The TGF-β co-receptor, CD109, promotes internalization and degradation of TGF-β receptors

Transforming growth factor-β (TGF-β) is implicated in numerous pathological disorders, including cancer and mediates a broad range of biological responses by signaling through the type I and II TGF-β receptors. Internalization of these receptors via the clathrin-coated pits pathway facilitates SMAD-mediated signaling, whereas internalization via the caveolae pathway is associated with receptor degradation. Thus, molecules that modulate receptor endocytosis are likely to play a critical role in regulating TGF-β action. We previously identified CD109, a GPI-anchored protein, as a TGF-β co-receptor and a negative regulator of TGF-β signaling. Here, we demonstrate that CD109 associates with caveolin-1, a major component of the caveolae. Moreover, CD109 increases binding of TGF-β to its receptors and enhances their internalization via the caveolae. In addition, CD109 promotes localization of the TGF-β receptors into the caveolar compartment in the presence of ligand and facilitates TGF-β-receptor degradation. Thus, CD109 regulates TGF-β receptor endocytosis and degradation to inhibit TGF-β signaling.     

The proximal hydrogen bond network modulates Bacillus subtilis nitric-oxide synthase electronic and structural properties

Bacterial nitric-oxide synthase (NOS)-like proteins are believed to be genuine NOSs. As for cytochromes P450 (CYPs), NOS-proximal ligand is a thiolate that exerts a push effect crucial for the process of dioxygen activation. Unlike CYPs, this catalytic electron donation seems controlled by a hydrogen bond (H-bond) interaction between the thiolate ligand and a vicinal tryptophan. Variations of the strength of this H-bond could provide a direct way to tune the stability along with the electronic and structural properties of NOS. We generated five different mutations of bsNOS Trp66, which can modulate this proximal H-bond. We investigated the effects of these mutations on different NOS complexes (FeIII, FeIICO, and FeIINO), using a combination of UV-visible absorption, EPR, FTIR, and resonance Raman spectroscopies. Our results indicate that (i) the proximal H-bond modulation can selectively decrease or increase the electron donating properties of the proximal thiolate, (ii) this modulation controls the σ-competition between distal and proximal ligands, (iii) this H-bond controls the stability of various NOS intermediates, and (iv) a fine tuning of the electron donation by the proximal ligand is required to allow at the same time oxygen activation and to prevent uncoupling reactions.     

Activation of RXR–PPAR heterodimers by organotin environmental endocrine disruptors

The nuclear receptor retinoid X receptor‐α (RXR‐α)–peroxisome proliferator‐activated receptor‐γ (PPAR‐γ) heterodimer was recently reported to have a crucial function in mediating the deleterious effects of organotin compounds, which are ubiquitous environmental contaminants. However, because organotins are unrelated to known RXR‐α and PPAR‐γ ligands, the mechanism by which these compounds bind to and activate the RXR‐α–PPAR‐γ heterodimer at nanomolar concentrations has remained elusive. Here, we show that tributyltin (TBT) activates all three RXR–PPAR‐α, ‐γ, ‐δ heterodimers, primarily through its interaction with RXR. In addition, the 1.9 Å resolution structure of the RXR‐α ligand‐binding domain in complex with TBT shows a covalent bond between the tin atom and residue Cys 432 of helix H11. This interaction largely accounts for the high binding affinity of TBT, which only partly occupies the RXR‐α ligand‐binding pocket. Our data allow an understanding of the binding and activation properties of the various organotins and suggest a mechanism by which these tin compounds could affect other nuclear receptor signalling pathways.     

A tandem of SH3-like domains participates in RNA binding in KIN17, a human protein activated in response to genotoxics

The human KIN17 protein is an essential nuclear protein conserved from yeast to human and expressed ubiquitously in mammals. Suppression of Rts2, the yeast equivalent of gene KIN17, renders the cells unviable, and silencing the human KIN17 gene slows cell growth dramatically. Moreover, the human gene KIN17 is up-regulated following exposure to ionizing radiations and UV light, depending on the integrity of the human global genome repair machinery. Its ectopic over-expression blocks S-phase progression by inhibiting DNA synthesis. The C-terminal region of human KIN17 is crucial for this anti-proliferation effect. Its high-resolution structure, presented here, reveals a tandem of SH3-like subdomains. This domain binds to ribonucleotide homopolymers with the same preferences as the whole protein. Analysis of its structure complexed with tungstate shows structural variability within the domain. The interaction with tungstate is mediated by several lysine residues located within a positively charged groove at the interface between the two subdomains. This groove could be the site of interaction with RNA, since mutagenesis of two of these highly conserved lysine residue weakens RNA binding.     

How did common ragweed (Ambrosia artemisiifolia L.) spread in Québec? A historical analysis using herbarium records

Aim To reconstruct the spread of common ragweed (Ambrosia artemisiifolia L.; Asteraceae) using herbarium specimens to document whether the habitat preferences of this plant have shifted through time. Location Southern Québec. Methods Herbarium specimens stored in the main herbaria of southern Québec were used to reconstruct the spread of common ragweed. All data (sampling location, year of sampling, habitat characteristics, etc.) were incorporated into a geographical information system. Maps indicating the spatial distribution of common ragweed were produced for four time periods. The cumulative number of locations was plotted against time to construct invasion curves. The sequence of habitats where herbarium specimens were collected was also reconstructed. Results A data base incorporating 707 common ragweed herbarium specimens was constructed for this study. The spread of common ragweed in most regions of southern Québec was initiated at the beginning of the 20th century. Herbarium specimens suggest that common ragweed first spread along river corridors. Specimens of common ragweed were not collected in agricultural fields before the mid‐1920s, nor along roads and railways before the mid‐1930s. The colonization of a large number of agricultural fields by common ragweed probably began with seed‐contaminated crops, but was certainly accelerated by the dispersal of seeds from populations growing along nearby roads. Main conclusions Herbarium specimens suggest that common ragweed has been present in southern Québec for at least 200 years, but the species was probably restricted to the Montréal area during the 19th century. It is likely that the development of the road network in Québec since the mid‐1930s significantly contributed to the spread of common ragweed. Controlling common ragweed solely in agricultural fields would not prevent the re‐infestation of crops, because roadsides would act as refuges for the weed.     

Virulence of Vibrio harveyi ORM4 towards the European abalone Haliotis tuberculata involves both quorum sensing and a type III secretion system

Environmental Vibrio strains represent a major threat in aquaculture, but the understanding of their virulence mechanisms heavily relies on the transposition of knowledge from human-pathogen vibrios. Here, the genetic bases of the virulence of Vibrio harveyi ORM4 towards the European abalone Haliotis tuberculata were characterized. We demonstrated that luxO, encoding a major regulator of the quorum sensing system, is crucial for the virulence of this strain, and that its deletion leads to a decrease in swimming motility, biofilm formation, and exopolysaccharide production. Furthermore, the biofilm formation by V. harveyi ORM4 was increased by abalone serum, which required LuxO. The absence of LuxO in V. harveyi ORM4 yielded opposite phenotypes compared with other Vibrio species including V. campbellii (still frequently named V. harveyi). In addition, we report a full type III secretion system (T3SS) gene cluster in the V. harveyi ORM4 genome. LuxO was shown to negatively regulate the promoter activity of exsA, encoding the major regulator of the T3SS genes, and the deletion of exsA abolished the virulence of V. harveyi ORM4. These results unveil virulence mechanisms set up by this environmentally important bacterial pathogen and pave the way for a better molecular understanding of the regulation of its pathogenicity.