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Autophagy-independent function of MAP-LC3 during intracellular propagation of Chlamydia trachomatis

Hesham M Al-Younes1, Munir A Al-Zeer, Hany Khalil

  • 1Department of Molecular Biology, Max Planck Institute for Infection Biology, Berlin, Germany.

Autophagy
|April 6, 2011
PubMed

Insights

Microtubule-associated protein 1 (MAP1) light chain 3 (LC3) has a novel role beyond autophagy. LC3 interacts with Chlamydia trachomatis inclusions, crucial for bacterial growth, independent of its autophagosome function.

Area of Science:

  • Microbiology
  • Cell Biology
  • Infectious Diseases

Background:

  • Microtubule-associated protein 1 (MAP1) light chain 3 (LC3) is a known autophagosome marker.
  • LC3's function extends beyond autophagosome formation.
  • Previous work indicated LC3 associates with intracellular Chlamydia trachomatis inclusions.

Purpose of the Study:

  • To investigate the specific role of LC3 in Chlamydia trachomatis infection.
  • To differentiate LC3's function in autophagy versus its interaction with bacterial inclusions.
  • To determine the necessity of LC3 and MAP1 for C. trachomatis intracellular survival.

Main Methods:

  • Immunofluorescence microscopy to visualize LC3 and MAP1 association with C. trachomatis inclusions.
  • Microtubule depolymerization experiments to assess the role of the microtubular network.
  • siRNA-mediated gene silencing of LC3 and MAP1 proteins.
  • Analysis of C. trachomatis growth in cells with varying autophagy and LC3/MAP1 levels.

Main Results:

  • LC3, particularly the non-lipidated form, interacts with C. trachomatis inclusions as a microtubule-associated protein, not an autophagosome component.
  • N-terminally GFP-tagged LC3 specifically localized to autophagosomes, distinct from inclusions.
  • LC3 and MAP1 subunits A and B associate with inclusions early in infection and are linked to the microtubular network.
  • Microtubule disruption impairs LC3/MAP1 association with inclusions.
  • Silencing LC3 or MAP1 significantly inhibits intracellular C. trachomatis growth.
  • Autophagy deficiency enhances chlamydial growth, but LC3 depletion reduces it even in autophagy-deficient cells.

Conclusions:

  • LC3 plays a critical, autophagy-independent role in intracellular Chlamydia trachomatis pathogenesis by associating with bacterial inclusions via the microtubule network.
  • MAP1 proteins are also essential for C. trachomatis intracellular survival.
  • The host autophagic machinery may exert a suppressive effect on C. trachomatis development.

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