Studies on the angiotensin-converting enzyme and the kinin B2 receptor in the rabbit jugular vein: modulation of contractile response to bradykinin

The rabbit jugular vein (rbJV) was used as a bioassay system to validate some early and new hypothetical interactions between the angiotensin-converting enzyme (ACE) and the B2 receptor, which may be influenced by ACE inhibitors (ACE-I). These involve the potentiation of the contractile effect of bradykinin (BK) and BK analogues, which are inactivated by ACE (e.g., [Hyp3, Tyr(Me8)]-BK (R556)), the prevention of BK-induced B2 receptor desensitisation, and the restoration of receptor sensitivity in tissues desensitised with B2 receptor agonists. Enzymatic degradation studies performed in vitro and in vivo revealed that BK and R556 are readily degraded by rabbit ACE whereas [Phe8psi(CH2-NH)Arg9]-BK (R379) is totally resistant. BK, R556, and R379 contracted endothelium-denuded veins with similar potencies (pEC50 range 8.10-8.50). Tissues pretreated with ACE-I showed an increase in pEC50 values for BK and R556 but not for R379. ACE-I (captopril, enalaprilat) were unable to prevent B2 receptor desensitisation induced by BK (1 microM). ACE-I partially restored B2 receptor-mediated contraction in tissues initially exposed to BK but not to R379. These effects were antagonised by HOE 140 (0.1 microM) but were unaffected by AcLys[Dbeta-Nal7, Ile8]-desArg9BK (R715) (1 microM) or by Losartan (1 microM). In conclusion, the potentiation of BK and its analogues relates exclusively on prevention of their metabolism, B2 receptor desensitisation is not affected by ACE-I, and restoration of tissue responsiveness to BK by ACE-I may be attributed to changes in BK concentrations in the vicinity of the B2 receptor.     

LTD₄ induces HB-EGF-dependent CXCL8 release through EGFR activation in human bronchial epithelial cells

Airway epithelial cells release proinflammatory mediators that may contribute to airway remodeling and leukocyte recruitment. We explored the hypothesis that leukotriene D? (LTD?) may trigger the release of proremodeling factors through activation of the EGF receptor (EGFR). We particularly focused on the effects of LTD? on release of heparin-binding EGF-like factor (HB-EGF) and IL-8 (CXCL8), a potent neutrophil chemoattractant that may be released downstream of EGFR activation. To address this hypothesis, both primary (NHBE) and transformed bronchial human epithelial cells (BEAS-2B) were grown on an air-liquid interface and stimulated with LTD?. HB-EGF and CXCL8 were evaluated by ELISA in cell culture supernatants. To explore the EGFR signaling pathway, we used a broad-spectrum matrix metalloproteinase (MMP) inhibitor, GM-6001, two selective EGFR tyrosine kinase inhibitors, AG-1478 and PD-153035, an HB-EGF neutralizing antibody, and a specific small interfering RNA (siRNA) against the EGFR. Expression of the CysLT? cysteinyl leukotriene receptor was demonstrated by RT-PCR and immunocytochemistry in both BEAS-2B and NHBE cells. Four hours after stimulation with LTD?, HB-EGF and CXCL8 were significantly increased in cell culture supernatant. GM-6001 and montelukast, a specific CysLT? receptor antagonist, blocked the LTD?-induced increase in HB-EGF. All inhibitors/antagonists decreased LTD?-induced CXCL8 release. siRNA against EGFR abrogated CXCL8 release following stimulation with LTD? and exogenous HB-EGF. These findings suggest LTD? induced EGFR transactivation through the release of HB-EGF in human bronchial epithelial cells with downstream release of CXCL8. These effects may contribute to epithelial-mediated airway remodeling in asthma and other conditions associated with cysteinyl leukotriene release.     

The protein that binds to DNA base J in trypanosomatids has features of a thymidine hydroxylase

Trypanosomatids contain an unusual DNA base J (beta-d-glucosylhydroxymethyluracil), which replaces a fraction of thymine in telomeric and other DNA repeats. To determine the function of base J, we have searched for enzymes that catalyze J biosynthesis. We present evidence that a protein that binds to J in DNA, the J-binding protein 1 (JBP1), may also catalyze the first step in J biosynthesis, the conversion of thymine in DNA into hydroxymethyluracil. We show that JBP1 belongs to the family of Fe(2+) and 2-oxoglutarate-dependent dioxygenases and that replacement of conserved residues putatively involved in Fe(2+) and 2-oxoglutarate-binding inactivates the ability of JBP1 to contribute to J synthesis without affecting its ability to bind to J-DNA. We propose that JBP1 is a thymidine hydroxylase responsible for the local amplification of J inserted by JBP2, another putative thymidine hydroxylase.     

