Invasion

Question 1

pathogen invasion (3)

Answer 1

• pathogens can enter and survive in host cells
• allows them to breach host epithelial barrier
• provides them with protected niche for replication and persistence

Question 2

pathogen mechanism of invasion (2)

Answer 2

• can actively direct their entry into host cells
• usually done by a protein called “invasin”

Question 3

invasins (2)

Answer 3

• activate a receptor
• leads to a signaling event that enables uptake through cytoskeletal rearrangements

Question 4

mechanisms of particle update into cells (2)

Answer 4

• zippers
• triggers

Question 5

mechanisms of particle update into cells: zippers (3)

Answer 5

• sequential engagement of phagocytic membrane with particle surface
• pseudopod advances no further than receptor-ligand interaction permits
• partial engulfment where receptor-ligand interactions are

Question 6

mechanisms of particle update into cells: triggers (2)

Answer 6

• all-or-nothing effect
• complete phagocytosis

Question 7

zipper uptake steps (4)

Answer 7

1. initial contact (adherence)
2. receptor clustering
3. phagocytic cup formation involving actin polymerization and membrane extension
4. closure of phagocytic cup and retraction involving actin depolymerization

Question 8

Yersinia (2)

Answer 8

• enteric pathogens that infect Peyers Patches in the intestine
• pathogenesis involves translocation across intestinal barrier via M cells, an easy cells for bacteria to breach

Question 9

M cells (2)

Answer 9

• epithelial cells that lack mucus on their surface and lack microvilli
• sample their environment and take up particle nutrients and microbes

Question 10

Yersinia and Invasion: what mechanism does Yersinia use for invasion

Answer 10

• zipper-mediated invasion

Question 11

Yersinia and Invasion: how does Yersinia access enterocyte cells

Answer 11

• Yersinia translocated through M cells and enters neighbouring enterocytes via the basolateral membrane

Question 12

Yersinia and Invasion: what proteins are involved in Yersinia invading enterocyte cells (2)

Answer 12

• invasin protein involved in entering enterocytes
• binds integrin receptor only expressed on basolateral side of enterocytes

Question 13

Yersinia and Invasion: when is invasion acheived

Answer 13

• when there are sufficient numbers of receptors bound to the invasin through zipper-medicated uptake

Question 14

How is Yersinia competing with ECM proteins

Answer 14

• integrin receptors bind ECM proteins and use actin to remain in proper formation

Question 15

Yersinia and Invasion: invasin and ECM affinity to integrin (2)

Answer 15

• affinity of integrin for invasin is very high
• affinity for invasin is 100x higher than affinity for ECM proteins

Question 16

Yersinia and Invasion: what occurs as a result of the sufficient amounts of integrin bound to invasin (3)

Answer 16

• tyrosine phosphorylation
• involves FAK (kinase), PI3 kinases, GTPases Src and Rac
• cytoskeletal rearrangements and pseudopod engulfment result

Question 17

Listeria monocytogenes and Invasion: what mechanism of invasion

Answer 17

• zipper-mediated invasion

Question 18

Listeria monocytogenes and Invasion: invasin ligand and receptor in enterocytes (2)

Answer 18

• the invasin is Internalin A (InlA)
• the receptor is E-cadherin

Question 19

Listeria monocytogenes and Invasion: invasin ligand and receptor in hepatocytes (2)

Answer 19

• the invasin is Internalin B (InlB)
• the receptor is a protein called “Met”

Question 20

Listeria monocytogenes and Invasion: what does uptake involve

Answer 20

• involves clathrin-mediated endocytosis and cytoskeletal rearrangements

Question 21

trigger uptake mechanisms (3)

Answer 21

• mechanism similar to micropinocytosis
• macropinosomes
• surface ruffling

Question 22

trigger uptake: mechanism similar to micropinocytosis

Answer 22

• a form of endocytosis that is accompanies by cell surface ruffling

Question 23

trigger uptake: macropinosomes

Answer 23

• large vesicles that serve as a route for cells to take up macromolecules non-selectively

Question 24

trigger uptake: membrane ruffling (2)

Answer 24

• unguided pseudopodia
• ruffles fall back onto bacteria and this leads to formation of large endosomes, which eventually become smaller

Question 25

trigger: distinct steps (3)

Answer 25

1. filopode formation: membrane ruffles 2. lamellipode formation: membrane ruffles filled with actin support through polymerization 3. formation of phagocytic cup made of actin or through adherence

Question 26

Shigella flexneri (3)

Answer 26

- originates from the colon and is extremely infectious - initially invades M cells - causes "bloody" diarrhea and inflammation, which is crucial for its pathogenesis

Question 27

Shigella and Invasion (2)

Answer 27

- involves over 30 bacterial proteins that mostly encode T3SS apparatus, while the rest are effectors - hijacks normal cell signaling pathways to cause massive cytoskeletal rearrangements

Question 28

Shigella Invasion: trigger step 1 (3)

Answer 28

- bacterial proteins IpaB and IpaC form pore in host cell membrane (T3SS) and serve as ligands for host cell receptors - this becomes a portal for effectors to enter the host cell - triggering results in local destabilization of microtubules by Shigella protein VirA

Question 29

Shigella invasion: trigger step 2 (3)

Answer 29

- activation of cell signaling occurs via many GTP-binding proteins such as CDC42/Rac - leads to lamellipode formation - several host proteins are involved in mediating actin polymerization and cytoskeletal rearrangements

Question 30

Shigella invasion: trigger step 3 (2)

Answer 30

- final step is actin depolymerization mediated by Shigella protein IpaA - IpaA binds host protein vinculin to induce actin depolymerization, resulting in Shigella uptake

Question 31

zipper vs trigger (2)

Answer 31

- zipper results in localized contact-dependent receptor-medicated particle engulfment - trigger results in generalized engulfment event that could include neighbouring particles

Question 32

anti-phagocytosis (2)

Answer 32

- some bacteria actively inhibit their uptake - secrete protein YopH through T3SS

Question 33

YopH

Answer 33

- phosphatase that overrides kinase that is activated by invasin

Question 34

can one pathogen exhibit both zipper and trigger mediated invasion

Answer 34

- yes, for instance, salmonella can invade host cell using different routes and mechanisms