Biomedical subjects

David J Banks

Publications and source records attributed to David J Banks.

7 recordsLinked to original sources

PubMed2006

SILENCE: a new forward genetic technology.

Silencing induced by long terminal repeat (LTR)-encoded cis-acting response element, termed SILENCE, is a forward genetic system that allows for conditional, epigenetic control of host-gene transcription. This new research tool is independent of gene mutation or disruption, does not require complementation, and conditional gene repression appears complete at the level of protein function. SILENCE functions in hypodiploid cells and is a platform technology with broad applications in gene discovery.

Animals↗

PubMed2006

New insights into the functions of anthrax toxin.

Anthrax is the disease caused by the Gram-positive bacterium Bacillus anthracis. Two toxins secreted by B. anthracis - lethal toxin (LT) and oedema toxin (OT) - contribute significantly to virulence. Although these toxins have been studied for half a century, recent evidence indicates that LT and OT have several roles during infection not previously ascribed to them. Research on toxin-induced effects other than cytolysis of target cells has revealed that LT and OT influence cell types previously thought to be insensitive to toxin. Multiple host factors that confer sensitivity to anthrax toxin have been identified recently, and evidence indicates that the toxins probably contribute to colonisation and invasion of the host. Additionally, the toxins are now known to cause a wide spectrum of tissue and organ pathophysiologies associated with anthrax. Taken together, these new findings indicate that anthrax-toxin-associated pathogenesis is much more complex than has been traditionally recognised.

Animals↗

PubMed2005

Anthrax toxin receptor 2 mediates Bacillus anthracis killing of macrophages following spore challenge.

Initiation of inhalation anthrax is believed to involve phagocytosis of Bacillus anthracis spores by alveolar macrophages, followed by spore germination within the phagolysosome. In order to establish a systemic infection, it is predicted that bacilli then escape from the macrophage and replicate extracellularly. Mechanisms utilized by B. anthracis to escape from the macrophage are not well characterized, but a role for anthrax toxin has been proposed. Here we report the isolation of an anthrax toxin-resistant cell line (R3D) following chemical mutagenesis of toxin-sensitive RAW 264.7 murine macrophage cells. Both R3D and RAW 264.7 cells phagocytize spores of a B. anthracis Sterne strain. However, RAW 264.7 cells are killed following spore challenge, whereas R3D cells survive. Resistance to toxin and spore challenge correlates with loss of expression of anthrax toxin receptor 2 (ANTXR2/CMG-2). When R3D cells are complemented with cDNA encoding either murine ANTXR2 or human anthrax toxin receptor 1 (ANTXR1/TEM-8), toxin and spore challenge susceptibility are restored, indicating that over-expression of either ANTXR can confer susceptibility to anthrax spore challenge. Taken together, these results indicate that anthrax toxin expression by the germinated spore enables B. anthracis killing of the macrophage from within.

Animals↗

PubMed2004

Progress toward characterization of the group A Streptococcus metagenome: complete genome sequence of a macrolide-resistant serotype M6 strain.

We describe the genome sequence of a macrolide-resistant strain (MGAS10394) of serotype M6 group A Streptococcus (GAS). The genome is 1,900,156 bp in length, and 8 prophage-like elements or remnants compose 12.4% of the chromosome. A 8.3-kb prophage remnant encodes the SpeA4 variant of streptococcal pyrogenic exotoxin A. The genome of strain MGAS10394 contains a chimeric genetic element composed of prophage genes and a transposon encoding the mefA gene conferring macrolide resistance. This chimeric element also has a gene encoding a novel surface-exposed protein (designated "R6 protein"), with an LPKTG cell-anchor motif located at the carboxyterminus. Surface expression of this protein was confirmed by flow cytometry. Humans with GAS pharyngitis caused by serotype M6 strains had antibody against the R6 protein present in convalescent, but not acute, serum samples. Our studies add to the theme that GAS prophage-encoded extracellular proteins contribute to host-pathogen interactions in a strain-specific fashion.

