Attachment and chemotaxis of melanocytes after ultraviolet irradiation in vitro

Because ultraviolet (UV) radiation is able to influence the spatial distrib ution of melanocytes in melanocytic naevi in vivo, we investigated the infl uence of UV radiation on the ability of melanocytes to adhere to the extrac ellular 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, keratinocy tes and fibroblasts as attractants. Melanocyte attachment to fibronectin wa s significantly increased 48 h after a single UV irradiation at 30 mJ/ cm(2 ) in comparison with that of non-irradiated melanocytes, whereas attachment to laminin and collagen type IV showed only minor changes after UV exposur e. The UV-induced increase in attachment to fibronectin was suppressed by p reincubation with antibodies against alpha(5)beta(1) Or alpha(v)beta(3) int egrin. Both immunohistochemistry and flow cytometric analysis showed an inc rease in alpha(5)beta(1) integrin expression on melanocytes after UV exposu re. The chemotaxis of melanocytes to fibronectin was not influenced by UV e xposure. A decreasing migration rate of melanocytes towards the supernatant s of UVA-irradiated fibroblasts was observed with increasing UVA doses. The chemotactic effects of conditioned medium of keratinocytes towards melanoc ytes 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 subs trates by modification of integrin expression, Because fibronectin, as the major target protein of UV-altered attachment, is located in the dermis, th e UV-induced morphological changes in melanocytic lesions, with an increase in suprabasally located melanocytes within the epidermis, may be due to ot her changes in the adhesive properties of melanocytes.