Invasion (4)

Evade immune recognition

antigenic variation, attract host proteins to mimic host, attract Fc region of Ab, secretory Iga proteases

Reasons to invade

become inaccessible to host complement, antibodies and phagocytes, adherence mechs no longer needed, lots of nutrients and gain access to deeper tissue

Extracellular pathogens

remain in tissues and fluids and do not enter host cells during diseases ie yersinia pestis

Intracellular pathogens

grow and multiple withing host cells

Facultative intracellular pathogens

reside within cells but can also grow in environment ie listeria moncytogenes

Obligate intracellular pathogens

cannot replicate outside host cell ie viruses, chlamydia and rickettsia and malarial parasites

Phagocytosis

professional cells do this ie macrophages, monocytes, neutrophils and DCs, is actin dependent and requires little metabolic input from pathogen

Macrophages, monocytes, neutrophils, DCs

professional phagocytes

Induced endocytosis/phagocytosis

entry into non professional phagocytes ie epithelia requires metabolic input from both host cell and pathogen includes zipper and trigger mechansims and invasome

Adhesion, engulfment/zippering, internalization

3 steps of induced endocytosis

Adhesion

contact and adherence, ligand binds receptor, receptor clustering and activation

Engulfment/zippering

formation of a phagocytic cup, activation of signal transduction cascades and actin rearrangement

Internalization

cup closure, retraction and actin depolymerization

Cytoskeleton

regulates cell shape, endocytosis, vesicle trafficking, cell migration and motility, cytokinesis

Actin remodeling

highly dynamic and can be rapidly altered during phagocytosis to change shape of the cell and perform various cell functions, polymers concentrated beneath plasma membrane

Nucleation, elongation, steady state

steps of actin polymerization

Nucleation

three actin monomers form a complex

Elongation

actin monomers are added to the end of the complex

Steady state

actin monomers are being added to one end at the same rate as they are being removed from the other end

Rho

family of GTPases that regulate actin, control signal transduction and cellular functions including cytoskeletal rearrangement and vesicle trafficking

Membrane

GTPases are usually associated with the ___

GDP

inactive form of GTPases

GTP

active form of GTPases

GEF

exchange GDP for GTP to activate GTPases

GAP

hydrolyze GTP to GDP to inactive GTPases

GTPases

active ____ initiate downstream signaling cascades

Arp2/3 complex

promotes actin nucleation/assembly by binding to a side of existing filament to generate a new branched filament activated by nucleation promoting factors (NPFs)

Nucleation promoting factors (NPFs)

in an autoinhibited state and require binding of a small GTPase for activation eg NWASP

N WASP

functions as a scaffold for the recruitment of actin and Arp2/3 which it activates

N WASP + activated Arp2/3

where is actin recruited?

Zipper mechanism

binding, signal transduction and cytoskeletal reorganization (actin reorganization) and engulfment (host membrane gradually curves and closes around bacterium in a ___ fashion

Invasins and internalins

bacterial surface proteins that provoke endocytic uptake in zipper mechanism fashion

E cadherin and integrins

invasins and internalins bind to host cell receptors like…

Invasin

coats bacterial surface for multiple contact sites for zipper

Listeria and yersinia

zipper mechanism is used by…

Receptor clustering

many invasin contact sites results in ___ which trigger intracellular signals which promote cytoskeletal rearrangements and membrane protrusions needed for engulfment

InlA and InlB

Listeria internalins used for zipper mechanism

InlA

listeria internalin that binds to E cadherin (found on epithelial cells)

Inlb

listeria internalin that binds to Met a hepatocyte growth factor

InlA to E Cad

binding of __ to ____ mimics natural cell cell adhesion processes and signals host cell to forma close association with the bacterium

Alpha and beta catenins

mediate the attachmet of E cad to actin, therefore when listeria is bound to E cad it has a direct link to cytoskeleton via actin which it can rearrange to curve around the bacteria

Zipper

mechanism listeria uses to engulf the bacteria into the host cell

Trigger mechanism

bacterial secretion system inject effector protein into cytoplasm and usually target Rho GTPases leading to extensive actin rearrangement and this forms membrane protrusions on host cell that engulf the bacteria.

