Who cares about Rho GTPases?

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Who cares about Rho GTPases?
Clostridium spp.
Salmonella spp.
Bordetella spp. Neisseria spp.
http//www.geocities.com/CapeCanaveral/3504/galler
y.htm
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Historical GTPase Events

• 1985 isolation of Rho Ras homolog
• 1989 C3 transferase shown to inactivate RhoC gt
  actin disruption in host cells. Isolation of Rac
  Ras substrate of C3.
• 1990s Rho/Rac GTPases shown to act as switches
  to control membrane receptors and actin
  cytoskeleton plasticity.

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Salmonella enterica
Type III Secretion System (TTSS) for
translocation of virulence factors http//info
.med.yale.edu/micropath/galan/Pages/galan_overview
.html
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Salmonella chaperone proteins
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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.
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Salmonella invasion summary
http//info.med.yale.edu/micropath/galan/Pages/gal
an_overview.html
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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
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Fig. 1. Rho GTPases are targets for bacterial
virulence factors.
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Fig. 2. Bacterial virulence factors affect
spatial and temporal regulation of Rho.
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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.

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Fig. 3. Virulence factors can adapt or mimic
eukaryotic mechanisms.
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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

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Fig. 4. Domain organization of virulence factors
activating or inhibiting Rho GTPases.
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Fig. 5. Mechanisms to transfer Rho virulence
factors into the cell cytosol.
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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.

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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.

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Fig. 5. Comparison of activation-deactivation of
Rac by Salmonella SopE/Sptp and E. coli CNF1.
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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?

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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?

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The End