Browsing Department of molecular bacteriology (MOBA) by Subjects
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Mast cells initiate early anti-Listeria host defences.The Gram-positive bacterium Listeria monocytogenes (L. m.) is the aetiological agent of listeriosis. The early phase listeriosis is characterized by strong innate host responses that play a major role in bacterial clearance. This is emphasized by the fact that mice deficient in T and B cells have a remarkable ability to control infection. Mast cells, among the principal effectors of innate immunity, have largely been studied in the context of hyper-reactive conditions such as allergy and autoimmune diseases. In the present study, we evaluated the significance of mast cells during the early phase of listeriosis. Compared with controls, mice depleted of mast cells showed hundred-fold higher bacterial burden in spleen and liver and were significantly impaired in neutrophil mobilization. Although L. m. interacts with and triggers mast cell degranulation, bacteria were hardly found within such cells. Mainly neutrophils and macrophages phagozytosed L. m. Thus, mast cells control infection not via direct bacterial uptake, but by initiating neutrophils influx to the site of infection. We show that this is initiated by pre-synthesized TNF-alpha, rapidly secreted by mast cell upon activation by L. m. We also show that upon recruitment, neutrophils also become activated and additionally secrete TNF-alpha thus amplifying the anti-L. m. inflammatory response.
Methylome analysis and integrative profiling of human HCCs identify novel protumorigenic factors.To identify new tumor-suppressor gene candidates relevant for human hepatocarcinogenesis, we performed genome-wide methylation profiling and vertical integration with array-based comparative genomic hybridization (aCGH), as well as expression data from a cohort of well-characterized human hepatocellular carcinomas (HCCs). Bisulfite-converted DNAs from 63 HCCs and 10 healthy control livers were analyzed for the methylation status of more than 14,000 genes. After defining the differentially methylated genes in HCCs, we integrated their DNA copy-number alterations as determined by aCGH data and correlated them with gene expression to identify genes potentially silenced by promoter hypermethylation. Aberrant methylation of candidates was further confirmed by pyrosequencing, and methylation dependency of silencing was determined by 5-aza-2'-deoxycytidine (5-aza-dC) treatment. Methylation profiling revealed 2,226 CpG sites that showed methylation differences between healthy control livers and HCCs. Of these, 537 CpG sites were hypermethylated in the tumor DNA, whereas 1,689 sites showed promoter hypomethylation. The hypermethylated set was enriched for genes known to be inactivated by the polycomb repressive complex 2, whereas the group of hypomethylated genes was enriched for imprinted genes. We identified three genes matching all of our selection criteria for a tumor-suppressor gene (period homolog 3 [PER3], insulin-like growth-factor-binding protein, acid labile subunit [IGFALS], and protein Z). PER3 was down-regulated in human HCCs, compared to peritumorous and healthy liver tissues. 5-aza-dC treatment restored PER3 expression in HCC cell lines, indicating that promoter hypermethylation was indeed responsible for gene silencing. Additionally, functional analysis supported a tumor-suppressive function for PER3 and IGFALS in vitro. CONCLUSION: The present study illustrates that vertical integration of methylation data with high-resolution genomic and transcriptomic data facilitates the identification of new tumor-suppressor gene candidates in human HCC.