Antimicrobial peptides are an important component of the innate response in many species. Here we describe the isolation of the gene Dermcidin, which encodes an antimicrobial peptide that has a broad spectrum of activity and no homology to other known antimicrobial peptides. This protein was specifically and constitutively expressed in the sweat glands, secreted into the sweat and transported to the epidermal surface. In sweat, a proteolytically processed 47-amino acid peptide was generated that showed antimicrobial activity in response to a variety of pathogenic microorganisms. The activity of the peptide was maintained over a broad pH range and in high salt concentrations that resembled the conditions in human sweat. This indicated that sweat plays a role in the regulation of human skin flora through the presence of an antimicrobial peptide. This peptide may help limit infection by potential pathogens in the first few hours following bacterial colonization.

In previous studies we identified the transcription/translation factor Y-box-binding protein (YB-1) as a gene that is upregulated in primary melanoma and melanoma metastases when compared to benign melanocytic nevi. To analyze whether YB-1 expression correlates with melanoma progression in vitro and in vivo, we performed expression analysis on melanoma cell lines representing different stages of melanoma progression and on tissues of melanocytic nevi, primary melanoma and melanoma metastases. Our data indicate that compared to benign melanocytes YB-1 expression is increased in melanoma cells in vitro and in vivo and that YB-1 is translocated into the nucleus in invasive and metastatic melanoma cells. To reveal the functional role of YB-1 in melanoma progression we achieved a stable downregulation of YB-1 using shRNA in metastatic melanoma cells. Interestingly, YB-1 downregulation resulted in a pronounced reduced rate of proliferation and an increased rate of apoptotic cell death. In addition, migration and invasion of melanoma cells in monolayer and in a three-dimensional skin reconstruct in vitro was significantly reduced. These effects were accompanied by downregulation of genes involved in proliferation, survival and migration/invasion of melanoma cells such as MMP-2, bcl-2, Cyclin D1, p53 and p16INK4A. Furthermore, melanoma cells with a reduced YB-1 expression showed a decreased resistance to the chemotherapeutic agents cisplatin and etoposide. These data suggest that YB-1 is involved in malignant transformation of melanocytes and contributes to the stimulation of proliferation, tumor invasion, survival and chemoresistance. Thus, YB-1 may be a promising molecular target in melanoma therapy. ' 2007 Wiley-Liss, Inc.

Beta-catenin plays an important role in embryogenesis and carcinogenesis by controlling either cadherin-mediated cell adhesion or transcriptional activation of target gene expression. In many types of cancers nuclear translocation of beta-catenin has been observed. Our data indicate that during melanoma progression an increased dependency on the transcriptional function of beta-catenin takes place. Blockade of beta-catenin in metastatic melanoma cell lines efficiently induces apoptosis, inhibits proliferation, migration and invasion in monolayer and 3-dimensional skin reconstructs and decreases chemoresistance. In addition, subcutaneous melanoma growth in SCID mice was almost completely inhibited by an inducible beta-catenin knockdown. In contrast, the survival of benign melanocytes and primary melanoma cell lines was less affected by beta-catenin depletion. However, enhanced expression of beta-catenin in primary melanoma cell lines increased invasive capacity in vitro and tumor growth in the SCID mouse model. These data suggest that beta-catenin is an essential survival factor for metastatic melanoma cells, whereas it is dispensable for the survival of benign melanocytes and primary, non-invasive melanoma cells. Furthermore, beta-catenin increases tumorigenicity of primary melanoma cell lines. The differential requirements for beta-catenin signaling in aggressive melanoma versus benign melanocytic cells make beta-catenin a possible new target in melanoma therapy.

These results indicate that, unlike human cathelicidins and beta-defensins which are inducible peptides that primarily function in response to injury and inflammation, DCD is exclusively part of the constitutive innate defence of human skin. By modulating surface colonization, DCD may help to prevent local and systemic invasion of pathogens.

Casein kinase 1 α (CK1α) is a multifunctional Ser/Thr kinase that phosphorylates several substrates. Among those is β-catenin, an important player in cell adhesion and Wnt signaling. Phosphorylation of β-catenin by CK1α at Ser45 is the priming reaction for the proteasomal degradation of β-catenin. Interestingly, aside from this role in β-catenin degradation, very little is known about the expression and functional role of CK1α in tumor cells. Here, we show that CK1α expression in different tumor types is either strongly suppressed or completely lost during tumor progression and that CK1α is a key factor determining β-catenin stability and transcriptional activity in tumor cells. CK1α reexpression in metastatic melanoma cells reduces growth in vitro and metastasis formation in vivo, and induces cell cycle arrest and apoptosis, whereas suppression of CK1α in primary melanoma cells induces invasive tumor growth. Inactivation of CK1α promotes tumor progression by regulating a switch in β-catenin-mediated signaling. These results show that melanoma cells developed an efficient new mechanism to activate the β-catenin signaling pathway and define CK1α as a novel tumor suppressor. Cancer Res; 70(17); 6999-7009. ©2010 AACR.