Similar structures and shared switch mechanisms of the beta2-adrenoceptor and the parathyroid hormone receptor. Zn(II) bridges between helices III and VI block activation

The seven transmembrane helices of serpentine receptors comprise a conserved switch that relays signals from extracellular stimuli to heterotrimeric G proteins on the cytoplasmic face of the membrane. By substituting histidines for residues at the cytoplasmic ends of helices III and VI in retinal rhodopsin, we engineered a metal-binding site whose occupancy by Zn(II) prevented the receptor from activating a retinal G protein, Gt (Sheikh, S. P., Zvyaga, T. A. , Lichtarge, O., Sakmar, T. P., and Bourne, H. R. (1996) Nature 383, 347-350). Now we report engineering of metal-binding sites bridging the cytoplasmic ends of these two helices in two other serpentine receptors, the beta2-adrenoreceptor and the parathyroid hormone receptor; occupancy of the metal-binding site by Zn(II) markedly impairs the ability of each receptor to mediate ligand-dependent activation of Gs, the stimulatory regulator of adenylyl cyclase. We infer that these two receptors share with rhodopsin a common three-dimensional architecture and an activation switch that requires movement, relative to one another, of helices III and VI; these inferences are surprising in the case of the parathyroid hormone receptor, a receptor that contains seven stretches of hydrophobic sequence but whose amino acid sequence otherwise shows no apparent similarity to those of receptors in the rhodopsin family. These findings highlight the evolutionary conservation of the switch mechanism of serpentine receptors and help to constrain models of how the switch works.     

Method for enhancing solubility of the expressed recombinant proteins in Escherichia coli

The production of correctly folded protein in Escherichia coli is often challenging because of aggregation of the overexpressed protein into inclusion bodies. Although a number of general and protein-specific techniques are available, their effectiveness varies widely. We report a novel method for enhancing the solubility of overexpressed proteins. Presence of a dipeptide, glycylglycine, in the range of 100 mM to 1 M in the medium was found to significantly enhance the solubility (up to 170-fold) of the expressed proteins. The method has been validated using mycobacterial proteins, resulting in improved solubilization, which were otherwise difficult to express as soluble proteins in E. coli. This method can also be used to enhance the solubility of other heterologous recombinant proteins expressed in a bacterial system.     

Perinatal transmission of SHIV-SF162P3 in Macaca nemestrina

We developed a SHIV/macaque model of transmission from infected dams to their infants. Ten pregnant dams were infected intravenously with 100 MID(50) of macaque-titered SHIV-SF162P3 during the second trimester. Nine infants were born; the seven surviving beyond day of birth suckled for 6 months. Four of nine infants were infected (transmission rate = 44.4%), with one infection in utero, and three intrapartum and/or immediately post-birth via suckling. Varying levels of binding and neutralizing antibodies were transplacentally transferred to infants. Passive antibodies were detected in plasma on the day of birth and persisted for 5 weeks. Infants infected at or after birth controlled acute and post-acute viremia. Exposure to maternal SHIV-SF162P3 during birth and suckling in the presence of autologous maternal neutralizing antibodies may have affected transmission or pathogenesis in the infants. This transmission model can allow investigation of key parameters involved in perinatal transmission of HIV.     

Identification of a core set of genes that signifies pathways underlying cardiac hypertrophy

Although the molecular signals underlying cardiac hypertrophy have been the subject of intense investigation, the extent of common and distinct gene regulation between different forms of cardiac hypertrophy remains unclear. We hypothesized that a general and comparative analysis of hypertrophic gene expression, using microarray technology in multiple models of cardiac hypertrophy, including aortic banding, myocardial infarction, an arteriovenous shunt and pharmacologically induced hypertrophy, would uncover networks of conserved hypertrophy-specific genes and identify novel genes involved in hypertrophic signalling. From gene expression analyses (8740 probe sets, n = 46) of rat ventricular RNA, we identified a core set of 139 genes with consistent differential expression in all hypertrophy models as compared to their controls, including 78 genes not previously associated with hypertrophy and 61 genes whose altered expression had previously been reported. We identified a single common gene program underlying hypertrophic remodelling, regardless of how the hypertrophy was induced. These genes constitute the molecular basis for the existence of one main form of cardiac hypertrophy and may be useful for prediction of a common therapeutic approach. Supplementary material for this article can be found at: http://www.interscience.wiley.com/jpages/1531-6912/suppmat.     

