Expression patterns of S100 proteins in melanocytes and melanocytic lesions.

S100 proteins are differentially expressed in tumours of epithelial origin. Little is known about their expression in melanocyte-derived tumours of neuroectodermal origin. We have analysed the expression of some S100 proteins in this line of lesions using SAGE Genie informatics, cell culture and human tumour tissue. The pattern of expression of six S100 proteins was investigated at both the mRNA and protein levels, using quantitative real-time PCR, western blotting and immunohistochemical analysis. No differential expression was observed with respect to S100A4, S100A7, S100A8, S100A9 and S100A11. In contrast, S100A10 was downregulated in three melanoma cell lines compared with normal melanocytes. Using SAGE informatics, two-dimensional displays of microarray expression data from the NCI60_Novartis cell lines displayed a positive correlation between the expression of S100A10 and the expression of the proliferation marker, Ki67. Our data suggest that S100A10, like its binding partners S100A7 and annexin A2, is an oxidant-sensitive protein. In addition, higher expression of S100A10 was detected in melanocyte cell lines with long projections compared with melanoma cell lines with small ripples. In a panel of 47 melanocyte-derived lesions comprising melanocytic naevi and melanomas, S100A10 was expressed to varying degrees in the melanocytic lesions. The antigen was primarily expressed in regions with a strong proliferating or differentiating capacity, especially in regions in or near the epidermis. We suggest that S100A10 may play a role in the regulation of the proliferation or early maturation sequence of melanocytic lesions, and that it merits further study as a potential biomarker of activity.