Transcript Document 7741184

Who cares about Rho GTPases?
Clostridium spp.
Salmonella spp.
Bordetella spp.
http://www.geocities.com/CapeCanaveral/3504/gallery.htm
Neisseria spp.
Historical GTPase Events
• 1985 – isolation of Rho = ‘Ras homolog’
• 1989 – C3 transferase shown to inactivate
RhoC => actin disruption in host cells.
Isolation of Rac = ‘Ras substrate of C3’.
• 1990’s – Rho/Rac GTPases shown to act
as switches to control membrane
receptors and actin cytoskeleton plasticity.
Salmonella enterica
Type III Secretion
System (TTSS) for
translocation of
virulence factors
http://info.med.yale.edu/micropath/g
alan/Pages/galan_overview.html
Salmonella chaperone proteins
…after effector translocation…
Bacterial changes:
transient bacterial
‘invasome’ appendages
Host cell changes: macropinocytosis for uptake of
Salmonella in nonphagocytic cells
bacterial induced
apoptosis in
phagocytic cells.
Salmonella
invasion
summary
http://info.med.yale.edu/micropath/galan/
Pages/galan_overview.html
Bacterial Strategies
RHO FAMILY GTPASES: Rho, Rac, Cdc42
BACTERIAL INHIBITION OF RHO PROTEINS:
-Large clostridial toxins: Toxin A, B, Lethal Toxin
-C. botulinum C3 transferase
-Salmonella SptP, Yersinia YopE
BACTERIAL ACTIVATION OF RHO PROTEINS:
-E.coli CNF1 and 2 Toxins
-Bordetella dermonecrotizing toxin (DNT)
-Salmonella SopE, Yersinia CNFY
Fig. 1. Rho GTPases are targets for bacterial virulence factors.
Fig. 2. Bacterial virulence factors affect
spatial and temporal regulation of Rho.
Why target Rho GTPases?
• Invasion can be dangerous!
– Innate immunity – recognize ‘non-self’ and
opsonize for phagocytic cell recognition. LPS
recognized by TLRs stimulates NF-KB and
leads to transcription of antibacterial factors.
– Cell shedding removes adhered bacteria.
– Adaptive immunity… takes time.
• Virulence factors help microbes invade on
their own terms! Rho GTPases are key.
Fig. 3. Virulence factors can adapt or mimic
eukaryotic mechanisms.
How do virulence factors enter?
• Toxins
– Can act distantly to bacteria because all
required elements for virulence self-contained.
– Diptheria A-B example:
• A region – catalytically active, delivered to cytosol.
• B region – for binding host cell and translocating the
A-enzymatic fragment to host cytosol at low pH.
• Type III or IV Secretion Systems
Fig. 4. Domain organization of virulence factors
activating or inhibiting Rho GTPases.
Fig. 5. Mechanisms to transfer Rho virulence factors
into the cell cytosol.
Rho Inhibitors
• Classical model:
– Toxins effects were irreversible, while TTSS
induced reversible changes in Rho.
• Large clostridial toxins (LCTs)
– Toxins A, B, Lethal Toxin.
• Type Three Secretion Systems
– Pseudomonas ExoS, ExoT.
– Salmonella SptP, Yersinia YopT, YopE.
• C3 transferases, YopT: spatial regulation.
Rho activators
• E.coli CNF, Bordetella DNF:
– Block RhoGAP activity so GTPase is
permanently active until ubiquitinylation and
proteosomal degradation.
– Is proteosomal degradation of overactivated
Rho a cellular defense that microbes are
taking advantage of?
• Salmonella SopE, E2:
– Rho GEF function to activate Rho but is
counterbalanced by SptP GAP activity.
Fig. 5. Comparison of activation-deactivation of Rac by
Salmonella SopE/Sptp and E. coli CNF1.
Why activation/deactivation?
• Whether the bacteria supplies the Rho
counterbalance (Salmonella) to virulence or the
host cell provides it (E.coli)…
-is it simply to return to ‘normal’ cell function?
-or to enhance bacterial uptake?
-or to avoid non-physiologic cell environs that
prevent bacterial uptake at all?
Summary
• Rho GTPases can be influenced by:
– Activities from separate bacterial factors
• Salmonella SopE, SptP; Yersinia YopE,YopT
– Dual activity factors
• Pseudomonas ExoS, ExoT
– Single activity proteins
• E. coli CNF1 Toxin
• What is the future of the host-pathogen
interaction? Extremes vs balance?
The End