[Enrichment and screening of up-regulated genes of the mosquito Anopheles stephensi in response to malaria parasite]

OBJECTIVE

To isolate and identify genes related to malaria parasite infection in vector mosquito, and to explore the mechanisms.

METHODS

Anopheles stephensi infected with Plasmodium yoelii was used as tester (T) group, while uninfected but normal blood fed as driver (D) one. Engorged female mosquitoes of two groups were collected separately at 24 hours after biting. An enriched subtractive cDNA pool was generated through the course of suppression subtractive hybridization (SSH) and selective PCR amplification. The subtracted library was screened by hybridization using T and D cDNA mixture as probes, respectively. The positive clones, which produced stronger signal when probed with T than with D, were sequenced and their sequence homologues in GenBank database were searched with BLAST by internet.

RESULTS

The analysis of subtraction efficiency showed that the differentially expressed genes in T comparing to in D were enriched significantly. In dot blot screening, 24 of 58 randomly selected clones (41.4%) were shown up-regulation in malaria infected mosquitoes. The BLAST search of 23 genes revealed that 12 were homologous to functionally known genes, 4 were homologous to functionally unknown entries, and 7 were novel without any relatives. Nine of the 23 genes (39.1%) also hit homologous sequences in the An. gambiae EST database generated from an immune competent cell line treated with lipopolysaccharide (LPS).

CONCLUSION

An enriched cDNA pool of the mosquito genes which up-regulated responsively at the early stage of malaria parasite infection was obtained. Expression screening against the pool indicated that various biochemical processes and mechanisms might be involved in the response of mosquito to parasite infection, especially those related with the innate immune system and energy metabolism.

Transition Metal-Organic Polycarboxylate Coordination Polymer Chemistry. Hydrothermal Synthesis and Structural Characterization of a One-Dimensional Coordination Polymer [Fe(bzta)2(ox)]n (bzta = benzotriazole, ox = oxalato)

Complex [Fe(bzta)2(ox)]n (1) was synthesized from K3[Fe(ox)3]·3H2O and benzotriazole. Single-crystal X-ray diffraction study of complex 1 has established a novel structure containing several kinds of secondary bonding interactions. All these interactions make it display a three-dimensional supramolecular network.

[The bottleneck steps limiting maturation of penicillin G acylase in Escherichia coli]

We have identified the bottleneck steps limiting maturation of penicillin G acylase (PAC) through comparison of the maturation performance for various PAC-expression systems (Pac, Tac, T7, Vgb + T7) with different efficiencies of proteolysis, subunit folding and assembly. The maturation of PAC could be limited by various steps, such as translocation, periplasmic proteolysis, subunit folding and assembly depending on the host/vector systems. In BL21(pPA6) cells, maturation of PAC were limited by proteolysis and folding steps; the efficiency of proteolysis was 57.2%; the subunit folding and assembly capacity was 0.72. In BL21(pKKpacSP) cells, the stability and folding of alpha subunit was bottleneck steps. In T7 and dissolved-oxygen regulation expression systems, PAC proprecursor could be maturated efficiently. Results also indicate that the folding of alpha peptide plays a key role in folding of precursor for PAC in E. coli. Developing proper host/vector systems and fermentation technology with superior abilities on subunit folding and assembly of precursor for PAC could be plausible for enhancing production of PAC. In this study, pac could be expressed (transcribed, translated and maturated) efficiently under the control of T7 promoter.

Inhibition of malignant trophoblastic cell proliferation in vitro and in vivo by melatonin

Melatonin inhibited thymidine incorporation into human choriocarcinoma JEG-3 cells at physiological and pharmacological concentrations in the present study. Gene expression of MT2 receptor, but not that of mt1 receptor, was detected in JEG-3 cells by reverse transcription-polymerase chain reaction (RT-PCR). The gene expression profile of the two human melatonin receptor subtypes in JEG-3 cells was identical to that previously reported for JAr cells, whose proliferation had also been shown to be similarly inhibited by physiological and pharmacological concentrations of melatonin. In contrast, melatonin had no effect on thymidine incorporation into 3A-Sub-E cells (a transformed trophoblast cell line), in which gene expression of both receptor subtypes could not be detected. The data suggest that in human placental trophoblasts, a correlation may exist between MT2 receptor gene expression and the direct anti-proliferative action of melatonin. Although melatonin has been reported to induce G1/S delay in cell cycle progression of JAr cells, no significant changes in the percentages of JEG-3 cells in different cell cycle phases upon melatonin treatment was recorded by flow cytometric analysis. This indicates that G1/S transition delay is probably not an important cellular mechanism in the direct anti-proliferative action of melatonin on human JEG-3 cells in vitro. Furthermore, melatonin inhibited the growth of both JAr and JEG-3 xenograft tumors in athymic nude mice, and prolonged the survival of those animals that developed choriocarcinoma. While the number of apoptotic tumor cells was not increased by melatonin, the pineal hormone induced significant decreases in the numbers of JAr and JEG-3 cells expressing proliferating cell nuclear antigen (PCNA) and cyclin A in the tumors. Taking into account both the in vitro and in vivo findings, it is likely that the inhibitory effect of melatonin on choriocarcinoma JAr and JEG-3 cell proliferation in vivo is largely a direct action of the hormone on the tumor cells.