Internalization

in the trigger mechanism step, protrusions fold over and enclose bacteria

Rho GTPases

effectors in the trigger mechanism secreted by bacterial secretion systems typically target…

Membrane protrusions

in the trigger mechanism, reorganization of actin cytoskeleton causes…

3 and 4

major secretion systems for trigger mechanism

Filopodia

thin finger like extensions made by actin rearrangement

Lamellipodia

broad sheet like protrusions made by actin rearrangement

Salmonella, shigella

bacteria that use trigger mechanisms of induced endocytosis

T3SS

salmonella uses a ____ system for trigger mechanisms

SopE and SopE2

Guanine nucleotide exchange factors (GEFs) secreted by salmonella T3SS that activate Rho GTPases (Rac1 and Cdc42) to initiate actin rearrangement

Rho GTPases

GEFs SopE and SopE2 activate…

Rac1 and Cdc42

what are the Rho GTPases activated (by transfer of GDP for GTP) by SopE and SopE2 in salmonella trigger mechanism

Cytoskeletal rearrangement

activated Rac1 and Cdc42 initiate in salmonella trigger mechanism

SipA

actin binding protein that stabilizes actin filaments and promotes actin polymerization, plays a key role in enhancing efficiency of salmonella internalization via the trigger mechanism

Actin filaments

secreted by a T3SS, SipA binds to … decreasing their critical concentration and inhibiting their depolymerization

Stabilizes

SipA ____ actin filaments, thereby making more pronounced ruffles facilitating engulfment of bacteria like salmonella

Spatial localization

this function of SipA enhances bacterial uptake

TmeA

chlamydia trachomatis effector ___ hijacks NWASP ARP2/3 actin remodeling axis to facilitate cellular invasion

Bartonella

use an invasome (cluster of bacteria engulfed together)

BadA and Comps

bacterial outer membrane proteins on bartonella that bind to ECM components and to membrane proteins on host cell PM

Beps

injection by T4SS from bartonella which interfere with the internalization process and transport of attached bacteria on host PM which leads to bacterial clustering which are eventually engulfed as a group of a large cluster of bacteria

IpaB, IpaC

shigella effector proteins for the trigger mechanism

CagA

effector proteins for helicobacter zipper mechanism

BepA, C, F, G

effector proteins for bartonella invasome mechanism

Integrin B1 mediated

host cytoskeletal rearrangement is induced by what type of signalling in invasome formation

Host cell adhesion interactions

host cytoskeletal rearrangement is induced by what in zipper mechanism

Bacterial effector proteins

host cytoskeletal rearrangement is induced by what in trigger mechanisms

High

trigger and invasome mechanism entry efficiency is

Low

zipper mechanism entry efficiency is ___

Pedestal formation

done by Enteropathogenic e. coli (EPEC) and is not invasion but a niche formation that remodels actin through secretion systems to mediate a strong adherence to intestinal epithelia and remain there even through diarrhea

T3SS

what secretion system does EPEC use in pedestal formation

Tir

inserted into host cell by EPEC by T3SS with a loop region that bind to intimin (B OM P) and when phosphorylated anchors the bacterium to host membrane

Nck and NWASP

phosphorylated Tir recruits …. In EPEC pedestal formation

Intimin

bacterial outer membrane protein that binds to Tir in pedestal formation

Arp2/3

N WASP activates … leading to polymerization of actin at site of bacterial attachment creating a raised pedestal

Cell to cell spread

actin tails can be used for …

Arp2/3, NWASP, Toca1

host proteins that regulate actin nucleation

Eva/Vasp profilin, lamellipodin

host proteins that regulate the elongation of actin

Nexilin, a actinin

host proteins that regulate actin cross linking

Capping protein, cofilin

host proteins that regulate actin dynamics and recycling

ActA

listeria monocytogenes utilizes … to hijack host actin host actin polymerization machinery, use it to recruit actin and host actin binding portiens including arp2/3 and then polarize one pole of the bacterium and drive actin polymerization and propel the bacterium forward