MODULATION OF THE HOST UNFOLDED PROTEIN RESPONSE BY LEGIONELLA PNEUMOPHILA.
pneumophila, the causative agent of Legionnairesʹ disease, is a Gram-negative
intracellular pathogen that replicates within alveolar macrophages during disease. The
ability of L. pneumophila to replicate within a host cell is dependent on the Icm/Dot
type IV secretion system (T4SS), which delivers Icm/Dot translocated substrates (IDTS)
into the host cell cytosol. Many of ... read morethese IDTS are involved in the generation of the
Legionella-containing vacuole (LCV), which is composed of endoplasmic reticulum
(ER)-derived membrane. Here, I report the identification and characterization of MavT,
an IDTS that, when expressed in eukaryotic cells, induces the dramatic reorganization of
ER structure. MavT binds to members of the Hsp70 family and contains a J domain, which
stimulates ATP hydrolysis and substrate binding by Hsp70, consistent with MavT
functioning through the manipulation of host cell chaperones. Furthermore, the J domain
is clearly functional, as it is shown here to be able to rescue a thermosensitive E.
coli mutant. L. pneumophila manipulation of host cell chaperone function and its
downstream effects on protein folding led to the hypothesis that the bacterium targets
folding pathways associated with the host ER. Many intracellular pathogens that interact
with the ER induce or modulate an ER stress response to misfolded proteins, termed the
unfolded protein response (UPR). During host cell challenge, I show that L. pneumophila
inhibits chemical induction of the IRE1 branch of the UPR, in a manner dependent on the
Icm/Dot T4SS and, specifically, five translocated substrates that inhibit host cell
translation elongation. L. pneumophila-derived pathogen associated molecular products
(PAMPs), as well as a strain lacking the five translocated elongation inhibitors,
induced this branch of the UPR, indicating the functionality of mechanisms to inhibit
UPR during host cell challenge. As many pathogens inhibit translation elongation, this
may be a common strategy to inhibit the host UPR. These studies further our knowledge of
the broad ways by which Legionella modulates the host cell ER and its signaling pathways
Thesis (Ph.D.)--Tufts University, 2015.
Submitted to the Dept. of Molecular Microbiology.
Advisor: Ralph Isberg.
Committee: Andrew Camilli, Ekaterina Heldwein, and Alexander Poltorak.
Keyword: Microbiology.read less