Abstract
OBJECTIVES: Melanoma, the 5(th) most common cancer in the US, is the most aggressive form of skin cancer. Excess adiposity is associated with an increased risk of melanoma in males, and a high-fat diet promotes melanoma tumor growth in mice. Our group found that lipid droplet (LD) content increases with melanoma cell aggressiveness and that fatty acid uptake inhibition reduces cell proliferation and migration; however, the function of these lipids in melanoma is unknown. Since lipids can be used to produce energy by fatty acid oxidation (FAO), we sought to determine whether melanoma cells were using FAO to maintain aggressiveness. METHODS: Gene expression microarray was used to identify differences in gene expression, which was confirmed by RT-qPCR. WM983A, WM983B, 1205Lu and A375 human melanoma cells were treated with 5 µM Etomoxir and cell proliferation, migration, and respiration were quantified using the Quant-iT™ PicoGreen™ dsDNA Assay Kit, Boyden Chamber transwell migration, and Seahorse XFe96 Flux Analyzer, respectively. RESULTS: The most significantly altered genes expressed between four invasive, lipid-rich and four non-invasive, lipid-poor melanoma cells pertained to fatty acid metabolism. Carnitine palmitoyltransferase 1A (CPT1a), the rate limiting enzyme in mitochondrial FAO (mFAO), mRNA was increased in lipid-rich cells compared to the lipid-poor cells (p < 0.05, n = 6–7), indicating that melanoma cells may use LD lipids for mFAO. To determine the importance of mFAO to melanoma cells, we inhibited mFAO with etomoxir, an irreversible CPT1 inhibitor. Treatment of lipid-rich 1205Lu and A375 cells or lipid-poor WM983A and WM983B cells with etomoxir for 4 days had no effect on cell proliferation. Extracellular flux analysis of cells with or without etomoxir showed no difference in ATP production, indicating that melanoma cells do not use mFAO to generate energy under normal conditions. In motile cells, etomoxir reduced lipid-rich A375 cell migration by 8.8% (p = 0.05, n = 2). CONCLUSIONS: Lipids play a role in melanoma aggressiveness; however, our results indicate that mFAO of lipids is not vital to melanoma cell proliferation or migration. Further studies are required to understand the implication of excess adiposity and circulating lipids in melanoma development and progression. FUNDING SOURCES: Institutional Department Fund