Wnt-beta-catenin signaling initiates taste papilla development

Fungiform taste papillae form a regular array on the dorsal tongue. Taste buds arise from papilla epithelium and, unusually for epithelial derivatives, synapse with neurons, release neurotransmitters and generate receptor and action potentials. Despite the importance of taste as one of our five senses, genetic analyses of taste papilla and bud development are lacking. We demonstrate that Wnt-beta-catenin signaling is activated in developing fungiform placodes and taste bud cells. A dominant stabilizing mutation of epithelial beta-catenin causes massive overproduction of enlarged fungiform papillae and taste buds. Likewise, genetic deletion of epithelial beta-catenin or inhibition of Wnt-beta-catenin signaling by ectopic dickkopf1 (Dkk1) blocks initiation of fungiform papilla morphogenesis. Ectopic papillae are innervated in the stabilizing beta-catenin mutant, whereas ectopic Dkk1 causes absence of lingual epithelial innervation. Thus, Wnt-beta-catenin signaling is critical for fungiform papilla and taste bud development. Altered regulation of this pathway may underlie evolutionary changes in taste papilla patterning.     

Targeted inhibition of Livin resensitizes renal cancer cells towards apoptosis

Cancer cells are typically characterized by apoptosis deficiency. In order to investigate a possible role for the anti-apoptotic livin gene in renal cell cancer (RCC), we analyzed its expression in tumor tissue samples and in RCC-derived cell lines. In addition, we studied the contribution of livin to the apoptotic resistance of RCC cells by RNA interference (RNAi). Livin gene expression was detected in a significant portion of RCC tumor tissue specimens (13/14, 92.9%) and tumor-derived cell lines (12/15, 80.0%). Moreover, targeted inhibition of livin by RNAi markedly sensitized RCC cells towards proapoptotic stimuli, such as UV irradiation or the chemotherapeutic drugs etoposide, 5-fluorouracil, and vinblastine. These effects were specific for livin expressing tumor cells. We conclude that livin can contribute significantly to the apoptosis resistance of RCC cells. Targeted inhibition of livin could represent a novel therapeutic strategy to increase the sensitivity of renal cancers towards pro-apoptotic agents. Received 30 November 2006; received after revision 22 February 2007; accepted 20 March 2007     

Podocalyxin enhances the adherence of cells to platelets

Podocalyxin (PODXL) is a mucin protein of the CD34 family expressed in kidney glomerular podocytes, vascular endothelium, progenitor bone marrow and tumor cells. It is assumed that PODXL plays an anti-adherent role in kidney podocytes. CHO cells stably expressing human PODXL (CHO-PODXL) or human tumor cells (Tera-1) inherently expressing PODXL showed increased adherence to platelets. The adherence of cells was inhibited (70%) by blockers of platelet P-selectin, prevented by the soluble ectodomain of human PODXL (PODXL-Δ) or by the arginine-glycine-aspartate (RGDS) peptide and partially impeded by inhibition of integrin αVβ3/αVβ5, suggesting a coordinated action of P-selectin and integrins. Colocalization of platelet P-selectin and PODXL expressed on CHO cells was demonstrated by confocal immunofluorescence. No adherence to platelets was observed when PODXL was expressed in glycomutant CHO cells deficient in sialic acid. Received 14 August 2007; received after revision 12 September 2007; accepted 13 September 2007     

The cold case: Are rhinoviruses perfectly adapted pathogens?

Rhinoviruses, which cause common cold, belong to the Picornaviridae family, small non-enveloped viruses (diameter 15-30 nm) containing a single-stranded RNA genome (about 7 kb). Over 100 different rhinoviral serotypes have been identified thus far, establishing rhinoviruses as the most diverse group of Picornaviridae. Based on receptor binding properties, rhinoviruses are divided into two classes: the major group binding to intracellular adhesion molecule-1 and the minor group binding to the very low density lipoprotein receptors. Interactions between virus and the receptor molecules cause a conformational change in the capsid, which is a prerequisite for viral uptake. Rhinoviruses trigger a chemokine response upon infection that may lead to exacerbation of the symptoms of common cold, i.e. asthma and inflammation. The following review aims to summarize the knowledge about rhinoviral infections and discusses therapeutical approaches against this almost perfectly adapted pathogen.     

Conotoxins of the O-superfamily affecting voltage-gated sodium channels

The venoms of predatory cone snails harbor a rich repertoire of peptide toxins that are valuable research tools, but recently have also proven to be useful drugs. Among the conotoxins with several disulfide bridges, the O-superfamily toxins are characterized by a conserved cysteine knot pattern: C-C-CC-C-C. While ω-conotoxins and κ-conotoxins block Ca²⁺ and K⁺ channels, respectively, the closely related δ- and μO-conotoxins affect voltage-gated Na⁺ channels (Na_v channels). δ-conotoxins mainly remove the fast inactivation of Na_v channels and, thus, functionally resemble long-chain scorpion α-toxins. μO-conotoxins are functionally similar to μ-conotoxins, since they inhibit the ion flow through Na_v channels. Recent results from functional and structural assays have gained insight into the underlying molecular mechanisms. Both types of toxins are voltage-sensor toxins interfering with the voltage-sensor elements of Na_v channels. Received 27 December 2006; received after revision 30 January 2007; accepted 19 February 2007     

Genetic studies of diseases

Genomic alterations lead to cancer complexity and form a major hurdle for comprehensive understanding of the molecular mechanisms underlying oncogenesis. In this review, we describe recent advances in studying cancer-associated genes from a systems biology point of view. The integration of known cancer genes onto protein and signaling networks reveals the characteristics of cancer genes within networks. This approach shows that cancer genes often function as network hub proteins which are involved in many cellular processes and form focal nodes in information exchange between many signaling pathways. Literature mining allows constructing gene-gene networks, in which new cancer genes can be identified. The gene expression profiles of cancer cells are used for reconstructing gene regulatory networks. By doing so, genes which are involved in the regulation of cancer progression can be picked up from these networks, after which their functions can be further confirmed in the laboratory.     

Cellular internalization of proinsulin C-peptide

Proinsulin C-peptide is known to bind specifically to cell membranes and to exert intracellular effects, but whether it is internalized in target cells is unknown. In this study, using confocal microscopy and immunostained or rhodamine-labeled peptide, we show that C-peptide is internalized and localized to the cytosol of Swiss 3T3 and HEK-293 cells. In addition, transport into nuclei was found using the labeled peptide. The internalization was followed at 37°C for up to 1 h, and was reduced at 4°C and after preincubation with pertussis toxin. Hence, it is concluded to occur via an energy-dependent, pertussis toxin-sensitive mechanism and without detectable degradation within the experimental time course. Surface plasmon resonance measurements demonstrated binding of HEK-293 cell extract components to C-peptide, and subsequent elution of bound material revealed the components to be intracellular proteins. The identification of C-peptide cellular internalization, intracellular binding proteins, absence of rapid subsequent C-peptide degradation and apparent nuclear internalization support a maintained activity similar to that of an intracrine peptide hormone. Hence, the data suggest the possibility of one further C-peptide site of action. Received 31 October 2006; received after revision 27 December 2006; accepted 30 December 2006