Pituitary prolactin-secreting tumor formation: recent developments

Prolactinoma is the most common type of primary pituitary tumors. It occurs more frequently in women than in men. Dopaminergic agonists are effective in the shrinkage of prolactin-secreting pituitary tumor and are preferred in some patients. However, pituitary radiotherapy may enable the long-term removal of prolactin-secreting tumor cells. Recent evidence suggests that prolactinoma is a heterogeneous disorder with complicated and multifactorial etiology and pathogenesis. Apparently, a thorough understanding of prolactinoma tumorigenesis would be important. To facilitate investigations on tumorigenesis of prolactinoma, animal models for prolactinomas have been developed. These models have expedited our progress in the recent years. Many researchers consider the F(344) rat to be the most sensitive strain of rats to estrogen (E(2))-induced prolactinoma formation. Nonetheless, E(2) treatment for 60 days also induces the formation of pituitary prolactin-secreting adenoma in male Sprague-Dawley (SD) rats. Evidently, the SD rat is also a good animal for prolactinoma investigations. Following E(2) implantation, prolactinomas developed in the eutopic adenohypophysis in situ and/or ectopic pituitary grafted under the renal capsule in SD rats. These observations favor the hypothesis that prolactinoma growth is the result of pathological changes in the adenohypophysis and/or hypothalamus. In the latter case, abnormal release of hypothalamic dopamine, GABA, or brain-gut peptides (such as cholecystokinin, vasoactive intestinal polypeptide, galanin, angiotensin, opioid peptide, gastrin, gastrin-releasing peptide, pancreatic polypeptide, and adrenocorticotropic hormone) results in some of the pathological changes that may lead to hyperprolactinemia and/or prolactinoma development. Dysregulation of prolactin synthesis and secretion may be the result of prolactin gene modulation. In E(2)-induced rat prolactinomas, prolactin mRNA contents and the expression of some proto-oncogenes, e.g. c-myc and c-ras, TGFalpha and TGFbeta1 mRNA were significantly changed. The above findings are consistent with results in human prolactinoma development. In addition, in rats abnormal expression of the prolactin gene was correlated with hypomethylated status of CpG sites in exons 1, 2 and 4 of the prolactin gene, as well as the increase in hypersensitive sites to DNase 1 in the encoding region of the prolactin gene. In E(2)-treated rats, a point mutation with a base substitution from cytidine (C) to adenine (A) was found at the -36-bp site of the proximal promoter of the prolactin gene in eutopic pituitary prolactinomas, but no change was observed in the same sequence of the prolactin gene in ectopic prolactinoma. The association of a base substitution with the hyperexpression of the prolactin gene in eutopic prolactinomas suggests that different mechanisms may mediate the formation of eutopic and ectopic prolactin-secreting tumors. Melatonin decreases the expression of the prolactin gene in vitro suggesting that this pineal hormone may be a potential anticarcinogen in vivo. It has also been shown that MT(2) (Mel(1b)) melatonin receptors are expressed in anterior pituitary cells. The use of melatonin as a preventive or therapeutic drug for prolactinomas should be further investigated. In summary, improved knowledge on tumorigenesis of prolactinomas, especially in the rat model, was noted. These E(2)-induced rat prolactinoma models would facilitate future investigations, and expected results shall be fruitful and exciting for the development of future drug designs for the prevention and/or treatment of prolactin-secreting pituitary tumors.

Melatonin-induced inhibition of proliferation and G1/S cell cycle transition delay of human choriocarcinoma JAr cells: possible involvement of MT2 (MEL1B) receptor

Melatonin, the pineal neurohormone, is an evolutionarily conserved photoperiodic signaling molecule with diverse functions that include the entrainment of human circadian rhythms. Although evidence supporting a direct inhibitory action of melatonin on human cancer cell proliferation exists in the literature, the molecular and cellular signaling mechanisms involved are largely undefined. In our study, significant inhibition of human choriocarcinoma JAr cell proliferation at physiological and pharmacological concentrations of melatonin was observed. 2-Iodomelatonin, a high affinity melatonin receptor agonist, was more potent than melatonin in inhibiting JAr cell proliferation. In addition, the presence of putative melatonin receptors in choriocarcinoma was suggested by the demonstration of specific 2-[125I]iodomelatonin binding to the tumor. Interestingly, the selective MT2 melatonin receptor ligand, 4-phenyl-2-propionamidotetraline (4-P-PDOT), was found to exert not only concentration-dependent anti-proliferative actions on JAr cells, but also additive effects with melatonin in inhibiting JAr cell proliferation. Furthermore, MT2 melatonin receptor gene expression by JAr cells was demonstrated by reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization (ISH). Taken together, our data suggest that the reported anti-proliferative action of melatonin on human choriocarcinoma JAr cells may be mediated, in part, by MT2 melatonin receptor. Moreover, analysis of melatonin effect on cell cycle kinetics indicated that G1/S transition delay may underlie the observed inhibition of choriocarcinoma cell proliferation by melatonin.

