USP13 enzyme regulates Siah2 ligase stability and activity via noncatalytic ubiquitin-binding domains

The RING finger E3 ubiquitin ligase Siah2 is implicated in control of diverse cellular biological events, including MAPK signaling and hypoxia. Here we demonstrate that Siah2 is subject to regulation by the deubiquitinating enzyme USP13. Overexpression of USP13 increases Siah2 stability by attenuating its autodegradation. Consequently, the ability of Siah2 to target its substrates prolyl hydroxylase 3 and Spry2 (Sprouty2) for ubiquitin-mediated proteasomal degradation is attenuated. Conversely, inhibition of USP13 expression with corresponding shRNA decreases the stability of both Siah2 and its substrate Spry2. Thus, USP13 limits Siah2 autodegradation and its ubiquitin ligase activity against its target substrates. Strikingly, the effect of USP13 on Siah2 is not mediated by its isopeptidase activity: mutations in its ubiquitin-binding sequences positioned within the ubiquitin-specific processing protease and ubiquitin-binding domains, but not within putative catalytic sites, abolish USP13 binding to and effect on Siah2 autodegradation and targeted ubiquitination. Notably, USP13 expression is attenuated in melanoma cells maintained under hypoxia, thereby relieving Siah2 inhibition and increasing its activity under low oxygen levels. Significantly, on melanoma tissue microarray, high nuclear expression of USP13 coincided with high nuclear expression of Siah2. Overall, this study identifies a new layer of Siah2 regulation mediated by USP13 binding to ubiquitinated Siah2 protein with a concomitant inhibitory effect on its activity under normoxia.     

Autoregulation and homodimerization are involved in the activation of the plant steroid receptor BRI1

The leucine-rich-repeat receptor serine/threonine kinase, BRI1, is a cell-surface receptor for brassinosteroids (BRs), the steroid hormones of plants, yet its activation mechanism is unknown. Here, we report a unique autoregulatory mechanism of BRI1 activation. Removal of BRI1's C terminus leads to a hypersensitive receptor, indicated by suppression of dwarfism of BR-deficient and BR-perception mutants and by enhanced BR signaling as a result of elevated phosphorylation of BRI1. Several sites in the C-terminal region can be phosphorylated in vitro, and transgenic Arabidopsis expressing BRI1 mutated at these sites demonstrates an essential role of phosphorylation in BRI1 activation. BRI1 is a ligand-independent homo-oligomer, as evidenced by the transphosphorylation of BRI1 kinase in vitro, the dominant-negative effect of a kinase-inactive BRI1 in transgenic Arabidopsis, and coimmunoprecipitation experiments. Our results support a BRI1-activation model that involves inhibition of kinase activity by its C-terminal domain, which is relieved upon ligand binding to the extracellular domain.     

Pseudomonas aeruginosa survives in epithelia by ExoS‐mediated inhibition of autophagy and mTOR

One major factor that contributes to the virulence of Pseudomonas aeruginosa is its ability to reside and replicate unchallenged inside airway epithelial cells. The mechanism by which P. aeruginosa escapes destruction by intracellular host defense mechanisms, such as autophagy, is not known. Here, we show that the type III secretion system effector protein ExoS facilitates P. aeruginosa survival in airway epithelial cells by inhibiting autophagy in host cells. Autophagy inhibition is independent of mTOR activity, as the latter is also inhibited by ExoS, albeit by a different mechanism. Deficiency of the critical autophagy gene Atg7 in airway epithelial cells, both in vitro and in mouse models, greatly enhances the survival of ExoS‐deficient P. aeruginosa but does not affect the survival of ExoS‐containing bacteria. The inhibitory effect of ExoS on autophagy and mTOR depends on the activity of its ADP‐ribosyltransferase domain. Inhibition of mTOR is caused by ExoS‐mediated ADP ribosylation of RAS, whereas autophagy inhibition is due to the suppression of autophagic Vps34 kinase activity.     

Analysis of the Escherichia coli glycogen gene cluster suggests that catabolic enzymes are encoded among the biosynthetic genes

The nucleotide sequences of the Escherichia coli genome between the glycogen biosynthetic genes glgB and glgC, and 1170 bp of DNA which follows glgA have been determined. The region between glgB and glgC contains an open reading frame (ORF) of 1521 bp which we call glgX. This ORF is capable of coding for an M_r 56 684 protein. The deduced amino acid (aa) sequence for the putative product shows significant similarity to the E. coli glycogen branching enzyme, and to several different glucan hydrolases and transferases. The regions of sequence similarity include residues which have been reported to be involved in substrate binding and catalysis by taka-amylase. This suggests that the proposed product may catalyze hydrolysis or glycosyltransferase reactions. The cloned region which follows glgA contains an incomplete ORF (1149 bp), glgY, which appears to encode 383 aa of the N terminus of glycogen phosphorylase, based upon sequence similarity with the enzyme from rabbit muscle (47% identical aa residues) and with maltodextrin phosphorylase from E. coli (37% identical aa residues). Results suggest that neither ORF is required for glycogen biosynthesis. The localization of glycogen biosynthetic and degradative genes together in a cluster may facilitate the regulation of these systems in vivo.     

