RESUMO
Edwardsiella piscicida is an important fish pathogen with a broad host that causes substantial economic losses in the aquaculture industry. Ferric uptake regulator (Fur) is a global transcriptional regulator and contains two typical domains, the DNA-binding domain and dimerization domain. In a previous study, we obtained a mutant strain of full-length fur of E. piscicida, TX01Δfur, which displayed increased siderophore production and stress resistance factors and decreased pathogenicity. To further reveal the regulatory mechanism of Fur, the DNA-binding domain (N-terminal) of Fur was knocked out in this study and the mutant was named TX01Δfur2. We found that TX01Δfur2 displayed increased siderophore production and enhanced adversity tolerance, including a low pH, manganese, and high temperature stress, which was consistent with the phenotype of TX01Δfur. Contrary to TX01Δfur, whose virulence was weakened, TX01Δfur2 displayed an ascended invasion of nonphagocytic cells and enhanced destruction of phagocytes via inducing overpowering or uncontrollable pyroptosis, which was confirmed by the fact that TX01Δfur2 induced higher levels of cytotoxicity, IL-1ß, and p10 in macrophages than TX01. More importantly, TX01Δfur2 displayed an increased global virulence to the host, which was confirmed by the result that TX01Δfur2 caused higher lethality outcomes for healthy tilapias than TX01. These results demonstrate that the mutation of the Fur N-terminal domain augments the resistance level against the stress and pathogenicity of E. piscicida, which is not dependent on the bacterial number in host cells or host tissues, although the capabilities of biofilm formation and the motility of TX01Δfur2 decline. These interesting findings provide a new insight into the functional analysis of Fur concerning the regulation of virulence in E. piscicida and prompt us to explore the subtle regulation mechanism of Fur in the future.
RESUMO
Previous studies report the upregulation of the secretory Rab27B small GTPase in human breast cancer, which could promote invasive growth and metastasis in estrogen receptor (ER)-positive breast cancer cells. However, there is limited evidence for its role in ER-negative breast cancer, along with the signaling pathways. Consistent with previous studies, we here confirmed that Rab27B is upregulated in breast tumor tissue in comparison with normal breast tissue. In addition, in ER-negative breast cancer cell line MDA-MB-231, when the levels of Rab27B expression were further elevated by transduction with recombinant lentivirus vector, migration and invasion assays demonstrated that cell migration and invasion was significantly stimulated. Moreover, Rab27B overexpression increased levels of ß-catenin, followed by upregulation of vascular endothelial growth factor (VEGF). Our findings reveal a key function for the Rab27B-mediated modulation of ß-catenin and VEGF in ER-negative breast cancer cell metastasis. Notably, the suppressed expression of Rab27B, ß-catenin and VEGF was found in calycosin-treated MDA-MB-231 cells, accompanied with decreased invasive and migratory potential of these cells. What's more, these inhibitory effects of calycosin were all attenuated by Rab27B overexpression. The results demonstrated that calycosin-induced inhibition of migration and invasion in ER-negative breast cancer cells may be associated with the inactivation of Rab27B-dependent signaling, and suggest that antagonism of this pathway by calycosin may offer alternative therapeutic strategy for the aggressive breast cancer.
