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The p90 ribosomal S6 kinases (RSKs) contain two distinct catalytic kinase domains, the N-terminal and C-terminal kinase domains (NTKD and CTKD, respectively). The activation of CTKD is regulated by phosphorylation by extracellular signal-regulated kinase (ERK1/2) and an autoinhibitory αL helix. Through a mutational seriesin vitroof the RSK CTKDs, we found a complex mechanism lifting autoinhibition that led us to design constitutively active RSK CTKDs. These are based on a phosphomimetic mutation and a C-terminal truncation (e.g. RSK2 T577E D694*) where a high activity in absence of ERK phosphorylation is obtained. Using these constructs, we characterize IC50values of ATP-competitive inhibitors and provide a setup for determining specificity constants (kinact/Ki) of covalent CTKD inhibitors.

Stereology is a set of mathematical and statistical tools to estimate three-dimensional (3-D) characteristics of objects from regular two-dimensional (2-D) sections. In medicine and biology, it can be used to estimate features such as cell volume, cell membrane surface area, total length of blood vessels per volume tissue and total number of cells. The unbiased quantification of these 3-D features allows for a better understanding of morphology in vivo compared with 2-D methods. This review provides an introduction to the field of stereology with specific emphasis on the application of stereology to dermatological research by supplying a short insight into the theoretical basis behind the technique and presenting previous dermatological studies in which stereology was an integral part. Both the theory supporting stereology and a practical approach in a dermatological setting are reviewed with the aim to provide the reader with the capability to better assess papers employing stereological estimators and to design stereological studies independently.

The proinflammatory cytokine Tumor Necrosis Factor alpha (TNF-) is upregulated in inflammatory psoriatic skin. The increased level of TNF- protein is thought to cause keratinocyte hyperproliferation, leukocyte infiltration as well as growth and dilation of superficial blood vessels, which are all characteristics of human psoriasis skin. Blockade of TNF- function with specific inhibitors at the protein level has resulted in a rapid clinical improvement in psoriasis patients, demonstrating that TNF- inhibition offers a promising therapy of psoriasis. Whether TNF--encoding RNA is a valid therapeutic target, however, is still a matter of speculation, as recent findings have suggested that the level of TNF- is not increased in psoriatic skin. To test the hypothesis that TNF- in skin can be stably down-regulated by RNA interference (RNAi), we designed a panel of short hairpin RNAs (shRNAs) targeting human TNF-. Their efficiency in down-regulating TNF- protein expression was evaluated using a Renilla luciferase screening-assay based upon targeting of luc-TNF- fusion RNAs and a transient co-transfection assay. The three most potent shRNAs, which at most reduced the expression from target templates to 15% of the control samples treated with irrelevant shRNAs, were selected and cloned into lentiviral vectors. The lentiviral vectors expressing TNF- shRNAs were used to transduce HEK-293 cells and verify vector-derived knock-down of stable TNF- expression in vitro. The most efficient TNF--directed shRNA, which in cell lines reduced the amount of released TNF- more than 50% upon viral transduction, was selected for in vivo studies. In vivo studies were carried out in a xenograft mouse model in which human psoriatic plaques keratome skin biopsies were transplanted onto SCID mice. Initial studies using eGFP-encoding lentiviral vectors demonstrated efficient transduction of human psoriatic skin. Grafted psoriatic skin was exposed to viral vector-encoded TNF- shRNAs by a single intradermal injection of purified VSV-G-pseudotyped lentiviral vectors (150l containing 46.4 ng p24/l was injected at a single site). Biopsies were taken three weeks after injection. qPCR-based measurements of TNF- mRNA in skin treated with lentiviral vector-encoded TNF- shRNA demonstrated a 50% reduction in the level of TNF- mRNA. Most interestingly, the epidermal thickness of the human psoriatic plaques was reduced relative to mice treated with lentiviral vectors encoding an irrelevant shRNA. In conclusion, our results demonstrate that lentiviral vector-encoded TNF- shRNAs have the potential to down-regulate TNF- production both in vitro and in vivo. Phenotypic changes in shRNA-treated psoriatic skin suggest that TNF--encoding RNA is a valid therapeutic target in psoriasis treatment.

TNF-α is a well known target in psoriasis treatment and biological treatments targeting TNF-a are already clinically used against psoriasis and psoriasis arthritis. Attention is however given to a novel therapeutic tool: RNA interference that controls gene silencing. This study investigates the efficiency of targeting TNF-a with specific short hairpin RNA (shRNA) and explores its potential in treating psoriasis. ShRNAs targeting human TNF-α mRNA were generated. Their efficiency in down-regulating TNF-a protein expression was evaluated using a Renilla luciferase screening-assay and a transient co-transfection assay. The expression cassette encoding the most efficient TNF-a shRNA was inserted into a lentiviral vector, allowing proficient gene delivery. The lentiviral vector is integrated into the host genome and establishes life-long infection and persistent shRNA expression. The lentiviral vector expressing TNF-a shRNA was used to transduce HEK293 cells and verify vector-derived TNF-a knockdown in vitro. In vivo, psoriasis skin was exposed to lentiviral TNF-a shRNAs by a single intra-dermal injection. Psoriasis skin for the in vivo study was obtained from psoriatic plaque skin biopsies that were transplanted onto SCID mice employing the psoriasis xenograft model. Three weeks after exposure, biopsies were taken and the epidermal thickness as an endpoint for evaluating psoriasis and the levels of TNF-a mRNA were measured. The lentiviral TNF-a shRNAs down-regulated the TNF-a expression in vitro and in vivo by 50% and, most interestingly, the epidermal thickness of the psoriatic plaques was reduced. In conclusion, our results demonstrate that lentiviral TNF-a shRNAs have the potential to down-regulate TNF-a production in vitro and in vivo. The decreased epidermal thickness suggests a potential role for TNF-a shRNAs as a new therapeutic agent in psoriasis treatment.