Expression of the platelet-activating factor receptor enhances benzyl isothiocyanate-induced apoptosis in murine and human melanoma cells

Melanoma cells often express platelet-activating factor receptor (PAF-R), which has been demonstrated to increase metastatic behavior. However, the effect of PAF-R on the responsiveness of melanoma to naturally occurring cytotoxic agents remains to be elucidated. The present study aimed to determine the relative cytotoxicity and mechanism of benzyl isothiocyanate (BITC), a component of cruciferous vegetables, in melanoma cells expressing PAF-R. To evaluate the importance of PAF-R signaling in melanoma cell growth, PAF-R-negative murine B16F10 cells were transduced with a retrovirus containing the cDNA for PAF-R to generate cells stably expressing PAF-R (B16-PAF-R) or an empty vector (MSCV) to generate PAF-R-deficient B16-MSCV control cells. Activation of PAF-R, using the PAF-R agonist, 1-hexadecyl-2-N-methylcarbamoyl-3-glycerophosphocholine, induced an increase in the proliferation of B16-PAF-R cells compared with the B16-MSCV cells. Reverse transcription quantitative polymerase chain reaction revealed the presence of functional PAF-R in human melanoma SK23MEL cells, but not in SK5MEL cells. The present study investigated the effect of BITC treatments on the survival of murine and human melanoma cells, in the presence or absence of functional PAF-R. The results revealed that treatment with BITC decreased the survival rate of the PAF-R-positive and negative murine and human melanoma cells. However, the expression of PAF-R substantially augmented BITC-mediated cytotoxicity in the PAF-R-positive cells at lower concentrations compared with the PAF-R-negative cells. In order to determine the underlying mechanism, flow cytometric analysis was used, which demonstrated a significant increase in the generation of reactive oxygen species (ROS) in the B16-PAF-R cells compared with the B16-MSCV cells, which enhanced apoptosis by BITC, as measured by increased caspase-3/7 luminescence. Notably, the BITC-mediated decreased cell survival rate, increased ROS and increased apoptosis in the B16-PAF-R cells were significantly attenuated by the antioxidant, vitamin C, indicating ROS involvement. Additionally, the WEB2086 PAF-R antagonist, inhibited the BITC-mediated enhancement of apoptosis in the B16-PAF-R cells, indicating a role for PAF-R-signaling in the BITC-mediated effects. These findings indicated that the selectivity of BITC towards PAF-R in melanoma offers a promising chemopreventive agent for PAF-R-positive melanoma treatment.