The proinflammatory cytokine interleukin-1β (IL-1β) plays a central role in the pathogenesis and the course of inflammatory skin diseases, including psoriasis. Posttranscriptional activation of IL-1β is mediated by inflammasomes; however, the mechanisms triggering IL-1β processing remain unknown. Recently, cytosolic DNA has been identified as a danger signal that activates inflammasomes containing the DNA sensor AIM2. In this study, we detected abundant cytosolic DNA and increased AIM2 expression in keratinocytes in psoriatic lesions but not in healthy skin. In cultured keratinocytes, interferon-γ induced AIM2, and cytosolic DNA triggered the release of IL-1β via the AIM2 inflammasome. Moreover, the antimicrobial cathelicidin peptide LL-37, which can interact with DNA in psoriatic skin, neutralized cytosolic DNA in keratinocytes and blocked AIM2 inflammasome activation. Together, these data suggest that cytosolic DNA is an important disease-associated molecular pattern that can trigger AIM2 inflammasome and IL-1β activation in psoriasis. Furthermore, cathelicidin LL-37 interfered with DNA-sensing inflammasomes, which thereby suggests an anti-inflammatory function for this peptide. Thus, our data reveal a link between the AIM2 inflammasome, cathelicidin LL-37, and autoinflammation in psoriasis, providing new potential targets for the treatment of this chronic skin disease.

Arakawa et al. discovered that the autoimmune response in psoriasis is directed against melanocytes. They show that the main psoriasis risk allele HLA-C*06:02 mediates melanocyte-specific autoimmunity and identify ADAMTSL5 as a melanocyte autoantigen, which stimulates IL-17 and IFN-γ production in CD8+ T cells.

The major histocompatibility complex (MHC) class II transactivator CIITA plays a pivotal role in the control of the cellular immune response through the quantitative regulation of MHC class II expression. We have analyzed a region of CIITA with similarity to leucine-rich repeats (LRRs). CIITA LRR alanine mutations abolish both the transactivation capacity of full-length CIITA and the dominant-negative phenotype of CIITA mutants with N-terminal deletions. We demonstrate direct interaction of CIITA with the MHC class II promoter binding protein RFX5 and could also detect novel interactions with RFXANK, NF-YB, and -YC. However, none of these interactions is influenced by CIITA LRR mutagenesis. On the other hand, chromatin immunoprecipitation shows that in vivo binding of CIITA to the MHC class II promoter is dependent on LRR integrity. LRR mutations lead to an impaired nuclear localization of CIITA, indicating that a major function of the CIITA LRRs is in nucleocytoplasmic translocation. There is, however, evidence that the CIITA LRRs are also involved more directly in MHC class II gene transactivation. CIITA interacts with a novel protein of 33 kDa in a manner sensitive to LRR mutagenesis. CIITA is therefore imported into the nucleus by an LRRdependent mechanism, where it activates transcription through multiple protein-protein interactions with the MHC class II promoter binding complex.The expression of major histocompatibility complex class II (MHC-II) molecules, which play a critical role in immune responses by presenting processed exogenous antigens to CD4 ϩ T lymphocytes, is controlled in a highly complex manner. MHC-II molecules are expressed constitutively only on a restricted set of cell types specialized in antigen presentation, such as B lymphocytes, macrophages, and dendritic cells, whereas MHC-II gene expression can be induced and modulated on many other cell types by different stimuli, most prominently gamma interferon (IFN-␥) (16,27). In humans, three MHC-II isotypes are known, human leukocyte antigen DR (HLA-DR), -DQ, and -DP. Expression is controlled mainly at the level of transcription via conserved upstream sequence elements in the proximal promoters, the W (S), X, X2, and Y boxes, which mediate constitutive and IFN-␥-induced expression of the MHC-II genes (reviewed in references 16 and 27).Four essential MHC-II regulatory factors were discovered through analysis of cell lines derived from patients suffering from hereditary HLA class II deficiency (also known as bare lymphocyte syndrome [BLS]), a genetically heterogeneous disease of gene regulation, or of in vitro-generated mutant cell lines (18,27). These factors, called RFX5 (regulatory factor binding to X box 5), RFXAP (RFX-associated protein), RFXANK (RFX protein containing ankyrin repeats; also called RFX-B), and CIITA (class II transactivator), are essential for the expression of all MHC-II genes (12,30,33,44,45). Mutations in the corresponding regulatory genes could be identified in BLS patients in all four complementation groups. RFX5, RF...

