TRPV1 Antagonists Elevate Cell Surface Populations of Receptor Protein and Exacerbate TRPV1-Mediated Toxicities in Human Lung Epithelial Cells

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Abstract
TRPV1 mediates cell death and pro-inflammatory cytokine production in lung epithelial cells exposed to prototypical receptor agonists. This study shows that NHBE, BEAS-2B and TRPV1 over-expressing BEAS-2B cells pre-treated with various TRPV1 antagonists become sensitized to the prototypical TRPV1 agonist, nonivamide, via a mechanism that involves translocation of existing receptor from the endoplasmic reticulum to the plasma membrane. As such, typical cellular responses to agonist treatment, as measured by calcium flux, inflammatory cytokine gene induction, and cytotoxicity were exacerbated. These data were in contrast to the results obtained when TRPV1 antagonists were co-administered with nonivamide; conditions which inhibited TRPV1-mediated effects. The antagonists LJO-328, SC0030, and capsazepine increased the cytotoxicity of nonivamide by approximately 20-fold and agonist-induced calcium flux by approximately 6-fold. Inflammatory-cytokine gene induction by nonivamide was also increased significantly by pre-treatment with the antagonists. The enhanced responses were inhibited by the co-administration of antagonists with nonivamide, confirming that increases in sensitivity were attributable to increased TRPV1-associated activity. Sensitization was attenuated by brefeldin A (a golgi transport inhibitor), but not cycloheximide (a protein synthesis inhibitor), or actinomycin D (a transcription inhibitor). Sensitized cells exhibited increased calcium flux from extracellular calcium sources, while unsensitized cells exhibited calcium flux originating primarily from intracellular stores. These results demonstrate the presence of a novel mechanism for regulating the sub-cellular distribution of TRPV1 and subsequent control of cellular sensitivity to TRPV1 agonists.

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