Malignant melanoma is the most aggressive form of human skin cancer and shows an increasing incidence. The transformation from a normal melanocyte to a melanoma cell is a stepwise process and the complex mechanisms during early stages of tumor development remain incompletely understood. Based on the increased tumor incidence in Epidermolysis bullosa simplex (EBS), we hypothesize that keratinocytes affect early melanoma development through direct interactions or via indirect mechanisms involving cell-cell contacts, cytoskeletal proteins and by secretion of growth factors. The aim of this project is to characterize underlying mechanisms by which mutations in keratinocyte cytoskeletal proteins affect proliferation, cell-cell-contacts, adhesion and migration of melanoma cells. To determine the influence of keratin mutations on the proliferation and migration of melanoma cells, keratinocytes with mutations associated with EBS were co-cultured with melanoma cells. This revealed an increased proliferation of melanoma cells co-cultured with keratinocytes expressing EBS-associated keratin 5- and keratin 14-mutants in comparison to wild type keratinocytes. In this setting, migration of melanoma cells remained unaffected. Epidermal keratinocytes from regions bordering the tumour were collected from human malignant melanoma samples using laser capture microdissection to identify novel keratinocyte mutations, followed by whole-exome sequencing. Preliminary data suggest somatic mutations in genes related to cell adhesion and cell structure such as FAT1/2, FLG2, LAMA3, JUP, ITGAE, MUC16 and FN1 could be associated with melanoma development. Taken together, mutations in keratin and additional genes involved in cell-cell interactions and the cytoskeleton exert an influence on melanoma cell proliferation. In future experiments, we will examine whether mutations originating in keratinocytes act on melanoma cells directly or indirectly.