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Infection and Immunity
Article . 2017 . Peer-reviewed
License: ASM Journals Non-Commercial TDM
Data sources: Crossref
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Ehrlichia Activation of Wnt-PI3K-mTOR Signaling Inhibits Autolysosome Generation and Autophagic Destruction by the Mononuclear Phagocyte

Authors: Taslima T. Lina; Tian Luo; Thangam-Sudha Velayutham; Seema Das; Jere W. McBride;

Ehrlichia Activation of Wnt-PI3K-mTOR Signaling Inhibits Autolysosome Generation and Autophagic Destruction by the Mononuclear Phagocyte

Abstract

ABSTRACT In multicellular organisms, autophagy is induced as an innate defense mechanism. Notably, the obligate intracellular bacterium Ehrlichia chaffeensis resides in early endosome-like vacuoles and circumvents lysosomal fusion through an unknown mechanism, thereby avoiding destruction in the autophagolysosome. In this report, we reveal that Wnt signaling plays a crucial role in inhibition of lysosomal fusion and autolysosomal destruction of ehrlichiae. During early infection, autophagosomes fuse with ehrlichial vacuoles to form an amphisome indicated by the presence of autophagy markers such as LC3 (microtubule-associated protein 1 light chain 3), Beclin-1, and p62. LC3 colocalized with ehrlichial morulae on days 1, 2, and 3 postinfection, and increased LC3II levels were detected during infection, reaching a maximal level on day 3. Ehrlichial vacuoles did not colocalize with the lysosomal marker LAMP2, and lysosomes were redistributed and dramatically reduced in level in the infected cells. An inhibitor specific for the Wnt receptor signaling component Dishevelled induced lysosomal fusion with ehrlichial inclusions corresponding to p62 degradation and promoted transcription factor EB (TFEB) nuclear localization. E. chaffeensis infection activated the phosphatidylinositol 3-kinase (PI3K)–Akt–mTOR (mechanistic target of rapamycin) pathway, and activation was induced by three ehrlichial tandem repeat protein (TRP) effectors, with TRP120 inducing the strongest activation. Moreover, induction of glycogen synthase kinase-3 (GSK3) performed using a Wnt inhibitor and small interfering RNA (siRNA) knockdown of critical components of PI3K-GSK3-mTOR signaling decreased ehrlichial survival. This report reveals Ehrlichia exploitation of the evolutionarily conserved Wnt pathway to inhibit autolysosome generation, thereby leading to evasion of this important innate immune defense mechanism.

Keywords

THP-1 Cells, TOR Serine-Threonine Kinases, Monocytes, Ehrlichia chaffeensis, Phagocytosis, Host-Pathogen Interactions, Autophagy, Humans, Phosphatidylinositol 3-Kinase, Wnt Signaling Pathway, Immune Evasion

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    26
    popularity
    This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
    Top 10%
    influence
    This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
    Average
    impulse
    This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
    Top 10%
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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
26
Top 10%
Average
Top 10%
bronze