Disabled is a bona fide component of the Abl signaling network

Abl is an essential regulator of cell migration and morphogenesis in both vertebrates and invertebrates. It has long been speculated that the adaptor protein Disabled (Dab), which is a key regulator of neuronal migration in the vertebrate brain, might be a component of this signaling pathway, but this idea has been controversial. We now demonstrate that null mutations of Drosophila Dab result in phenotypes that mimic Abl mutant phenotypes, both in axon guidance and epithelial morphogenesis. The Dab mutant interacts genetically with mutations in Abl, and with mutations in the Abl accessory factors trio and enabled (ena). Genetic epistasis tests show that Dab functions upstream of Abl and ena, and, consistent with this, we show that Dab is required for the subcellular localization of these two proteins. We therefore infer that Dab is a bona fide component of the core Abl signaling pathway in Drosophila.     

A method for the analysis of six thyroid hormones in thyroid gland by liquid chromatography–tandem mass spectrometry

Perchlorate can competitively inhibit iodide uptake by the thyroid gland (TG) via the sodium/iodide symporter, consequently reducing the production of thyroid hormones (THs). Until recently, the effects of perchlorate on TH homeostasis are being examined through measurement of serum levels of TH, by immunoassay (IA)-based methods. IA methods are fast, but for TH analysis, they are compromised by the lack of adequate specificity. Therefore, selective and sensitive methods for the analysis of THs in TG are needed, for assessment of the effects of perchlorate on TH homeostasis. In this study, we developed a method for the analysis of six THs: l-thyroxine (T₄), 3,3′,5-triiodo-l-thyronine (T₃), 3,3′,5′-triiodo-l-thyronine (rT₃), 3,5-diiodo-l-thyronine (3,5-T₂), 3,3′-diiodo-l-thyronine (3,3′-T₂), and 3-iodo-l-thyronine (3-T₁) in TG, using liquid chromatography (LC)–tandem mass spectrometry (MS/MS). TGs used in this study were from rats that had been placed on either iodide-deficient diet or iodide-sufficient diet, and that had either been provided with perchlorate in drinking water (10 mg/kg/day) or control water. TGs were extracted by pronase digestion and then analyzed by LC–MS/MS. The instrumental calibration range for each TH ranged from 1 to 200 ng/ml and showed a high linearity (r > 0.99). The method quantification limits (LOQs) were determined to be 0.25 ng/mg TG for 3-T₁; 0.33 ng/mg TG for 3,3′- and 3,5-T₂; and 0.52 ng/mg TG for rT₃, T₃, and T₄. Rats were placed on an iodide-deficient or -sufficient diet for 2.5 months, and for the last 2 weeks of that period were provided either perchlorate (10 mg/kg/day) in drinking water or control water. Iodide deficiency and perchlorate administration both reduced TG stores of rT₃, T₃, and T₄. In iodide-deficient rats, perchlorate exacerbated the reduction in levels of THs in TG. With the advances in analytical methodology, the use of LC–MS/MS for measurement of hormone levels in TG will allow more comprehensive evaluations of the hypothalamic-pituitary–thyroid axis.     

Research on marine actinobacteria in India

Marine actinobacteriology is one of the major emerging areas of research in tropics. Marine actinobacteria occur on the sediments and in water and also other biomass (mangrove) and substrates (animal). These organisms are gaining importance not only for their taxonomic and ecological perspectives, but also for their unique metabolites and enzymes. Many earlier studies on these organisms were confined only to the temperate regions. In tropical environment, investigations on them have gained importance only in the last two decades. So far, from the Indian peninsula, 41 species of actinobacteria belonging to 8 genera have been recorded. The genus, Streptomyces of marine origin has been more frequently recorded. Of 9 maritime states of India, only 4 have been extensively covered for the study of marine actinobacteria. Most of the studies conducted pertain to isolation, identification and maintenance of these organisms in different culture media. Further, attention has been focused on studying their antagonistic properties against different pathogens. Their biotechnological potentials are yet to be fully explored.     

