Bidirectional effect of Wnt signaling antagonist DKK1 on the modulation of anthrax toxin uptake

Area of Science:

• Cell Biology
• Molecular Biology
• Toxicology

Background:

• Low-density lipoprotein receptor-related protein 6 (LRP6) is a co-receptor for Wnt morphogens and mediates endocytosis of anthrax complexes.
• Dickkopf1 (DKK1) is a secreted antagonist of LRP6-mediated Wnt signaling.

Purpose of the Study:

• To investigate the role of Dickkopf1 (DKK1) in modulating cellular sensitivity to anthrax toxins.
• To elucidate the molecular mechanisms by which DKK1 influences anthrax toxin internalization and toxicity.

Main Methods:

• shRNA-mediated gene silencing and TALEN-mediated gene knockout of DKK1.
• Fluorescence microscopy and biochemical analyses to study toxin-receptor complex formation and internalization.
• Assessment of cell sensitivity to anthrax toxins (PA-dependent hybrid toxins and anthrax lethal toxin - LT).
• Treatment with monoclonal antibodies against DKK1.

Main Results:

• Gene silencing or knockout of DKK1 reduced cellular sensitivity to PA-dependent hybrid toxins.
• DKK1 overexpression had bidirectional effects on anthrax toxicity, dependent on endogenous expression and cell context.
• DKK1 was shown to facilitate the internalization of anthrax toxins and their receptors through a DKK1-LRP6-Kremen2 complex.
• Monoclonal antibodies targeting DKK1 provided dose-dependent protection to macrophages against anthrax lethal toxin (LT).

Conclusions:

• DKK1 acts as a modulator of anthrax toxin sensitivity, independent of its canonical Wnt signaling inhibitory function.
• DKK1 forms a ternary complex with LRP6 and Kremen2 to promote the internalization of anthrax toxins.
• This interaction reveals a mechanism by which bacteria exploit host cell machinery for toxin entry, presenting a potential therapeutic target for anthrax toxin neutralization.