Two-pore channels (TPCs) are endolysosomal cation channels. Two members exist in humans, TPC1 and TPC2. Functional roles associated with the ubiquitously expressed TPCs include VEGF-induced neoangiogenesis, LDL-cholesterol trafficking and degradation, physical endurance under fasting conditions, autophagy regulation, the acrosome reaction in sperm, cancer cell migration, and intracellular trafficking of pathogens such as Ebola virus or bacterial toxins (e.g., cholera toxin). In a genome-wide association study for variants associated with human pigmentation characteristics two coding variants of TPC2, rs35264875 (encoding M484L) and rs3829241 (encoding G734E), have been found to be associated with a shift from brown to blond hair color. In two recent follow-up studies a role for TPC2 in pigmentation has been further confirmed. However, these human polymorphic variants have not been functionally characterized until now. The development of endolysosomal patch-clamp techniques has made it possible to investigate directly ion channel activities and characteristics in isolated endolysosomal organelles. We applied this technique here to scrutinize channel characteristics of the polymorphic TPC2 variants in direct comparison with WT. We found that both polymorphisms lead to a gain of channel function by independent mechanisms. We next conducted a clinical study with more than 100 blond- and brown/black-haired individuals. We performed a genotype/phenotype analysis and subsequently isolated fibroblasts from WT and polymorphic variant carriers for endolysosomal patch-clamp experimentation to confirm key in vitro findings.

Melanoma is an often fatal form of skin cancer which is remarkably resistant against radio- and chemotherapy. Even new strategies that target RAS/RAF signaling and display unprecedented efficacy are characterized by resistance mechanisms. The targeting of survival pathways would be an attractive alternative strategy, if tumor-specific cell death can be achieved. Bcl-2 proteins play a central role in regulating survival of tumor cells. In this study, we systematically investigated the relevance of antiapoptotic Bcl-2 proteins, i.e., Bcl-2, Bcl-xL, Bcl-w, Mcl-1, and A1, in melanoma cell lines and non-malignant cells using RNAi. We found that melanoma cells required the presence of specific antiapoptotic Bcl-2 proteins: Inhibition of Mcl-1 and A1 strongly induced cell death in some melanoma cell lines, whereas non-malignant cells, i.e., primary human fibroblasts or keratinocytes were not affected. This specific sensitivity of melanoma cells was further enhanced by the combined inhibition of Mcl-1 and A1 and resulted in 60% to 80% cell death in all melanoma cell lines tested. This treatment was successfully combined with chemotherapy, which killed a substantial proportion of cells that survived Mcl-1 and A1 inhibition. Together, these results identify antiapoptotic proteins on which specifically melanoma cells rely on and, thus, provide a basis for the development of new Bcl-2 protein-targeting therapies.

No abstract

Selected sequences in the DNA double helix can be specifically recognized by oligonucleotides via hydrogen bonding interactions. The resulting triple helix can modulate DNA metabolism and especially interfere with transcription in a gene-specific manner. To explore the potential of triplex-forming oligonucleotides (TFOs) as gene repressors, a TFO was designed to target a 16-bp sequence within the third intron of the human intercellular-adhesion molecule-1 (ICAM-1) gene, which plays a key role in initiating inflammation. TFO binding to its ICAM-1 target sequence was characterized in vitro and also demonstrated in cell nuclei with the set-up of a novel magnetic capture assay, which represents a general experimental approach to the detection of specific TFO binding and to the determination of the accessibility of a given genomic DNA locus. In a human keratinocyte cell line (A431), we observed that: (i) the ICAM-1 target sequence in the chromatin context within the nuclei is still available for triplex formation and (ii) TFO inhibits sequence and gene-specific interferon-␥-induced ICAM-1 surface expression. Collectively, the data demonstrate effective and specific inhibition of ICAM-1 expression by TFO treatment and support the view that triplex-mediated gene targeting might be a valuable technique for anti-inflammatory or anticancer strategies.

Pigment cells and neuronal cells both are derived from the neural crest. Here, we describe the Pit-Oct-Unc (POU) domain transcription factor Brn3a, normally involved in neuronal development, to be frequently expressed in melanoma, but not in melanocytes and nevi. RNAi-mediated silencing of Brn3a strongly reduced the viability of melanoma cell lines and decreased tumour growth in vivo. In melanoma cell lines, inhibition of Brn3a caused DNA double-strand breaks as evidenced by Mre11/Rad50-containing nuclear foci. Activated DNA damage signalling caused stabilization of the tumour suppressor p53, which resulted in cell cycle arrest and apoptosis. When Brn3a was ectopically expressed in primary melanocytes and fibroblasts, anchorage-independent growth was increased. In tumourigenic melanocytes and fibroblasts, Brn3a accelerated tumour growth in vivo. Furthermore, Brn3a cooperated with proliferation pathways such as oncogenic BRAF, by reducing oncogene-induced senescence in non-malignant melanocytes. Together, these results identify Brn3a as a new factor in melanoma that is essential for melanoma cell survival and that promotes melanocytic transformation and tumourigenesis.