؉ influx through the receptor. This process appears strongly modulated by PKA-dependent phosphorylation. Taken together, these findings indicate that TRPV1 agonists induce long-term receptor down-regulation by modulating the expression level of the channel through a mechanism that promotes receptor endocytosis and degradation and lend support to the notion that cAMP signaling sensitizes nociceptors through several mechanisms

Objectives

Results

Conclusion