Fatty acid receptor GPR120: a novel marker for human melanoma

The correlation between ultraviolet radiation of the skin and melanoma incidence in humans is well established. Interestingly, epidemiologic data suggest also a correlation to an increased BMI pointing to metabolic trigger factors in melanoma pathogenesis. To substantiate this connection, we studied the expression of G-protein-coupled receptor 120 (GPR120), a receptor sensitive to unsaturated long-chain free fatty acids in melanoma tissues. One-hundred fourteen tissue sections histologically confirmed as nevi (n=32), primary melanoma (n=39), and melanoma metastasis (n=43) were immunohistochemically stained against GPR120. The staining was evaluated by three trained dermatopathologists and independently scored. Compared with nevi, primary melanoma and melanoma metastasis showed significantly higher levels of GPR120 staining. Only three out of 32 nevi showed strong GPR120 expression [median immunoreactivity-scoring system (IRS) score: 1, range: 0-10], whereas in primary melanomas 14 out of 39 were highly GPR120-positive (median IRS score: 7, range: 0-12) and in melanoma metastasis 27 out of 43 were highly GPR120-positive (median IRS score: 9, range: 0-12). GPR120 expression and tumor thickness (mm) show a statistically significant correlation in primary melanoma (P=0.011). Moreover, GPR120-positive staining was found throughout the epidermis and in sebaceous and sweat glands, which is yet not described. This study identified GPR120 as a novel marker for melanoma, indicating that melanoma cells are sensitive to free fatty acids. It is tempting to speculate that pharmacologically interfering with GPR120 signaling might improve melanoma therapy.