Formation of glycidyl methacrylate-DNA adducts in vivo

In in vivo test, rats were orally administrated with glycidyl methacrylate (GMA) at respective doses of 250 mg/kg, 125 mg/kg and 62.5 mg/kg, 31.25 mg/kg and solvent as control for 14 days. DNA adducts produced in the liver, kidney, blood and testis were analyzed by RP-HPLC and nuclease P1 mediated 32P-postlabelling method. Results showed that several potential GMA-DNA adducts were formed in various organs (4 adducts in blood, 3 adducts in liver and kidney, 1 adduct in testis). A linear dose-response relationship was observed within certain dose levels. The relative adduct labeling values failed to further increase any more when the concentration went up to 125 mg/kg. The order of adduct level with GMA was kidney, liver, blood and testis. The GMA adduct N3-methacrylate-2-hydroxypropyl-dCMP was found in kidney, liver and blood. These results indicated that GMA could react with negatively charged centers on DNA and form GMA-DNA adducts. If carcinogen induced DNA damage exceeds the ability of repair systems, gene mutation is induced. Therefore, study on molecular mechanism of gene mutation induced by DNA adducts is not only an important part of chemical-carcinogenesis, but also provides information on critical biomarkers for monitoring human exposure to genetic toxins.

Molecular and cellular analyses of melatonin receptor-mediated cAMP signaling in rat corpus epididymis

By using 2-[125I]iodomelatonin receptor binding studies, we have previously demonstrated high affinity melatonin receptors, the binding activities of which are regulated by testosterone, in the corpus epididymis of rats. In this report, some of the basic molecular and cellular characteristics of these high affinity melatonin receptors in rat corpus epididymis were analyzed. MEL1A and MEL1B receptor mRNAs were expressed by rat corpus epididymal epithelial cells as revealed by in situ hybridization. Functionally, these high affinity melatonin receptors are negatively coupled to adenylyl cyclase via pertussis toxin (PTX) sensitive Gi protein and the inhibitory effects of melatonin on forskolin-stimulated cAMP accumulation were enhanced by 5alpha-dihydrotestosterone (5alpha-DHT). Interestingly, opposing interactions between melatonin and beta-adrenergic receptor signaling in rat epididymal epithelial cells were observed with melatonin inhibiting norepinephrine- and isoproterenol-stimulated cAMP accumulation. In conclusion, our data support a modulatory action of melatonin, mediated via pertussis toxin-sensitive Gi-coupled MEL1A and MEL1B receptors, in androgenic and adrenergic regulation of rat corpus epididymal epithelial cell functions.

Ribosomal DNA difference between species A and D of the Anopheles dirus complex of mosquitoes from China

Species A and D of the Anopheles dirus complex were found in China. Ribosomal DNA second internal transcribed spacers (ITS2) of both species A and D were sequenced and found to be 716 and 710 base-pairs in length, respectively, with 69% GC content. No evidence of intraspecific variation was detected in the ITS2 sequence of species A, whereas the sequence of species D showed variation at one position in the ITS2. A large number of simple repeat motifs were dispersed throughout the ITS2 sequences. The level of interspecific difference was 5.4% of the nucleotide sequences. Some of the interspecific differences were located in regions with subrepeat structure.

Cellular H- and M-type lactate dehydrogenase (LDH) isoenzymes and tumour diagnosis--an immunohistochemical assessment

Cellular H- and M-type lactate dehydrogenase (LDH) isoenzymes were determined immunohistochemically in a wide range of normal, inflammatory, benign neoplastic, and malignant tissues to assess the possible value of the isoenzymes in tumour diagnosis. Both types of LDH were detected almost ubiquitously in normal tissues. Increased staining intensity of LDH, especially M-type LDH, was demonstrated in most types of malignant tumours studied. Similar increased staining intensity of the isoenzymes was also noted to parallel the proliferative activity of the cells in non-neoplastic diseases and benign neoplasms. The results suggest that changes of cellular H- and M-type LDH isoenzymes are not specific for any type of malignant tumours. The increase in cellular H- and M-type LDH isoenzymes appears to be related to proliferation of cells in general.

Budd-Chiari syndrome. Surgical treatment of 45 cases

Fourty-five patients with Budd-Chiari syndrome were treated surgically from December 1985 to May 1988. The procedures consisted of cavoatrial shunt, mesoatrial shunt, transcardiac membranotomy, splenopneumopexy, portal vein-systemic vein shunt and re-opened umbilical vein-right auricle shunt, etc. Two of the patients died postoperatively. Others showed improvement after follow-up for 3-24 months. Recurrent hemorrhage from varices did not occur after operation in all patients. The diagnosis, surgical indications, and various methods of surgery for Budd-Chiari syndrome were discussed.