Protease-activated receptor 2 in regulation of bronchomotor tone: effect of tobacco smoking

Protease-activated receptors are G protein-coupled receptors activated by serine-proteases. Protease-activated receptor 2 is involved in the regulation of airway smooth muscle tone but its effects vary according to species and experimental conditions. We determined the effects of protease-activated receptor 2 activation on smooth muscle tone and airway reactivity to histamine in guinea pigs and smoking or non-smoking humans. The effects of trypsin and protease-activated receptor activating peptide on the isometric tension and response to histamine of guinea pig tracheal and human bronchial rings were studied. Human tissues were obtained from 6 smokers and 4 non-smokers. We assessed the effects of epithelial removal, inhibitors of cyclooxygenases, nitric oxide synthases, neutral endopeptidase and antagonists of acetylcholine, histamine, bradykinin and tachykinin receptors. Bronchomotor responses to protease-activated receptor 2 activation were variable in guinea pig, in half of animals PAR2 activation induced smooth muscle relaxation through the epithelial release of prostanoids but not of nitric oxide. In human airways, protease-activated receptor 2 activation reduced responsiveness to histamine in bronchial rings from smokers but increased responsiveness in bronchi from non-smokers. This study demonstrates an influence of tobacco smoking on the effect of protease-activated receptor 2 activation on airway responsiveness in humans, with an increased protection against histamine-induced contractions, probably through an increased epithelial release of prostanoids. The role of airway protease-activated receptor 2 may be to maintain smooth muscle tone homeostasis.     

Olfactory attraction of egg parasitoids to virgin females of noctuid stemborers

To locate hosts, egg parasitoids rely on infochemicals of the adult host stage, e.g. pheromones, rather than cues emitted by the inconspicuous egg themselves. Here, we show that three different egg parasitoid species the scelionids Telenomus busseolae Gahan and Telenomus isis Polaszek and the trichogrammatid Trichogramma bournieri Pintureau & Babault were attracted to both calling and non-calling females of the noctuids Busseola fusca (Fuller), Sesamia calamistis (Hampson) and Sesamia nonagrioides (Lefebvre). In Y-tube olfactometer experiments this study revealed a preference of all three parasitoids for non-calling (general odors of virgin females) and calling moth (sex pheromone) over the control (clean air), and for calling over the non-calling moth. However, the three parasitoids were equally attracted to calling moth of B. fusca and S. calamistis indicating low host specificity. The findings indicated that all three parasitoids used the pheromones released by the calling moth in host finding. It is suggested that the low host specificity may affect egg parasitism of the target pest in crop fields.     

Characteristics of Spinach Chloroplast Envelope, Thylakoid and Stroma Polypeptides as Revealed by Triton X-114 Phase Partition

Comparison of the SDS-PAGE profiles of the spinach chloroplaststroma, thylakoid and envelope membranes shows that severalpolypeptides have the same electrophoretic mobility. To simplifythese somewhat complex electrophoretic profiles and to verifywhether the polypeptides having similar electrophoretic mobilityare identical, we used Triton X-114 phase partition to obtaina separation of the polypeptides according to their relativehydrophobicity. The stroma polypeptides partitioned essentiallyin the aqueous phase. About half of the thylakoid and envelopemembrane polypeptides were exclusively recovered in either oneof the two phases. Therefore, the phase partitioning of membranepolypeptides proved to be useful, as the organic phase containedtrue intrinsic polypeptides, while the aqueous phase was composedof peripheral ones and stroma components. Particularly interestingwas the release of the RubisCO large subunit known to copurifywith the envelope membranes. Additional experimental approacheswere used (immunology, proteosynthesis in organello) to furthercharacterize proteins which had apparent ambiguous phase partitioning.Here, we show that Triton X-l 14 is an excellent tool to unmaskpolypeptides having identical electrophoretic mobility but differentbehaviour towards this detergent; its use leads to a clarificationof the polypeptide SDS-PAGE profiles of chloroplast membranes. (Received April 2, 1990; Accepted August 28, 1990)     

Influence of Dietary Experience on the Induction of Preference of Adult Moths and Larvae for a New Olfactory Cue

In Lepidoptera, host plant selection is first conditioned by oviposition site preference of adult females followed by feeding site preference of larvae. Dietary experience to plant volatile cues can induce larval and adult host plant preference. We investigated how the parent’s and self-experience induce host preference in adult females and larvae of three lepidopteran stem borer species with different host plant ranges, namely the polyphagous Sesamia nonagrioides, the oligophagous Busseola fusca and the monophagous Busseola nairobica, and whether this induction can be linked to a neurophysiological phenotypic plasticity. The three species were conditioned to artificial diet enriched with vanillin from the neonate larvae to the adult stage during two generations. Thereafter, two-choice tests on both larvae and adults using a Y-tube olfactometer and electrophysiological (electroantennography [EAG] recordings) experiments on adults were carried out. In the polyphagous species, the induction of preference for a new olfactory cue (vanillin) by females and 3^rd instar larvae was determined by parents’ and self-experiences, without any modification of the sensitivity of the females antennae. No preference induction was found in the oligophagous and monophagous species. Our results suggest that lepidopteran stem borers may acquire preferences for new olfactory cues from the larval to the adult stage as described by Hopkins’ host selection principle (HHSP), neo-Hopkins’ principle, and the concept of ‘chemical legacy.’