In an effort to better understand the mechanism of toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin, we employed an iterative search of human expressed sequence tags to identify novel basic-helix-loop-helix-PAS (bHLH-PAS) proteins that interact with either the Ah receptor (AHR) or the Ah receptor nuclear translocator (ARNT). We characterized five new "members of the PAS superfamily," or MOPs 1-5, that are similar in size and structural organization to the AHR and ARNT. MOPs 1-4 have N-terminal bHLH and PAS domains and C-terminal variable regions. MOP5 contained the characteristic PAS domain and a variable C terminus; it is possible that the cDNA contains a bHLH domain, but the entire open reading frame has yet to be completed. Coimmunoprecipitation studies, yeast two-hybrid analysis, and transient transfection experiments demonstrated that MOP1 and MOP2 dimerize with ARNT and that these complexes are transcriptionally active at defined DNA enhancer sequences in vivo. MOP3 was found to associate with the AHR in vitro but not in vivo. This observation, coupled with the fact that MOP3 formed tighter associations with the 90-kDa heat shock protein than the human AHR, suggests that MOP3 may be a conditionally active bHLH-PAS protein that requires activation by an unknown ligand. The expression profiles of the AHR, MOP1, and MOP2 mRNAs, coupled with the observation that they all share ARNT as a common dimeric partner, suggests that the cellular pathways mediated by MOP1 and MOP2 may influence or respond to the dioxin signaling pathway.

The research of active and sustainable electrocatalysts toward oxygen reduction reaction (ORR) is of great importance for industrial application of fuel cells. Here, we report a remarkable ORR catalyst with both excellent mass activity and durability based on sub 2 nm thick Rh-doped Pt nanowires, which combine the merits of high utilization efficiency of Pt atoms, anisotropic one-dimensional nanostructure, and doping of Rh atoms. Compared with commercial Pt/C catalyst, the Rh-doped Pt nanowires/C catalyst shows a 7.8 and 5.4-fold enhancement in mass activity and specific activity, respectively. The combination of extended X-ray absorption fine structure analysis and density functional theory calculations reveals that the compressive strain and ligand effect in Rh-doped Pt nanowires optimize the adsorption energy of hydroxyl and in turn enhance the specific activity. Moreover, even after 10000 cycles of accelerated durability test in O condition, the Rh-doped Pt nanowires/C catalyst exhibits a drop of 9.2% in mass activity, against a big decrease of 72.3% for commercial Pt/C. The improved durability can be rationalized by the increased vacancy formation energy of Pt atoms for Rh-doped Pt nanowires.

The aryl hydrocarbon receptor (AHR) and the ␣-class hypoxia inducible factors (HIF1␣, HIF2␣, and HIF3␣) are basic helix-loop-helix PAS (bHLH-PAS) proteins that heterodimerize with ARNT. In response to 2,3,7,8-tetrachlorodibenzo-p-dioxin, the AHR⅐ARNT complex binds to "dioxin responsive enhancers" (DREs) and activates genes involved in the metabolism of xenobiotics, e.g. cytochrome P4501A1 (Cyp1a1). The HIF1␣⅐ARNT complex binds to "hypoxia responsive enhancers" and activates the transcription of genes that regulate adaptation to low oxygen, e.g. erythropoietin (Epo). We postulated that activation of one pathway would inhibit the other due to competition for ARNT or other limiting cellular factors. Using pathway specific reporters in transient transfection assays, we observed that DRE driven transcription was markedly inhibited by hypoxia and that hypoxia responsive enhancer driven transcription was inhibited by AHR agonists. When we attempted to support this cross-talk model using endogenous loci, we observed that activation of the hypoxia pathway inhibited Cyp1a1 up-regulation, but that activation of the AHR actually enhanced the induction of Epo by hypoxia. To explain this unexpected additivity, we examined the Epo gene and found that its promoter harbors DREs immediately upstream of its transcriptional start site. These experiments outline conditions where inhibitory and additive cross-talk occur between the hypoxia and dioxin signal transduction pathways and identify Epo as an AHR-regulated gene. The AHR1 regulates a variety of biological responses to environmentally ubiquitous polycyclic aromatic hydrocarbons and dioxins (1,2). In what can be defined as an adaptive pathway, the AHR up-regulates a battery of XMEs that often metabolize many of these agonists to more soluble and excretable products. A classic example of this pathway is observed upon exposure to benzo [a]pyrene. This chemical binds to the AHR leading to the up-regulation of a battery of genes including Cyp1a1, Cyp1a2, and Cyp1b1 (3). The enzymes encoded by these loci have metabolic activity toward benzo[a]pyrene and thus play an important role in its elimination (4). At present, we understand many of the molecular events in what appears to be an adaptive response to polycyclic aromatic hydrocarbon exposure. In brief, the up-regulation of genes like Cyp1a1 are regulated by an agonist-induced heterodimerization between two bHLH-PAS proteins, the AHR and ARNT (5, 6). This heterodimeric pair interacts with DREs upstream of the regulated promoters leading to an increase in their transcription rate and a resultant increase in XME activity (7).Although we have developed models to describe how the AHR regulates the expression of XMEs, we still have very little knowledge about how this protein mediates the toxicity of potent agonists like dioxin. The molecular mechanisms of dioxin-induced effects like lymphoid involution, epithelial hyperplasia, tumor promotion, teratogenesis, or even death remain unclear. Moreover, although genetic studies indicate the ...

