Human Lung Epithelial Cells Express a Functional Cold-Sensing TRPM8 Variant

Abstract

Several transient receptor potential (TRP) ion channels sense and respond to changes in ambient temperature. Chemical agonists of TRP channels, including menthol and capsaicin, also elicit sensations of temperature change. TRPM8 is a cold-and menthol-sensing ion channel that converts thermal and chemical stimuli into neuronal signals and sensations of cooling/cold. However, the expression and function of TRPM8 receptors in non-neuronal cells and tissues is a relatively unexplored area. Results presented here document the expression and function of a truncated TRPM8 variant in human bronchial epithelial cells. Expression of the TRPM8 variant was demonstrated by RT-PCR, cloning, and immunohistology. Receptor function was characterized using the prototypical TRPM8 agonist, menthol, and exposure of cells to reduced temperature (188C). The TRPM8 variant was expressed primarily within endoplasmic reticulum membranes of lung epithelial cells and its activation was attenuated by thapsigargin, the cell-permeable TRPM8 antagonist N-(4-tert-butylphenyl)-4-(3-chloropyridin-2-yl)piperazine-1-carboxamide, and shRNA-induced suppression of TRPM8 expression. Activation of the TRPM8 variant in lung cells was coupled with enhanced expression of the inflammatory cytokines IL-6 and IL-8. Collectively, our results suggest that this novel TRPM8 variant receptor may function as a modulator of respiratory physiology caused by cold air, and may partially explain asthmatic respiratory hypersensitivity to cold air.Keywords: TRP family; TRPM8; menthol; calcium; lung epithelial cells Temperature detection is essential for mammalian homeostasis. Several members of the transient receptor potential (TRP) superfamily of ion channels function as molecular transducers of thermal stimuli (1-3). Thermo-TRP channels, which include TRPV1 (4, 5), TRPV2 (6), TRPV3 (7), TRPV4 (8), TRPM8 (9, 10), and TRPA1 (11), are activated over distinct temperature ranges (1). Combined, these thermo-TRPs account for the detection of the entire spectrum of temperature sensations perceived by mammals.TRP channels consist of six putative transmembrane (TM)-spanning segments flanked by intracellular N-and C-terminal domains (12, 13) of variable length and an ion-conducting poreloop region located between TM segments five and six (12)(13)(14). Residues within the N-and C-terminal regions are proposed to associate with cellular proteins and cytoplasmic factors (15, 16) that determine channel activation properties and subcellular localization. The sequence similarity between the TRP subfamilies is highest in the sixth TM region and in the highly conserved ''TRP'' domain, located in the intracellular C-terminal region (2,12,17).TRPM8 (or Trp-p8), a member of the melastatin subfamily, functions as a transducer of innocuous cold stimuli in the somatosensory system. It is a ligand-gated, cation channel, with moderate to high selectivity for calcium (Ca 21 ) ions (9, 10). TRPM8 is activated by temperatures in the range of 8 to 228C, with an activation threshold at approximately 22...

Overexpression of short TRPM8 variant α promotes cell migration and invasion, and decreases starvation-induced apoptosis in prostate cancer LNCaP cells

“…At least three short TRPM8 isoforms, each exhibiting their own pathophysiological functions, have been reported in previous studies. Sabnis et al (6) reported that the full-length TRPM8 transcript was absent in human lung epithelial cells and identified a novel truncated TRPM8 variant that was selectively expressed as a modulator of respiratory physiology in cold air. Furthermore, Bidaux et al (8) reported the following two novel short splice variants of TRPM8, which were cloned from prostate cancer cells, using a model of HEK293 cells: sM8α and sM8β.…”

The TRPM8 Protein Is a Testosterone Receptor

“…The TRPM8 protein is expressed in various tissues, including the brain, sensory neurons, lungs, heart, and, notably, the prostate (6,7). Although the role of TRPM8 as the cold and menthol receptor has been well established in the peripheral nervous system (8 -10), its role in other tissues is not well understood because no endogenous agonists of TRPM8 have been identified thus far.…”

Activation of Transient Receptor Potential Ankyrin-1 by Insoluble Particulate Material and Association with Asthma

“…TRPA1 and TRPV1, as well as other TRP channels, are expressed by various airway epithelial and alveolar cells in addition to airway neurons. Activation of TRPA1 (10,11), TRPV1 (7,(12)(13)(14)(15)(16)(17), TRPV4 (18), and transient receptor potential cation channel, subfamily M, member 8 (TRPM8) (19) in these cell types by prototypical agonists, select environmental pollutants, and PM also has been demonstrated to cause proinflammatory cytokine/chemokine production and, in some cases, apoptosis.…”