Involvement of TRPA1 in Necrosis of Melanoma Cells via Phospholipase D1

The tumor microenvironment, including extracellular pH (pHe), has emerged as a key regulator of tumor cellular function. Although extracellular acidification sensing and function are well established, the effect of extracellular alkalinization on cellular functioning remains unclear. Here, we report that transient receptor potential ankyrin 1 (TRPA1) functions as an alkaline sensor and mediator of cell death in melanoma cells. Exposure to alkaline pHe (8.1) or allyl isothiocyanate (AITC), a TRPA1 agonist, significantly reduced melanoma cell viability. We found that cell death was propidium iodide-positive and annexin V-negative, suggesting that pHe or AITC treatment induced necrosis rather than apoptosis. TRPA1 activation induced sustained Ca2+ influx, which was suppressed by either extracellular Ca2+ removal or treatment with the TRPA1 inhibitor, HC-030031, both of which attenuated cell death. Pharmacological screening has identified phosphatidylcholine-specific phospholipase D1 (PLD1) as a positive regulator of cell death. We confirmed that transfection with PLD1 siRNA significantly reduced AITC-induced cell death, whereas PLD2, PLD3, and NAPE-PLD siRNAs had no effect. These observations suggest that the vulnerability of melanoma cells to alkaline pHe is mediated by activation of the TRPA1-PLD1 axis. Thus, TRPA1 and PLD1 are potential targets for therapeutic intervention in melanoma.