Biological actions of somatostatin are exerted via a family of receptors, for which five genes recently have been cloned. However, none of these receptor proteins has been visualized yet in the brain. In the present-study, the regional and cellular distribution of the somatostatin sst2A receptor was investigated via immunocytochemistry in the rat central nervous system by using an antibody generated against a unique sequence of the receptor protein. Specificity of the antiserum was demonstrated by immunoblot and immunocytochemistry on rat brain membranes and/or on cells transfected with cDNA encoding the different sst receptor subtypes. In rat brain sections, sst2A receptor immunoreactivity was concentrated either in perikarya and dendrites or in axon terminals distributed throughout the neuropil. Somatodendritic labeling was most prominent in the olfactory tubercle, layers II-III of the cerebral cortex, nucleus accumbens, pyramidal cells of CA1-CA2 subfields of the hippocampus, central and cortical amygdaloid nuclei, and locus coeruleus. Labeled terminals were detected mainly in the endopiriform nucleus, deep layers of the cortex, claustrum, substantia innominata, subiculum, basolateral amygdala, medial habenula, and periaqueductal gray. Electron microscopy confirmed the association of sst2A receptors with perikarya and dendrites in the former regions and with axon terminals in the latter. These results provide the first characterization of the cellular distribution of a somatostatin receptor in mammalian brain. The widespread distribution of the sst2A receptor in cerebral cortex and limbic structures suggests that it is involved in the transduction of both pre- and postsynaptic effects of somatostatin on cognition, learning, and memory.

Non‐volatile resistive switching (NVRS) is a widely available effect in transitional metal oxides, colloquially known as memristors, and of broad interest for memory technology and neuromorphic computing. Until recently, NVRS was not known in other transitional metal dichalcogenides (TMDs), an important material class owing to their atomic thinness enabling the ultimate dimensional scaling. Here, various monolayer or few‐layer 2D materials are presented in the conventional vertical structure that exhibit NVRS, including TMDs (MX2, M = transitional metal, e.g., Mo, W, Re, Sn, or Pt; X = chalcogen, e.g., S, Se, or Te), TMD heterostructure (WS2/MoS2), and an atomically thin insulator (h‐BN). These results indicate the universality of the phenomenon in 2D non‐conductive materials, and feature low switching voltage, large ON/OFF ratio, and forming‐free characteristic. A dissociation–diffusion–adsorption model is proposed, attributing the enhanced conductance to metal atoms/ions adsorption into intrinsic vacancies, a conductive‐point mechanism supported by first‐principle calculations and scanning tunneling microscopy characterizations. The results motivate further research in the understanding and applications of defects in 2D materials.

