Mast cell-/basophil-specific transcriptional regulation of human L-histidine decarboxylase gene by CpG methylation in the promoter region

L-Histidine decarboxylase (HDC) catalyzes the formation of histamine from L-histidine, and in hematopoietic cell lineages the gene is expressed only in mast cells and basophils. We attempted here to discover how HDC gene expression is restricted in these cells. In the cultured cell lines tested, only the mast cells and basophils strongly transcribed the HDC gene. However, in transient transfection analysis, the reporter constructs with the HDC promoter were active not only in expressing cells but also in nonexpressing cells. Detailed analyses of the HDC promoter region revealed that the GC box is essential for transactivation. Also, the promoter region of the HDC gene proved to be sensitive to DNase I and restriction endonucleases exclusively in HDC-expressing cells, suggesting that the promoter region is readily accessible to trans-acting factor(s). Furthermore, the promoter region in HDC-expressing cell lines was found to be selectively unmethylated. The correlation between HDC expression and hypomethylation was also found in primary human mast cells. Methylation of the HDC promoter in vitro reduced the luciferase reporter activity in transient expression analysis, suggesting that methylation of the promoter region is functionally important for HDC gene expression. These results imply that alteration of DNA methylation is one of the mechanisms regulating cell-specific expression of the HDC gene.     

Differential subsequence conservation of interspersed repetitive Streptococcus pneumoniae BOX elements in diverse bacteria

Evolutionary conservation of an interspersed repetitive DNA sequence, BOX, from Streptococcus pneumoniae was investigated to explore the mosaic nature of these elements. BOX elements consist of various combinations of three subunits, boxA, boxB, and boxC. Eight oligonucleotide probes were designed based on consensus DNA sequences of boxA, boxB, and boxC subunits. DNA hybridization studies and PCR using these probes/primers demonstrate that oligonucleotide sequences within the boxA subunit appear to be conserved among diverse bacterial species. The boxB and boxC subunits show only limited, if any, sequence conservation in bacteria other than S. pneumoniae. Intact BOX elements with boxA, boxB, and boxC subunits were only present in high copy number in pneumococcal strains. This pattern of differential conservation lends support to the modular nature of BOX repetitive elements in that boxA-like subsequences are effectively independent of boxB-like or boxC-like subunits in bacteria other than S. pneumoniae. Furthermore, dendrograms derived from repetitive sequence-based PCR (rep-PCR) fingerprints of S. pneumoniae isolates using the BOXA1R primer yielded clustering patterns that were similar to those obtained previously by other methods, suggesting that these repetitive sequence-based DNA fingerprints represent intrinsic properties of an S. pneumoniae strain's genome. Our results indicate widespread conservation of boxA-like subsequences in the bacterial kingdom, lend support to the mosaic nature of BOX in S. pneumoniae, and demonstrate the utility of boxA-based primers for rep-PCR fingerprinting of many microorganisms.     

The pathogenicity factors of Streptococcus pneumoniae strains causing meningitis

Pneumococcal meningitis was registered in St. Petersburg in 1985-1991, morbidity rate being 1.7-2.3 cases per 100,000 children, including 7.4-19.8 cases among children under 1 year. Two thirds of the pneumococcal strains isolated in cases of meningitis belonged to serovars 19, 1, 6, 15 and 2. The comparative study of pneumococcal strains revealed that the presence of capsules, pneumolysin, high hyaluronidase activity or belonging to serovars 1 and 2 (irrespective of their hyaluronidase titers) were the most important factors contributing to the development of generalized infection. The role of such a factor as virulence for mice is not yet clear.     

Structure of the has operon promoter and regulation of hyaluronic acid capsule expression in group A Streptococcus

The death of poliovirus-infected cells may occur in two forms: canonical cytopathic effect (CPE) (on productive infections) or apoptosis (when the viral reproduction is hindered by certain drugs or some other restrictive conditions). Morphological manifestations of the CPE and apoptosis, being distinct, share some traits (e.g., chromatin condensation and nuclear deformation). It was shown here that a permeable caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-(OMe) fluoromethyl ketone (zVAD.fmk), prevented the development of the poliovirus-induced apoptosis on abortive infection. The apoptotic pathway could be dissected by an inhibitor of chymotrypsin-like serine proteases, N-tosyl-l-phenylalanine chloromethyl ketone (TPCK), which prevented the cleavage of DNA to oligonucleosome-sized pieces and nuclear fragmentation but did not suppress cellular shrinkage, cytoplasmic blebbing, and partial chromatin condensation. These results demonstrate that caspase activation is involved in the execution phase of the viral apoptosis and suggest that a nuclear subset of the apoptotic program is under a separate control, involving a TPCK-sensitive event. Neither zVAD.fmk nor TPCK, at the concentrations affecting the apoptotic response, exerted appreciable influence on the virus growth or cellular pathological changes on productive infection, indicating that the pathways leading to the poliovirus-evoked CPE and apoptosis are different.     

Reduction by cefodizime of the pulmonary inflammatory response induced by heat-killed Streptococcus pneumoniae in mice

It has recently become apparent that overwhelming inflammatory reactions contribute to the high mortality rate associated with pneumococcal infection in immunocompetent hosts. Cefodizime (CEF) is an antibiotic that seems to be endowed with immunomodulating properties. To investigate the influence of CEF on the pulmonary inflammatory response induced by Streptococcus pneumoniae, we infected mice with repeated intranasal inoculations of 10(7) CFU of heat-killed fluorescein isothiocyanate-labeled bacteria, which are insensitive to the killing properties of the drug. CEF downregulated but did not abolish the strong polymorphonuclear leukocyte (PMN) recruitment induced by S. pneumoniae. PMN recruitment was not primarily mediated by leukotriene B4 in this model. The drug did not interfere with intrinsic mechanisms of phagocytosis by PMNs and alveolar macrophages. CEF totally abrogated the pneumococcus-induced tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) secretion in bronchoalveolar lavage fluid. The drug also prevented IL-6 release in lung homogenates and partly inhibited TNF-alpha, but it did not interfere with IL-1alpha secretion in the lungs of infected mice. The fractional and selective downregulation of inflammatory cells and cytokines by CEF suggests cell-specific and intracellular specific mechanisms of interaction of the drug. The immunomodulatory properties of CEF may help restrain excessive inflammatory reactions, thus contributing to the reported good clinical efficacy of the drug against lower respiratory tract infections.