Alleles↗

PubMed2003

Structure and distribution of an unusual chimeric genetic element encoding macrolide resistance in phylogenetically diverse clones of group A Streptococcus.

The resistance of group A Streptococcus (GAS) to macrolide antibiotics is now a worldwide problem. Preliminary sequencing of the genome of an erythromycin-resistant serotype M6 clone that was responsible for a pharyngitis outbreak in Pittsburgh, Pennsylvania, was conducted to determine the structure of the genetic element containing the mefA gene, which encodes a macrolide efflux protein. The mefA gene is associated with a 58.8-kb chimeric genetic element composed of a transposon inserted into a prophage. This element also encodes a putative extracellular protein with a cell-wall anchoring motif (LPKTG) located at the carboxyterminus. The mefA element was present in phylogenetically diverse GAS strains isolated throughout the United States. Culture supernatants, prepared after mitomycin C treatment, of a strain representing the outbreak clone contained mefA element DNA in a DNAse-resistant form. Together, these data provide new information about the molecular genetic basis of macrolide resistance and dissemination in GAS strains.

Amino Acid Motifs↗

PubMed2003

Prophage induction and expression of prophage-encoded virulence factors in group A Streptococcus serotype M3 strain MGAS315.

The genome of the highly virulent group A Streptococcus (GAS) serotype M3 strain MGAS315 has six prophages that encode six proven or putative virulence factors. We examined prophage induction and expression of prophage-encoded virulence factors by this strain under in vitro conditions inferred to approximate in vivo conditions. Coculture of strain MGAS315 with Detroit 562 (D562) human epithelial pharyngeal cells induced the prophage encoding streptococcal pyrogenic exotoxin K (SpeK) and extracellular phospholipase A(2) (Sla) and the prophage encoding streptodornase (Sdn). Increased gene copy numbers after induction correlated with increased speK, sla, and sdn transcript levels. Although speK and sla are located contiguously in prophage Phi315.4, these genes were transcribed independently. Whereas production of immunoreactive SpeK was either absent or minimal during coculture of GAS with D562 cells, production of immunoreactive Sla increased substantially. In contrast, despite a lack of induction of the prophage encoding speA during coculture of GAS with D562 cells, the speA transcript level and production of immunoreactive streptococcal pyrogenic exotoxin A (SpeA) increased. Exposure of strain MGAS315 to hydrogen peroxide, an oxidative stressor, induced the prophage encoding mitogenic factor 4 (MF4), and there was a concomitant increase in the mf4 transcript. All prophages of strain MGAS315 that encode virulence factors were induced during culture with mitomycin C, a DNA-damaging agent. However, the virulence factor gene transcript levels and production of the encoded proteins decreased after mitomycin C treatment. Taken together, the results indicate that a complex relationship exists among environmental culture conditions, prophage induction, and production of prophage-encoded virulence factors.

Bacterial Proteins↗

PubMed2002

The fundamental contribution of phages to GAS evolution, genome diversification and strain emergence.

The human bacterial pathogen group A Streptococcus (GAS) causes many different diseases including pharyngitis, tonsillitis, impetigo, scarlet fever, streptococcal toxic shock syndrome, necrotizing fasciitis and myositis, and the post-infection sequelae glomerulonephritis and rheumatic fever. The frequency and severity of GAS infections increased in the 1980s and 1990s, but the cause of this increase is unknown. Recently, genome sequencing of serotype M1, M3 and M18 strains revealed many new proven or putative virulence factors that are encoded by phages or phage-like elements. Importantly, these genetic elements account for an unexpectedly large proportion of the difference in gene content between the three strains. These new genome-sequencing studies have provided evidence that temporally and geographically distinct epidemics, and the complex array of GAS clinical presentations, might be related in part to the acquisition or evolution of phage-encoded virulence factors. We anticipate that new phage-encoded virulence factors will be identified by sequencing the genomes of additional GAS strains, including organisms non-randomly associated with particular clinical syndromes.

Amino Acid Sequence↗