TRPA1 is functionally expressed in melanoma cells but is not critical for impaired proliferation caused by allyl isothiocyanate or cinnamaldehyde

Abstract

Melanoma is the most dangerous form of skin cancer occurring in Caucasians with rising incidence. They are remarkably resistant to conventional anti-tumour therapies like chemotherapy and radiotherapy. Therefore, new treatment strategies are urgently needed. Anti-tumour effects of phytochemicals such as allyl isothiocyanate or cinnamaldehyde have been demonstrated in various melanoma models in vitro and in vivo. Considering their high potency as transient receptor potential A1 (TRPA1)-activating compounds, we examined the functional expression of TRPA1 channels in different melanoma cell lines as well as in non-malignantly transformed primary melanocytes. The presence of TRPA1 transcripts could be detected in most of the melanoma cell lines. Furthermore, single-cell calcium imaging and patch clamp electrophysiology confirmed the presence of functional TRPA1 channels in those cell lines. Proliferation assays revealed that allyl isothiocyanate and cinnamaldehyde clearly reduce the proliferation of melanoma cells, but this effect is independent of an activation of TRPA1 channels, making it unlikely that ionic currents through TRPA1 are responsible for the anti-tumour effects of mustard oil and cinnamaldehyde.

Inflammatory pain control by blocking oxidized phospholipid-mediated TRP channel activation

“…For ratiometric single cell calcium analysis, either DRG neurons or HEK-293 cells were labeled with 6 µM Fura-2/AM for 30 min at 37 °C in imaging solution (in mM): 134 NaCl, 6 KCl, 1 MgCl 2 , 1 CaCl 2 , 10 HEPES, 5.5 glucose, pH 7.4 adjusted with NaOH 86 . All measurements were performed at room temperature using a Nikon TE2000-E microscope.…”

“…Pipettes with 2.5–5 MΩ resistances were pulled from borosilicate glass (GB 150-8P, Science Products, Hofheim, Germany) with a P-97 micropipette puller (Sutter Instruments, Novato, CA, USA). Whole cell patch clamp measurements were performed with HEKA EPC-10 USB and controlled by patch master software (HEKA Electronic, Lambrecht, Germany) 86 . Ramps from −100 to +100 mV of 500 ms duration were sampled continuously at 5 kHz every second.…”

TRP Channels in Skin Biology and Pathophysiology

“…Several human melanoma-derived cell lines were also shown to express TRPA1 and to exhibit calcium responses to TRPA1 agonists that could be suppressed by a TRPA1 selective antagonist. However, in the same study, TRPA1 agonist-induced changes in cellular proliferation were insensitive to this same antagonist, potentially arguing against a clear role for this channel as a target of melanoma therapy [191]. Given these findings, additional tools and experiments will be required to precisely define the sites at which TRPA1 produces its effects on skin biology and the mechanisms by which it does so.…”

Ion transport in pigmentation

“…TRPA1 is expressed and functions in human epidermal melanocytes (25-27). TRPA1 mediates a non-selective, Ca 2+ -permeant current activated by chemical irritants and reactive oxygen species and modulated by Ca 2+ and other cellular messengers (28).…”