Objective To identify biomarkers that distinguish between active ANCA-associated vasculitis (AAV) and remission in a manner superior or complementary to established markers of systemic inflammation. Methods Markers of vascular injury and angiogenesis were measured before and after treatment in a large clinical trial in AAV. 163 subjects enrolled in the Rituximab in ANCA-Associated Vasculitis (RAVE) trial were studied. Serum levels of E-selectin, ICAM-3, MMP1, MMP3, MMP9, P-selectin, thrombomodulin, and VEGF were measured at study screening (time of active disease) and at month 6. ESR and CRP levels had been measured at the time of the clinical visit. The primary outcome was the difference in marker level between screening and month 6 among patients in remission (BVAS/WG score of 0) at month 6. Results All subjects had severe active vasculitis (mean BVAS/WG score 8.6 +/− 3.2 SD) at screening. Among the 123 subjects clinically in remission at month 6, levels of all markers except E-selectin showed significant declines. MMP3 levels were also higher among the 23 subjects with active disease at month 6 than among the 123 subjects in remission. MMP3 levels correlated weakly with ESR and CRP. Conclusion Many markers of vascular injury and angiogenesis are elevated in severe active AAV and decline with treatment, but MMP3 appears to distinguish active AAV from remission better than the other markers studied. Further study of MMP3 is warranted to determine its clinical utility in combination with conventional markers of inflammation and ANCA titers.

Somatostatin initiates its actions via a family of seven-transmembrane domain receptors. Of the five somatostatin receptor genes cloned, sst2 exists as two splice variants with the sst2A isoform being predominantly expressed. This receptor is widely distributed in endocrine, exocrine, and neuronal cells, as well as in hormonally responsive tumors, and leads to inhibition of secretion, electrical excitability, and cell proliferation. To investigate the specificity of signal transduction by the sst2A receptor, we developed antibodies against two overlapping peptides located within the C terminus of the receptor protein: peptide 2C(SG), containing amino acids 334-348, and peptide 2C(ER), containing amino acids 339-359. Although antibodies to both peptides bound the inducing antigen with high affinity, only the antibodies against peptide 2C(ER) precipitated the receptor. The best antibody, R2-88, precipitated about 80% of the sst2A receptor-ligand complex solubilized from transfected CHO cells and was specific for the sst2A receptor isotype. Addition of GTPgammaS (10 microM) to the immunoprecipitated ligand-sst2A receptor complex markedly accelerated ligand dissociation, indicating that G proteins remained functionally associated with the receptor in the immunoprecipitate. Analysis of the G proteins coprecipitated with the sst2A receptor by immunoblotting with G protein antibodies showed that both G(alpha) and G(beta) subunits were bound to the hormone-receptor complex. Immunoprecipitation of the receptor was not affected by the presence of bound ligand. However, G protein subunits were coprecipitated only with the hormone-occupied receptor. Thus, the unoccupied receptor has low affinity for G proteins, and hormone binding stabilizes the receptor-G protein complex. Use of subtype-specific G protein antisera further showed that G alpha(i1), G alpha(i2), and G alpha(i3) were complexed with the sst2A receptor whereas Galpha(o), G alpha(z), and G alpha(q) were not. Together, these studies demonstrate that the sst2A receptor interacts selectively with G alpha(i) proteins in a hormone-dependent manner. The finding that this receptor couples to all three G alpha(i) subunits may help explain how somatostatin can regulate multiple signaling pathways.

Fracture healing is closely related to the number and activity of bone marrow mesenchymal stem cells (BMSCs) near the fracture site. The present study was to investigate the effect of Rg1 on osteogenic differentiation of cultured BMSCs and related mechanisms and on the fracture healing in a fracture model. In vitro experiments showed that Rg1 promoted the proliferation and osteogenic differentiation of BMSCs. Western blot analyses demonstrated that Rg1 promoted osteogenic differentiation of BMSCs through the glucocorticoid receptor (GR)-dependent BMP-2/Smad signaling pathway. In vivo, X-ray examination showed that callus growth in rats treated with Rg1 was substantially faster than that in control rats after fracture. The results of H&E and Safranin-O/Fast Green staining revealed that, compared with controls, rats in the Rg1 treatment group had a significantly higher proportion of trabecular bone but a much lower proportion of fibers and cartilage components inside the callus. Micro-CT suggested that bone mineral density (BMD), percent bone volume (BV/TV), trabecular number (Tb.N), and trabecular thickness (Tb.Th) were significantly increased in the treatment group, whereas trabecular separation (Tb.Sp) was significantly reduced. Thus, Rg1 promotes osteogenic differentiation by activating the GR/BMP-2 signaling pathway, enhances bone calcification, and ultimately accelerates the fracture healing in rats.