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Altered signaling pathways are key regulators of cellular functions in tumor cells. Constitutive activation of signal transducer and activator of transcription (STAT)3 and -5 may be involved in tumor formation and progression. We have investigated the role of STAT5 in cutaneous melanoma metastases using various RNA and protein techniques. In melanoma specimens, Stat5b transcripts were upregulated approximately 3.8-fold. In 13 of 21 (62%) human melanoma metastases, STAT5 was phosphorylated in comparison to normal human melanocytes and benign nevi. The STAT5 target gene Bcl-2 was frequently upregulated. The investigation of the underlying mechanism revealed specific STAT5 activation by recombinant human epidermal growth factor (rEGF). rEGF-induced activation of STAT5 occurred in vitro through the non-receptor tyrosine kinases transforming gene (src) of Rous Sarcoma virus and Janus kinase 1. Inhibition of Stat5b expression by small interfering RNA strongly reduced the expression of Bcl-2 and led to decreased cell viability and increased apoptosis in the melanoma cell lines A375 and BLM. Transfection with dominant-negative Stat5b caused enhanced cell death and G1 arrest in A375 cells. Our study identifies phosphorylated STAT5 in melanoma and shows regulation through rEGF; STAT5 may thus act as a survival factor for growth of human melanoma and may represent a potential target for molecular therapy.

Urea is an endogenous metabolite, known to enhance stratum corneum hydration. Yet, topical urea anecdotally also improves permeability barrier function, and it appears to exhibit antimicrobial activity. Hence, we hypothesized that urea is not merely a passive metabolite, but a small-molecule regulator of epidermal structure and function. In 21 human volunteers, topical urea improved barrier function in parallel with enhanced antimicrobial peptide (LL-37 and β-defensin-2) expression. Urea both stimulates expression of, and is transported into keratinocytes by two urea transporters, UT-A1 and UT-A2, and by aquaporin 3, 7 and 9. Inhibitors of these urea transporters block the downstream biological effects of urea, which include increased mRNA and protein levels for: (i) transglutaminase-1, involucrin, loricrin and filaggrin; (ii) epidermal lipid synthetic enzymes, and (iii) cathelicidin/LL-37 and β-defensin-2. Finally, we explored the potential clinical utility of urea, showing that topical urea applications normalized both barrier function and antimicrobial peptide expression in a murine model of atopic dermatitis (AD). Together, these results show that urea is a small-molecule regulator of epidermal permeability barrier function and antimicrobial peptide expression after transporter uptake, followed by gene regulatory activity in normal epidermis, with potential therapeutic applications in diseased skin.

Recombinant human erythropoietin (Epo) is used to prevent and treat tumor-related anemia and improve quality of life in cancer patients. Recent evidence suggested that Epo may adversely affect the survival of selected cancer patients by promoting tumor growth, inhibition of apoptosis, and induction of migration. Epo unfolds its effect on the Epo receptor (EpoR). We show--to the best of our knowledge for the first time--significantly increased EpoR expression in clinical melanoma metastases and primary melanomas in comparison with different sets of nevi by quantitative real-time reverse transcriptase-PCR, immunohistochemistry, and western blot analysis. When assessing the functionality of the EpoR-signaling pathway, recombinant human Epo led to the phosphorylation of JAK-2, signal transducers and activators of transcription 3 (STAT3), and ERK1/2 in several of the melanoma cell lines that were analyzed. Besides, Epo counteracted cisplatin-induced cell death in BLM and MV3 cells. Finally, Epo promoted cell migration of MV3 cells, whereas inhibition of the JAK/STAT and ERK1/2 pathways reduced Epo-mediated migration. In summary, we show the overexpression of functional EpoR expression in about half of the analyzed clinical melanoma metastasis specimens and show anti-apoptotic as well as pro-migratory effects of Epo, which is of importance for the treatment of anemia in advanced melanoma.