Solar waveband interactions and melanomagenesis

In spite of recent advances in the treatment of patients with metastasized malignant melanoma these patients have still very limited survival rates. Hence, beside early diagnosis melanoma prevention is an important issue. However, since the etiology of melanoma is not clear, melanoma prevention is still an unresolved issue. Whereas it is known that non-melanoma skin cancer is caused by chronic sun exposures, the exact correlation between melanoma and sun light is not clear. Almost all studies so far investigated the effect of single solar wavebands, in particular mostly ultraviolet (UV) light, on human skin. In contrast, in the present proposal it is intended to study the effect of waveband interactions between infrared radiation or long waveband UV (UVA) radiation on medium waveband UV (UVB)-induced programmed cell death (apoptosis), DNA-damage and repair in human primary melanoyctes of different skin types. Malignant transformation of melanocytes is regarded as a prerequisite of melanoma formation. Although infrared radiation accounts for the majority of terrestrial solar irradiation, relatively little is known about its impact on human skin. Apoptosis will be detected using a cell death detection ELISA and Annexin-FACS-analysis. In addition the expression of several apoptosis-related proteins (BAX, BCLX-L, and FLIPL) will be determined using FACS analysis. Furthermore, the activity of caspases 8 and 9 will be measured. DNA damage will be detected by Southwestern dot blot analysis using an antibody against cyclobutane pyrimidine dimers (CPDs). From the amount of CPDs at several time points a repair kinetic will be calculated. In the proposal waveband interactions are not only studied in vitro using primary human melanocytes, but also in vivo employing C57BL/6 mice. The animals will be exposed to a single neonatal irradiation with a combination of infrared radiation and UVB or UVA and UVB followed by a longterm irradiation protocol with the respective spectral combinations. The effect of infrared radiation, UVA, and UVB on melanoma formation will be studied. Taken together the data from the proposal might add important information on how solar irradiation might be involved in melanoma formation. In addition, new insights on melanoma prevention might be deduced.

Terrestrial sun light comprises a wide spectrum of optical wavebands ranging from ultraviolet radiation (UVR, on the earth surface consisting of UVA and UVB) over visible light (VIS) to infrared radiation (IR). Until recently most researchers focused on high energetic UVR, a full carcinogen which has been shown to be a main cause of many forms of non-melanoma skin cancer (NMSC). Although sun-exposed skin encounters always a mixture of optical solar wavebands (UVR, VIS, IR), possible interactions between these wavebands have rarely been considered. Recent research revealed that also IR exerts waveband-specific effects in tissues and cells distinct from heat. This is of particular interest, since exposure of skin to the sun always implies not only subjection to UVR but also to IR. After keratinocytes, melanocytes are the second most abundant cells in the human epidermis, comprising about one percent of epidermal cells. Malignantly transformed melanocytes are regarded to be the precursors of melanoma, still one of the deadliest of all skin cancers if not diagnosed at an early stage. In the present project the effect of the interplay between IR and UVB on the one hand and UVA and UVB on the other hand on primary human melanocytes was studied. Experiments revealed that although IR alone does not affect programmed cell death (apoptosis), IR decreases UVB-induced apoptosis. On the other hand IR has no impact on the repair of UVB-induced DNA damage. Further experiments revealed that UVA reduces the repair of UVB-induced DNA damage, while it has no effect on UVB-induced apoptosis in normal human melanocytes. Summing up, our data indicate that IR as well as UVA might contribute to melanomagenesis as they facilitate the survival of UVB-damaged melanocytes. Our findings might play a part in our understanding of the development of sun-induced melanomas. In turn, this might contribute to new preventive strategies against these types of melanoma.