Inducing antitumor T cell immunity: comparative functional analysis of interstitial versus Langerhans dendritic cells in a human cell line model

Dendritic cells (DC) are increasingly applied as a cellular adjuvant in immunotherapy of cancer. Two major myeloid DC subsets are recognized: interstitial DC (IDC) that infiltrate connective tissues and Langerhans cells (LC) that line epithelial surfaces. Yet, functional differences between IDC and LC remain to be defined. We recently showed that the CD34(+) acute myeloid leukemia cell line MUTZ-3 supports differentiation of both DC-SIGN(+) IDC and Langerin-positive Birbeck granule-expressing LC. By comparative functional characterization of MUTZ-3 IDC and MUTZ-3 LC, we aimed to elucidate the relative abilities of these two DC subsets to induce a specific T cell response and reveal the more suitable candidate for use as a clinical vehicle of tumor vaccines. Although mature LC and IDC displayed comparable lymph node-homing potential, mature LC showed higher allogeneic T cell stimulatory capacity. Nevertheless, IDC supported the induction of tumor Ag-specific CD8(+) T cells at an overall higher efficiency. This might be related to the observed inability of LC to release T cell stimulatory cytokines such as IL-12p70, IL-23, and IL-15. Although this inability did not result in a detectable deviation in the cytokine expression profile of primed T cells, transduction with IL-12p70 significantly improved priming efficiency of LC, and ensured a functional equivalence with IDC in this regard. In conclusion, except for the inability of LC to release distinct type 1 T cell stimulatory cytokines, in vitro function of LC and IDC suggests comparable abilities of both subsets for the in vivo induction of antitumor T cells.     

Adaptor protein Lnk associates with Tyr(568) in c-Kit

The adaptor protein Lnk is expressed in haemopoietic cells and plays a critical role in haemopoiesis. Animal model studies demonstrated that Lnk acts as a broad inhibitor of signalling pathways in haemopoietic lineages. Lnk belongs to a family of proteins sharing several structural motifs, including an SH2 (Src homology 2) domain which binds phosphotyrosine residues in various signal-transducing proteins. The SH2 domain is essential for Lnk-mediated negative regulation of several cytokine receptors [e.g. Mpl, EpoR (erythropoietin receptor), c-Kit]. Therefore inhibition of the binding of Lnk to cytokine receptors might lead to enhanced downstream signalling of the receptor and thereby to improved haemopoiesis in response to exposure to cytokines (e.g. erythropoietin in anaemic patients). This hypothesis led us to define the exact binding site of Lnk to the stem cell factor receptor c-Kit. Pull-down experiments using GST (glutathione transferase)-fusion proteins of the different domains of c-Kit showed that Lnk almost exclusively binds to the phosphorylated juxtamembrane domain. Binding of Lnk to the juxtamembrane domain was abolished by point mutation of Tyr(568) and was competed by peptides with a phosphotyrosine residue at position 568. Co-immunoprecipitation with full-length wild-type or Y568F mutant c-Kit and Lnk confirmed these results, thus showing the importance of this phosphorylated tyrosine residue. Lnk bound directly to c-Kit without requiring other interacting partners. The identification of the binding site of Lnk to c-Kit will be useful to discover inhibitory molecules that prevent the binding of these two proteins, thus making haemopoietic cells more sensitive to growth factors.     

11beta-hydroxysteroid dehydrogenase 2 activity is elevated in severe obesity and negatively associated with insulin sensitivity

Alterations in glucocorticoid (GC) metabolism may contribute to the development of obesity and insulin resistance. We aimed to study the role of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) in human adiposity, paying special attention to the association between altered GC metabolism and insulin sensitivity. In 24-h urine samples of 72 extremely obese (mean BMI 45.5 +/- 1.1 kg/m(2)), but otherwise healthy patients urinary free cortisol (UFF), urinary free cortisone (UFE), tetrahydrocortisol (THF), 5alpha-tetrahydrocortisol (5alpha-THF), and tetrahydrocortisone (THE) were quantified by radioimmunoassay. The sum of the three major tetrahydrometabolites is an estimate for daily GC secretion, and the sum of UFF and UFE represents potentially bioactive-free-GCs. Thirty healthy lean subjects (BMI 22.3 +/- 0.3 kg/m(2)) served as controls. In obese subjects, absolute daily GC secretion and the potentially bioactive-free-GCs were significantly (P < 0.005) higher than in lean controls (11.8 +/- 0.7 vs. 8.0 +/- 0.6 mg/d; and 171.8 +/- 11.2 vs. 117.6 +/- 9.2 mug/d, respectively). However, when these values were corrected for body surface area (BSA), significant differences were no longer detectable. While enzyme activity indices for 5alpha-reductase and 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) were similar in lean and obese subjects, 11beta-HSD2 was markedly elevated in adiposity (3.7 +/- 0.2 vs. 2.1 +/- 0.1; P < 0.0001). This increase was accompanied by a significant reduction in UFF excretion corrected for BSA (16.5 +/- 1.2 vs. 21.7 +/- 2.0 mug/d/m(2); P = 0.0222). Besides, 11beta-HSD2 activity was significantly correlated with insulin sensitivity (P = 0.0262). When body size is accounted for, both adrenal GC secretion and potentially bioactive-free-GCs are indistinguishable between lean and extremely obese subjects. However in obesity, the kidney appears to intensify its supply of the direct substrate cortisone for extrarenal 11beta-HSD1, which may fuel visceral adiposity and insulin resistance.     

