Attachment and chemotaxis of melanocytes after ultraviolet irradiation in vitro

Because ultraviolet (UV) radiation is able to influence the spatial distribution of melanocytes in melanocytic naevi in vivo, we investigated the influence of UV radiation on the ability of melanocytes to adhere to the extracellular matrix proteins fibronectin, laminin and collagen type IV in vitro. In addition, chemotaxis of melanocytes was studied using both fibronectin and the supernatants from irradiated, as well as non-irradiated, keratinocytes and fibroblasts as attractants. Melanocyte attachment to fibronectin was significantly increased 48 h after a single UV irradiation at 30 mJ/cm2 in comparison with that of non-irradiated melanocytes, whereas attachment to laminin and collagen type IV showed only minor changes after UV exposure. The UV-induced increase in attachment to fibronectin was suppressed by preincubation with antibodies against alpha5beta1 or alphavbeta3 integrin. Both immunohistochemistry and flow cytometric analysis showed an increase in alpha5beta1 integrin expression on melanocytes after UV exposure. The chemotaxis of melanocytes to fibronectin was not influenced by UV exposure. A decreasing migration rate of melanocytes towards the supernatants of UVA-irradiated fibroblasts was observed with increasing UVA doses. The chemotactic effects of conditioned medium of keratinocytes towards melanocytes was not influenced either by UVB or by UVA. The results indicate that UV radiation may alter the ability of melanocytes to adhere to certain substrates by modification of integrin expression. Because fibronectin, as the major target protein of UV-altered attachment, is located in the dermis, the UV-induced morphological changes in melanocytic lesions, with an increase in suprabasally located melanocytes within the epidermis, may be due to other changes in the adhesive properties of melanocytes.