VEGF, upon binding to its endothelial cell specific receptors VEGF-R1 and VEGF-R2, can induce endothelial cell migration, proliferation and angiogenesis. However, the molecular mechanism of these effects still remains unclear. In this study, we investigated whether VEGF promotes human umbilical vascular endothelial cell (HUVEC) migration and proliferation through activator protein-1 transcription factor (AP-1) family. We first showed that VEGF induces immediate-early genes AP-1 family gene expression differentially with the profound induction of JunB (both mRNA and protein) under various conditions (PBS, DMSO or control adenoviruses). The increase in AP-1 mRNA expression occurs primarily at the transcriptional level. Inhibition of AP-1 DNA binding activity by adenovirus expressing a potent dominant negative form of c-Fos (Afos) significantly attenuated VEGF-induced HUVEC migration and proliferation and cyclin D1 expression. Knockdown of JunB with adenovirus expressing JunB shRNA reduces VEGF-induced JunB expression and attenuated HUVEC migration. However the shJunB-expressing virus has no effect on VEGF-induced cyclin D1 protein expression and proliferation. These results suggest that VEGF-induced endothelial migration is mediated primarily by induction of JunB whereas the promotion of endothelial proliferation by VEGF is mediated by JunB-independent AP-1 family members.

Patients with overexpression of CD44s and CD44v6 and low expression of nm23 mRNA have a higher lymph node metastatic rate and invasion. In addition, overexpression of CD44v6 is closely related to the degree of cell differentiation. Detection of the three genes is able to provide a reliable index to evaluate the invasion and metastasis of tumor cells.

BackgroundN-acylhomoserine lactone (AHL)-based quorum sensing (QS) systems have been described in many plant-associated Gram-negative bacteria to control certain beneficial phenotypic traits, such as production of biocontrol factors and plant growth promotion. However, the role of AHL-mediated signalling in the endophytic strains of plant-associated Serratia is still poorly understood. An endophytic Serratia sp. G3 with biocontrol potential and high levels of AHL signal production was isolated from the stems of wheat and the role of QS in this isolate was determined.ResultsStrain G3 classified as Serratia plymuthica based on 16S rRNA was subjected to phylogenetic analysis. Using primers to conserved sequences of luxIR homologues from the Serratia genus, splIR and spsIR from the chromosome of strain G3 were cloned and sequenced. AHL profiles from strain G3 and Escherichia coli DH5α expressing splI or spsI from recombinant plasmids were identified by liquid chromatography-tandem mass spectrometry. This revealed that the most abundant AHL signals produced by SplI in E. coli were N-3-oxo-hexanoylhomoserine lactone (3-oxo-C6-HSL), N-3-oxo-heptanoylhomoserine lactone (3-oxo-C7-HSL), N-3-hydroxy-hexanoylhomoserine lactone (3-hydroxy-C6-HSL), N-hexanoylhomoserine lactone (C6-HSL), and N-heptanoyl homoserine lactone (C7-HSL); whereas SpsI was primarily responsible for the synthesis of N-butyrylhomoserine lactone (C4-HSL) and N-pentanoylhomoserine lactone (C5-HSL). Furthermore, a quorum quenching analysis by heterologous expression of the Bacillus A24 AiiA lactonase in strain G3 enabled the identification of the AHL-regulated biocontrol-related traits. Depletion of AHLs with this lactonase resulted in altered adhesion and biofilm formation using a microtiter plate assay and flow cells coupled with confocal laser scanning microscopy respectively. This was different from the closely related S. plymuthica strains HRO-C48 and RVH1, where biofilm formation for both strains is AHL-independent. In addition, QS in G3 positively regulated antifungal activity, production of exoenzymes, but negatively regulated production of indol-3-acetic acid (IAA), which is in agreement with previous reports in strain HRO-C48. However, in contrast to HRO-C48, swimming motility was not controlled by AHL-mediated QS.ConclusionsThis is the first report of the characterisation of two AHL-based quorum sensing systems in the same isolate of the genus Serratia. Our results show that the QS network is involved in the global regulation of biocontrol-related traits in the endophytic strain G3. However, although free-living and endophytic S. plymuthica share some conservation on QS phenotypic regulation, the control of motility and biofilm formation seems to be strain-specific and possible linked to the life-style of this organism.

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Biological control is being considered as an alternative or a supplemental way of reducing the use of chemicals in agriculture. An endophytic strain G3 with potential as a biocontrol agent was isolated from the stems of Triticum aestivum L. It was classified by 16S rDNA sequencing as a member of Serratia. Strain G3 displayed a broad spectrum of antifungal activity in vitro against a number of phytopathogens such as Botrytis cinerea, Cryphonectria parasitica, Rhizoctonia cerealis and Valsa sordida. Molecular mechanisms involved in biocontrol by Serratia sp. G3 was investigated for its potential application to plant health management. The results showed that G3 produces an array of antimicrobial exoproducts, including chitinase, protease, antibiotic pyrrolnitrin, and siderophores for iron competition. Moreover, it also produced the plant growth hormone indole-3-acetic acid, suggesting that multiple mechanisms and their synergistic effects may be involved in biocontrol of plant diseases. Additionally, strain G3 can produce at least ten N-acyl homoserine lactones (AHLs) signal molecules for cell to cell communication, including unsubstituted, 3-oxo, and 3-hydroxy at the C3 position through liquid chromatography-tandem mass spectrometry (LC-MS/MS), which is different from the previously reported Serraia species. For the first time, N-3-oxo-heptanoyl-homoserine lactone, one of the main molecules was reported in the genus Serratia. The role of AHL-dependent quorum sensing system in the interactions between the endophytic strain G3 and host plants and its potential application in improving biocontrol efficacy will be further explored.