Peters Plus syndrome is a new congenital disorder of glycosylation and involves defective Omicron-glycosylation of thrombospondin type 1 repeats

Peters Plus syndrome is an autosomal recessive disorder characterized by anterior eye chamber defects, disproportionate short stature, developmental delay, and cleft lip and/or palate. It is caused by splice site mutations in what was thought to be a beta1,3-galactosyltransferase-like gene (B3GALTL). Recently, we and others found this gene to encode a beta1,3-glucosyltransferase involved in the synthesis of the disaccharide Glc-beta1,3-Fuc-Omicron-that occurs on thrombospondin type 1 repeats of many biologically important proteins. No functional tests have been performed to date on the presumed glycosylation defect in Peters Plus syndrome. We have established a sensitive immunopurification-mass spectrometry method, using multiple reaction monitoring, to analyze Omicron-fucosyl glycans. It was used to compare the reporter protein properdin from Peters Plus patients with that from control heterozygous relatives. In properdin from patients, we could not detect the Glc-beta1,3-Fuc-Omicron-disaccharide, and we only found Fuc-Omicron-at all four Omicron-fucosylation sites. In contrast, properdin from heterozygous relatives and a healthy volunteer carried the Glc-beta1,3-Fuc-Omicron-disaccharide. These data firmly establish Peters Plus syndrome as a new congenital disorder of glycosylation.     

Hepatocellular toxicity of kava leaf and root extracts.

Kava extracts are used widely for different purposes and were thought to be safe. Recently, several cases of hepatotoxicity have been published. To explore possible mechanisms of kava hepatotoxicity, we prepared and analyzed three different kava extracts (a methanolic and an acetonic root and a methanolic leaf extract), and investigated their toxicity on HepG2 cells and isolated rat liver mitochondria. All three extracts showed cytotoxicity starting at a concentration of 50 microg/ml (lactate dehydrogenase leakage) or 1 microg/ml (MTT test). The mitochondrial membrane potential was decreased (root extracts starting at 50 microg/ml) and the respiratory chain inhibited and uncoupled (root extracts) or only uncoupled (leaf extract) at 150 microg/ml, and mitochondrial beta-oxidation was inhibited by all extracts starting at 100 microg/ml. The ratio oxidized to reduced glutathione was increased in HepG2 cells, whereas the cellular ATP content was maintained. Induction of apoptosis was demonstrated by all extracts at a concentration of 150 microg/ml. These results indicate that the kava extracts are toxic to mitochondria, leading to inhibition of the respiratory chain, increased ROS production, a decrease in the mitochondrial membrane potential and eventually to apoptosis of exposed cells. In predisposed patients, mitochondrial toxicity of kava extract may explain hepatic adverse reactions of this drug.     

The ubiquitin-proteasome system in cardiac dysfunction

Since proteins play crucial roles in all biological processes, the finely tuned equilibrium between their synthesis and degradation regulates cellular homeostasis. Controlling the quality of proteome informational content is essential for cell survival and function. After initial synthesis, membrane and secretory proteins are modified, folded, and assembled in the endoplasmic reticulum, whereas other proteins are synthesized and processed in the cytosol. Cells have different protein quality control systems, the molecular chaperones, which help protein folding and stabilization, and the ubiquitin-proteasome system (UPS) and lysosomes, which degrade proteins. It has generally been assumed that UPS and lysosomes are regulated independently and serve distinct functions. The UPS degrades both cytosolic, nuclear proteins, and myofibrillar proteins, whereas the lysosomes degrade most membrane and extracellular proteins by endocytosis as well as cytosolic proteins and organelles via autophagy. Over the last two decades, the UPS has been increasingly recognized as a major system in several biological processes including cell proliferation, adaptation to stress and cell death. More recently, activation or impairment of the UPS has been reported in cardiac disease and recent evidence indicate that autophagy is a key mechanism to maintain cardiac structure and function. This review mainly focuses on the UPS and its various components in healthy and diseased heart, but also summarizes recent data suggesting parallel activation of the UPS and autophagy in cardiac disease.     

Preventing aneuploidy: the contribution of mitotic checkpoint proteins

Aneuploidy, an abnormal number of chromosomes, is a trait shared by most solid tumors. Chromosomal instability (CIN) manifested as aneuploidy might promote tumorigenesis and cause increased resistance to anti-cancer therapies. The mitotic checkpoint or spindle assembly checkpoint is a major signaling pathway involved in the prevention of CIN. We review current knowledge on the contribution of misregulation of mitotic checkpoint proteins to tumor formation and will address to what extent this contribution is due to chromosome segregation errors directly. We propose that both checkpoint and non-checkpoint functions of these proteins contribute to the wide array of oncogenic phenotypes seen upon their misregulation.