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.

Melanoma shows highly aggressive behavior (i.e., local invasion and metastasis). Matrix metalloprotease-3 (MMP-3), a zinc-dependent endopeptidase, degrades several extracellular substrates and contributes to local invasion by creating a microenvironment suitable for tumor development. Here, we report that interleukin-1β (IL-1β) triggers the MMP-3 expression in canine melanoma cells. The activity of MMP-3 in the culture supernatant was increased in IL-1β-treated melanoma cells. IL-1β time- and dose-dependently provoked the mRNA expression of MMP-3. IL-1β induced the migration of melanoma cells; however, this migration was attenuated by UK356618, an MMP-3 inhibitor. When the cells were treated with the nuclear factor-κB (NF-κB) inhibitor TPCA-1, the inhibition of MMP-3 expression was observed. In IL-1β-treated cells, the phosphorylation both of p65/RelA and p105 was detected, indicating NF-κB pathway activation. In p65/RelA-depleted melanoma cells, IL-1β-mediated mRNA expression of MMP-3 was inhibited, whereas this reduction was not observed in p105-depleted cells. These findings suggest that MMP-3 expression in melanoma cells is regulated through IL-1β-mediated p65/RelA activation, which is involved in melanoma cell migration.

The rate of glucose uptake dramatically increases in cancer cells even in the presence of oxygen and fully functioning mitochondria. Cancer cells produce ATP by glycolysis rather than oxidative phosphorylation under aerobic conditions, a process termed as the “Warburg effect.” In the present study, we treated canine melanoma cells with the glucose analog 2-deoxy-D-glucose (2-DG) and investigated its effect on cell growth. 2-DG attenuated cell growth in a time- and dose-dependent manner. Cell growth was also inhibited following treatment with the glucose transporter (GLUT) inhibitor WZB-117. The treatment of 2-DG and WZB-117 attenuated the glucose consumption, lactate secretion and glucose uptake of the cells. The mRNA expression of the subtypes of GLUT was examined and GLUT1 and GLUT3 were found to be expressed in melanoma cells. The growth, glucose consumption and lactate secretion of melanoma cells transfected with siRNAs of specific for GLUT1 and GLUT3 was suppressed. These findings suggest that glucose uptake via GLUT1 and GLUT3 plays a crucial role for the growth of canine melanoma cells.