Glucagon signalling in the dorsal vagal complex is sufficient and necessary for high‐protein feeding to regulate glucose homeostasis in vivo

High‐protein feeding acutely lowers postprandial glucose concentration compared to low‐protein feeding, despite a dichotomous rise of circulating glucagon levels. The physiological role of this glucagon rise has been largely overlooked. We here first report that glucagon signalling in the dorsal vagal complex (DVC) of the brain is sufficient to lower glucose production by activating a Gcgr–PKA–ERK–K_ATP channel signalling cascade in the DVC of rats in vivo. We further demonstrate that direct blockade of DVC Gcgr signalling negates the acute ability of high‐ vs. low‐protein feeding to reduce plasma glucose concentration, indicating that the elevated circulating glucagon during high‐protein feeding acts in the brain to lower plasma glucose levels. These data revise the physiological role of glucagon and argue that brain glucagon signalling contributes to glucose homeostasis during dietary protein intake.     

541. Corylus × Vilmorinii

Summary.  The hybrid hazel, Corylus  ×  vilmorinii Rehder is described and illustrated. Its robust habit and showy catkins make it an interesting and worthwhile tree to cultivate.     

Effects of climate change on the delivery of soil‐mediated ecosystem services within the primary sector in temperate ecosystems: a review and New Zealand case study

Future human well‐being under climate change depends on the ongoing delivery of food, fibre and wood from the land‐based primary sector. The ability to deliver these provisioning services depends on soil‐based ecosystem services (e.g. carbon, nutrient and water cycling and storage), yet we lack an in‐depth understanding of the likely response of soil‐based ecosystem services to climate change. We review the current knowledge on this topic for temperate ecosystems, focusing on mechanisms that are likely to underpin differences in climate change responses between four primary sector systems: cropping, intensive grazing, extensive grazing and plantation forestry. We then illustrate how our findings can be applied to assess service delivery under climate change in a specific region, using New Zealand as an example system. Differences in the climate change responses of carbon and nutrient‐related services between systems will largely be driven by whether they are reliant on externally added or internally cycled nutrients, the extent to which plant communities could influence responses, and variation in vulnerability to erosion. The ability of soils to regulate water under climate change will mostly be driven by changes in rainfall, but can be influenced by different primary sector systems' vulnerability to soil water repellency and differences in evapotranspiration rates. These changes in regulating services resulted in different potentials for increased biomass production across systems, with intensively managed systems being the most likely to benefit from climate change. Quantitative prediction of net effects of climate change on soil ecosystem services remains a challenge, in part due to knowledge gaps, but also due to the complex interactions between different aspects of climate change. Despite this challenge, it is critical to gain the information required to make such predictions as robust as possible given the fundamental role of soils in supporting human well‐being.     

Critical negative regulation of type 1 T cell immunity and immunopathology by signaling adaptor DAP12 during intracellular infection

Transmembrane signaling adaptor DAP12 has increasingly been recognized for its important role in innate responses. However, its role in the regulation of antimicrobial T cell responses has remained unknown. In our current study, we have examined host defense, T cell responses, and tissue immunopathology in models of intracellular infection established in wild-type and DAP12-deficient mice. During mycobacterial infection, lack of DAP12 leads to pronounced proinflammatory and Th1 cytokine responses, overactivation of Ag-specific CD4 and CD8 T cells of type 1 phenotype, and heightened immunopathology both in the lung and lymphoid organs. DAP12-deficient airway APC display enhanced NF-kappaB activation and cytokine responses upon TLR stimulation or mycobacterial infection in vitro. Of importance, adoptive transfer of Ag-loaded DAP12-deficient APC alone could lead to overactivation of transferred transgenic or endogenous wild-type T cells in vivo. We have further found that the immune regulatory role by DAP12 is not restricted only to intracellular bacterial infection, since lack of this molecule also leads to uncontrolled type 1 T cell activation and severe immunopathology and tissue injury during intracellular viral infection. Our study thus identifies DAP12 as an important novel immune regulatory molecule that acts, via APC, to control the level of antimicrobial type 1 T cell activation and immunopathology.     

A genomewide association study of skin pigmentation in a South Asian population

We have conducted a multistage genomewide association study, using 1,620,742 single-nucleotide polymorphisms to systematically investigate the genetic factors influencing intrinsic skin pigmentation in a population of South Asian descent. Polymorphisms in three genes—SLC24A5, TYR, and SLC45A2—yielded highly significant replicated associations with skin-reflectance measurements, an indirect measure of melanin content in the skin. The associations detected in these three genes, in an additive manner, collectively account for a large fraction of the natural variation of skin pigmentation in a South Asian population. Our study is the first to interrogate polymorphisms across the genome, to find genetic determinants of the natural variation of skin pigmentation within a human population.