UVA, metabolism and melanoma: UVA makes melanoma hungry for metastasis.

Ultraviolet (UV) radiation has a plethora of effects on human tissues. In the UV spectrum, wavelengths above 320 nm fall into the UVA range, and for these, it has been shown that they induce reactive oxygen species (ROS), DNA mutations and are capable to induce melanoma in mice. In addition to this, it was recently shown that UVA irradiation and UVA-induced ROS also increase glucose metabolism of melanoma cells. UVA irradiation causes a persistent increase in glucose consumption, accompanied by increased glycolysis, increased lactic acid production and activation of the pentose phosphate pathway. Furthermore, it was shown that the enhanced secretion of lactic acid is important for invasion of melanoma in vitro. The current knowledge of this link between UVA, metabolism and melanoma, possible mechanisms of UVA-induced glucose metabolism and their starting points are discussed in this review with focus on ROS- and UVA-induced cellular stress signalling, DNA damage signalling and DNA repair systems. When looking at the benefits of UVA-induced glucose metabolism, it becomes apparent that there are more advantages of these metabolic changes than one would expect. Besides the role of lactic acid as initiator of protease expression and invasion, its role for immune escape of melanoma cells and the pentose phosphate pathway-derived nicotinamide adenine dinucleotide phosphate (NADPH) as part of a ROS detoxification strategy are discussed.