TRPM8-independent Menthol-induced Ca2+ Release from Endoplasmic Reticulum and Golgi

Abstract

Menthol, a secondary alcohol produced by the peppermint herb, Mentha piperita, is widely used in the food and pharmaceutical industries as a cooling/soothing compound and odorant. It induces Ca 2؉ influx in a subset of sensory neurons from dorsal root and trigeminal ganglia, due to activation of TRPM8, a Ca 2؉ -permeable, cold-activated member of the TRP superfamily of cation channels. Menthol also induces Ca 2؉ release from intracellular stores in several TRPM8-expressing cell types, which has led to the suggestion that TRPM8 can function as an intracellular Ca 2؉ -release channel. Here we show that menthol induces Ca 2؉ release from intracellular stores in four widely used cell lines (HEK293, lymph node carcinoma of the prostate (LNCaP), Chinese hamster ovary (CHO), and COS), and provide several lines of evidence indicating that this release pathway is TRPM8-independent: 1) menthol-induced Ca 2؉ release was potentiated at higher temperatures, which contrasts to the cold activation of TRPM8; 2) overexpression of TRPM8 did not enhance the menthol-induced Ca 2؉ release; 3) menthol-induced Ca 2؉ release was mimicked by geraniol and linalool, which are structurally related to menthol, but not by the more potent TRPM8 agonists icilin or eucalyptol; and 4) TRPM8 expression in HEK293 cells was undetectable at the protein and mRNA levels. Moreover, using a novel TRPM8-specific antibody we demonstrate that both heterologously expressed TRPM8 (in HEK293 cells) and endogenous TRPM8 (in LNCaP cells) are mainly localized in the plasma membrane, which contrast to previous localization studies using commercial anti-TRPM8 antibodies. Finally, aequorin-based measurements demonstrate that the TRPM8-independent menthol-induced Ca 2؉ release originates from both endoplasmic reticulum and Golgi compartments.Menthol is a naturally occurring compound responsible for the minty flavor and smell of the mint plant (Mentha piperita). Whereas the first descriptions of the use of menthol as a cooling/soothing compound and odorant date back to ϳ2000 years ago, menthol is still extensively used as an additive in a wide variety of products ranging from ointments and candies to cigarettes. The soothing, refreshing and invigorating feature of the oil made from the peppermint herb is useful in massage for muscle fatigue. It is also used in the treatment of asthma, colic, exhaustion, fever, flatulence, headache, nausea, scabies, sinusitis, and vertigo (1). Currently the best described molecular target of menthol is TRPM8, 2 a member of the melastatin branch of the TRP superfamily of cation channels. TRPM8 was initially identified in a screening procedure aimed at identifying mRNAs that are up-regulated in prostate cancer (2). Subsequently, TRPM8 expression was also demonstrated to be strongly up-regulated in several other primary tumor types including breast, colon, lung, and skin (2). The following studies identified TRPM8 in a subset of dorsal root and trigeminal neurons (3), and found it to function as a plasma membrane Ca 2ϩ -permeable cation ...

TRPM8 Mechanism of Cold Allodynia after Chronic Nerve Injury

“…However, others have observed that some menthol-sensitive cells did not respond to cold (Nealen et al, 2003;Mahieu et al, 2006;Dhaka et al, 2007) and that the menthol responses in these cells were attributable to TRPM8-independent Ca 2ϩ release. Factors that might contribute to the discrepancy include the concentrations of menthol, the degree of cooling temperatures, the threshold setting for detecting Ca 2ϩ responses, and the cell types.…”

Shivering and tachycardic responses to external cooling in mice are substantially suppressed by TRPV1 activation but not by TRPM8 inhibition

“…Accordingly, a series of recent in vivo studies using pharmacological antagonism and/or genetic deletion have established that TRPM8 plays a significant role in most individual thermoregulatory responses to cold: behavioral thermoregulation, BAT activation, peripheral vasoconstriction, and total metabolic response to cold (1,2,6,8,17,33). TRPM8 was also implicated in shivering thermogenesis in two studies using menthol as a TRPM8 agonist, which, however, were not conclusive due to possible TRPM8-independent actions of menthol (15,18,21,34). Despite this caveat, these and other studies seemed to have formed a prevailing implicit view in the literature that TRPM8 is a "universal" cold sensor, insofar as it controls every physiological response to cold.…”

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

“…TRPM8 expression has been shown to be up-regulated in prostate cancer cells, as well as in several other nonprostatic primary cancers, including melanoma, colorectal carcinomas, and breast carcinomas (25,26). Studies have demonstrated that TRPM8 is expressed on the plasma and the endoplasmic reticulum (ER) membranes of cells, where it facilitates the influx or release of Ca 21 from extracellular sources and the ER stores, respectively (24,26,27). A study by Thebault and coworkers (24) established that TRPM8 was preferentially localized to the ER of androgen-responsive LNCaP prostate cancer cells.…”