Multiple positive and negative regulators of signaling by the EGF-receptor

Signaling via the epidermal growth factor (EGF)-receptor family is subject to regulation and modulation by multiple ligands, effectors and negative regulators, as well as regulation by heterodimerization between family members and crosstalk between heterologous signaling pathways. Besides serving as a paradigm for receptor tyrosine kinases in general, this family is crucial for development and is often mutated or amplified in human tumors.     

Fine tuning of hepcidin expression by positive and negative regulators

Hepcidin, the systemic regulator of iron homeostasis is activated by proteins responsible for hereditary hemochromatosis, bone morphogenetic proteins (BMPs), and inflammatory cytokines. Three recent publications now identify a novel hepcidin suppressor, the transmembrane serine protease TMPRSS6 (also known as matriptase-2), which is required to sense iron deficiency.     

Annotations and functional analyses of the rice WRKY gene superfamily reveal positive and negative regulators of abscisic acid signaling in aleurone cells

The WRKY proteins are a superfamily of regulators that control diverse developmental and physiological processes. This family was believed to be plant specific until the recent identification of WRKY genes in nonphotosynthetic eukaryotes. We have undertaken a comprehensive computational analysis of the rice (Oryza sativa) genomic sequences and predicted the structures of 81 OsWRKY genes, 48 of which are supported by full-length cDNA sequences. Eleven OsWRKY proteins contain two conserved WRKY domains, while the rest have only one. Phylogenetic analyses of the WRKY domain sequences provide support for the hypothesis that gene duplication of single- and two-domain WRKY genes, and loss of the WRKY domain, occurred in the evolutionary history of this gene family in rice. The phylogeny deduced from the WRKY domain peptide sequences is further supported by the position and phase of the intron in the regions encoding the WRKY domains. Analyses for chromosomal distributions reveal that 26% of the predicted OsWRKY genes are located on chromosome 1. Among the dozen genes tested, OsWRKY24, -51, -71, and -72 are induced by abscisic acid (ABA) in aleurone cells. Using a transient expression system, we have demonstrated that OsWRKY24 and -45 repress ABA induction of the HVA22 promoter-beta-glucuronidase construct, while OsWRKY72 and -77 synergistically interact with ABA to activate this reporter construct. This study provides a solid base for functional genomics studies of this important superfamily of regulatory genes in monocotyledonous plants and reveals a novel function for WRKY genes, i.e. mediating plant responses to ABA.     

Type IV collagens and Dpp positive and negative regulators of signaling

Decapentaplegic (Dpp) is an essential morphogen in the TGF-β/BMP superfamily which patterns fields of cells during multiple stages of Drosophila development, including the ovary and embryo. We have found that type IV collagens bind to Dpp and play essential roles in the regulation of its signaling during these two developmental stages. This article primarily focuses on type IV collagens and embryonic Dpp signaling to discuss aspects of the type IV collagen mutant phenotype in the context of additional data from the field. In addition, the restriction of Dpp signaling in the the ovary by type IV collagens is described, as the differences between the embryonic and ovarian Dpp sources result in distinct effects of collagen IV proteins in the two systems.     

A perspective on mammalian caspases as positive and negative regulators of inflammation

Members of the caspase family of cysteine proteases coordinate the morphological and biochemical events that typify apoptosis. However, neutralization of caspase activity in mammals fails to block death in response to most proapoptotic stimuli. This is because many cell death triggers provoke mitochondrial dysfunction upstream of caspase activation as a consequence of BAX/BAK channel opening. Although genetic or pharmacological inactivation of caspases fails to block cell death in most instances, it does convert the phenotype from apoptosis to necrosis. This has important implications for how the immune system responds to such cells, as necrotic cells provoke inflammation whereas apoptotic cells typically do not. Here, we propose an alternative perspective on apoptosis-associated caspase function by suggesting that these proteases are activated, not to kill, but to extinguish the proinflammatory properties of dying cells. This perspective unifies the mammalian caspase family as either positive or negative regulators of inflammation.     