Cytotoxic effect of achatininH (lectin) from Achatina fulica against a human mammary carcinoma cell line (MCF7)

The hemolymph-derived achatinin_H (lectin) from Achatina fulica showed a marked cytotoxic effect on MCF7, a human mammary carcinoma cell line. IC₅₀ values as measured by the 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide assay for achatinin_H ranged from 6 to 10 μg/ml in the MCF7 cells. MCF7 cells showed significant morphological changes leading to cell death. The above cell death was observed after 48 h of treatment with 8 μg/ml when compared to untreated cells. Alterations in the tumor marker enzymes, as well as in antioxidant enzymes, were observed after achatinin_H treatment. The specificity and purity of the achatinin_H was confirmed by the Western blot assay. Achatinin_H binding to MCF7 cells was detected by anti-achatinin_H, and visualization of the achatinin_H binding sites on confluent MCF7 cells was confirmed by flourescein isothiocyanate conjugated secondary antibody. MCF7-treated cells fluoresced, indicating the presence of achatinin_H binding sites. Fluorescence-activated cell sorting analysis of the cell cycle showed a significant increase in S-phase in MCF7 cells after 48 h of achatinin_H treatment. The cells were arrested in G₂/M phase of the cell cycle after 48 h with significant changes in cell viability. Cellular damage was confirmed by agarose gel electrophoresis with the characteristic appearance of a DNA streak in treated MCF7 cells indicating the ongoing apoptosis. An erratum to this article can be found at     

A Novel Antibody Engineering Strategy for Making Monovalent Bispecific Heterodimeric IgG Antibodies by Electrostatic Steering Mechanism

Producing pure and well behaved bispecific antibodies (bsAbs) on a large scale for preclinical and clinical testing is a challenging task. Here, we describe a new strategy for making monovalent bispecific heterodimeric IgG antibodies in mammalian cells. We applied an electrostatic steering mechanism to engineer antibody light chain-heavy chain (LC-HC) interface residues in such a way that each LC strongly favors its cognate HC when two different HCs and two different LCs are co-expressed in the same cell to assemble a functional bispecific antibody. We produced heterodimeric IgGs from transiently and stably transfected mammalian cells. The engineered heterodimeric IgG molecules maintain the overall IgG structure with correct LC-HC pairings, bind to two different antigens with comparable affinity when compared with their parental antibodies, and retain the functionality of parental antibodies in biological assays. In addition, the bispecific heterodimeric IgG derived from anti-HER2 and anti-EGF receptor (EGFR) antibody was shown to induce a higher level of receptor internalization than the combination of two parental antibodies. Mouse xenograft BxPC-3, Panc-1, and Calu-3 human tumor models showed that the heterodimeric IgGs strongly inhibited tumor growth. The described approach can be used to generate tools from two pre-existent antibodies and explore the potential of bispecific antibodies. The asymmetrically engineered Fc variants for antibody-dependent cellular cytotoxicity enhancement could be embedded in monovalent bispecific heterodimeric IgG to make best-in-class therapeutic antibodies.     

Conformational regulation of the EGFR kinase core by the juxtamembrane and C-terminal tail: a molecular dynamics study

The catalytic domain of epidermal growth factor receptor (EGFR) is activated by dimerization, which requires allosteric coupling between distal dimerization and catalytic sites. Although crystal structures of EGFR kinases, solved in various conformational states, have provided important insights into EGFR activation by dimerization, the atomic details of how dimerization signals are dynamically coupled to catalytic regions of the kinase core are not fully understood. In this study, we have performed unrestrained and targeted molecular dynamics simulations on the active and inactive states of EGFR, followed by principal component analysis on the simulated trajectories, to identify correlated motions in the EGFR kinase domain upon dimerization. Our analysis reveals that the conformational changes associated with the catalytic functions of the kinase core are highly correlated with motions in the juxtamembrane (JM) and C-terminal tail, two flexible structural elements that play an active role in EGFR kinase activation and dimerization. In particular, the opening and closing of the ATP binding lobe relative to the substrate binding lobe is highly correlated with motions in the JM and C-terminal tail, suggesting that ATP and substrate binding can be coordinated with dimerization through conformational changes in the JM and C-terminal tail. Our study pinpoints key residues involved in this conformational coupling, and provides new insights into the role of the JM and C-terminal tail segments in EGFR kinase functions.