Rapid upregulation of endothelial P-selectin expression via reactive oxygen species generation

Endothelial cell ICAM-1 upregulation in response to TNF-alpha is mediated in part by reactive oxygen species (ROS) generated by the endothelial membrane-associated NADPH oxidase and occurs maximally after 4 h as the synthesis of new protein is required. However, thrombin-stimulated P-selectin upregulation is bimodal, the first peak occurring within minutes. We hypothesize that this early peak, which results from the release of preformed P-selectin from within Weibel-Palade bodies, is mediated in part by ROS generated from the endothelial membrane-associated xanthine oxidase. We found that this rapid expression of P-selectin on the surface of endothelial cells was accompanied by qualitatively parallel increases in ROS generation. Both P-selectin expression and ROS generation were inhibited, dose dependently, by the exogenous administration of disparate cell-permeable antioxidants and also by the inhibition of either of the known membrane-associated ROS-generating enzymes NADPH oxidase or xanthine oxidase. This rapid, posttranslational cell signaling response, mediated by ROS generated not only by the classical NADPH oxidase but also by xanthine oxidase, may well represent an important physiological trigger of the microvascular inflammatory response.     

Regulation of cyclic adenosine 3',5'- monophosphate signaling and pulsatile neurosecretion by Gi-coupled plasma membrane estrogen receptors in immortalized gonadotrophin-releasing hormone neurons

Immortalized GnRH neurons (GT1-7) express receptors for estrogen [estrogen receptor-alpha and-13(ERa and ERI3)] and progesterone (progesterone receptor A) and exhibit positive immunostaining for both intracellular and plasma membrane ERs. Exposure of GT1-7 cells to picomolar estradiol concentrations for 5-60 min caused rapid, sustained,and dose-dependent inhibition of cAMP production. In contrast, treatment with nanomolar estradiol concentrations for 60 min increased cAMP production. The inhibitory and stimulatory actions of estradiol on cAMP formation were abolished by the ER antagonist, ICI 182,780. The estradiol-induced inhibition of cAMP production was prevented by treatment with pertussis toxin, consistent with coupling of the plasma membrane ER to an inhibitory G protein. Coimmunoprecipitation studies demonstrated an estradiol-regulated stimulatory interaction between ERa and G,3 that was prevented by the ER antagonist, ICI 182,780. Exposure of perifused GT1-7 cells and hypothalamic neurons to picomolar estradiol levels increased the GnRH peak interval, shortened peak duration, and increased peak amplitude. These findings indicate that occupancy of the plasma membrane-associated ERs expressed in GT1-7 neurons by physio-logical estradiol levels causes activation of a G, protein and modulates cAMP signaling and neuropeptide secretion.     

Multigene DNA prime-boost vaccines for SHIV89.6P

We assessed four prime-boost vaccine regimens with a Gene Gun component for SHIV89.6P in Macaca nemestrina. A dosing experiment using beta-galactosidase plasmid showed that 30 or 45 shots per dose elicited higher titer antibody than smaller doses. For SHIV89.6P, we administered a six-plasmid vaccine capable of producing non-infectious virions in vivo in combination with either vaccinia recombinants or inactivated virus. DNA prime/vaccinia boost, or the reverse, elicited strong immune responses. The SHIV89.6P challenge virus was grown in M. nemestrina peripheral blood mononuclear cells and titered in vivo intrarectally. As has been observed for SHIV89.6P in M. mulatta, the infected M. nemestrina experienced rapid and severe loss of circulating CD4+ T cells. Vaccinated macaques were challenged three weeks after the last boost. DNA prime/vaccina boost or vaccina prime/DNA boost protected 11/12 animals from acute CD4+ T cell depletion and disease, while other regimens were not effective.     

Some observations on the effect of Daflon (micronized purified flavonoid fraction of Rutaceae aurantiae) in bancroftian filarial lymphoedema

BACKGROUND: Morbidity management is a core component of the global programme for the elimination of lymphatic filariasis. In a double-blind clinical trial, the tolerability and efficacy of Daflon (500 mg) + DEC (25 mg) or DEC (25 mg) alone, twice daily for 90 days, was studied in 26 patients with bancroftian filarial lymphoedema. RESULTS: None of the patients in either drug group reported any adverse reaction throughout the treatment period (90 days). Haematological and biochemical parameters were within normal limits and there was no significant difference between the pre-treatment (day 0) and post-treatment (day 90) values. The group receiving Daflon showed significant reduction in oedema volume from day 90 (140.6 PlusMinus; 18.8 ml) to day 360 (71.8 PlusMinus; 20.7 ml) compared to the pre-treatment (day 0, 198.4 PlusMinus; 16.5 ml) value. This accounted for a 63.8% reduction in oedema volume by day 360 (considering the pre-treatment (day 0) as 100%). In the DEC group, the changes in oedema volume (between day 1 and day 360) were not significant when compared to the pre-treatment (day 0) value. The percentage reduction at day 360 was only 9%, which was not significant (P > 0.05). CONCLUSION: This study has shown that Daflon (500 mg, twice a day for 90 days) is both safe and efficacious in reducing oedema volume in bancroftian filarial lymphoedema. Further clinical trials are essential for strengthening the evidence base on the role of this drug in the morbidity management of lymphatic filariasis.