Immunomodulatory mast cells: negative, as well as positive, regulators of immunity

Mast cells can promote inflammation and other tissue changes in IgE-associated allergic disorders, as well as in certain innate and adaptive immune responses that are thought to be independent of IgE. However, mast cells can also have anti-inflammatory and immunosuppressive functions. Here, we review the evidence that mast cells can have negative, as well as positive, immunomodulatory roles in vivo, and we propose that mast cells can both enhance and later suppress certain features of an immune response.     

A modified yeast three-hybrid system enabling both positive and negative selections

Objective

To increase the reporter repertoire of the yeast three-hybrid system and introduce the option of negative selection.

Results

Two new versions of the yeast three-hybrid system were made by modifying the MS2 coat RNA-binding protein and fusing it to the Gal4 DNA-binding protein. This allows the use of Gal4 inducible reporters to measure RNA–protein interactions. We introduced two mutations, V29I and N55K into the tandem MS2 dimer and an 11 amino acid deletion to increase RNA–protein affinity and inhibit capsid formation. Introduction of these constructs into the yeast strains MaV204K and PJ69-2A (which contain more reporters than the conventional yeast three-hybrid strains L40-coat and YBZ-1) allows RNA–protein binding interactions with a wide range of affinities to be detected using histidine auxotrophy, and negative selection with 5-fluoroorotic acid.

Conclusion

This yeast three-hybrid system has advantages over previous versions as demonstrated by the increased dynamic range of detectable binding interactions using yeast survival assays and colony forming assays with multiple reporters using known RNA–protein interactions.

     

Ski and SnoN: negative regulators of TGF-beta signaling

Ski and SnoN are unique proto-oncoproteins in that they can induce both oncogenic transformation and terminal muscle differentiation when expressed at high levels. Recent studies using in vitro and in vivo approaches have begun to unravel the complex roles of Ski and SnoN in tumorigenesis and embryonic development. The identification of Ski and SnoN as important negative regulators of signal transduction by the transforming growth factor-beta superfamily of cytokines provides a valuable molecular basis for the complex functions of Ski and SnoN.     

Galectins and their ligands: negative regulators of anti-tumor immunity

Cytotoxic CD8⁺ T cells are major players of anti-tumor immune responses, as their functional activity can limit tumor growth and progression. Data show that cytotoxic T cells efficiently control the proliferation of tumor cells through major histocompatibility complex class I-mediated mechanisms; nevertheless, the presence of tumor-infiltrating CD8⁺ T cells in lesional tissue does not always correlate with better prognosis and increased survival of cancer patients. Similarly, adoptive transfer of tumor-specific cytotoxic T cells has only shown marginal improvement in life spans of patients with metastatic disease. In this report, we discuss experimental evidence showing that expression of tumor-derived galectins, galectin (Gal)-1, Gal-3 and Gal-9, and concomitant presence of their ligands on the surface of anti-tumor immunocytes directly compromise anti-tumor CD8⁺ T cell immune responses and, perhaps, undermine the promise of adoptive CD8⁺ T cell immunotherapy. Furthermore, we describe novel strategies designed to counteract Gal-1-, Gal-3- and Gal-9-mediated effects and highlight their targeting potential for creating more effective anti-tumor immune responses. We believe that Gal and their ligands represent an efficacious targeted molecular paradigm that warrants clinical evaluation.     

Aging and longevity of yeast colony populations: metabolic adaptation and differentiation

Yeast multicellular colonies possess several traits that are absent from individual yeasts. These include the ability to synchronize colony population development and adapt its metabolism to different environmental changes, such as nutrient depletion. This, together with cell diversification to cell variants with distinct metabolic and other properties, contributes to the main goal of the colony population: to achieve longevity. In this respect, a benefit to individual cells is subordinated to the benefit to the whole population, exhibiting a kind of altruistic behaviour. For example, some colony cells located at particular positions undergo regulated cell dying and provide components to other cells located in more propitious areas. The enhancement of techniques that enable the in vivo investigation of three-dimensional spatiotemporal colony development may lead to new discoveries on metabolic differentiation and regulation in the near future.